Co-reporter:Adeline D. Fournet, Kylie J. Mitchell, Wolfgang Wernsdorfer, Khalil A. Abboud, and George Christou
Inorganic Chemistry September 5, 2017 Volume 56(Issue 17) pp:10706-10706
Publication Date(Web):August 22, 2017
DOI:10.1021/acs.inorgchem.7b01676
A new member of the Mn12 family of single-molecule magnets (SMMs) has been prepared and found to be the first of this family to give a 3-D ferromagnetic network. [Mn12O12(O2CC6H4-p-F)16(H2O)4] (2) was prepared by carboxylate substitution on the acetate derivative with p-F-benzoic acid and crystallizes as 2·8MeCN in space group I4̅2m with extensive formation of intermolecular C–H···F hydrogen-bonding. The latter leads to a combination of ferromagnetic (F) and antiferromagnetic (AF) interactions and an overall F network that gives a χMT value at low T that is abnormally high for an S = 10 ground state. 2·8MeCN undergoes solvent loss under vacuum to 2, with a decrease in unit-cell volume of 17%, primarily due to a 13% decrease in the c-axis. The χMT vs T plot for 2 indicates a switch to a net AF network. Exposure to air causes hydration to 2·3H2O, a concomitant increase in unit cell volume, and a switch back to a F network. The same conversion of 2·8MeCN to 2·3H2O can also be accomplished in one step rather than two steps, by leaving crystals of the former exposed to air at ambient temperature and pressure for 10 days, giving the same magnetic plots. Interestingly, the desolvation/solvation processes cause Jahn–Teller isomerism to occur, but the ratio of the faster-relaxing isomer to the normal slowly relaxing one does not change monotonically. Single-crystal micro-SQUID studies on 2·8MeCN show the expected magnetization hysteresis loops for a SMM and a small exchange-bias from the intermolecular interactions that is unexpectedly AF. Since the micro-SQUID study only identifies interactions along the easy-axis (z-axis) of the crystal, this is readily rationalized as due to the Jz components of the intermolecular interactions in 2·8MeCN being net AF. The combined results offer useful insights into the degree of sensitivity of the magnetic properties to small environmental perturbations.
Co-reporter:Olajuyigbe A. Adebayo, Khalil A. Abboud, and George Christou
Inorganic Chemistry September 18, 2017 Volume 56(Issue 18) pp:11352-11352
Publication Date(Web):August 30, 2017
DOI:10.1021/acs.inorgchem.7b01793
The syntheses, structures, and magnetochemical properties are reported for five new Mn clusters: [MnIII3O(O2PPh2)3(mpko)3](ClO4) (1), [MnIII3O(O2PPh2)3(ppko)3](ClO4) (2) [MnIII6O2(OMe)4(O2PPh2)4(mpko)4](ClO4)2 (3), [MnIII8MnIIO6(O2CMe)7(O3PPh)2(mpko)3(H2O)] (4), and [MnIII2MnIIO(mpko)3(H2O)4(ClO4)2](ClO4) (5), where mpko– (or ppko–) is the anion of methyl (or phenyl) 2-pyridyl ketone oxime. 1 was obtained by carboxylate substitution on [MnIII3O(O2CMe)3(mpko)3](ClO4) by treatment with diphenylphosphinic acid (Ph2PO2H). The comproportionation reaction between Mn(ClO4)2 and NBun4MnO4 in the presence of Ph2PO2H and ppkoH in EtOH, or mpkoH in MeOH, led to 2 and 3, respectively. 4 was obtained as was 3, but with phenylphosphonic acid (PhPO3H2) instead of Ph2PO2H. 5 was obtained by aerial oxidation of Mn(ClO4)2 in the presence of mpkoH. 1 and 2 contain a triangular Mn3 core, 3 comprises the fusion of two Mn3 units of 1 by MeO– bridges, and 4 has a cagelike structure. 5 is similar to 1 in possessing a triangular core. Variable-temperature, solid-state direct-current (dc) and alternating-current (ac) magnetic data were collected on 1–5: 1 and 2 exhibit ferromagnetic Mn····Mn exchange interactions, S = 6 ground states, and are new single-molecule magnets (SMMs). 3–5 possess S = 4, 5/2, and 5/2 ground states, respectively, from dominant antiferromagnetic interactions. Fits of dc magnetization data in the 1.8–10.0 K and 10–70 kG ranges gave D and g values of: −0.29(2) cm–1 and 1.94(1) for 1, −0.38(2) cm–1 and 1.99(1) for 2, −0.29(2) cm–1 and 1.96(1) for 3, −1.26(4) cm–1 and 1.99(2) for 4, −1.41(4) cm–1 and 1.98(2) for 5, where D is the axial zero-field splitting parameter.
Co-reporter:Eleni E. Moushi, Christos Lampropoulos, Wolfgang Wernsdorfer, Vassilios Nastopoulos, George Christou, and Anastasios J. Tasiopoulos
Journal of the American Chemical Society November 17, 2010 Volume 132(Issue 45) pp:16146-16155
Publication Date(Web):October 21, 2010
DOI:10.1021/ja106666h
The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn40Na4 and homometallic Mn44 loop-of-loops aggregates are reported. The reactions of [Mn3O(O2CMe)6(py)3]·py with 1,3-propanediol (pdH2) and 2-methyl-1,3-propanediol (mpdH2) in the presence of NaN3 afforded [Mn10Na(μ3-O)2(O2CMe)13(pd)6(py)2]4 (1)4 and [Mn10Na(μ3-O)2(O2CMe)13(mpd)6(py)(H2O)]4 (2)4, respectively. Mn40Na4 complexes (1)4 and (2)4 consist of four Mn10 loops linked through Na+ ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)4 showed that each Mn10 loop has an S = 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac susceptibility signals. It also exhibits hysteresis loops that, however, are not typical of single-molecule magnets (SMMs) due to the existence of interloop interactions between the neighboring Mn10 units of (1)4 through the diamagnetic Na+ ions, and also intermolecular interactions between different Mn40Na4 aggregates. The magnetically discrete Mn44 analogue was targeted with high priority and finally prepared from the reaction of [Mn3O(O2CMe)6(py)3]·py with pdH2 in the presence of Mn(ClO4)2·6H2O. The loop-of-loops structure of [Mn44(μ3-O)8(O2CMe)52(pd)24(py)8](ClO4)(OH)3 (3) is essentially identical to those of (1)4 and (2)4, with the most significant difference being that the four Na+ ions of (1)4 and (2)4 have been replaced with Mn2+ ions. Compound 3 is thus best described magnetically as a Mn44 cluster. In accord with this description and the stronger exchange coupling between the four Mn10 loops expected through the connecting Mn2+ ions, magnetic susceptibility measurements revealed that 3 has an S = 6 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac signals. Magnetization vs dc field sweeps on single-crystals of 3 displayed scan rate- and temperature-dependent hysteresis loops confirming that complex 3 is a new SMM, and is thus the second largest Mn cluster and SMM reported to date.
Co-reporter:Constantina Papatriantafyllopoulou, Eleni E. Moushi, George Christou and Anastasios J. Tasiopoulos
Chemical Society Reviews 2016 vol. 45(Issue 6) pp:1597-1628
Publication Date(Web):15 Jan 2016
DOI:10.1039/C5CS00590F
In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term “giant clusters” is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.
Co-reporter:Tu N. Nguyen, Wolfgang Wernsdorfer, Muhandis Shiddiq, Khalil A. Abboud, Stephen Hill and George Christou
Chemical Science 2016 vol. 7(Issue 2) pp:1156-1173
Publication Date(Web):2015/11/16
DOI:10.1039/C5SC02599K
The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn3 units are reported: dimeric [Mn6O2(O2CMe)8(CH3OH)2(pdpd)2] (3) and [Mn6O2(O2CMe)8(py)2(pdpd)2](ClO4)2 (4), and tetrameric [Mn12O4(O2CR)12(pdpd)6](ClO4)4 (R = Me (5), tBu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH2), either in direct synthesis reactions involving oxidation of MnII salts or in metathesis reactions with the preformed complex [Mn3O(O2CMe)6(py)3](ClO4) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [MnIII2MnII(μ3-O)]6+ and [MnIII3(μ3-O)]7+ units, respectively, linked by two pdpd2− groups. Complexes 5 and 6 contain four [MnIII3(μ3-O)]7+ units linked by six pdpd2− groups into a rectangular tetramer [MnIII3]4. Solid-state dc magnetic susceptibility studies showed that the Mn3 subunits in 3 and 4 have a ground-state spin of S = 3/2 and S = 2, respectively, while the Mn3 subunits in 5 and 6 possess an S = 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-of-phase (χ′′M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn3 single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5·2CH2Cl2 provided precise spin Hamiltonian parameters of D = −0.33 cm−1, |E| = 0.03 cm−1, B04 = −8.0 × 10−5 cm−1, and g = 2.0. Magnetization vs. dc field sweeps on a single crystal of 5·xCH2Cl2 gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn3 unit is exchange-coupled to the two neighbors linked to it by the pdpd2− linkers, with an antiferromagnetic inter-Mn3 exchange interaction of J/kB = −0.011 K (Ĥ = −2JŜi·Ŝj convention). The work demonstrates a rational approach to synthesizing magnetically-supramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.
Co-reporter:Alina Vinslava, Anastasios J. Tasiopoulos, Wolfgang Wernsdorfer, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2016 Volume 55(Issue 7) pp:3419-3430
Publication Date(Web):February 9, 2016
DOI:10.1021/acs.inorgchem.5b02790
Two Mn70 torus-like molecules have been obtained from the alcoholysis in EtOH and 2-ClC2H4OH of [Mn12O12(O2CMe)16(H2O)4]·4H2O·2MeCO2H (1) in the presence of NBun4MnO4 and an excess of MeCO2H. The reaction in EtOH afforded [Mn70O60(O2CMe)70(OEt)20(EtOH)16(H2O)22] (2), whereas the reaction in ClC2H4OH gave [Mn70O60(O2CMe)70(OC2H4Cl)20(ClC2H4OH)18(H2O)22] (3). The complexes are nearly isostructural, each possessing a Mn70 torus structure consisting of alternating near-linear [Mn3(μ3-O)4] and cubic [Mn4(μ3-O)2(μ3-OR)2] (R = OEt, 2; R = OC2H4Cl, 3) subunits, linked together via syn,syn-μ-bridging MeCO2– and μ3-bridging O2– groups. 2 and 3 have an overall diameter of ∼4 nm and crystallize as highly ordered supramolecular nanotubes. Alternating current (ac) magnetic susceptibility measurements, performed on microcrystalline samples in the 1.8–10 K range and a 3.5 G ac field with oscillation frequencies in the 5–1500 Hz range, revealed frequency-dependent out-of-phase signals below ∼2.4 K for both molecules indicative of the slow magnetization relaxation of single-molecule magnets (SMMs). Single-crystal, magnetization vs field studies on both complexes revealed hysteresis loops below 1.5 K, thus confirming 2 and 3 to be new SMMs. The hysteresis loops do not show the steps that are characteristic of quantum tunneling of magnetization (QTM). However, low-temperature studies revealed temperature-independent relaxation rates below ∼0.2 K for both compounds, the signature of ground state QTM. Fitting of relaxation data to the Arrhenius equation gave effective barriers for magnetization reversal (Ueff) of 23 and 18 K for 2 and 3, respectively. Because the Mn70 molecule is close to the classical limit, it was also studied using a method based on the Néel–Brown model of thermally activated magnetization reversal in a classical single-domain magnetic nanoparticle. The field and sweep-rate dependence of the coercive field was investigated and yielded the energy barrier, the spin, the Arrhenius pre-exponential, and the cross-over temperature from the classical to the quantum regime. The validity of this approach emphasizes that large SMMs can be considered as being at or near the quantum–classical nanoparticle interface.
Co-reporter:Kylie J. Mitchell, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2016 Volume 55(Issue 13) pp:6597
Publication Date(Web):June 13, 2016
DOI:10.1021/acs.inorgchem.6b00769
The synthesis and characterization are reported of two new polynuclear FeIII complexes containing the anion of 8-hydroxyquinoline (hqnH), an N,O-chelating ligand. The complexes are [Fe8O4(O2CPh)10(hqn)4(OMe)2] (1) and [Fe6O2(OH)2(O2CPh)10(hqn)2] (2) and were obtained from reactions in MeOH (1) or H2O (2) using either low-nuclearity preformed clusters or simple metal salts as starting materials. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out and indicate S = 0 and S = 5 ground states for 1 and 2, respectively. In order to rationalize the ground states of these and other higher-nuclearity FeIII/O clusters, a magnetostructural correlation (MSC) has been developed specifically for polynuclear FeIII/O systems that predicts the exchange interaction constant (Jij) between two FeIII atoms based on the Fe–O distances and Fe–O–Fe angles at monoatomically bridging ligands. This correlation was refined using selected tri- and tetranuclear complexes in the literature for which both crystal structures and reliable experimentally determined Jij values were available. The predictive capability of the MSC was evaluated by rationalizing the ground-state spins of 1, 2, and other Fe5–Fe8 clusters, simulating the dc magnetic susceptibility data of polynuclear FeIII complexes, and fitting experimental dc magnetic susceptibility vs T data. The latter fits were evaluated to identify and eliminate systematic errors, and this allowed a protocol to be developed for application of this MSC to other polynuclear FeIII/oxo clusters.
Co-reporter:Ritwik Modak, Yeasin Sikdar, Annaliese E. Thuijs, George Christou, and Sanchita Goswami
Inorganic Chemistry 2016 Volume 55(Issue 20) pp:10192-10202
Publication Date(Web):October 3, 2016
DOI:10.1021/acs.inorgchem.6b01402
We report herein the syntheses and investigation of the magnetic properties of a CoII4 compound, a series of trinuclear CoII2LnIII (LnIII = NdIII, SmIII, GdIII, TbIII, DyIII) complexes, and a CoII7 complex. The homometallic CoII4 core was obtained from the reaction of Ln(NO3)3·xH2O/Co(NO3)2·6H2O/H2vab/Et3N in a 0.5:0.5:1:2 ratio in methanol. Variation in synthetic conditions was necessary to get the desired CoII–LnIII complexes. The CoII–LnIII assembly was synthesized from Ln(NO3)3·xH2O/Co(OAc)2·4H2O/H2vab/NaOMe in a 0.4:0.5:1:1 ratio in methanol. The isostructural CoII2LnIII complexes have a core structure with the general formula [Co2Ln(Hvab)4(NO3)](NO3)2·MeOH·H2O, (where H2vab = 2-[(2-hydroxymethyl-phenylimino)-methyl]-6-methoxy-phenol) with simultaneous crystallization of CoII7 complex in each reaction. The magnetic investigation of these complexes reveals that both homometallic complexes and four CoII–LnIII complexes (except CoII–NdIII) display behavior characteristic of single molecule magnets.
Co-reporter:Nicole E. Chakov, Annaliese E. Thuijs, Wolfgang Wernsdorfer, Arnold L. Rheingold, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2016 Volume 55(Issue 17) pp:8468-8477
Publication Date(Web):August 9, 2016
DOI:10.1021/acs.inorgchem.6b01077
Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in MnIII/IV cluster chemistry, [Mn4O4(O2AsMe2)6] (3; 2MnIII, 2MnIV), and [Mn16X4O8(O2CPh)16(Me2AsO2)24] (X = Ca2+ (4) or Sr2+ (5); 16MnIII). They were obtained from reactions with [Mn12O12(O2CR)16(H2O)4] (R = Me, Ph) either without (3) or with (4 and 5) the addition of X2+ salts. Complex 3 contains a [Mn4O4]6+ cubane, whereas isostructural 4 and 5 contain a planar loop structure comprising four Mn4 asymmetric “butterfly” units linked by alternating anti,anti μ-O2AsMe2 and {X2(O2AsMe2)(O2CPh)2} units. Variable-temperature magnetic susceptibility (χM) data were collected on dried microcrystalline samples of 3–5 in the 5.0–300 K range in a 0.1 T (1000 G) direct-current (dc) magnetic field. Data for 3 were fit to the appropriate Van Vleck equation (using the = −2JŜi·Ŝj convention) for a cubane of virtual C2v symmetry, giving J33 = 0.0(1) cm–1, J34 = −3.4(4) cm–1, J44 = −9.8(2) cm–1, and g = 1.99(1), where the Jij subscripts refer to the oxidation states of the interacting Mn atoms. The ground state thus consists of two coupled MnIV and two essentially noninteracting MnIII. For 4 and 5, low-lying excited states from the high nuclearity and weak couplings prevent fits of dc magnetization data, but in-phase alternating current susceptibility χ′MT data down to 1.8 K indicate them to possess S = 4 ground states, if considered single Mn16 units. If instead they are treated as tetramers of weakly coupled Mn4 units, then each of the latter has an S = 2 ground state. Complexes 4 and 5 also exhibit very weak out-of-phase χ″M signals characteristic of slow relaxation, and magnetization versus dc field scans on a single crystal of 4·15MeCN at T ≥ 0.04 K showed hysteresis loops but with unusual features suggesting the magnetization relaxation barrier consists of more than one contribution.
Co-reporter:Tu N. Nguyen, Khalil A. Abboud, George Christou
Polyhedron 2016 Volume 103(Part A) pp:150-156
Publication Date(Web):8 January 2016
DOI:10.1016/j.poly.2015.09.039
[Mn3O(dhb)3(mpko)3](ClO4) (4) has been obtained from the carboxylate substitution reaction of triangular [Mn3O(O2CMe)3(mpko)3](ClO4) (mpkoH = methyl(2-pyridyl)ketone oxime) with 3,5-dihydroxybenzoic acid (dhbH). Complex 4 possesses an equilateral triangle [Mn3O]7+ core with the dhb− and mpko− ligands on opposite sides of the Mn3 plane. All dhb− and mpko− groups are involved in π–π stacking interactions with those on neighboring Mn3 molecules to give a 3-D supramolecular network resembling a metal–organic framework (MOF), with periodic voids resulting from a repeating unit comprising an [Mn3]8 rhombohedron. Variable-temperature, solid-state magnetic susceptibility studies in the 5.0–300 K temperature range reveal the predominance of antiferromagnetic inter-Mn3 exchange couplings. Alternating current magnetic susceptibility studies on 4 show that the single-molecule magnet (SMM) behavior characteristic of [Mn3O(O2CR)3(mpko)3]+ complexes has been lost. This work demonstrates that constructing MOF-like networks from SMMs by weak interactions is feasible but that even these can introduce significant inter-SMM exchange interactions that weaken or destroy the SMM properties.The carboxylate substitution reaction of triangular [Mn3O(O2CMe)3(mpko)3](ClO4) (mpkoH = methyl(2-pyridyl)ketone oxime) with 3,5-dihydroxybenzoic acid (dhbH) has yielded a MOF-like 3-D network formed by extensive formation of inter-Mn3 π–π stacking interactions. The repeating unit is an [Mn3]8 rhombohedron, and the voids in the network each contain eight MeCN molecules. VT magnetic susceptibility studies reveal antiferromagnetic inter-Mn3 exchange couplings.
Co-reporter:Annaliese E. Thuijs, Andrea Marton, Theocharis C. Stamatatos, Khalil A. Abboud, George Christou
Polyhedron 2016 Volume 103(Part B) pp:288-294
Publication Date(Web):8 January 2016
DOI:10.1016/j.poly.2015.03.017
The syntheses, structures, and magnetic properties are reported of two new high nuclearity Ce–Mn oxo carboxylate clusters at high CeIV/MnIII oxidation states and with nuclearities of Ce5Mn11 and Ce3Mn7. The compounds are (NnBu4)2[Ce5Mn11O13(OH)2(O2CPh)24(NO3)2](NO3) (1) and [Ce3Mn7O8(O2CPh)17(H2O)4] (2). 1 was prepared from the oxidation of Mn(O2CPh)2 by (NnBu4)2Ce(NO3)6, whereas 2 was obtained from the comproportionation reaction of Mn(O2CPh)2 and NnBu4MnO4 in the presence of Ce(NO3)3. Both compounds possess unprecedented structures, comprising an irregular metal topology of several edge-fused triangular units with overall virtual C2 symmetry. Variable-temperature, solid-state dc and ac magnetization studies on 1 and 2 in the 1.8–300 K range revealed predominantly weak antiferromagnetic exchange interactions within the complexes. For 1, the combined dc and ac data indicate an S = 5 ground state but with low-lying excited states consistent with the high nuclearity. For 2, even lower-lying excited states were observed, precluding clear determination of the ground state but with an estimate of S = 2 or 3, or less. Complexes 1 and 2 are new additions to the Ce–Mn family of clusters and the broader class of 3d/4f molecular systems, and 1 is the highest nuclearity Ce–Mn cluster to date.The syntheses, structures, and magnetic properties are reported of two new high nuclearity Ce–Mn oxo carboxylate clusters at high CeIV/MnIII oxidation states and with nuclearities of Ce5Mn11 and Ce3Mn7. The Ce5Mn11 cluster is the highest nuclearity Ce–Mn cluster to date.
Co-reporter:Tu N. Nguyen; Muhandis Shiddiq; Tuhin Ghosh; Khalil A. Abboud; Stephen Hill
Journal of the American Chemical Society 2015 Volume 137(Issue 22) pp:7160-7168
Publication Date(Web):June 1, 2015
DOI:10.1021/jacs.5b02677
[Mn3O(O2CMe)3(dpd)3/2)]2(I3)2 has been obtained from the reaction of 1,3-di(pyridin-2-yl)propane-1,3-dione dioxime (dpdH2) with triangular [MnIII3O(O2CMe)(py)3](ClO4). It comprises two [MnIII3O]7+ triangular units linked covalently by three dioximate ligands into a [Mn3]2 dimer. Solid state dc and ac magnetic susceptibility measurements reveal that each Mn3 subunit of the dimer is a separate single-molecule magnet (SMM) with an S = 6 ground state and that the two SMM units are very weakly ferromagnetically exchange coupled. High-frequency EPR spectroscopy on a single crystal displays signal splittings indicative of quantum superposition/entanglement of the two SMMs, and parallel studies on MeCN/toluene (1:1) frozen solutions reveal the same spectral features. The dimer thus retains its structure and inter-Mn3 coupling upon dissolution. This work establishes that covalently linked molecular oligomers of exchange-coupled SMMs can be prepared that retain their oligomeric nature and attendant inter-SMM quantum mechanical coupling in solution, providing a second phase for their study and demonstrating the feasibility of using solution methods for their deposition on surfaces and related substrates for study.
Co-reporter:Annaliese E. Thuijs; Philippa King; Khalil A. Abboud
Inorganic Chemistry 2015 Volume 54(Issue 18) pp:9127-9137
Publication Date(Web):September 9, 2015
DOI:10.1021/acs.inorgchem.5b01553
Two new Mn16 clusters are reported: [Mn16O10(OH)3(OMe)8(O2CPhBut)17(MeOH)5] (2) and [Mn16O16(OMe)6(O2CPh)12(NO3)4(MeOH)2(H2O)4] (3). The complexes were obtained by reductive aggregation of MnO4– in CH2Cl2/MeOH, and oxidation of MnII and preformed (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] with CeIV, respectively. The core of 2 has a Mn16III core with an unusual 1:2:3:4:3:2:1 layer structure and a W-shaped pleated topology, whereas 3 contains a central 2 × 3 Mn6IV planar grid held within a nonplanar Mn10III loop and is a rare example of a complex with nitrate ions bridging like carboxylate ions. Variable-temperature, solid-state dc susceptibility, and ac susceptibility studies reveal that 2 and 3 possess S = 12 and S = 8 ground states, respectively. Fits of dc magnetization data collected over a temperature range of 1.8–4.0 K and a magnetization range of 0.1–4 T were fit to give S = 12, D = −0.16(2) cm–1, g = 1.98(3) for 2 and S = 8, D = −0.22(1) cm–1, g = 1.99(2) for 3, where D is the axial zero-field splitting parameter. The ac in-phase (χM′T) susceptibility below 15 K confirmed the ground-state spin values of 2 and 3, as determined from dc data, and the appearance of frequency-dependent out-of-phase (χM″) signals revealed that both complexes are new single-molecule magnets (SMMs). Fits of the ac data gave Ueff = 49.7(1) K and τ0 = 4.32 × 10–9 s for 2 and Ueff ≈ 14.0 ± 2 cm–1 and τ0 ≈ 3.2 ± 0.5 × 10–8 s for 3, where Ueff is the effective barrier to magnetization relaxation and τ0 is the pre-exponential factor. Thus, complexes 2 and 3 are two new members of a growing family of Mn16 clusters, and two new examples of high-nuclearity SMMs, with the Ueff for 2 approaching the value for the prototypical SMM family, [Mn12O12(O2CR)16(H2O)4].
Co-reporter:Christos Lampropoulos, Annaliese E. Thuijs, Kylie J. Mitchell, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2014 Volume 53(Issue 13) pp:6805-6816
Publication Date(Web):June 6, 2014
DOI:10.1021/ic500617f
The syntheses, structures, and magnetic properties are reported for three new Ce/Mn clusters with different Ce/Mn ratios: [Ce6Mn4O12(O2CMe)10(NO3)4(py)4] (py = pyridine) (1), [CeMn8O8(O2CCH2tBu)12(DMF)14] (DMF = dimethylformamide) (2), and [Ce2Mn4O2(O2CMe)6(NO3)4(hmp)4] (3; hmp– is the anion of 2-(hydroxymethyl)pyridine). 1 and 2 were obtained from the reaction of CeIV with [Mn12O12(O2CMe)16(H2O)4] (MnIII8MnIV4) and [Mn8O2(O2CCH2tBu)14(tBuCH2CO2H)4] (MnII6MnIII2), respectively, whereas 3 resulted from the oxidation of MnII acetate with CeIV in the presence of hmpH. Cluster 1 possesses an unusual [Ce6Mn4O12]14+ core topology consisting of a [Ce6O8] face-capped octahedron, which is face-fused at each end to a [CeIV2MnIIIMnIVO4] cubane. Cluster 2 possesses a nonplanar, saddlelike loop of eight MnIII atoms bridged by eight μ3-O2– ions to a central CeIV atom. Cluster 3 is similar to 1 in possessing an octahedral core, but this is now a [Ce2Mn4] octahedron consisting of a CeIII atom on either side of a Mn4 parallelogram, with the metal atoms bridged by two μ4-O2– ions, the alkoxide arms of four hmp– groups, and six acetates. Clusters 1, 2, and 3 are thus at the CeIV6MnIII2MnIV2, CeIVMnIII8, and CeIII2MnIII4 oxidation levels, respectively. Variable-temperature, solid-state direct current (DC) and alternating current (AC) magnetization studies on 1–3 in the 5.0–300 K range revealed predominantly antiferromagnetic exchange interactions within the complexes. For 1, fitting of the DC data to the theoretical expression for a dinuclear MnIIIMnIV complex derived using the Van Vleck equation and an isotropic spin Hamiltonian (ℋ = −2JŜi·Ŝj convention) gave a value for the exchange coupling parameter (J) of −60.4(7) cm–1 and a Landé factor g = 2.00(1), indicating an S = 1/2 ground state. For 2, both DC and AC data indicate an S = 0 ground state, which is unprecedented for a member of the CeMn8 family and now means members of the latter have been made that span the whole range of possible ground states from S = 0 to the maximum S = 16. Cluster 3 possesses an S = 0 ground state for its Mn4 fragment, with the paramagnetism remaining at low temperature coming from the weakly coupled CeIII centers. These three species are new additions to the Mn–Ce family of clusters and the broader class of 3d/4f molecular systems.
Co-reporter:Shreya Mukherjee, Khalil A. Abboud, Wolfgang Wernsdorfer, and George Christou
Inorganic Chemistry 2013 Volume 52(Issue 2) pp:873-884
Publication Date(Web):December 28, 2012
DOI:10.1021/ic302021a
The comproportionation reaction between MnII and MnVII reagents under acidic conditions has been investigated in the presence of pivalic acid as a route to new high oxidation state manganese pivalate clusters containing some MnIV. The reaction of Mn(O2CBut)2 and NBun4MnO4 with an excess of pivalic acid in the presence of Mn(ClO4)2 and NBun4Cl in hot MeCN led to the isolation of [Mn8O6(OH)(O2CBut)9Cl3(ButCO2H)0.5(MeCN)0.5] (1). In contrast, the reaction of Mn(NO3)2 and NBun4MnO4 in hot MeCN with an excess of pivalic acid gave a different octanuclear complex, [Mn8O9(O2CBut)12] (2). The latter reaction but with Mn(O2CBut)2 in place of Mn(NO3)2, and in a MeCN/THF solvent medium, gave [Mn9O7(O2CBut)13(THF)2] (3). Complexes 1–3 possess rare or unprecedented Mnx topologies: 1 possesses a [MnIII7MnIV(μ3-O)4(μ4-O)2(μ3-OH)(μ4-Cl)(μ2-Cl)]8+ core consisting of two body-fused Mn4 butterfly units attached to the remaining Mn atoms via bridging O2–, OH–, and Cl– ions. In contrast, 2 possesses a [Mn6IVMn2III(μ3-O)6(μ-O)3]12+ core consisting of two [Mn3O4] incomplete cubanes linked by their O2– ions to two MnIII atoms. The cores of 1 and 2 are unprecedented in Mn chemistry. The [MnIII9(μ3-O)7]13+ core of 3 also contains two body-fused Mn4 butterfly units, but they are linked to the remaining Mn atoms in a different manner than in 1. Solid-state direct current (dc) and/or alternating current (ac) magnetic susceptibility data established S = 15/2, S = 2, and S = 1 ground states for 1·MeCN, 2·1/4MeCN, and 3, respectively. The ac susceptibility data also revealed nonzero, frequency-dependent out-of-phase (χ″M) signals for 1·MeCN at temperatures below 3 K, suggesting possible single-molecule magnet behavior, which was confirmed by single-crystal magnetization vs dc field scans that exhibited hysteresis loops. The combined work thus demonstrates the continuing potential of comproportionation reactions for isolating high oxidation state Mnx clusters, and the sensitivity of the product identity to minor changes in the reaction conditions.
Co-reporter:Christos Lampropoulos ; Muralee Murugesu ; Andrew G. Harter ; Wolfgang Wernsdofer ; Stephen Hill ; Naresh S. Dalal ; Arneil P. Reyes ; Philip L. Kuhns ; Khalil A. Abboud
Inorganic Chemistry 2013 Volume 52(Issue 1) pp:258-272
Publication Date(Web):December 10, 2012
DOI:10.1021/ic301764t
The synthesis and properties are reported of a rare example of a Mn12 single-molecule magnet (SMM) in truly axial symmetry (tetragonal, I4̅). [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH (3·MeOH) was synthesized by carboxylate substitution on [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1). The complex was found to possess an S = 10 ground state, as is typical for the Mn12 family, and displayed both frequency-dependent out-of-phase AC susceptibility signals and hysteresis loops in single-crystal magnetization vs DC field sweeps. The loops also exhibited quantum tunneling of magnetization steps at periodic field values. Single-crystal, high-frequency electron paramagnetic resonance spectra on 3·MeOH using frequencies up to 360 GHz revealed perceptibly sharper signals than for 1. Moreover, careful studies as a function of the magnetic field orientation did not reveal any satellite peaks, as observed for 1, suggesting that the crystals of 3 are homogeneous and do not contain multiple Mn12 environments. In the single-crystal 55Mn NMR spectrum in zero applied field, three well-resolved peaks were observed, which yielded hyperfine and quadrupole splitting at three distinct sites. However, observation of a slight asymmetry in the Mn4+ peak was detectable, suggesting a possible decrease in the local symmetry of the Mn4+ site. Spin–lattice (T1) relaxation studies were performed on single crystals of 3·MeOH down to 400 mK in an effort to approach the quantum tunneling regime, and fitting of the data using multiple functions was employed. The present work and other recent studies continue to emphasize that the new generation of truly high-symmetry Mn12 complexes are better models for thorough investigation of the physical properties of SMMs than their predecessors such as 1.
Co-reporter:Antonio Masello, Khalil A. Abboud, Wolfgang Wernsdorfer, and George Christou
Inorganic Chemistry 2013 Volume 52(Issue 18) pp:10414-10423
Publication Date(Web):August 23, 2013
DOI:10.1021/ic4011955
The syntheses, structures, and magnetic properties are reported of a new Mn8 cluster obtained from the reaction of ferrocene-1,1′-dicarboxylic acid (fdcH2) with [Mn12O12(O2CMe)16(H2O)4] and mononuclear Mn salts under different conditions and limited light exposure. The product was obtained in two forms: [Mn8O4(fdc)6(DMF)2(H2O)2] (1) and [Mn8O4(fdc)6(DMF)4] (2), differing in the bound solvent ligands. The structures are otherwise almost identical, comprising very similar cores that both contain 4MnIII and 4MnII atoms bridged by four O2– ions and six fdc2– groups. The [MnIII4MnII4(μ4-O)4] cores have virtual Td symmetry and can be described as a central [MnIII4(μ4-O)4]4+ cubane unit whose four O2– ions are μ4, because they each attach to an external MnII atom. Peripheral ligation about the core is provided by six bridging fdc2– groups and the terminal solvent ligands, one each on the MnII atoms. The differences in solvent ligands between 1 and 2, and different packing from the different crystal space groups, lead to significant differences in metric parameters within the core, which are reflected in significantly different magnetic properties. Variable-temperature, solid-state dc and ac susceptibility measurements reveal the clusters to be predominantly antiferromagnetically coupled, and to possess ground state spin values of S = 5 and S = 2 for 1 and 2, respectively. The difference in ground states is assigned to the small but distinct structural differences seen in the central cubane. Alternating current (AC) susceptibility data indicate 1 and 2 to be new single-molecule magnet, and this was confirmed by magnetization versus direct current (DC) field scans on a single crystal of 1·4DMF·4H2O, which exhibited hysteresis.
Co-reporter:Andrew M. Mowson ; Tu N. Nguyen ; Khalil A. Abboud
Inorganic Chemistry 2013 Volume 52(Issue 21) pp:12320-12322
Publication Date(Web):October 24, 2013
DOI:10.1021/ic402155h
[Mn3]2 and [Mn3]4 supramolecular aggregates of weakly exchange-coupled MnIII3 single-molecule magnets (SMMs) with S = 6 have been prepared by carboxylate substitution on [Mn3O(O2CMe)3(mpko)3]+ [mpkoH = methyl(pyridine-2-yl) ketone oxime)] with the dicarboxylic acids α-truxillic acid and fumaric acid, respectively. The method opens up a new approach to Mn3 SMM aggregates of various size and topology.
Co-reporter:Tu N. Nguyen, Khalil A. Abboud, George Christou
Polyhedron 2013 Volume 66() pp:171-178
Publication Date(Web):13 December 2013
DOI:10.1016/j.poly.2013.03.041
The reaction between Mn(pc)2·4H2O (pcH is 1-pyrenecarboxylic acid), N-methyldiethanolamine (mdaH2), and NEt3 in a 2:2:3 molar ratio in CH2Cl2 or CHCl3 gives the tetranuclear complex [Mn4(pc)4(mda)2(mdaH)2], isolated as the ·2CH2Cl2 (3) and ·2CHCl3 (4) solvates, respectively. Only crystals of 4 were of sufficient quality for single-crystal X-ray crystallography. Complex 4 possesses a [MnII2MnIII2] core with the Mn ions arranged in a planar rhombus that can be described as two Mn3 triangles fused at one edge. Additional monoatomic bridging by mda2− or mdaH−μ- and μ3-O atoms on each edge and at the center of the Mn3 triangular units gives a defective-dicubane core structure. Ligation is completed by two bridging and two monodentate pc− groups, each of which is involved in π–π stacking interactions with those on neighboring Mn4 molecules to give a 2D network. Variable-temperature solid-state magnetic susceptibility studies of 3 and 4 in the temperature range 5.0–300 K. Various fitting and simulation models were employed in analyzing the data for 3, which shows no evidence of significant intermolecular interactions, and it was concluded that it contains three symmetry-inequivalent exchange interactions, J = +2.34 cm−1, J′ = +7.70 cm−1, J″ = −1.33 cm−1 and g = 1.99, where J′ is the MnIII⋯MnIII interaction, and J and J″ are the MnII⋯MnIII interactions. This indicates an S = 8 ground state with a very low-lying an S = 9 excited state. This conclusion was supported by fits of reduced magnetization data, which gave an S = 8 ground state with axial zero-field splitting parameter D = −0.19(1) cm−1, and g = 1.94(1). Ac susceptibility studies on 3 show that it is a single-molecule magnet (SMM). Complex 4 shows different magnetic behavior from 3 due to the intermolecular interactions.Reaction of 1-pyrenecarboxylic acid (pcH) and N-methyldiethanolamine (mdaH2) with MnII in CH2Cl2 or CHCl3 gives [Mn4(pc)4(mda)2(mdaH)2], possessing a defective-dicubane structure, as the ·2CH2Cl2 (3) and ·2CHCl3 (4) solvates, respectively. Magnetic data indicate 3 has an S = 8 ground state and is a single-molecule magnet. Complex 4 shows different magnetic behavior due to extensive π–π stacking and intermolecular exchange interactions.
Co-reporter:Linh Pham, Khalil A. Abboud, Wolfgang Wernsdorfer, George Christou
Polyhedron 2013 66() pp: 205-211
Publication Date(Web):
DOI:10.1016/j.poly.2013.04.024
Co-reporter:Constantina Papatriantafyllopoulou, Khalil A. Abboud, George Christou
Polyhedron 2013 52() pp: 196-206
Publication Date(Web):
DOI:10.1016/j.poly.2012.09.052
Co-reporter:George Christou, Allan G. Blackman, Spyros P. Perlepes, Natia L. Frank
Polyhedron 2013 52() pp: 1-2
Publication Date(Web):
DOI:10.1016/j.poly.2013.01.013
Co-reporter:Jamie A. Stull;Shreya Mukherjee;Junko Yano;Theocharis C. Stamatatos;Konstantina Pringouri;Troy A. Stich;Khalil A. Abboud;R. David Britt;Vittal K. Yachandra
PNAS 2012 Volume 109 (Issue 7 ) pp:
Publication Date(Web):2012-02-14
DOI:10.1073/pnas.1115290109
The laboratory synthesis of the oxygen-evolving complex (OEC) of photosystem II has been the objective of synthetic chemists
since the early 1970s. However, the absence of structural information on the OEC has hampered these efforts. Crystallographic
reports on photosystem II that have been appearing at ever-improving resolution over the past ten years have finally provided
invaluable structural information on the OEC and show that it comprises a [Mn3CaO4] distorted cubane, to which is attached a fourth, external Mn atom, and the whole unit attached to polypeptides primarily
by aspartate and glutamate carboxylate groups. Such a heterometallic Mn/Ca cubane with an additional metal attached to it
has been unknown in the literature. This paper reports the laboratory synthesis of such an asymmetric cubane-containing compound
with a bound external metal atom, [(1)] . All peripheral ligands are carboxylate or carboxylic acid groups. Variable-temperature magnetic susceptibility data have
established 1 to possess an S = 9/2 ground state. EPR spectroscopy confirms this, and the Davies electron nuclear double resonance data reveal similar
hyperfine couplings to those of other MnIV species, including the OEC S2 state. Comparison of the X-ray absorption data with those for the OEC reveal 1 to possess structural parameters that make it a close structural model of the asymmetric-cubane OEC unit. This geometric
and electronic structural correspondence opens up a new front in the multidisciplinary study of the properties and function
of this important biological unit.
Co-reporter:Tu N. Nguyen ; Wolfgang Wernsdorfer ; Khalil A. Abboud
Journal of the American Chemical Society 2011 Volume 133(Issue 51) pp:20688-20691
Publication Date(Web):December 2, 2011
DOI:10.1021/ja2087344
The reaction between 3-phenyl-1,5-bis(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH2) and triangular [MnIII3O(O2CMe)(py)3](ClO4) (1) affords [Mn12O4(O2CMe)12(pdpd)6)](ClO4)4 (3). Complex 3 has a rectangular shape and consists of four [MnIII3O]7+ triangular units linked covalently by the dioximate ligands into a supramolecular [Mn3]4 tetramer. Solid-state dc and ac magnetic susceptibility measurements revealed that [Mn3]4 contains four Mn3 single-molecule magnets (SMMs), each with an S = 6 ground state. Magnetization versus dc-field sweeps on a single crystal gave hysteresis loops below 1 K that exhibited exchange-biased quantum tunneling of magnetization steps, confirming 3 to be a supramolecular aggregate of four weakly exchange-coupled SMM units.
Co-reporter:Constantina Papatriantafyllopoulou, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2011 Volume 50(Issue 18) pp:8959-8966
Publication Date(Web):August 22, 2011
DOI:10.1021/ic2011106
The initial employment of 2-(hydroxymethyl)pyridine for the synthesis of Mn/Ln (Ln = lanthanide) and Mn/Y clusters, in the absence of an ancillary organic ligand, has afforded a family of tetranuclear [MnIII2MIII2(OH)2(NO3)4(hmp)4(H2O)4](NO3)2 (M = Dy, 1; Tb, 2; Gd, 3; Y; 4) anionic compounds. 1–4 possess a planar butterfly (or rhombus) core and are rare examples of carboxylate-free Mn/Ln and Mn/Y clusters. Variable-temperature dc and ac studies established that 1 and 2, which contain highly anisotropic LnIII atoms, exhibit slow relaxation of their magnetization vector. Fitting of the obtained magnetization (M) versus field (H) and temperature (T) data for 3 by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) showed the ground state to be S = 3. Complex 4 has an S = 0 ground state. Fitting of the magnetic susceptibility data collected in the 5–300 K range for 3 and 4 to the appropriate van Vleck equations revealed, as expected, extremely weak antiferromagnetic interactions between the paramagnetic ions; for 3, J1 = −0.16(2) cm–1 and J2 = −0.12(1) cm–1 for the MnIII···MnIII and MnIII···GdIII interactions, respectively. The S = 3 ground state of 3 has been rationalized on the basis of the spin frustration pattern in the molecule. For 4, J = −0.75(3) cm–1 for the MnIII···MnIII interaction. Spin frustration effects in 3 have been quantitatively analyzed for all possible combinations of sign of J1 and J2.
Co-reporter:Shreya Mukherjee, Rashmi Bagai, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2011 Volume 50(Issue 9) pp:3849-3851
Publication Date(Web):March 29, 2011
DOI:10.1021/ic200256j
Two clusters with a new type of FeIII7 disklike structure have been prepared; in contrast to other FeIII7 disks, they possess high ground-state spins (S = 15/2 and 21/2), which have been rationalized by analysis of the spin-frustration patterns.
Co-reporter:Theocharis C. Stamatatos ; Katie Oliver ; Khalil A. Abboud
Inorganic Chemistry 2011 Volume 50(Issue 11) pp:5272-5282
Publication Date(Web):April 26, 2011
DOI:10.1021/ic200656q
The first high nuclearity, mixed-metal BiIII/MnIV and BiIII/MnIII complexes are reported. The former complexes are [Bi2MnIV6O9(O2CEt)9(HO2CEt)(NO3)3] (1) and [Bi2MnIV6O9(O2CPh)9(HO2CPh)(NO3)3] (2) and were obtained from the comproportionation reaction between Mn(O2CR)2 and MnO4– in a 10:3 ratio in the presence of Bi(NO3)3 (3 equiv) in either a H2O/EtCO2H (1) or MeCN/PhCO2H (2) solvent medium. The same reaction that gives 2, but with Bi(O2CMe)3 and MeNO2 in place of Bi(NO3)3 and MeCN, gave the lower oxidation state product [BiMnIII10O8(O2CPh)17(HO2CPh)(H2O)] (3). Complexes 1 and 2 are near-isostructural and possess an unusual and high symmetry core topology consisting of a MnIV6 wheel with two central BiIII atoms capping the wheel on each side. In contrast, the [BiMnIII10O8]17+ core of 3 is low symmetry, comprising a [BiMn3(μ3-O)2]8+ butterfly unit, four [BiMn3(μ4-O)]10+ tetrahedra, and two [BiMn2(μ3-O)]7+ triangles all fused together by sharing common Mn and Bi vertices. Variable-temperature, solid-state dc and ac magnetization data on 1–3 in the 1.8–300 K range revealed that 1 and 2 possess an S = 0 ground state spin, whereas 3 possesses an S = 2 ground state. The work offers the possibility of access to molecular analogs of the multifunctional Bi/Mn/O solids that are of such great interest in materials science.
Co-reporter:Antonio Masello ; Yiannis Sanakis ; Athanassios K. Boudalis ; Khalil A. Abboud
Inorganic Chemistry 2011 Volume 50(Issue 12) pp:5646-5654
Publication Date(Web):May 16, 2011
DOI:10.1021/ic200348s
The synthesis and properties are reported of a new Fe7 cluster obtained from the reaction of ferrocene-1,1′-dicarboxylic acid (fdcH2) with FeCl2·4H2O in MeOH under ambient light conditions. The compound is the mixed-anion salt [Fe7O3(OMe)(fdc)6(MeOH)3][FeCl4]Cl2 (1; 8FeIII), containing six (fdcn–) groups as peripheral ligands. The cation of 1 has virtual C3 symmetry and contains a central [Fe4(μ3-O)3(μ3-OMe)]5+ cubane unit whose three oxide ions each become μ4 by attaching to a fourth Fe atom outside the cubane. The resulting [Fe7(μ3-O3)(μ3-OMe)]14+ core is surrounded by six fdcn– (n = 1, 2) groups, which divide into two sets by virtual symmetry. The blue color of the complex suggested that some of these ligands are in their oxidized fdc– ferricenium (FeIII) state, and various data point to there being one fdc– ligand in the compound, the initial example of the group acting as a ligand in inorganic chemistry. Variable-temperature, solid-state DC and AC susceptibility measurements reveal the cation to be antiferromagnetically coupled, as expected for high-spin FeIII, and to have an S = 2 ground state, consistent with an S = 5/2 Fe7 inner core coupled antiferromagnetically to the one paramagnetic fdc– (S = 1/2) ligand. Complex 1 displays multiple reductions and oxidations when investigated by electrochemistry in MeCN. 57Fe Mössbauer spectroscopy supports the presence of only five fdc2– ligands, but cannot resolve the signals from the various FeIII sites.
Co-reporter:Constantina Papatriantafyllopoulou ; Wolfgang Wernsdorfer ; Khalil A. Abboud
Inorganic Chemistry 2011 Volume 50(Issue 2) pp:421-423
Publication Date(Web):December 13, 2010
DOI:10.1021/ic102378u
A high-oxidation-state MnIII,IV21DyIII cluster with an unusual structure is reported. It also possesses a record barrier to magnetization reversal for a 3d/4f single-molecule magnet (SMM) and provides insight into how the full benefit of lanthanides to the mixed 3d/4f SMM field might be realized.
Co-reporter:Galia Maayan and George Christou
Inorganic Chemistry 2011 Volume 50(Issue 15) pp:7015-7021
Publication Date(Web):July 5, 2011
DOI:10.1021/ic200393y
The family of polynuclear manganese clusters of formula [Mn12O12(O2CR)16(H2O)4] (R = Et, Ph, etc.) has been investigated in great detail over the years for their ability to function as single-molecule magnets (SMMs), but they have not been employed as oxidation catalysts. In the present report, the ability is described of these clusters to act as catalysts in the selective oxidation of benzyl alcohol to benzaldehyde using molecular O2 as the primary oxidant and the nitroxyl radical TEMPO as a cocatalyst. A systematic investigation of Mn clusters varied in their R group, oxidation state, and size was conducted in order to realize the electronic requirements that will lead to the best catalytic activity. The best reactivity (>99%) was obtained when the catalyst was the mixed-metal cluster [CeMn6O9(O2CMe)9(NO3)(H2O)2], which contains Ce4+Mn4+6 ions; in this case, lower loadings of catalysts (cluster and TEMPO) are required and the reaction can proceed even without a solvent. In addition, it has been demonstrated that the high efficiency can be only achieved when both high oxidation Ce4+ and Mn4+ ions are present within the same cluster.
Co-reporter:Arpita Saha, Michael Thompson, Khalil A. Abboud, Wolfgang Wernsdorfer, and George Christou
Inorganic Chemistry 2011 Volume 50(Issue 20) pp:10476-10485
Publication Date(Web):September 22, 2011
DOI:10.1021/ic201683p
The synthesis and characterization of a family of Mn2IIIMn2IILnIII2 complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn4Ln2O2(O2CBut)6(edteH2)2(NO3)2] are reported, where edteH4 is N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn4Y2 (5) complex has also been prepared. They were obtained from reaction of Ln(NO3)3 or Y(NO3)3 with Mn(O2CBut)2, edteH4, and NEt3 in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn4Ln2(μ4-O2–)2(μ3-OR)4] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d–4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1–5 were carried out. Fitting of dc χMT vs T data for 5 gave Jbb (MnIII···MnIII) = –32.6(9) cm–1, Jwb (MnII···MnIII) = +0.5(2) cm–1, and g = 1.96(1), indicating a |n, 0, n⟩ (n = 0–5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm–1, and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the MnII···GdIII interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn4Tb2 analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d–4f SMM to do so.
Co-reporter:Arpita Saha, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2011 Volume 50(Issue 24) pp:12774-12784
Publication Date(Web):November 9, 2011
DOI:10.1021/ic201916d
The syntheses, crystal structures, and magnetochemical characterization are reported for the new mixed-valent Mn clusters [Mn2IIMnIII(O2CMe)2(edteH2)2](ClO4) (1), [MnII2MnIII2(edteH2)2(hmp)2Cl2](MnIICl4) (2), [MnIII6O2(O2CBut)6(edteH)2(N3)2] (3), [Na2MnIII8MnII2O4(OMe)2(O2CEt)6(edte)2(N3)6] (4), and (NEt4)2[Mn8IIIMn2IIO4(OH)2-(O2CEt)6(edte)2(N3)6](5), where edteH4 is N,N,N′,N′-tetrakis-(2-hydroxyethyl)ethylenediamine and hmpH is 2-(hydroxymethyl)pyridine. 1–5 resulted from a systematic exploration of the effect of different Mn sources, carboxylates, the presence of azide, and other conditions, on the Mn/edteH4 reaction system. The core of 1 consists of a linear MnIIMnIIIMnII unit, whereas that of 2 is a planar Mn4 rhombus within a [MnII2MnIII2(μ3-OR)2] incomplete-dicubane unit. The core of 3 comprises a central [MnIII4(OR)2] incomplete-dicubane on either side of which is edge-fused a triangular [MnIII3(μ3-O)] unit. The cores of 4 and 5 are similar and consist of a central [MnII2MnIII2(μ3-OR)2] incomplete-dicubane on either side of which is edge-fused a distorted [MnIIMnIII3(μ3-O)2(μ3-OR)2] cubane unit. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out on 1–5 in the 5.0–300 K range, and they established the complexes to have ground state spin values of S = 3 for 1, S = 9 for 2, and S = 4 for 3. The study of 3 provided an interesting caveat of potential pitfalls from particularly low-lying excited states. For 4 and 5, the ground state is in the S = 0–4 range, but its identification is precluded by a high density of low-lying excited states.
Co-reporter:Taketo Taguchi ; Wolfgang Wernsdorfer ; Khalil A. Abboud
Inorganic Chemistry 2010 Volume 49(Issue 1) pp:199-208
Publication Date(Web):December 4, 2009
DOI:10.1021/ic901741n
The syntheses, crystal structures, and magnetochemical characterization are reported for two new Mn clusters, [Mn7O3(OH)3(O2CBut)7(dmhmp)4] (1) and [Mn12O7(OH)(OMe)2(O2CPh)12(dmhmp)4(H2O)] (2). They were obtained from the use of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a more bulky version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dmhmpH with MnCl2·4H2O and NaO2CBut in MeCN/MeOH led to the heptanuclear complex 1, whereas the analogous reaction with Mn(O2CPh)2 gave dodecanuclear complex 2. Complexes 1 and 2 are both mixed-valent and are of unprecedented structural types. Complex 1 (MnII, 6MnIII) can be described as the fusion of butterfly-like [Mn4(μ3-O)2] and tetrahedral [Mn4(μ4-O)] units by the sharing of a common Mn atom. Complex 2 (3MnII, 9MnIII) possesses a central [Mn4O6] face-sharing incomplete dicubane, on either side of which is a tetrahedral [Mn4(μ4-O)] unit attached to the oxide ions of the former. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess unusual S = 7/2 and 13/2 ground states, respectively. The ac susceptibility studies on 2 revealed nonzero frequency-dependent out-of-phase (χM′′) signals at temperatures below 3 K, indicating a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2·3CH2Cl2 down to 0.04 K exhibited hysteresis, thus confirming complex 2 to be a new half-integer SMM.
Co-reporter:Christos Lampropoulos ; Gage Redler ; Saiti Data ; Khalil A. Abboud ; Stephen Hill
Inorganic Chemistry 2010 Volume 49(Issue 4) pp:1325-1336
Publication Date(Web):January 21, 2010
DOI:10.1021/ic901480y
Two new members of the Mn12 family of single-molecule magnets (SMMs), [Mn12O12(O2CCH2But)16(ButOH)(H2O)3]·2ButOH (3·2ButOH) and [Mn12O12(O2CCH2But)16(C5H11OH)4] (4) (C5H11OH is 1-pentanol), are reported. They were synthesized from [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes 3 and 4 are new members of the recently established [Mn12O12(O2CCH2But)16(solv)4] (solv = H2O, alcohols) family of SMMs. Only one bulky ButOH can be accommodated into 3, and even this causes significant distortion of the [Mn12O12] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes 3 and 4, and they established that both possess an S = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with 4 showing out-of-phase AC peaks at higher temperatures than 3. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of 3·2ButOH and 4, and these revealed that the axial zero-field splitting constant, D, is very different for the two compounds. Furthermore, it was established that 4 is the Mn12 SMM with the highest kinetic barrier (Ueff) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn12 SMMs without major change to the ligation or oxidation state.
Co-reporter:Constantina Papatriantafyllopoulou ; Theocharis C. Stamatatos ; Constantinos G. Efthymiou ; Luis Cunha-Silva ; Filipe A. Almeida Paz ; Spyros P. Perlepes
Inorganic Chemistry 2010 Volume 49(Issue 21) pp:9743-9745
Publication Date(Web):October 4, 2010
DOI:10.1021/ic101581g
The initial employment of 2-pyridinealdoxime in 3d/4f chemistry has led to a NiII8DyIII8 cluster with an unprecedented metal topology; the compound has an unusual structure, is the highest-nuclearity metal oxime cluster to date, and exhibits slow magnetization relaxation.
Co-reporter:Taketo Taguchi, Wolfgang Wernsdorfer, Khalil A. Abboud, and George Christou
Inorganic Chemistry 2010 Volume 49(Issue 22) pp:10579-10589
Publication Date(Web):October 20, 2010
DOI:10.1021/ic101594d
The synthesis, crystal structures, and magnetochemical characterization of two new Mn clusters [Mn8O2(O2CPh)10(hmp)4(MeOH)2] (1; 6MnII, 2MnIII) and [Mn16O8(OH)2(O2CPh)12(hmp)10(H2O)2](O2CPh)2 (2; 6MnII, 10MnIII) are reported. They were obtained from the use of 2-(hydroxymethyl)pyridine (hmpH) under the same reaction conditions but differing in the presence or absence of added base. Thus, the reaction of hmpH with Mn(O2CPh)2 in CH2Cl2/MeOH led to isolation of octanuclear complex 1, whereas the analogous reaction in the presence of NEt3 gave hexadecanuclear complex 2. Complexes 1 and 2 possess either very rare or unprecedented core structures that are related to each other: that of 1 can be described as a linked pair of incomplete [Mn4O3] cubanes, while that of 2 consists of a linked pair of complete [Mn4O4] cubanes, on either side of which is attached a tetrahedral [Mn4(μ4-O)] unit. Solid-state direct current (dc) and alternating current (ac) magnetic susceptibility measurements on 1 and 2 establish that they possess S = 5 and 8 ground states, respectively. Complex 2 exhibits frequency-dependent out-of-phase (χM′′) ac susceptibility signals at temperatures below 3 K suggestive of a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2·10MeOH down to 0.04 K exhibited hysteresis, confirming 2 to be a new SMM. Comparison of the structure of 2 (Mn16) with Mn12 or Mn6 clusters previously obtained under the same reaction conditions but with two Me or two Ph groups, respectively, added next to the alkoxide O atom of hmp− indicate their influence on the nuclearity and structure of the products as being due to the overall bulk of the chelate plus the decreased ability of the O atom to bridge.
Co-reporter:Constantinos G. Efthymiou ; Theocharis C. Stamatatos ; Constantina Papatriantafyllopoulou ; Anastasios J. Tasiopoulos ; Wolfgang Wernsdorfer ; Spyros P. Perlepes
Inorganic Chemistry 2010 Volume 49(Issue 21) pp:9737-9739
Publication Date(Web):September 28, 2010
DOI:10.1021/ic101504c
Unusual {NiII3LnIII(μ-OR)6}3+ complexes with a “star” topology have been prepared with ligands derived from the metal-promoted reduction of di-2-pyridyl ketone under solvothermal conditions; the DyIII member shows weak single-molecule-magnet behavior.
Co-reporter:Taketo Taguchi, Michael S. Thompson, Khalil A. Abboud and George Christou
Dalton Transactions 2010 vol. 39(Issue 38) pp:9131-9139
Publication Date(Web):27 Aug 2010
DOI:10.1039/C0DT00635A
The syntheses, crystal structures and magnetochemical characterization are reported for two new FeIII complexes [Fe18O6(OH)8(pdm)10(pdmH)4(H2O)4](ClO4)10 (3) and [Fe9O4(OH)2(O2CMe)10(pdm)(pdmH)4](NO3) (4). They were synthesized from the use of the potentially O,N,O tridentate chelate, 2,6-pyridinedimethanol (pdmH2), in the presence or absence of carboxylate groups. Octadecanuclear complex 3 was obtained during reactivity studies on previously-reported [Fe8O3(OEt)(pdm)4(pdmH)4(EtOH)2](ClO4)5 (2), the latter undergoing hydrolysis to 3 on recrystallization from undried MeCN. The reaction of pdmH2 with preformed [Fe3O(O2CMe)6(py)3](NO3) in CH2Cl2 gave enneanuclear complex 4. Both complexes 3 and 4 are unprecedented structural types. The core of 3 comprises a central [Fe4O6] defective-dicubane attached on either side to a [Fe7O11] unit, which can be described as two [Fe4(μ4-O)] tetrahedra fused at a common Fe atom. The core of 4 can be considered as four vertex-fused triangular [Fe3(μ3-O)] units. Variable-temperature (T) and -field (H) solid-state dc and ac magnetization (M) studies were carried out on complexes 3 and 4 in the 1.8–300 K range. Analysis of the obtained data revealed that complexes 3 and 4 possess an S = 4 and S = 5/2 ground state spin, respectively.
Co-reporter:Tian-Fu Liu, Theocharis C. Stamatatos, Khalil A. Abboud and George Christou
Dalton Transactions 2010 vol. 39(Issue 15) pp:3554-3556
Publication Date(Web):02 Mar 2010
DOI:10.1039/C002925B
A systematic investigation of the alcoholysis of copper(II) pivalate (piv−) solutions has led to a series of Cu2, Cu6, and Cu16 products, depending on the alcohol used as solvent. When PrnOH or BunOH was employed, the products were the clusters [Cu16O4(OH)4(OR)8(piv)12(ROH)] (R = Prn, Bun) that are almost isostructural. The Cu16 clusters are antiferromagnetically-coupled with an S = 0 spin ground state.
Co-reporter:Christos Lampropoulos;Theocharis C. Stamatatos;Manolis J. Manos;Anastasios J. Tasiopoulos;Khalil A. Abboud
European Journal of Inorganic Chemistry 2010 Volume 2010( Issue 15) pp:2244-2253
Publication Date(Web):
DOI:10.1002/ejic.200901013
Abstract
The combined use of the anion of methyl 2-pyridyl ketone oxime (mpko–) and azides (N3–) in non-carboxylate Mn chemistry has afforded two new Mn6 clusters, [Mn6O3(N3)3(mpko)6(H2O)3](ClO4)2 (1) and [Mn6O3(N3)5(mpko)6(H2O)] (2), which are mixed-valence (MnII, 5 MnIII). The 1:1:1:1 reaction of Mn(ClO4)2·6H2O, mpkoH, NaN3 and NEt3 in MeOH gave the cationic complex 1, while a similar reaction using additional NaO2CMe led instead to the neutral complex 2. The structurally unprecedented cores of the two cages are very similar, and contain the six Mn ions in a topology comprising three vertex-sharing oxide-centered triangles bridged by two end-on azides. Variable-temperature, solid-state dc and ac magnetization studies were carried out for 1 and 2 in the 1.8–300 K range. The data reveal S = 5/2 ground states for both complexes, and fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization for 1 gave S = 5/2, D = –1.4(3) cm–1, and g = 1.99(1), where D is the axial zero-field splitting (ZFS) parameter. The combined results demonstrate the versatility of 2-pyridyl ketone oxime anions in the presence of suitable ancillary ligands, such as azides, for the synthesis of new Mn clusters, without requiring the co-presence of carboxylate ligands.
Co-reporter:Theocharis C. Stamatatos;Khalil A. Abboud
Journal of Cluster Science 2010 Volume 21( Issue 3) pp:485-501
Publication Date(Web):2010 September
DOI:10.1007/s10876-010-0324-8
The combined use of 1,1,1-tris(hydroxymethyl)ethane (thmeH3) and azides in Mn carboxylate chemistry has yielded a new family of decanuclear [Mn6Na4O(N3)(O2CR)5(thme)4(H2O)4] (R = Me (1); Et (2)) complexes consisting of mixed-valence Mn2IIMn4III units with a very rare [Mn6(μ6-O)]14+ octahedral core contained within a tetrahedron of four NaI atoms. The [Mn6Na4] units of 1 and 2 are connected via the Na atoms to neighboring units, giving 3-D supramolecular assemblies with large channel cavities. Variable-temperature, solid-state dc and ac magnetization studies carried out in the 1.8–300 K range reveal that the Mn6 units of 1 and 2 are antiferromagnetically coupled to give S = 0 ground states for both complexes.
Co-reporter:Rashmi Bagai and George Christou
Chemical Society Reviews 2009 vol. 38(Issue 4) pp:1011-1026
Publication Date(Web):23 Feb 2009
DOI:10.1039/B811963E
Single-molecule magnets (SMMs) are individual molecules that can function as nanoscale magnetic particles. The [Mn12O12(O2CR)16(H2O)4] (Mn12; R = Me, Et, etc.) family of SMMs was the first one discovered; it is also the one whose study has provided the majority of current knowledge on this interesting magnetic phenomenon, prompting its description here as the Drosophila of the field. This tutorial review will survey the various chemical studies that have been carried out to date on this family. This will include a discussion of methods that have been developed for their structural and redox transformation, and the effect of the latter on the magnetic and SMM properties.
Co-reporter:Theocharis C. Stamatatos, Shreya Mukherjee, Khalil A. Abboud and George Christou
Chemical Communications 2009 (Issue 1) pp:62-64
Publication Date(Web):17 Nov 2008
DOI:10.1039/B812721B
A Ga20 single-strand wheel has been prepared by a targeted, propane-1,3-diolate-induced size modification of the known Ga10‘gallic wheel’; the Ga20 reverts back to Ga10 on treatment with an excess of MeOH.
Co-reporter:Theocharis C. Stamatatos, Alina Vinslava, Khalil A. Abboud and George Christou
Chemical Communications 2009 (Issue 20) pp:2839-2841
Publication Date(Web):22 Apr 2009
DOI:10.1039/B902016K
A new high oxidation state MnIII/IV11carboxylate complex has been prepared and then converted to a MnII/III25 azide/carboxylate cluster with Me3SiN3; the Mn25 product is the initial example of a higher oxidation state Mn azide complex not stabilized by any chelate ligands.
Co-reporter:Christos Lampropoulos, Theocharis C. Stamatatos, Khalil A. Abboud and George Christou
Inorganic Chemistry 2009 Volume 48(Issue 2) pp:429-431
Publication Date(Web):December 15, 2008
DOI:10.1021/ic802005a
An unusual [MnIVGdIII2(μ3-O2−)]8+ triangular complex has been prepared from the initial use of 2,6-diacetylpyridine dioxime (dapdoH2) in 3d/4f cluster chemistry. The complex has an S = 13/2 ground state, with exchange parameters J = +0.49 cm−1 and J′ = −0.12 cm−1 [ℋ = −2J(Ŝi·Ŝj) convention] for the GdIII···MnIV and GdIII···GdIII interactions, respectively. The origin of this ground state has been rationalized by consideration of the spin frustration occurring within the complex as a function of the relative magnitude of the competing interactions.
Co-reporter:Christos Lampropoulos ; Khalil A. Abboud ; Theocharis C. Stamatatos
Inorganic Chemistry 2009 Volume 48(Issue 3) pp:813-815
Publication Date(Web):January 9, 2009
DOI:10.1021/ic802084h
The reaction between Mn(O2CMe)2·4H2O and hmcH3 [hmcH3 = 2,6-bis(hydroxymethyl)-p-cresol] in CH2Cl2 in the presence of NEt3 affords the MnIII3 complex [NEt3(CH2Cl)]2[Mn3O(hmcH)3(hmcH2)3] (1). The anion of 1 contains a [MnIII3(μ3-O)]7+ triangular core, with the central O2− ion lying above the Mn3 plane. The complex is ferromagnetically coupled with a resulting S = 6 ground state.
Co-reporter:Theocharis C. Stamatatos ; Khalil A. Abboud ; Wolfgang Wernsdorfer
Inorganic Chemistry 2009 Volume 48(Issue 3) pp:807-809
Publication Date(Web):December 22, 2008
DOI:10.1021/ic8020645
The synthesis, structure, and magnetochemical characterization of a new manganese single-chain magnet are reported. The compound is a chain of repeating Mn6 units bridged by end-on azide groups and exhibits magnetization hysteresis loops.
Co-reporter:Theocharis C. Stamatatos and George Christou
Inorganic Chemistry 2009 Volume 48(Issue 8) pp:3308-3322
Publication Date(Web):April 13, 2009
DOI:10.1021/ic801217j
This Forum Article overviews the recent amalgamation of two long-established areas, manganese/oxo coordination cluster chemistry involving the higher MnII/MnIV oxidation states and transition-metal azide (N3−) chemistry. The combination of azide and alkoxide- or carboxylate-containing ligands in Mn chemistry has led to a variety of new polynuclear clusters, high-spin molecules, and single-molecule magnets, with metal nuclearities ranging from Mn4 to Mn32 and with ground-state spin values as large as S = 83/2. The organic bridging/chelating ligands are discussed separately as follows: (i) pyridyl alkoxides [the anions of 2-(hydroxymethyl)pyridine (hmpH), 2,6-pyridinedimethanol (pdmH2), and the gem-diol form of di-2-pyridyl ketone (dpkdH2)]; (ii) non-pyridyl alkoxides [the anions of 1,1,1-tris(hydroxymethyl)ethane (thmeH3), triethanolamine (teaH3), and N-methyldiethanolamine (mdaH2)]; (iii) other alcohols [the anions of 2,6-dihydroxymethyl-4-methylphenol (LH3) and Schiff bases]; (iv) pyridyl monoximes/dioximes [the anions of methyl-2-pyridyl ketone oxime (mpkoH), phenyl-2-pyridyl ketone oxime (ppkoH), and 2,6-diacetylpyridine dioxime (dapdoH2)]; (v) non-pyridyl oximes [the anions of salicylaldoxime (saoH2) and its derivatives R-saoH2]. The large structural diversity of the resulting complexes stems from the combined ability of the azide and organic ligands to adopt a variety of ligation and bridging modes. The combined work demonstrates the synthetic novelty that arises when azide is used in conjunction with alcohol-based chelates, the aesthetic beauty of the resulting molecules, and the often fascinating magnetic properties that these compounds possess. This continues to emphasize the extensive and remarkable ability of Mn chemistry to satisfy a variety of different tastes.
Co-reporter:Eleni E. Moushi, Theocharis C. Stamatatos, Wolfgang Wernsdorfer, Vassilios Nastopoulos, George Christou and Anastasios J. Tasiopoulos
Inorganic Chemistry 2009 Volume 48(Issue 12) pp:5049-5051
Publication Date(Web):December 15, 2008
DOI:10.1021/ic801795x
A [MnIII11MnII6(μ4-O)8(μ3-L)4]25+ (L = N3− or OCN−) octahedral unit is reported, occurring within 1D (1)∞ and 2D (2)∞ coordination polymers, as well as the corresponding 0D discrete cluster 3. It possesses a giant ground-state spin value, determined in the case of 3 to be S = 37, the second largest to be reported to date. In addition, compound 3 displays single-molecule magnet (SMM) behavior, and is thus the largest-spin SMM.
Co-reporter:Taketo Taguchi, Matthew R. Daniels, Khalil A. Abboud and George Christou
Inorganic Chemistry 2009 Volume 48(Issue 19) pp:9325-9335
Publication Date(Web):September 3, 2009
DOI:10.1021/ic901306k
The synthesis, crystal structure, and magnetochemical characterization are reported of three new Mn clusters [Mn4O2(O2CBut)5(dphmp)3] (1), [Mn6O4(OMe)2(O2CPh)4(dphmp)4] (2), and [Mn11O7(OMe)7(O2CPh)7(dphmp)4(MeOH)2] (3). They were obtained from the use of diphenyl(pyridine-2-yl)methanol (dphmpH), a bulkier version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dphmpH with MnCl2·4H2O and NaO2CBut in MeCN/MeOH (30 mL, 5:1 v/v) led to the isolation of tetranuclear complex 1, whereas the analogous reaction with NaO2CPh gave hexanuclear complex 2. When the 5:1 solvent ratio in the latter reaction was changed to 1:29, the isolated product was now undecanuclear complex 3. Complexes 1−3 all possess rare or unprecedented Mnx topologies: Complex 1 possesses a [Mn4(μ3-O)2]8+ (4MnIII) butterfly core, one edge of which is additionally bridged by an alkoxide arm of a dphmp− chelate; complex 2 possesses a [Mn6(μ4-O)2(μ3-O)2(μ3-OMe)2]8+ (6MnIII) core with a face-sharing double cubane topology; and complex 3 (MnII, 10MnIII) possesses a [Mn4(μ4-O)3(μ3-OMe)]5+ cubane unit, attached on one side to a MnII atom by a μ4-O atom and alkoxide groups, and on the other side to a [Mn5(μ4-O)(μ3-O)3(μ3-OMe)(μ-OR)3]3+ unit consisting of three face-sharing defective cubanes linked to an additional MnIII atom by a μ3-O atom. Solid-state dc and ac magnetic susceptibility measurements on 1−3 establish that they possess S = 0, 3, and 5/2 ground states, respectively. ac susceptibility studies on 2 and 3 reveal weak non-zero frequency-dependent out-of-phase (χM′′) signals at temperatures below 3 K, possibly indicative of single-molecule magnets with very small barriers. The combined results demonstrate a ligating difference between bulky dphmp− and hmp−, and the resulting usefulness of the former to provide access to a variety of Mnx molecular species not known with the latter.
Co-reporter:Theocharis C. Stamatatos, Dolos Foguet-Albiol, Katye M. Poole, Wolfgang Wernsdorfer, Khalil A. Abboud, Ted A. O’Brien and George Christou
Inorganic Chemistry 2009 Volume 48(Issue 20) pp:9831-9845
Publication Date(Web):September 18, 2009
DOI:10.1021/ic901393m
The use has been explored in Mn cluster chemistry of N3− or Cl− in combination with N-methyldiethanolamine (mdaH2) or triethanolamine (teaH3). The reactions of Mn(ClO4)2·6H2O, NEt3, NaN3, and either mdaH2 or teaH3 (1:2:1:2) in DMF/MeOH afford {[Na(MeOH)3][Mn7(N3)6(mda)6]}n (1) and {Na[Mn7(N3)6(teaH)6]}n (2), respectively, whereas the 2:1:1 reaction of MnCl2·4H2O, mdaH2, and NEt3 in MeCN gives (NHEt3)[Mn7Cl6(mda)6] (3). Similar reactions using NBun4N3 in place of NaN3 gave (NHEt3)[Mn7(N3)6(mda)6] (4) and (NHEt3)[Mn7(N3)6(teaH)6] (5). The Mn7 anions consist of a Mn6 hexagon of alternating MnII and MnIII ions surrounding a central MnII ion. The remaining ligation is by six bridging and chelating mda2− or teaH2− groups, and either six terminal N3− (1, 2, 4, 5) or Cl− (3) ions. Each bridging mda2− or teaH2− ligand contains both μ- and μ3-O atoms, resulting in a similar, near-planar [Mn7(μ3-OR)6(μ-OR)6]5+ core for all three complexes. The Mn7 anions of 1 and 2 are connected via Na+ cations to yield one-dimensional zigzag chains and three-dimensional windmill-like “hexagons-of-hexagons”, respectively. In contrast, the Mn7 anion of 3 forms a strong hydrogen-bond between the NHEt3+ cation and a terminal Cl− ion giving a discrete ion-pair. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out in the 5.0−300 K range. Fits of dc magnetization versus field (H) and temperature (T) data by matrix diagonalization gave S = 11, g = 1.95, D = −0.15 cm−1 for 1, S = 16, g = 1.95, D = −0.02 cm−1 for 2, and S = 11, g = 1.92, D = −0.13 cm−1 for 3 (D is the axial zero-field splitting parameter). Complexes 4 and 5 were also found to possess S = 11 and S = 16 ground states, respectively. The different ground states of 1 and 2 were rationalized on the basis of the sign and magnitude of the various Mn2 exchange parameters obtained from density functional theory (DFT) calculations. This analysis confirmed the presence of spin frustration effects, with the ground states being determined by the relative magnitude of the two weakest interactions. The combined results demonstrate the usefulness of N-based dipodal and tripodal alkoxide-based chelates as a route to structurally and magnetically interesting Mn clusters.
Co-reporter:Gina C. Vlahopoulou, Theocharis C. Stamatatos, Vassilis Psycharis, Spyros P. Perlepes and George Christou
Dalton Transactions 2009 (Issue 19) pp:3646-3649
Publication Date(Web):17 Mar 2009
DOI:10.1039/B901990A
The initial employment of α-benzoin oxime (bzoxH2) in metal cluster chemistry has provided access to a new family of decanuclear CuII complexes with a loop or single-strand wheel topology; the CuII10clusters are antiferromagnetically-coupled with an S = 0 spin ground state, as expected for even-membered loop arrays of CuII atoms.
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud and George Christou
Dalton Transactions 2009 (Issue 1) pp:41-50
Publication Date(Web):23 Oct 2008
DOI:10.1039/B810701G
The use of the anion of 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (‘bis-tris’ or LH5) as a chelate in Mn cluster chemistry is reported, and two products [Mn(N3)(LH3)] (1) and [Mn5(LH2)3(LH5)(MeOH)2.5]Cl4 (2) are described. The reaction of Mn(ClO4)2·6H2O and NaN3 with LH5 and NEt3 in a 1:1:1:2 molar ratio in DMF gave complex 1. The reaction of 1, NEt3 and MnCl2·4H2O in a 2:2:1 ratio in MeOH gave the pentanulear complex 2. Complex 1 contains a distorted-octahedral MnIII atom exhibiting a Jahn–Teller axial elongation. Complex 2 has a mixed-valence MnII2MnIII3 trigonal bipyramidal Mn5 topology, with the apical positions of the [Mn5(μ-OR)7]6+ core occupied by the MnII atoms. Variable-temperature, solid-state dc and ac magnetization studies are reported for 1 and 2 in the 1.8–300 K range. The data for 1 are as expected for a high-spin d4 MnIII complex with S = 2; at low temperature, the effects of zero-field splitting (ZFS) and intermolecular antiferromagnetic interactions viaOH⋯O hydrogen bonds become evident. Fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization gave S = 2, D = −3.25 cm−1 and |E| = 0.32 cm−1, with g fixed at 2.00, where D and E are the axial and rhombic ZFS parameters, respectively. The analogous fit for 2 gave S = 3 and D = −0.68 cm−1. The combined results demonstrate the usefulness of ‘bis-tris’ as a new poly-alkoxide chelate for the synthesis of new Mn complexes.
Co-reporter:Constantinos C. Stoumpos, Theocharis C. Stamatatos, Harikleia Sartzi, Olivier Roubeau, Anastasios J. Tasiopoulos, Vassilios Nastopoulos, Simon J. Teat, George Christou and Spyros P. Perlepes
Dalton Transactions 2009 (Issue 6) pp:1004-1015
Publication Date(Web):09 Jan 2009
DOI:10.1039/B813828A
The employment of the anion of methyl 2-pyridyl ketone oxime (mpko−) as a tridentate chelating/bridging ligand in manganese chemistry is described. The inorganic anion (Br−, ClO4−) used in the reaction affects the identity of the product. The reaction of MnBr2 and one equivalent of mpkoH in the presence of a base affords [Mn3(OMe)2(mpko)4Br2] (3), which is mixed-valence (2MnII, MnIV). The central MnIV atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the η1:η1:η1:μ mpko− ligands, and two η1:μ MeO− groups, while six coordination at each terminal MnII atom is completed by four nitrogen atoms belonging to the ‘chelating’ part of two mpko− ligands, and one Br− ion. The MnII atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO4)2·6H2O, mpkoH and OH− (1:2:1) in MeOH gives [Mn8O4(OMe)(mpko)9(mpkoH)](ClO4)4 (4), which is also mixed-valence (2MnII, 6MnIII) and possesses the novel [Mn8(μ3-O)4(μ-OMe)(μ-OR″)2]11+ core. The latter possesses a U-shaped sequence of four fused {MnIIMnIII2(μ3-O)}6+ triangular units, with a MnIII-MnIII edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4. The dc susceptibility data for 3 in the 5.0–300 K range have been fit to a model with two J values, revealing weak ferromagnetic MnII⋯MnIV (J = +3.4 cm−1) and MnII⋯MnII (J′ = +0.3 cm−1) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm−1 for 3 and S = 3, D = −0.09 cm−1 for 4. The combined work demonstrates the usefulness of mpko− in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands.
Co-reporter:Christos Lampropoulos Dr.;Stephen Hill Dr. Dr.
ChemPhysChem 2009 Volume 10( Issue 14) pp:2397-2400
Publication Date(Web):
DOI:10.1002/cphc.200900420
Co-reporter:TheocharisC. Stamatatos Dr.;SimonJ. Teat Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 3) pp:521-524
Publication Date(Web):
DOI:10.1002/anie.200804286
Co-reporter:Theocharis C. Stamatatos, Konstantina V. Pringouri, Khalil A. Abboud, George Christou
Polyhedron 2009 28(9–10) pp: 1624-1627
Publication Date(Web):
DOI:10.1016/j.poly.2008.10.031
Co-reporter:Christos Lampropoulos, Theocharis C. Stamatatos, Khalil A. Abboud, George Christou
Polyhedron 2009 28(9–10) pp: 1958-1964
Publication Date(Web):
DOI:10.1016/j.poly.2008.11.026
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud, George Christou
Polyhedron 2009 28(9–10) pp: 1880-1882
Publication Date(Web):
DOI:10.1016/j.poly.2008.10.032
Co-reporter:TheocharisC. Stamatatos Dr.;SimonJ. Teat Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie 2009 Volume 121( Issue 3) pp:529-532
Publication Date(Web):
DOI:10.1002/ange.200804286
Co-reporter:Taketo Taguchi, Theocharis C. Stamatatos, Khalil A. Abboud, Candace M. Jones, Katye M. Poole, Ted A. O’Brien and George Christou
Inorganic Chemistry 2008 Volume 47(Issue 10) pp:4095-4108
Publication Date(Web):April 24, 2008
DOI:10.1021/ic701756p
The syntheses, crystal structures, magnetochemical characterization, and theoretical calculations are reported for three new iron clusters [Fe6O2(NO3)4(hmp)8(H2O)2](NO3)2 (1), [Fe4(N3)6(hmp)6] (2), and [Fe8O3(OMe)(pdm)4(pdmH)4(MeOH)2](ClO4)5 (3) (hmpH = 2-(hydroxymethyl)pyridine; pdmH2 = 2,6-pyridinedimethanol). The reaction of hmpH with iron(III) sources such as Fe(NO3)3·9H2O in the presence of NEt3 gave 1, whereas 2 was obtained from a similar reaction by adding an excess of NaN3. Complex 3 was obtained in good yield from the reaction of pdmH2 with Fe(ClO4)3·6H2O in MeOH in the presence of an organic base. The complexes all possess extremely rare or novel core topologies. The core of 1 comprises two oxide-centered [Fe3(µ3-O)]7+ triangular units linked together at two of their apexes by two sets of alkoxide arms of hmp− ligands. Complex 2 contains a zigzag array of four FeIII atoms within an [Fe4(µ-OR)6]6+ core, with the azide groups all bound terminally. Finally, complex 3 contains a central [Fe4(µ4-O)]10+ tetrahedron linked to two oxide-centered [Fe3(µ3-O)]7+ triangular units. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1−3 in the 5.0–300 K range. Fitting of the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) established that 1 possesses an S = 3 ground-state spin, with g = 2.08, and D = −0.44 cm−1. The magnetic susceptibility data for 2 up to 300 K were fit by matrix diagonalization and gave J1 = −9.2 cm−1, J2 = −12.5 cm−1, and g = 2.079, where J1 and J2 are the outer and middle nearest-neighbor exchange interactions, respectively. Thus, the interactions between the FeIII centers are all antiferromagnetic, giving an S = 0 ground state for 2. Similarly, complex 3 was found to have an S = 0 ground state. Theoretically computed values of the exchange constants in 2 were obtained with DFT calculations and the ZILSH method and were in good agreement with the values obtained from the experimental data. Exchange constants obtained with ZILSH for 3 successfully rationalized the experimental S = 0 ground state. The combined work demonstrates the ligating flexibility of pyridyl-alcohol chelates and their usefulness in the synthesis of new polynuclear Fex clusters without requiring the copresence of carboxylate ligands.
Co-reporter:Theocharis C. Stamatatos ; Katye M. Poole ; Khalil A. Abboud ; Wolfgang Wernsdorfer ; Ted A. O’Brien
Inorganic Chemistry 2008 Volume 47(Issue 11) pp:5006-5021
Publication Date(Web):May 3, 2008
DOI:10.1021/ic800268z
The use has been explored of both azide (N3−) and alkoxide-containing groups such as the anions of 2-(hydroxymethyl)pyridine (hmpH), 2,6-pyridinedimethanol (pdmH2), 1,1,1-tris(hydroxymethyl)ethane (thmeH3) and triethanolamine (teaH3) in Mn cluster chemistry. The 1:1:1:1 reactions of hmpH, NaN3 and NEt3 with Mn(ClO4)2·6H2O or Mn(NO3)2·H2O in MeCN/MeOH afford [MnII4MnIII6O4(N3)4(hmp)12](X)2 [X = ClO4− (1), N3− (2)]. The [Mn10(μ4-O)4(μ3-N3)4]14+ core of the cation has a tetra-face-capped octahedral topology, with a central MnIII6 octahedron, whose eight faces are bridged by four μ3-N3− and four μ4-O2- ions, the latter also bridging to four extrinsic MnII atoms. The core has Td symmetry, but the complete [MnII4MnIII6O4(N3)4(hmp)12]2+ cation has rare T symmetry, which is crystallographically imposed. A similar reaction of Mn(ClO4)2·6H2O with one equiv each of NaN3, thmeH3, pdmH2, and NEt3 in MeCN/MeOH led to [MnII4MnIII6O2(N3)6(pdmH)4(thme)4] (3). Complex 3 is at the same oxidation level as 1/2 but its core is structurally different, consisting of two edge-fused [MnII2MnIII4(μ4-O)]14+ octahedra. Replacement of thmeH3 with teaH3 in this reaction gave instead [MnII2MnIII2(N3)4(pdmH)2(teaH)2] (4), containing a planar Mn4 rhombus. Variable-temperature, solid-state dc and ac magnetization studies were carried out on 1−4 in the 5.0–300 K range. Complexes 1 and 2 are completely ferromagnetically coupled with a resulting S = 22 ground state, one of the highest yet reported. Fits of dc magnetization vs field (H) and temperature (T) data by matrix diagonalization gave S = 22, g = 2.00, and D ≈ 0.0 cm−1 (D is the axial zero-field splitting parameter). In contrast, the data for 3 revealed dominant antiferromagnetic interactions and a resulting S = 0 ground state. Complex 4 contains weakly ferromagnetically coupled Mn atoms, leading to an S = 9 ground-state and low-lying excited states, and exhibits out-of-phase ac susceptibility signals characteristic of a single-molecule magnet. Theoretical values of the exchange constants in 1 obtained with density functional theory and ZILSH calculations were in good agreement with experimental values. The combined work demonstrates the synthetic usefulness of alcohol-based chelates and azido ligands when used together, and the synthesis in the present work of two “isomeric” MnIII6MnII4 cores that differ in spin by a remarkable 22 units.
Co-reporter:Abhudaya Mishra ; Yulia Pushkar ; Junko Yano ; Vittal K. Yachandra ; Wolfgang Wernsdorfer ; Khalil A. Abboud
Inorganic Chemistry 2008 Volume 47(Issue 6) pp:1940-1948
Publication Date(Web):February 19, 2008
DOI:10.1021/ic701339p
The preparation and properties of the first strontium-manganese molecular complex are described. The reaction of (NBun4)[Mn4O2(O2CPh)9(H2O)] (4MnIII) with Sr(ClO4)2 in MeCN/MeOH led to the isolation of [SrMn14O11(OMe)3(O2CPh)18(MeCN)2] (1; 13MnIII, MnII). The structure of 1 consists of two [Mn4O3(OMe)] cubane units attached to a central, near-planar, trinuclear [Mn3O4] unit, to which are also attached a Mn and a Sr above the plane and a [Mn2O(OMe)] rhomb below the plane. Peripheral ligation is provided by 18 bridging benzoate and two terminal MeCN groups. Variable-temperature and -field dc magnetization (M) data were collected in the 1.8–10 K and 0.1–4.0 T ranges and fit by matrix diagonalization methods to give S = 9/2, D = −0.50(5) cm−1, and g = 1.88(10), where S is the ground-state spin and D is the axial zero-field splitting parameter. Magnetization versus dc field sweeps at various temperatures and scan rates exhibited hysteresis loops, confirming 1 to be a new single-molecule magnet. Because complex 1 is the initial molecular example of intimately associated Mn and Sr atoms, Sr EXAFS studies have been performed for the first time on a synthetic Sr-containing molecule. This has also allowed comparisons with the EXAFS data on the Sr-substituted water oxidizing complex (WOC) of Photosystem II (PS II), which contains a SrMn4 complex.
Co-reporter:Rashmi Bagai ; Matthew R. Daniels ; Khalil A. Abboud
Inorganic Chemistry 2008 Volume 47(Issue 8) pp:3318-3327
Publication Date(Web):March 14, 2008
DOI:10.1021/ic7024022
The syntheses, crystal structures, and magnetochemical characterization of five new iron clusters [Fe5O2(O2CPh)7(edte)(H2O)] (1), [Fe6O2(O2CBut)8(edteH)2] (2), [Fe12O4(OH)2(O2CMe)6(edte)4(H2O)2](ClO4)4 (3), [Fe12O4(OH)8(edte)4(H2O)2](ClO4)4 (4), and [Fe12O4(OH)8(edte)4(H2O)2](NO3)4 (5) (edteH4 = N,N,N′,N′-tetrakis(2-hydroxyethyl) ethylenediamine) are reported. The reaction of edteH4 with [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CBut)6(H2O)3](OH) gave 1 and 2, respectively. Complex 3 was obtained from the reaction of edteH4 and NaO2CMe with Fe(ClO4)3, whereas 4 and 5 were obtained from the reaction of edteH4 with Fe(ClO4)3 and Fe(NO3)3, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by four bridging O atoms. The core of 2 consists of two triangular [Fe3(μ3-O)]7+ units linked together by six bridging O atoms. Finally, the cores of 3−5 consist of an [Fe12(μ4-O)4(μ-OH)2]26+ unit. Variable-temperature (T) and -field (H) solid-state direct and alternating current magnetization (M) studies were carried out on complexes 1−3 in the 1.8–300 K range. Analysis of the obtained data revealed that 1, 2, and 3−5 possess an S = 5/2, 5, and 0 ground-state spin, respectively. The fitting of the obtained M/NμB vs H/T data was carried out by matrix diagonalization, and this gave values for the axial zero-field splitting (ZFS) parameter D of −0.50 cm−1 for 1 and –0.28 cm−1 for 2.
Co-reporter:Abhudaya Mishra ; Anastasios J. Tasiopoulos ; Wolfgang Wernsdorfer ; Eleni E. Moushi ; Brian Moulton ; Michael J. Zaworotko ; Khalil A. Abboud
Inorganic Chemistry 2008 Volume 47(Issue 11) pp:4832-4843
Publication Date(Web):April 15, 2008
DOI:10.1021/ic8001064
Four heterometallic, enneanuclear Mn8Ce clusters [Mn8CeO8(O2CMe)12(H2O)4] (4), [Mn8CeO8(O2CMe)12(py)4] (5), [Mn8CeO8(O2CPh)12(MeCN)4] [Mn8CeO8(O2CPh)12(dioxane)4] (6), and [Mn8CeO8(O2CCHPh2)12(H2O)4] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [MnIII8O8]8+ loop containing a central CeIV ion attached to the eight μ3-O2− ions. Peripheral ligation around the [Mn8CeO8]12+ core is provided by eight μ- and four μ3-O2CR− groups. Terminal ligation on four MnIII atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S = 16, S = 4 or 5, and S = 6 ± 1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent MnIII atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4·4H2O and 7·4H2O·3MeCN·2CH2Cl2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice–water molecules of crystallization.
Co-reporter:Theocharis C. Stamatatos ; Katye M. Poole ; Dolos Foguet-Albiol ; Khalil A. Abboud ; Ted A. O’Brien
Inorganic Chemistry 2008 Volume 47(Issue 15) pp:6593-6595
Publication Date(Web):June 28, 2008
DOI:10.1021/ic801024d
The S = 11 ground states of the Mn7 family of mixed-valence complexes with a metal-centered hexagonal topology have been found by density functional theory calculations to arise by spin frustration involving small differences in the magnitudes of the two weakest interactions controlling the alignment of the central spin. Targeted structural perturbation has allowed a complex with the central spin flipped to be discovered, which thus possesses the maximum S = 16 ground state.
Co-reporter:Theocharis C. Stamatatos ; Alexander G. Christou ; Shreya Mukherjee ; Katye M. Poole ; Christos Lampropoulos ; Khalil A. Abboud ; Ted A. O’Brien
Inorganic Chemistry 2008 Volume 47(Issue 19) pp:9021-9034
Publication Date(Web):August 13, 2008
DOI:10.1021/ic801038r
Convenient, high-yield routes have been developed to [Fe10(OMe)20(O2CR)10] (1) “ferric wheels” involving the alcoholysis of [Fe3O(O2CR)6(H2O)3]+ salts in MeOH in the presence of NEt3. Reactivity studies have established [Fe10(OMe)20(O2CMe)10] (1a) to undergo clean carboxylate substitution with a variety of other RCO2H groups to the corresponding [Fe10(OMe)20(O2CR)10] product. In contrast, the reaction with phenol causes a nuclearity change to give a smaller [Fe8(OH)4(OPh)8(O2CR)12] (2) wheel. Similarly, reactions of [Fe10(OMe)20(O2CR)10] with the bidentate chelate ethylenediamine (en) cause a structural change to give either [Fe8O5(O2CMe)8(en)8](ClO4)6 (3) or [Fe2O(O2CBut)(en)4](NO3)3 (4), depending on conditions. Complex 3 possesses a “Christmas-star” Fe8 topology comprising a central planar [Fe4(μ4-O)]10+ square subunit edge-fused to four oxide-centered [Fe3(μ3-O)]7+ triangular units. Variable-temperature, solid-state dc and ac magnetization studies on complexes 1a−4 in the 5.0−300 K range established that all the complexes possess an S = 0 ground state. The magnetic susceptibility data for 4 were fit to the theoretical χM versus T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed an antiferromagnetic exchange parameter with a value of J = −107.7(5) cm−1. This value is consistent with that predicted by a previously published magnetostructural relationship. Theoretically computed values of the exchange constants in 3 were obtained with the ZILSH method, and the pattern of spin frustration within its core and the origin of its S = 0 ground state have been analyzed in detail.
Co-reporter:Muralee Murugesu ; Susumu Takahashi ; Anthony Wilson ; Khalil A. Abboud ; Wolfgang Wernsdorfer ; Stephen Hill
Inorganic Chemistry 2008 Volume 47(Issue 20) pp:9459-9470
Publication Date(Web):September 13, 2008
DOI:10.1021/ic801142p
The synthesis and structural, spectroscopic, and magnetic characterization of a Mn25 coordination cluster with a large ground-state spin of S = 51/2 are reported. Reaction of MnCl2 with pyridine-2,6-dimethanol (pdmH2) and NaN3 in MeCN/MeOH gives the mixed valence cluster [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6]Cl2 (1; 6MnII, 18MnIII, MnIV), which has a barrel-like cage structure. Variable temperature direct current (dc) magnetic susceptibility data were collected in the 1.8−300 K temperature range in a 0.1 T field. Variable-temperature and -field magnetization (M) data were collected in the 1.8−4.0 K and 0.1−7 T ranges and fit by matrix diagonalization assuming only the ground state is occupied at these temperatures. The fit parameters were S = 51/2, D = −0.020(2) cm−1, and g = 1.87(3), where D is the axial zero-field splitting parameter. Alternating current (ac) susceptibility measurements in the 1.8−8.0 K range and a 3.5 G ac field oscillating at frequencies in the 50−1500 Hz range revealed a frequency-dependent out-of-phase (χM′′) signal below 3 K, suggesting 1 to be a single-molecule magnet (SMM). This was confirmed by magnetization vs dc field sweeps, which exhibited hysteresis loops but with no clear steps characteristic of resonant quantum tunneling of magnetization (QTM). However, magnetization decay data below 1 K were collected and used to construct an Arrhenius plot, and the fit of the thermally activated region above ∼0.5 K gave Ueff/k = 12 K, where Ueff is the effective relaxation barrier. The g value and the magnitude and sign of the D value were independently confirmed by detailed high-frequency electron paramagnetic resonance (HFEPR) spectroscopy on polycrystalline samples. The combined studies confirm both the high ground-state spin S = 51/2 of complex 1 and that it is a SMM that, in addition, exhibits QTM.
Co-reporter:Theocharis C. Stamatatos ; Vassilios Nastopoulos ; Anastasios J. Tasiopoulos ; Eleni E. Moushi ; Wolfgang Wernsdorfer ; George Christou ;Spyros P. Perlepes
Inorganic Chemistry 2008 Volume 47(Issue 21) pp:10081-10089
Publication Date(Web):October 8, 2008
DOI:10.1021/ic801342f
The employment of the dianion (dpkd2−) of the gem-diol form of di-2-pyridylketone (dpk) as a tetradentate chelate in manganese chemistry is reported, and the synthesis, crystal structure, and magnetochemical characterization of [Mn26O16(OMe)12(dpkd)12(MeOH)6](OH)6·solv (3·solv) are described. The reaction of Mn(ClO4)2·6H2O, dpk, NaOMe, and NEt3 (2:1:4:2) in MeCN/MeOH affords complex 3, which possesses a rare metal topology and is mixed-valence (4MnII, 22MnIII). The complicated [Mn26(μ4-O)10(μ3-O)6(μ3-OMe)12(μ-OR)12]18+ core of 3 consists of an internal MnIII16 cage of adjacent Mn4 tetrahedra surrounded by an external MnII4MnIII6 shell. The latter is held together by the alkoxide arms of twelve η1:η2:η1:η1:μ3 dpkd2− groups. Variable-temperature, solid-state direct current (dc), and alternating current (ac) magnetization studies were carried out on 3 in the 1.8−300 K range. Complex 3 is predominantly antiferromagnetically coupled with a resulting S = 6 ground state, a conclusion confirmed by the in-phase (χ′M) ac susceptibility data. The observation of out-of-phase (χ′′M) ac susceptibility signals suggested that 3 might be a single-molecule magnet, and this was confirmed by single-crystal magnetization vs dc field sweeps that exhibited hysteresis, the diagnostic property of a magnet. Combined ac χ′′M and magnetization decay vs time data collected below 1.1 K were used to construct an Arrhenius plot; the fit of the thermally activated region above ∼0.1 K gave Ueff = 30 K, where Ueff is the effective relaxation barrier. At lower temperatures, the complex exhibits temperature-independent relaxation, characteristic of ground-state quantum tunneling of magnetization between the lowest-lying Ms = ±6 levels. The combined work demonstrates the ligating flexibility of dipyridyl-diolate chelates and their usefulness in the synthesis of polynuclear Mnx clusters with interesting magnetic properties, without requiring the co-presence of carboxylate ligands.
Co-reporter:Theocharis C. Stamatatos, Albert Escuer, Khalil A. Abboud, Catherine P. Raptopoulou, Spyros P. Perlepes and George Christou
Inorganic Chemistry 2008 Volume 47(Issue 24) pp:11825-11838
Publication Date(Web):November 12, 2008
DOI:10.1021/ic801555e
Syntheses, crystal structures, and magnetochemical characterization are reported for the three new nickel(II) clusters [Ni14(OH)4(N3)8(pao)14(paoH)2(H2O)2](ClO4)2 (1), [Ni12Na2(OH)4(N3)8(pao)12(H2O)10](OH)2 (2), and [Ni5(ppko)5(H2O)7](NO3)5 (3) (paoH = pyridine-2-carbaldehyde oxime, ppkoH = di-2-pyridyl ketone oxime). The reaction of Ni(ClO4)2·6H2O with paoH and NBun4N3 in H2O/MeCN in the presence of NEt3, gave 1 in 65% yield. Complex 2 was obtained in 60% yield from the reaction of NiCl2·6H2O with paoH and NaN3 in H2O/MeCN in the presence of NaOH. The reaction of Ni(NO3)2·6H2O with ppkoH in EtOH in the presence of LiOH afforded complex 3 in 75% yield. The complexes all contain novel core topologies. The core of 1 comprises a central Ni4 rhombus between two Ni5. Complex 1 is the largest metal/oxime cluster discovered to date, as well as the first NiII14 coordination complex and the largest NiII/N3− cluster. Complex 2 has a Ni12Na2 topology that is very similar to that of 1, but with two central NiII atoms of 1 replaced with NaI atoms. The core of 3 consists of four NiII atoms forming a highly distorted tetrahedron, with the fifth NiII atom lying almost on one of the edges. Variable-temperature, solid-state dc susceptibility and magnetization studies were carried out on complexes 1−3, and these were complemented with ac susceptibility data for 1 and 2. Fitting of the obtained M/(NμB) vs H/T data by matrix diagonalization and including axial zero-field splitting (D) gave ground-state spin (S) and D values of S = 6, D = −0.12(3) cm−1 for 1 and S = 3, D = −0.20(5) cm−1 for each of the two essentially noninteracting S = 3 Ni6 subunits of 2. The data for 3 indicate antiferromagnetic exchange interactions and an S = 1 ground state. A simple 2-J model was found to be adequate to describe the variable-temperature dc susceptibility data. The combined work demonstrates the ligating flexibility of pao− and ppko−, and their usefulness in the synthesis of polynuclear Nix clusters with or without the presence of ancillary ligands.
Co-reporter:Christos Lampropoulos ; Changhyun Koo ; Stephen O. Hill ; Khalil Abboud
Inorganic Chemistry 2008 Volume 47(Issue 23) pp:11180-11190
Publication Date(Web):October 24, 2008
DOI:10.1021/ic801484g
Four mixed-valent (MnIVMnIII6MnII6) tridecanuclear Mn clusters [Mn13O8(OH)6(ndc)6] (1), [Mn13O8(OEt)5(OH)(ndc)6] (2), [Mn13O8(O2CPh)12(OEt)6] (3), and [Mn13O8(OMe)6(ndc)6] (4) are reported, where ndcH2 is 1,8-naphthalenedicarboxylic acid. This is the first use of the latter in Mn chemistry. Complexes 1−3 are essentially isostructural and possess a central core composed of three layers. The middle layer consists of a MnII6 hexagon containing a central MnIV atom, and above and below this are MnIII3 triangular units. These core Mn atoms are held together by a combination of O2-, RO−, or HO− bridging groups. The overall metal topology is an unusual one, with the overall geometry being a metal-centered cuboctahedron (heptaparallelohedron). Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1−4 in the 5.0−300 K range. Compound 1 was found to possess an S = 9/2 ground-state spin, whereas 2, 3, and 4 have an S = 11/2 ground state. Fitting of the magnetization (M) versus field (H) and temperature (T) data by matrix diagonalization and including only axial zero-field splitting, D, gave D = −0.14 cm−1 for 1. High-frequency EPR studies were carried out on single crystals of 1·xDMF, and these confirmed D to be very small, that is, 1 is essentially isotropic. The combined work demonstrates the ligating ability of 1,8-naphthalenedicarboxylate, notwithstanding its robust organic backbone and the restricted parallel disposition of its two carboxylate moieties, and its usefulness in the synthesis of new polynuclear Mnx clusters. The work also demonstrates a sensitivity of the ground-state spin in this Mn13 family of complexes to relatively small structural perturbations, while the high-frequency EPR study demonstrated the magnetically isotropic nature of the Mn13 core.
Co-reporter:Joan Cano, Thomas Cauchy, Eliseo Ruiz, Constantinos J. Milios, Constantinos C. Stoumpos, Theocharis C. Stamatatos, Spyros P. Perlepes, George Christou and Euan K. Brechin
Dalton Transactions 2008 (Issue 2) pp:234-240
Publication Date(Web):19 Oct 2007
DOI:10.1039/B710055H
DFT calculations reveal the unusual ferromagnetic exchange observed in an oxo-centered MnIII triangle may originate from a combination of the ‘non-planarity’ of the bridging oxime ligands and the non-parallel alignment of the Jahn–Teller axes.
Co-reporter:TheocharisC. Stamatatos Dr.;KhalilA. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 50) pp:
Publication Date(Web):
DOI:10.1002/anie.200890259
No abstract is available for this article.
Co-reporter:TheocharisC. Stamatatos Dr.;KhalilA. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie 2008 Volume 120( Issue 35) pp:6796-6800
Publication Date(Web):
DOI:10.1002/ange.200801393
Co-reporter:TheocharisC. Stamatatos Dr.;KhalilA. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie 2008 Volume 120( Issue 50) pp:
Publication Date(Web):
DOI:10.1002/ange.200890308
No abstract is available for this article.
Co-reporter:TheocharisC. Stamatatos Dr.;KhalilA. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 35) pp:6694-6698
Publication Date(Web):
DOI:10.1002/anie.200801393
Co-reporter:Rashmi Bagai, Khalil A. Abboud and George Christou
Chemical Communications 2007 (Issue 32) pp:3359-3361
Publication Date(Web):23 Jul 2007
DOI:10.1039/B708783G
The use of a new O,N,N,O chelate has led to two new Fe6 and Fe18 molecular compounds, the latter with an unusual double-headed serpentine chain structure.
Co-reporter:Abhudaya Mishra, Junko Yano, Yulia Pushkar, Vittal K. Yachandra, Khalil A. Abboud and George Christou
Chemical Communications 2007 (Issue 15) pp:1538-1540
Publication Date(Web):19 Mar 2007
DOI:10.1039/B701355H
Heterometallic Mn–Ca and Mn–Sr complexes have been prepared and employed as model complexes for Ca and Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); these have revealed similarities that support the presence of at least one O atom bridge between the Mn and Ca/Sr in the OEC.
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud, Spyros P. Perlepes and George Christou
Dalton Transactions 2007 (Issue 35) pp:3861-3863
Publication Date(Web):2007/07/30
DOI:10.1039/B708189H
The reactions of 2-pyridinealdoxime [(py)CHNOH] with Ni(ClO4)2·6H2O in the presence of NaOH and NaN3 have led to NiII14 and NiII12Na2 clusters; the Ni14 compound is the biggest metal oxime cluster discovered to date, as well as the largest Ni azide cluster.
Co-reporter:Theocharis C. Stamatatos Dr.;Khalil A. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie 2007 Volume 119(Issue 6) pp:
Publication Date(Web):19 DEC 2006
DOI:10.1002/ange.200603254
Der Spin wird aufgemotzt: Der ohnehin schon hohe Spin (S=51/2) eines Mn25-Komplexes ließ sich um weitere ca. 20 % steigern (S=61/2), indem Azidliganden gezielt gegen N,O-Chelatgruppen ausgetauscht wurden. Dieses Verfahren zur Spinerhöhung deutet darauf hin, dass komplexen, vielkernigen Molekülen mit hohem Spin durch Modifizieren der Ligandenumgebung unterschiedliche Grundzustandsspins verliehen werden können.
Co-reporter:Theocharis C. Stamatatos Dr.;Khalil A. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 6) pp:
Publication Date(Web):19 DEC 2006
DOI:10.1002/anie.200603254
Spin doctoring: The already high spin of S=51/2 of a Mn25 complex has been pushed even higher, by approximately 20 %, to S=61/2 by targeted substitution of the azide ligands with an N,O-chelating group. This significant adjustment, or tweaking, of the spin suggests the general possibility that a given type of complicated, high-nuclearity, high-spin molecule can exhibit differing ground states by appropriate modification of the peripheral ligation.
Co-reporter:Rashmi Bagai, Khalil A. Abboud and George Christou
Dalton Transactions 2006 (Issue 27) pp:3306-3312
Publication Date(Web):12 Apr 2006
DOI:10.1039/B602192A
The reaction of the pentadentate Schiff-base ligand 1,3-bis(salicylideneamino)-2-propanol (salproH3) with [Mn3O(O2CR)6(py)3] (R = Me, Et, But) gives the corresponding tetranuclear manganese product [Mn4O2(O2CR)5(salpro)] (4MnIII). The syntheses, structure and magnetochemical characterization of these complexes are reported. The structure of the [Mn4(µ3-O)2]8+ is butterfly-like much more closed than in previous complexes with this core as a result of the alkoxide oxygen of the salpro ligand bridging the two wingtip Mn atoms. Variable-temperature, solid-state magnetic susceptibility studies reveal that these complexes possess S = 0 ground state spins. Fitting of the magnetic susceptibility data to the theoretical χMTvs. T expression derived for a C2v symmetry complex, assuming an isotropic Heisenberg spin-Hamiltonian and using the Van Vleck equation, revealed that the various exchange parameters are all antiferromagnetic, and the core thus experiences spin frustration effects.
Co-reporter:Muralee Murugesu, Wolfgang Wernsdorfer, Khalil A. Abboud, Euan K. Brechin and George Christou
Dalton Transactions 2006 (Issue 19) pp:2285-2287
Publication Date(Web):19 Apr 2006
DOI:10.1039/B517108C
Dodecanuclear Mn clusters based on edge-sharing bioctahedra display the scan-rate- and temperature-dependent hysteresis loops that are indicative of single-molecule magnetism behaviour.
Co-reporter:Eleni E. Moushi;Theocharis C. Stamatatos Dr.;Wolfgang Wernsdorfer Dr.;Vassilios Nastopoulos Dr. Dr.;Anastasios J. Tasiopoulos Dr.
Angewandte Chemie 2006 Volume 118(Issue 46) pp:
Publication Date(Web):30 OCT 2006
DOI:10.1002/ange.200603498
Mit 1,3-Propandiol und 2-Methyl-1,3-propandiol sind zwei Mangancarboxylat-3D-Koordinationspolymere mit einer bislang unbekannten Mn19-Wiederholungseinheit zugänglich. Die offenen Netzwerkstrukturen der Verbindungen enthalten nanometergroße Hohlräume (siehe Struktur; Na nicht erkennbar, Mn blau, O rot, C grau). Die Mn19-Einheiten haben einen Spingrundzustand von S=23/2 und zeigen das Verhalten von Einzelmolekülmagneten.
Co-reporter:Theocharis C. Stamatatos;Khalil A. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie 2006 Volume 118(Issue 25) pp:
Publication Date(Web):16 MAY 2006
DOI:10.1002/ange.200600691
Hoch, höher, am höchsten: Die Kombination von Azid- und hmp−-Liganden (hmpH=2-(Hydroxymethyl)pyridin) ermöglichte die Synthese zweier Salze eines neuen Mn10-Kations mit hoch symmetrischer Struktur (siehe Strukturausschnitt; MnII gelb, MnIII blau, O rot, N grün, C grau). Das Kation ist vollständig ferromagnetisch gekoppelt und hat einen S=22-Grundzustand – einer der höchsten je beschriebenen Werte.
Co-reporter:Philippa King Dr.;Theocharis C. Stamatatos;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2006 Volume 45(Issue 44) pp:
Publication Date(Web):18 OCT 2006
DOI:10.1002/anie.200602743
Wheelin' and dealin': The M10 molecular wheels [M10(OMe)20(O2CR)10] (M=Ga, R=Me; M=Fe, R=Ph) were modified to M18 wheels in a nontemplate synthesis upon incorporation of a diolate ligand (see space-filling model of [Ga18(pd)12(pdH)12(O2CMe)6(NO3)6]6+; Ga yellow, O red, N blue, C gray; pdH2=1,3-propanediol). Remarkably, dissolution in MeOH converts both M18 wheels back into the M10 wheels.
Co-reporter:Theocharis C. Stamatatos;Khalil A. Abboud Dr.;Wolfgang Wernsdorfer Dr. Dr.
Angewandte Chemie International Edition 2006 Volume 45(Issue 25) pp:
Publication Date(Web):16 MAY 2006
DOI:10.1002/anie.200600691
Taking the high road: The unification of azide and hmp− (hmpH=2-(hydroxymethyl)pyridine) ligands has provided a route to two salts of a new Mn10 cation with an aesthetically pleasing, high-symmetry structure. The cation (see excerpt of structure; MnII yellow, MnIII blue, O red, N green, C gray) is completely ferromagnetically coupled and possesses an S=22 ground state, one of the highest values ever reported.
Co-reporter:Eleni E. Moushi;Theocharis C. Stamatatos Dr.;Wolfgang Wernsdorfer Dr.;Vassilios Nastopoulos Dr. Dr.;Anastasios J. Tasiopoulos Dr.
Angewandte Chemie International Edition 2006 Volume 45(Issue 46) pp:
Publication Date(Web):30 OCT 2006
DOI:10.1002/anie.200603498
Singles networks: The use of 1,3-propanediol and of 2-methyl-1,3-propanediol in manganese carboxylate chemistry leads to two new 3D coordination polymers with an unprecedented Mn19 repeating unit. The polymers have open framework structures with nanometer-sized cavities (see picture; Na not visible, Mn blue, O red, C gray). The Mn19 units have a ground spin state of S=23/2 and behave as single-molecule magnets.
Co-reporter:Dolos Foguet-Albiol, Khalil A. Abboud and George Christou
Chemical Communications 2005 (Issue 34) pp:4282-4284
Publication Date(Web):03 Aug 2005
DOI:10.1039/B507748F
The use of N-methyldiethanolamine (mdaH2) in reactions with Fe(III) and Ni(II) sources has led to Fe22 and Ni24 products; the clusters are the highest and second-highest, respectively, homometallic clusters for these metals to date, and possess S
= 0 and S
= 6 ground states, respectively.
Co-reporter:Abhudaya Mishra, Wolfgang Wernsdorfer, Khalil A. Abboud and George Christou
Chemical Communications 2005 (Issue 1) pp:54-56
Publication Date(Web):25 Nov 2004
DOI:10.1039/B413680B
Synthetic entry has been achieved into high oxidation state Mn–Ca cluster chemistry with the preparation of [Mn13Ca2O10(OH)2(OMe)2(O2CPh)18(H2O)4]; the structure contains [Mn4CaO4] sub-units similar to that found in the photosynthetic water oxidizing complex.
Co-reporter:Dolos Foguet-Albiol;Ted A. O'Brien Dr.;Wolfgang Wernsdorfer Dr.;Brian Moulton Dr.;Michael J. Zaworotko Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2005 Volume 117(Issue 6) pp:
Publication Date(Web):28 DEC 2004
DOI:10.1002/ange.200461820
Magnetismus – jetzt geht's rund! Der Ligand N-Methyldiethanolamin (mdaH2) ist Bestandteil neuer Mn12- und Mn4-Einzelmolekülmagnete (SMMs) mit Grundzustandsspins von S=7 bzw. S=9. Die abgebildete Mn12-Spezies (MnIII grün, MnII orange, O rot, N blau, C grau) ist einer von wenigen bekannten SMMs mit cyclischer Struktur. Der für eine MnIII6MnII6-Spezies ungewöhnliche S=7-Grundzustand wird durch Dichtefunktionalrechnungen erklärt.
Co-reporter:Muralee Murugesu Dr.;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2005 Volume 117(Issue 6) pp:
Publication Date(Web):28 DEC 2004
DOI:10.1002/ange.200461703
Fest im Sattel: Der potenziell vierzähnige Ligand Triethanolamin (teaH3) öffnet eine Syntheseroute zu gemischtvalenten Manganclustern mit drei neuen Strukturtypen, darunter eine annähernd rechteckige Topologie und eine Sattelform (siehe Bild: MnIII violett, MnII gelb, O rot, N blau, C grau). Zwei dieser Komplexe sind Einzelmokülmagnete.
Co-reporter:Dolos Foguet-Albiol;Ted A. O'Brien Dr.;Wolfgang Wernsdorfer Dr.;Brian Moulton Dr.;Michael J. Zaworotko Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2005 Volume 44(Issue 6) pp:
Publication Date(Web):28 DEC 2004
DOI:10.1002/anie.200461820
Loopy about magnetism: The use of N-methyldiethanolamine (mdaH2) leads to new Mn12 and Mn4 single-molecule magnets (SMMs) with S=7 and S=9 ground-state spins, respectively. The Mn12 species (see structure: MnIII green, MnII orange, O red, N blue, C gray) is a rare example of an SMM with a loop structure. Its unusual S=7 ground state for an MnIII6MnII6 species is rationalized by DFT calculations.
Co-reporter:Muralee Murugesu Dr.;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2005 Volume 44(Issue 6) pp:
Publication Date(Web):28 DEC 2004
DOI:10.1002/anie.200461703
Saddle seen: The use of the potentially tetradentate triethanolamine (teaH3) ligand provides a useful route to three new structural types in mixed-valent manganese cluster chemistry, which include near-rectangular and closed-sinusoidal (saddle-shaped; see structure: MnIII purple, MnII yellow, O red, N blue, C gray) topologies. Further, two of these complexes are also new single-molecule magnets (SMMs).
Co-reporter:Anastasios J. Tasiopoulos Dr.;Alina Vinslava;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 16) pp:
Publication Date(Web):9 MAR 2004
DOI:10.1002/anie.200353352
A meeting of two magnetic worlds: The giant (ca. 4.2 nm) {Mn84} cluster, shown, has a torus structure and is a single-molecule magnet (SMM). It represents a meeting of the molecular (bottom-up) and classical (top-down) approaches to nanoscale magnetic materials, and it crystallizes as nanotubular stacks.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Alina Vinslava;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 16) pp:
Publication Date(Web):6 APR 2004
DOI:10.1002/anie.200490044
Co-reporter:Anastasios J. Tasiopoulos Dr.;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 46) pp:
Publication Date(Web):23 NOV 2004
DOI:10.1002/anie.200461551
Axes of power: Jahn–Teller isomerism (that is, Jahn–Teller distortion along different axes) accounts for the presence of both faster and slower relaxing magnetization dynamics of the title compound (see core structure; blue Mn, red O, gray C), which is a single-molecule magnet (SMM). The new compound is a structural variant of the [Mn12] family of SMMs and is prepared by a reductive aggregation of [MnO4]− in a mixture of MeOH/PhCO2H.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Alina Vinslava;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2004 Volume 116(Issue 16) pp:
Publication Date(Web):9 MAR 2004
DOI:10.1002/ange.200353352
Magnetischer Schulterschluss: Der ringförmige Riesencluster {Mn84} (Ø ca. 4.2 nm) verhält sich wie ein Einzelmolekülmagnet und kristallisiert in Form stapelförmiger Aggregate. Molekulare (bottom-up) und klassische Ansätze (top-down) zum Aufbau nanoskaliger magnetischer Materialien werden hierdurch kombiniert.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Ted A. O'Brien Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2004 Volume 116(Issue 3) pp:
Publication Date(Web):29 DEC 2003
DOI:10.1002/ange.200352898
Gutes Rad ist billig: Eine neue Familie gemischter CeIV-MnIV-Cluster mit Ce:Mn-Verhältnissen zwischen 3:2 und 1:6 wurde hergestellt. Das Bild zeigt den Kern des CeMn6-Komplexes (Ce grün, Mn blau, O rot). Alle Verbindungen weisen antiferromagnetische Wechselwirkungen zwischen den MnIV-Ionen auf.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2004 Volume 116(Issue 46) pp:
Publication Date(Web):23 NOV 2004
DOI:10.1002/ange.200461551
Eine Jahn-Teller-Isomerie (d. h. eine Jahn-Teller-Verzerrung entlang verschiedener Achsen) erklärt, warum in der Titelverbindung, einem Einzelmolekülmagnet (SMM; siehe Kernstruktur: blau Mn, rot O, grau C), eine schneller und eine langsamer relaxierende Magnetisierung auftritt. Die Verbindung ist eine Strukturvariante der [Mn12]-SMM-Familie und wurde durch reduktive Aggregation von [MnO4]− in einer MeOH/PhCO2H-Mischung erhalten.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Ted A. O'Brien Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 3) pp:
Publication Date(Web):29 DEC 2003
DOI:10.1002/anie.200352898
Wheels within wheels: A new family of mixed cerium(IV)–manganese(IV) clusters has been prepared spanning a range of Ce:Mn ratios from 3:2 to 1:6. The unusual core of the latter CeMn6 complex is shown (Ce green, Mn blue, O red). All the compounds exhibit antiferromagnetic interactions between their constituent MnIV ions.
Co-reporter:Anastasios J. Tasiopoulos Dr.;Alina Vinslava;Wolfgang Wernsdorfer Dr.;Khalil A. Abboud Dr. Dr.
Angewandte Chemie 2004 Volume 116(Issue 16) pp:
Publication Date(Web):6 APR 2004
DOI:10.1002/ange.200490044
Co-reporter:Cristina Cañada-Vilalta, Maren Pink and George Christou
Chemical Communications 2003 (Issue 11) pp:1240-1241
Publication Date(Web):30 Apr 2003
DOI:10.1039/B301792C
Alcoholysis of [Fe6O2(OH)2(O2CBut)10(hep)2]
(1) affords ferric wheels of different nuclearities: methanol yields [Fe10(OMe)20(O2CBut)10], whereas phenol gives the structurally unprecedented wheel [Fe8(OH)4(OPh)8(O2CBut)12], and the first to contain phenoxide.
Co-reporter:Mònica Soler, Wolfgang Wernsdorfer, Ziming Sun, John C. Huffman, David N. Hendrickson and George Christou
Chemical Communications 2003 (Issue 21) pp:2672-2673
Publication Date(Web):25 Sep 2003
DOI:10.1039/B306246E
Faster- and slower-relaxing versions of the title Mn12 compound have been obtained in pure forms that crystallize in the same space group and differ only in the identity of one lattice solvent molecule; solvent loss causes isomerization from the faster- to the slower-relaxing form.
Co-reporter:Anastasios J. Tasiopoulos, Khalil A. Abboud and George Christou
Chemical Communications 2003 (Issue 5) pp:580-581
Publication Date(Web):29 Jan 2003
DOI:10.1039/B211345G
The synthesis, characterization and initial reactivity studies are reported of the mixed-valence (MnIV6MnIII2) title compound, which possesses an unusual serpentine-like core and is the highest average oxidation state (+3.75) Mnx (x > 4) cluster to date.
Co-reporter:Cristina Cañada-Vilalta, Maren Pink and George Christou
Dalton Transactions 2003 (Issue 6) pp:1121-1125
Publication Date(Web):11 Feb 2003
DOI:10.1039/B209237A
The synthesis and characterisation are reported of the new decanuclear manganese compound [NH2Et2][Mn10(OH)3(phth)9(bpy)6]
(2; phthH2
= phthalic acid, bpy = 2,2′-bipyridine), obtained from the reaction of phthH2, bpy and NEt3 with either [Mn12O12(O2CMe)16(H2O)4]
(1) or manganese(II) acetate; the latter is by far the superior method. Complex 2 is the highest nuclearity MnII cluster yet prepared, and it crystallizes in the triclinic space group P. The structure of the anion consists of a pinwheel-like arrangement of ten MnII ions bridged by three μ3-OH− ions and nine bridging phth2− groups. Six chelating bpy groups complete octahedral coordination at each MnII ion. There are three different bridging modes for the phth2− groups, some of them unprecedented. Solid-state, variable-temperature dc and ac magnetic susceptibility measurements reveal weak, antiferromagnetic exchange interactions between the MnII ions resulting in a low-spin ground state of S
≈ 2 and low-lying excited states. The non-zero ground state is rationalized as due to the presence of competing exchange interactions (spin frustration) within the Mn10 topology.
Co-reporter:Nicole E. Chakov, Wolfgang Wernsdorfer, Khalil A. Abboud, David N. Hendrickson and George Christou
Dalton Transactions 2003 (Issue 11) pp:2243-2248
Publication Date(Web):17 Apr 2003
DOI:10.1039/B301785K
The synthesis and magnetic properties of a new member of the Mn12 single-molecule magnet family, [Mn12O12(O2CMe)8(O3SPh)8(H2O)4]
(2), are reported. The compound was prepared by treatment of [Mn12O12(O2CMe)16(H2O)4]
(1) with eight equivalents of PhSO3H in MeCN. Complex 2·4CH2Cl2 crystallizes in the triclinic space group P. The complex consists of a central [MnIV4O4] cubane held within a nonplanar ring of eight MnIII ions by eight μ3-O2− ions. Eight bridging acetate groups occupying equatorial sites, eight bridging benzenesulfonate groups in axial sites, and four terminal water molecules complete the peripheral ligation of the molecule. The spin of the ground state was established by magnetization measurements in the 2.00–7.00 T field range and 1.80–4.00 K temperature range. Fitting of the reduced magnetization data by full matrix diagonalization, incorporating only axial anisotropy, gave S
= 10, g
= 1.96 and D
=
−0.34 cm−1. The cluster exhibits out-of-phase ac susceptibility signals and temperature-dependent hysteresis loops at temperatures below 4.00 K, establishing 2 as a new single-molecule magnet.
Co-reporter:Muralee Murugesu, Khalil A. Abboud and George Christou
Dalton Transactions 2003 (Issue 23) pp:4552-4556
Publication Date(Web):26 Sep 2003
DOI:10.1039/B310030H
The syntheses, structures and magnetic properties are reported of new iron(III) complexes with Fe6 wheel and Fe8 cage topologies, and containing tripodal ligands. The compound [Fe8O3(O2CPh)9(tea)(teaH)3]·MeCN (1·MeCN), where teaH3 is triethanolamine, was obtained from the reaction of two equivalents of teaH3 with [Fe3O(O2CPh)6(H2O)3](O2CPh) in MeCN. Similarly, the compound [Fe6(bic)6]·4H2O·4MeOH (2·4H2O·4MeOH), where bicH3 is bicine, was prepared by the analogous reaction but with two equivalents of bicine. Variable-temperature solid-state magnetic susceptibility studies of 1 and 2 in the temperature range 5.00–300 K reveal that both complexes possess S
= 0 ground state spins, consistent with the expected antiferromagnetic exchange interactions between the constituent iron(III) ions.
Co-reporter:Euan K. Brechin, George Christou, Monica Soler, Madeleine Helliwell and Simon J. Teat
Dalton Transactions 2003 (Issue 4) pp:513-514
Publication Date(Web):27 Jan 2003
DOI:10.1039/B212347A
The syntheses, structures and initial magnetic properties of three new high nuclearity manganese clusters containing new topologies of metal ions are reported.
Co-reporter:Euan K. Brechin, Monica Soler, James Davidson, David N. Hendrickson, Simon Parsons and George Christou
Chemical Communications 2002 (Issue 19) pp:2252-2253
Publication Date(Web):09 Sep 2002
DOI:10.1039/B206386G
The reaction of [Mn3O(OAc)6(py)3] with 1,1,1-tris(hydroxymethyl)ethane (H3thme) gives the Mn(IV)3Mn(III)4Mn(II)2 complex [Mn9O7(OAc)11(thme)(py)3(H2O)2], which has an S = 17/2 ground state and displays strong out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet.
Co-reporter:Sumit Bhaduri, Maren Pink and George Christou
Chemical Communications 2002 (Issue 20) pp:2352-2353
Publication Date(Web):16 Sep 2002
DOI:10.1039/B206302F
The 3 MnIV title compound has been prepared and characterized by X-ray crystallography and magnetochemistry; the complex contains a [Mn(μ-O)2Mn(μ-O)2Mn]4+ core and possesses an S = 3/2 ground state.
Co-reporter:Cristina Cañada-Vilalta, Evan Rumberger, Euan K. Brechin, Wolfgang Wernsdorfer, Kirsten Folting, Ernest R. Davidson, David N. Hendrickson and George Christou
Dalton Transactions 2002 (Issue 21) pp:4005-4010
Publication Date(Web):02 Oct 2002
DOI:10.1039/B204903A
The synthesis and magnetic properties of two new hexanuclear iron complexes [Fe6O2(OH)2(O2CR)10L2]
(R = But
(3), Me (4); LH = 2-(2-hydroxyethyl)pyridine (hepH)
(3), 6-methyl-2-(hydroxymethyl)pyridine (Me-hmpH)
(4)) are reported. Both compounds are prepared by treatment of [Fe3O(O2CR)6(H2O)3]+ with three equivalents of LH in MeCN. The X-ray crystal structure of 3·2CHCl3·2H2O is presented. It consists of a planar array of six Fe3+ ions comprising two [Fe3(μ3-O)] subunits that are related by an inversion centre and linked at two of their apices, each linkage consisting of one μ-hydroxo and two μ-carboxylato groups. DC magnetic susceptibility measurements at 1.0 and 0.10 Tesla in the 2.0–300 K range show an increase in the effective magnetic moment with decreasing temperature, corresponding to a high spin (S) ground state. The spin of the ground state was established by magnetization measurements in the 1.0–7.0 T field range and 1.7–4.0 K temperature range. Fitting of the reduced magnetization data by full matrix diagonalization, incorporating both axial and rhombic anisotropy, gave S
= 5, g
= 1.96, D
= 0.46 cm−1 and |E|
= 0.046 cm−1 for 3, and S
= 5, g
= 2.07, D
= 0.27 cm−1 and |E|
= 0 cm−1 for 4. Alternative fits with a negative ZFS were rejected based on their relative fitting error as well as on measurements of the magnetization relaxation behaviour of the complexes at very low temperature (≥0.04 K), where no hysteresis characteristic of a single-molecule magnet was observed.
Co-reporter:Jonathan T. Brockman;John C. Huffman Dr. Dr.
Angewandte Chemie International Edition 2002 Volume 41(Issue 14) pp:
Publication Date(Web):15 JUL 2002
DOI:10.1002/1521-3773(20020715)41:14<2506::AID-ANIE2506>3.0.CO;2-M
Beautiful offspring: Manganese/oxide/carboxylate-cluster chemistry continues to surprise with its rich variety of structural types. Here a new Mn21 cluster (see picture Mn4+ (red), Mn3+ (green)) with a 12 MnIII9 MnIV oxidation level and an approximately planar core is reported.
Co-reporter:Jonathan T. Brockman;John C. Huffman Dr. Dr.
Angewandte Chemie 2002 Volume 114(Issue 14) pp:
Publication Date(Web):15 JUL 2002
DOI:10.1002/1521-3757(20020715)114:14<2616::AID-ANGE2616>3.0.CO;2-G
Weiterhin für Überraschungen gut ist die Manganoxid/carboxylat-Cluster-Chemie mit ihren sehr vielseitigen Strukturtypen. Hier wird ein neuer Mn21-Cluster beschrieben (siehe Abbildung Mn4+ (rot), Mn3+ (grün)), der aus 12 MnIII- und 9 MnIV-Ionen besteht und einen annähernd planaren Kern aufweist.
Co-reporter:Wolfgang Wernsdorfer,
Núria Aliaga-Alcalde,
David N. Hendrickson
and
George Christou
Nature 2002 416(6879) pp:406
Publication Date(Web):
DOI:10.1038/416406a
Various present and future specialized applications of magnets require monodisperse, small magnetic particles, and the discovery of molecules that can function as nanoscale magnets was an important development in this regard1, 2, 3. These molecules act as single-domain magnetic particles that, below their blocking temperature, exhibit magnetization hysteresis, a classical property of macroscopic magnets. Such 'single-molecule magnets' (SMMs)4 straddle the interface between classical and quantum mechanical behaviour because they also display quantum tunnelling of magnetization5, 6 and quantum phase interference7. Quantum tunnelling of magnetization can be advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states required for quantum computing8. However, it is a disadvantage in other applications, such as information storage, where it would lead to information loss. Thus it is important to both understand and control the quantum properties of SMMs. Here we report a supramolecular SMM dimer in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. This system may also prove useful for studying quantum tunnelling of relevance to mesoscopic antiferromagnets.
Co-reporter:Olajuyigbe A. Adebayo, Khalil A. Abboud, George Christou
Polyhedron (28 January 2017) Volume 122() pp:
Publication Date(Web):28 January 2017
DOI:10.1016/j.poly.2016.10.018
The syntheses, crystal structures and magnetic properties are reported of two new and unusual mixed-valence Mn clusters [MnII4MnIVO(mpko)5(MeO-hmp)(mpko-hmp)(H2O)](ClO4)3 (1) and [MnII4MnIVO(ppko)5(MeO-hmp)(ppko-hmp)(H2O)](ClO4)3 (2). They were obtained from the reaction of mpkoH or ppkoH and hmpH with Mn(ClO4)2 in the presence of NaOMe, where mpkoH is methyl(pyridin-2-yl)ketone oxime, ppkoH is phenyl(pyridin-2-yl)ketone oxime, and hmpH is 2-(hydroxymethyl)pyridine. Complex 1 possesses a distorted MnII4 cubane core attached to an external MnIV by the O2− ion. The peripheral ligation includes two unprecedented hemiacetal ligands formed in situ from the reaction of hmpH with MeOH or mpkoH/ppkoH. Solid-state dc and ac magnetic susceptibility measurements established that both 1 and 2 possess an S = 7/2 ground state, which was confirmed by ac in-phase susceptibility data. Simulations of the χMT versus T data established the presence of dominant antiferromagnetic exchange interactions, rationalizing the observed ground state.Reaction of Mn2+ in MeOH with hmpH (2-(hydroxymethyl)pyridine) and mpkoH (methyl(pyridin-2-yl)ketone oxime), or its Ph analogue ppkoH, gives products containing a distorted MnII4 cubane attached to an external MnIV. Ligation includes two different hemiacetals formed from oxidation and alcoholysis of hmpH. The ground state spin is S = 7/2, rationalized by χMT versus T simulations and competing AF interactions.
Co-reporter:George Christou, Allan G. Blackman, Spyros P. Perlepes, Natia L. Frank
Polyhedron (22 March 2013) Volume 52() pp:1-2
Publication Date(Web):22 March 2013
DOI:10.1016/j.poly.2013.01.013
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud, George Christou
Journal of Molecular Structure (12 November 2008) Volume 890(Issues 1–3) pp:
Publication Date(Web):12 November 2008
DOI:10.1016/j.molstruc.2008.04.031
The use of 1,3,5-trihydroxybenzene (thbH3) in manganese carboxylate chemistry has been investigated. The reactions of thbH3 with 4 and 6 equivalents of Mn(O2CEt)2 in MeOH afford the complexes [Mn6(O2CEt)8(L)(MeOH)4(H2O)2] (1) and [Mn8O2(O2CEt)14(MeOH)4] (2), respectively. In the case of complex 1, the product of the in situ organic ligand transformation has been observed, namely the conversion of the tridentate thbH3 group to a new octadentate ligand L4−; the latter has never been previously reported. Both complexes possess rare topologies, with 1 containing 6MnII ions, whereas 2 is mixed-valent 6MnII, 2MnIII. The core of 1 consists of two [Mn3(μ3-OR)]5+ triangles linked by the bulky octadentate ligand L. The [Mn8(μ4-O)2(μ-OR)8]6+ core of 2 can be considered an extension of the common [Mn6(μ4-O)2]10+ (4MnII, 2MnIII) core, comprising two edge-sharing tetrahedra, with two additional Mn atoms at one end. Peripheral ligation in both 1 and 2 is provided by eight and fourteen bridging EtCO2- groups, respectively. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1 and 2 in the 1.8–300 K range. The magnetic susceptibility data for 1 were fit to the theoretical χM vs T expression, derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, for two essentially non-interacting triangular [Mn3(μ3-OR)(μ-OR)2]3+ units. The fitting procedure revealed the two pairwise exchange parameters to be weakly ferromagnetic (Jbasal = J′ = + 0.79(3) cm−1) and antiferromagnetic (Jside = J = −2.04(3) cm−1), respectively, resulting in an S = 5/2 spin ground state. In contrast, the data for 2 revealed dominant antiferromagnetic interactions and a resulting S = 0 ground state; the latter value is rationalized in terms of the strong antiferromagnetic coupling within the central Mn2IIIO2 unit.
Co-reporter:Eleni E. Moushi ; Christos Lampropoulos ; Wolfgang Wernsdorfer ; Vassilios Nastopoulos ; George Christou ;Anastasios J. Tasiopoulos
Journal of the American Chemical Society () pp:
Publication Date(Web):October 21, 2010
DOI:10.1021/ja106666h
The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn40Na4 and homometallic Mn44 loop-of-loops aggregates are reported. The reactions of [Mn3O(O2CMe)6(py)3]·py with 1,3-propanediol (pdH2) and 2-methyl-1,3-propanediol (mpdH2) in the presence of NaN3 afforded [Mn10Na(μ3-O)2(O2CMe)13(pd)6(py)2]4 (1)4 and [Mn10Na(μ3-O)2(O2CMe)13(mpd)6(py)(H2O)]4 (2)4, respectively. Mn40Na4 complexes (1)4 and (2)4 consist of four Mn10 loops linked through Na+ ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)4 showed that each Mn10 loop has an S = 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac susceptibility signals. It also exhibits hysteresis loops that, however, are not typical of single-molecule magnets (SMMs) due to the existence of interloop interactions between the neighboring Mn10 units of (1)4 through the diamagnetic Na+ ions, and also intermolecular interactions between different Mn40Na4 aggregates. The magnetically discrete Mn44 analogue was targeted with high priority and finally prepared from the reaction of [Mn3O(O2CMe)6(py)3]·py with pdH2 in the presence of Mn(ClO4)2·6H2O. The loop-of-loops structure of [Mn44(μ3-O)8(O2CMe)52(pd)24(py)8](ClO4)(OH)3 (3) is essentially identical to those of (1)4 and (2)4, with the most significant difference being that the four Na+ ions of (1)4 and (2)4 have been replaced with Mn2+ ions. Compound 3 is thus best described magnetically as a Mn44 cluster. In accord with this description and the stronger exchange coupling between the four Mn10 loops expected through the connecting Mn2+ ions, magnetic susceptibility measurements revealed that 3 has an S = 6 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac signals. Magnetization vs dc field sweeps on single-crystals of 3 displayed scan rate- and temperature-dependent hysteresis loops confirming that complex 3 is a new SMM, and is thus the second largest Mn cluster and SMM reported to date.
Co-reporter:Tu N. Nguyen, Wolfgang Wernsdorfer, Muhandis Shiddiq, Khalil A. Abboud, Stephen Hill and George Christou
Chemical Science (2010-Present) 2016 - vol. 7(Issue 2) pp:NaN1173-1173
Publication Date(Web):2015/11/16
DOI:10.1039/C5SC02599K
The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn3 units are reported: dimeric [Mn6O2(O2CMe)8(CH3OH)2(pdpd)2] (3) and [Mn6O2(O2CMe)8(py)2(pdpd)2](ClO4)2 (4), and tetrameric [Mn12O4(O2CR)12(pdpd)6](ClO4)4 (R = Me (5), tBu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH2), either in direct synthesis reactions involving oxidation of MnII salts or in metathesis reactions with the preformed complex [Mn3O(O2CMe)6(py)3](ClO4) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [MnIII2MnII(μ3-O)]6+ and [MnIII3(μ3-O)]7+ units, respectively, linked by two pdpd2− groups. Complexes 5 and 6 contain four [MnIII3(μ3-O)]7+ units linked by six pdpd2− groups into a rectangular tetramer [MnIII3]4. Solid-state dc magnetic susceptibility studies showed that the Mn3 subunits in 3 and 4 have a ground-state spin of S = 3/2 and S = 2, respectively, while the Mn3 subunits in 5 and 6 possess an S = 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-of-phase (χ′′M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn3 single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5·2CH2Cl2 provided precise spin Hamiltonian parameters of D = −0.33 cm−1, |E| = 0.03 cm−1, B04 = −8.0 × 10−5 cm−1, and g = 2.0. Magnetization vs. dc field sweeps on a single crystal of 5·xCH2Cl2 gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn3 unit is exchange-coupled to the two neighbors linked to it by the pdpd2− linkers, with an antiferromagnetic inter-Mn3 exchange interaction of J/kB = −0.011 K (Ĥ = −2JŜi·Ŝj convention). The work demonstrates a rational approach to synthesizing magnetically-supramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.
Co-reporter:Abhudaya Mishra, Junko Yano, Yulia Pushkar, Vittal K. Yachandra, Khalil A. Abboud and George Christou
Chemical Communications 2007(Issue 15) pp:NaN1540-1540
Publication Date(Web):2007/03/19
DOI:10.1039/B701355H
Heterometallic Mn–Ca and Mn–Sr complexes have been prepared and employed as model complexes for Ca and Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); these have revealed similarities that support the presence of at least one O atom bridge between the Mn and Ca/Sr in the OEC.
Co-reporter:Colette Boskovic, John C. Huffman and George Christou
Chemical Communications 2002(Issue 21) pp:NaN2503-2503
Publication Date(Web):2002/09/27
DOI:10.1039/B206751J
The reaction of [Mn12O12(O2CCH2But)16(H2O)4] (1) with a reducing agent followed by recrystallization from CH2Cl2/MeNO2 affords the novel octanuclear complex [Mn8O2(O2CCH2But)14(ButCH2CO2H)4] (2).
Co-reporter:Joan Cano, Thomas Cauchy, Eliseo Ruiz, Constantinos J. Milios, Constantinos C. Stoumpos, Theocharis C. Stamatatos, Spyros P. Perlepes, George Christou and Euan K. Brechin
Dalton Transactions 2008(Issue 2) pp:NaN240-240
Publication Date(Web):2007/10/19
DOI:10.1039/B710055H
DFT calculations reveal the unusual ferromagnetic exchange observed in an oxo-centered MnIII triangle may originate from a combination of the ‘non-planarity’ of the bridging oxime ligands and the non-parallel alignment of the Jahn–Teller axes.
Co-reporter:Constantinos C. Stoumpos, Theocharis C. Stamatatos, Harikleia Sartzi, Olivier Roubeau, Anastasios J. Tasiopoulos, Vassilios Nastopoulos, Simon J. Teat, George Christou and Spyros P. Perlepes
Dalton Transactions 2009(Issue 6) pp:NaN1015-1015
Publication Date(Web):2009/01/09
DOI:10.1039/B813828A
The employment of the anion of methyl 2-pyridyl ketone oxime (mpko−) as a tridentate chelating/bridging ligand in manganese chemistry is described. The inorganic anion (Br−, ClO4−) used in the reaction affects the identity of the product. The reaction of MnBr2 and one equivalent of mpkoH in the presence of a base affords [Mn3(OMe)2(mpko)4Br2] (3), which is mixed-valence (2MnII, MnIV). The central MnIV atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the η1:η1:η1:μ mpko− ligands, and two η1:μ MeO− groups, while six coordination at each terminal MnII atom is completed by four nitrogen atoms belonging to the ‘chelating’ part of two mpko− ligands, and one Br− ion. The MnII atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO4)2·6H2O, mpkoH and OH− (1:2:1) in MeOH gives [Mn8O4(OMe)(mpko)9(mpkoH)](ClO4)4 (4), which is also mixed-valence (2MnII, 6MnIII) and possesses the novel [Mn8(μ3-O)4(μ-OMe)(μ-OR″)2]11+ core. The latter possesses a U-shaped sequence of four fused {MnIIMnIII2(μ3-O)}6+ triangular units, with a MnIII-MnIII edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4. The dc susceptibility data for 3 in the 5.0–300 K range have been fit to a model with two J values, revealing weak ferromagnetic MnII⋯MnIV (J = +3.4 cm−1) and MnII⋯MnII (J′ = +0.3 cm−1) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm−1 for 3 and S = 3, D = −0.09 cm−1 for 4. The combined work demonstrates the usefulness of mpko− in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands.
Co-reporter:Constantina Papatriantafyllopoulou, Eleni E. Moushi, George Christou and Anastasios J. Tasiopoulos
Chemical Society Reviews 2016 - vol. 45(Issue 6) pp:NaN1628-1628
Publication Date(Web):2016/01/15
DOI:10.1039/C5CS00590F
In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term “giant clusters” is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.
Co-reporter:Theocharis C. Stamatatos, Alina Vinslava, Khalil A. Abboud and George Christou
Chemical Communications 2009(Issue 20) pp:NaN2841-2841
Publication Date(Web):2009/04/22
DOI:10.1039/B902016K
A new high oxidation state MnIII/IV11carboxylate complex has been prepared and then converted to a MnII/III25 azide/carboxylate cluster with Me3SiN3; the Mn25 product is the initial example of a higher oxidation state Mn azide complex not stabilized by any chelate ligands.
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud, Spyros P. Perlepes and George Christou
Dalton Transactions 2007(Issue 35) pp:NaN3863-3863
Publication Date(Web):2007/07/30
DOI:10.1039/B708189H
The reactions of 2-pyridinealdoxime [(py)CHNOH] with Ni(ClO4)2·6H2O in the presence of NaOH and NaN3 have led to NiII14 and NiII12Na2 clusters; the Ni14 compound is the biggest metal oxime cluster discovered to date, as well as the largest Ni azide cluster.
Co-reporter:Theocharis C. Stamatatos, Khalil A. Abboud and George Christou
Dalton Transactions 2009(Issue 1) pp:NaN50-50
Publication Date(Web):2008/10/23
DOI:10.1039/B810701G
The use of the anion of 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (‘bis-tris’ or LH5) as a chelate in Mn cluster chemistry is reported, and two products [Mn(N3)(LH3)] (1) and [Mn5(LH2)3(LH5)(MeOH)2.5]Cl4 (2) are described. The reaction of Mn(ClO4)2·6H2O and NaN3 with LH5 and NEt3 in a 1:1:1:2 molar ratio in DMF gave complex 1. The reaction of 1, NEt3 and MnCl2·4H2O in a 2:2:1 ratio in MeOH gave the pentanulear complex 2. Complex 1 contains a distorted-octahedral MnIII atom exhibiting a Jahn–Teller axial elongation. Complex 2 has a mixed-valence MnII2MnIII3 trigonal bipyramidal Mn5 topology, with the apical positions of the [Mn5(μ-OR)7]6+ core occupied by the MnII atoms. Variable-temperature, solid-state dc and ac magnetization studies are reported for 1 and 2 in the 1.8–300 K range. The data for 1 are as expected for a high-spin d4 MnIII complex with S = 2; at low temperature, the effects of zero-field splitting (ZFS) and intermolecular antiferromagnetic interactions viaOH⋯O hydrogen bonds become evident. Fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization gave S = 2, D = −3.25 cm−1 and |E| = 0.32 cm−1, with g fixed at 2.00, where D and E are the axial and rhombic ZFS parameters, respectively. The analogous fit for 2 gave S = 3 and D = −0.68 cm−1. The combined results demonstrate the usefulness of ‘bis-tris’ as a new poly-alkoxide chelate for the synthesis of new Mn complexes.
Co-reporter:Gina C. Vlahopoulou, Theocharis C. Stamatatos, Vassilis Psycharis, Spyros P. Perlepes and George Christou
Dalton Transactions 2009(Issue 19) pp:NaN3649-3649
Publication Date(Web):2009/03/17
DOI:10.1039/B901990A
The initial employment of α-benzoin oxime (bzoxH2) in metal cluster chemistry has provided access to a new family of decanuclear CuII complexes with a loop or single-strand wheel topology; the CuII10clusters are antiferromagnetically-coupled with an S = 0 spin ground state, as expected for even-membered loop arrays of CuII atoms.
Co-reporter:Theocharis C. Stamatatos, Shreya Mukherjee, Khalil A. Abboud and George Christou
Chemical Communications 2009(Issue 1) pp:NaN64-64
Publication Date(Web):2008/11/17
DOI:10.1039/B812721B
A Ga20 single-strand wheel has been prepared by a targeted, propane-1,3-diolate-induced size modification of the known Ga10‘gallic wheel’; the Ga20 reverts back to Ga10 on treatment with an excess of MeOH.
Co-reporter:Rashmi Bagai and George Christou
Chemical Society Reviews 2009 - vol. 38(Issue 4) pp:NaN1026-1026
Publication Date(Web):2009/02/23
DOI:10.1039/B811963E
Single-molecule magnets (SMMs) are individual molecules that can function as nanoscale magnetic particles. The [Mn12O12(O2CR)16(H2O)4] (Mn12; R = Me, Et, etc.) family of SMMs was the first one discovered; it is also the one whose study has provided the majority of current knowledge on this interesting magnetic phenomenon, prompting its description here as the Drosophila of the field. This tutorial review will survey the various chemical studies that have been carried out to date on this family. This will include a discussion of methods that have been developed for their structural and redox transformation, and the effect of the latter on the magnetic and SMM properties.
Co-reporter:Taketo Taguchi, Michael S. Thompson, Khalil A. Abboud and George Christou
Dalton Transactions 2010 - vol. 39(Issue 38) pp:NaN9139-9139
Publication Date(Web):2010/08/27
DOI:10.1039/C0DT00635A
The syntheses, crystal structures and magnetochemical characterization are reported for two new FeIII complexes [Fe18O6(OH)8(pdm)10(pdmH)4(H2O)4](ClO4)10 (3) and [Fe9O4(OH)2(O2CMe)10(pdm)(pdmH)4](NO3) (4). They were synthesized from the use of the potentially O,N,O tridentate chelate, 2,6-pyridinedimethanol (pdmH2), in the presence or absence of carboxylate groups. Octadecanuclear complex 3 was obtained during reactivity studies on previously-reported [Fe8O3(OEt)(pdm)4(pdmH)4(EtOH)2](ClO4)5 (2), the latter undergoing hydrolysis to 3 on recrystallization from undried MeCN. The reaction of pdmH2 with preformed [Fe3O(O2CMe)6(py)3](NO3) in CH2Cl2 gave enneanuclear complex 4. Both complexes 3 and 4 are unprecedented structural types. The core of 3 comprises a central [Fe4O6] defective-dicubane attached on either side to a [Fe7O11] unit, which can be described as two [Fe4(μ4-O)] tetrahedra fused at a common Fe atom. The core of 4 can be considered as four vertex-fused triangular [Fe3(μ3-O)] units. Variable-temperature (T) and -field (H) solid-state dc and ac magnetization (M) studies were carried out on complexes 3 and 4 in the 1.8–300 K range. Analysis of the obtained data revealed that complexes 3 and 4 possess an S = 4 and S = 5/2 ground state spin, respectively.
Co-reporter:Rashmi Bagai, Khalil A. Abboud and George Christou
Chemical Communications 2007(Issue 32) pp:NaN3361-3361
Publication Date(Web):2007/07/23
DOI:10.1039/B708783G
The use of a new O,N,N,O chelate has led to two new Fe6 and Fe18 molecular compounds, the latter with an unusual double-headed serpentine chain structure.
Co-reporter:Tian-Fu Liu, Theocharis C. Stamatatos, Khalil A. Abboud and George Christou
Dalton Transactions 2010 - vol. 39(Issue 15) pp:NaN3556-3556
Publication Date(Web):2010/03/02
DOI:10.1039/C002925B
A systematic investigation of the alcoholysis of copper(II) pivalate (piv−) solutions has led to a series of Cu2, Cu6, and Cu16 products, depending on the alcohol used as solvent. When PrnOH or BunOH was employed, the products were the clusters [Cu16O4(OH)4(OR)8(piv)12(ROH)] (R = Prn, Bun) that are almost isostructural. The Cu16 clusters are antiferromagnetically-coupled with an S = 0 spin ground state.
