Winfried Plass

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Organization: Friedrich-Schiller-Universit?t Jena , Germany

Department: Institut für Anorganische und Analytische Chemie

Title: (PhD)

TOPICS

Inorganic Chemistry

Molecular Magnetics

Chemicals
References

A robust anionic pillared-layer framework with triphenylamine-based linkers: ion exchange and counterion-dependent sorption properties

Co-reporter:Oluseun Akintola;Sven Ziegenbalg;Axel Buchholz;Helmar Görls

CrystEngComm (1999-Present) 2017 vol. 19(Issue 20) pp:2723-2732

Publication Date(Web):2017/05/22

DOI:10.1039/C7CE00369B

A new anionic pillared-layer cobalt(II) metal–organic framework combining 4,4′,4′′-nitrilotribenzoic acid (H3ntb) as a linker and terephthalic acid (H2bdc) as a pillar-ligand with the formula {((CH3)2NH2)2[Co3(ntb)2(bdc)]}n (JUMP-1, JUMP = Jena University Magnetic Polymer) has been solvothermally synthesized and characterized. The crystal structure of JUMP-1 was determined to belong to the orthorhombic space group Cmca. It displays a three-dimensional (3D) framework for which the topological analysis revealed a 3,8-connected net with a tfz-d topology. The 3-connected organic node is linked to an 8-connected secondary building unit composed of a linear trinuclear cobalt(II) cluster with a mixed arrangement of coordination geometries (Td–Oh–Td) leading to two-dimensional layers which are further linked by terephthalic acid to give the pillared-layer arrangement. The magnetic properties are characterized by an antiferromagnetic coupling between a central octahedrally coordinated cobalt(II) ion and two outer tetrahedral cobalt(II) centers, whereas only a very weak inter-cluster coupling is observed. Moreover, a moderate zero-field splitting is detected for the tetrahedral cobalt(II) ions. The organic counterions could successfully be exchanged by lithium ions under retention of the anionic 3D network leading to JUMP-1(Li). For both compounds JUMP-1 and JUMP-1(Li), N2 and CO2 adsorption isotherms were measured. The pore distribution analyses revealed improved microporosity for the lithium exchanged MOF.

Lanthanide(III) Sandwich and Half-Sandwich Complexes with Bulky Cyclooctatetraenyl Ligands: Synthesis, Structures, and Magnetic Properties

Co-reporter:Volker Lorenz;Phil Liebing;Michael Böhme;Axel Buchholz;Niklas Geue;Liane Hilfert;Sabine Busse;Felix Engelhardt;Cristian G. Hrib;Frank T. Edelmann

European Journal of Inorganic Chemistry 2017 Volume 2017(Issue 41) pp:4840-4849

Publication Date(Web):2017/11/09

DOI:10.1002/ejic.201700878

Five new lanthanide(III) sandwich and half-sandwich complexes with bulky cyclooctatetraenyl ligands have been prepared and fully characterized, including single-crystal X-ray structure determination. The treatment of anhydrous lanthanide(III) chlorides, LnCl3 (Ln = Pr, Tb, Yb), with 2 equivalents of Li2COT′′ [COT′′ = 1,4-bis(trimethylsilyl)cyclooctatetraene dianion] followed by crystallization in the presence of a coordinating solvent afforded the anionic sandwich complexes [Li(THF)4][Pr(COT′′)2] (1), [Li(DME)3][Tb(COT′′)2] (2; DME = 1,2-dimethoxyethane), and [Li(TMEDA)2][Yb(COT′′)2] (3; TMEDA = N,N,N′,N′-tetramethylethylenediamine). Attempted oxidation of 2 with silver iodide did not afford the neutral terbium(IV) sandwich complex [Tb(COT′′)2]. Instead, the tri(µ-iodido)-bridged dinuclear half-sandwich complex [Li(DME)2][Tb2(µ-I)3(COT′′)2] (4) was isolated in 72 % yield. In this complex, the Li(DME)2 fragment is attached to one of the µ-iodido ligands. A closely related binuclear lutetium complex, [Li(DME)3][Lu2(µ-Cl)3(COTbig)2]·DME (5), was obtained by using the “superbulky“ COTbig ligand [COTbig = 1,4-bis(triphenylsilyl)cyclooctatetraenyl dianion]. In addition to the spectroscopic and structural characterization, the magnetic properties of the paramagnetic terbium(III) derivative 2 have been investigated and further complemented by ab initio computational methods. These results have been used to discuss the structural requirements for potential terbium(III) single-ion magnets.

Solvent-dependent selective cation exchange in anionic frameworks based on cobalt(II) and triphenylamine linkers: reactor-dependent synthesis and sorption properties

Co-reporter:Oluseun Akintola;David Hornig;Axel Buchholz;Helmar Görls

Dalton Transactions 2017 vol. 46(Issue 25) pp:8037-8050

Publication Date(Web):2017/06/27

DOI:10.1039/C7DT01405H

Two cobalt(II) coordination polymers with anionic networks of formulae {(Me2NH2)2[CoCl(ntb)]}n (JUMP-2) and {(Me2NH2)2[Co5(ntb)4(H2O)3(Me2NH)]}n (previously reported as MIL-144 by Livage et al., Microporous Mesoporous Mater., 2012, 157, 37) have been obtained via a solvothermal reaction of cobalt chloride and 4,4′,4′′-nitrilotribenzoic acid (H3ntb) in DMF employing two differently-sized reactors, while using the same absolute amount of reactants. Structure analysis revealed that JUMP-2 crystallized in the monoclinic space group P21/n and displays a two-dimensional (2D) network, which by topological analysis was characterized as a layered 3-connected hcb net. The topological analysis of MIL-144 revealed a 3,6-connected net with 3,6T80 topology. The magnetic properties of JUMP-2 are indicative of independent single-ion behavior of the tetrahedral cobalt(II) ions and showed an out-of-phase signal in the alternating-current (ac) magnetic susceptibility below 2.5 K, whereas for MIL-144 an overall antiferromagnetic interaction within the di- and trinuclear secondary building units is observed and no indication for slow magnetization dynamics. The organic cations in both frameworks could successfully be exchanged with inorganic cations under retention of the respective network structure. In the process of exchange, both compounds displayed cation selectivity based on which solvent was utilized for immersing the solids. JUMP-2 shows a preference for europium(III) ions in DMF, whereas MIL-144 preferentially takes up lithium ions when ethanol is used. The N2 adsorption isotherms were measured before and after exchange and revealed a considerable improvement in the sorption properties of the exchanged samples.

Cobalt(II)-Based Single-Ion Magnets with Distorted Pseudotetrahedral [N2O2] Coordination: Experimental and Theoretical Investigations

Co-reporter:Sven Ziegenbalg, David Hornig, Helmar Görls, and Winfried Plass

Inorganic Chemistry 2016 Volume 55(Issue 8) pp:4047-4058

Publication Date(Web):April 5, 2016

DOI:10.1021/acs.inorgchem.6b00373

The synthesis and magnetic properties of cobalt(II) complexes with sterically demanding Schiff-base ligands are reported. The compounds [Co(LBr)2] (1) and [Co(LPh)2]·CH2Cl2 (2·CH2Cl2) are obtained by the reaction of cobalt(II) acetate with the ligands HLBr and HLPh in a dichloromethane/methanol mixture. 1 and 2 crystallize in the space groups P21212 and P1̅, respectively. X-ray diffraction studies revealed mononuclear constitution of both complexes. For 1, relatively short intermolecular Co–Co distances of 569 pm are observed. In compound 2, a hydrogen-bonded dichloromethane molecule is present, leading to a solvent aggregate with remarkable thermal stability for which desolvation is taking place between 150 and 210 °C. Magnetic measurements were performed to determine the zero-field-splitting (ZFS) parameter D for both complexes. Frequency-dependent susceptibility measurements revealed slow magnetic relaxation behavior with spin-reversal barriers of 36 cm–1 for 1 and 43 cm–1 for 2 at an applied external field of 400 Oe. This observation is related to an increasing distortion of the pseudotetrahedral coordination geometry for complex 2. These distortions can be decomposed in two major contributions. One is the elongation effect described by the parameter ϵT, which is the ratio of the averaged obtuse and acute bond angles. The other effect is related to a twisting distortion of the chelate coordination planes at the cobalt center. A comparison with literature examples reveals that the elongation effect seems to govern the overall magnetic behavior in pseudotetrahedral complexes with two bidentate chelate ligands. Ab initio calculations for complexes 1 and 2 using the CASPT2 method show strong splitting of the excited 4T2 term, which explains the observed strong ZFS. Spin–orbit calculations with the RASSI-SO method confirm the single-molecule-magnet behavior because only small transversal elements are found for the lowest Kramers doublet for both complexes.

Facile high-yield synthesis of unsymmetric end-off compartmental double Schiff-base ligands: easy access to mononuclear precursor and unsymmetric dinuclear complexes

Co-reporter:Markus Schmidt, Helmar Görls and Winfried Plass

RSC Advances 2016 vol. 6(Issue 79) pp:75844-75854

Publication Date(Web):03 Aug 2016

DOI:10.1039/C6RA16870A

A straightforward and easy to handle two-step synthetic route for unsymmetric double Schiff-base ligands is presented. The isolated intermediate single Schiff-base precursor ligands H2sc-difo and H2tsc-difo were derived by condensation of 2,6-diformyl-4-methylphenol with semicarbazide and thiosemicarbazide, respectively. Further reaction of the precursor ligands with different amine components, including both aliphatic and aromatic examples, allows the synthesis of ditopic unsymmetric double Schiff-base ligands in high yields and purity. As aliphatic cases we used (2-aminoethyl)bis(2-pyridylmethyl)-amine (H2sc-hydra and H2tsc-hydra) and 2-(aminomethyl)-pyridine (H2sc-ampy and H2tsc-ampy), whereas 2-aminophenol was used as an aromatic sample (H3sc-amph and H3tsc-amph). The overall synthetic route allows for the preparation of the employed ligands in large scale. To explore the coordination capabilities of the reported ligand systems a mononuclear nickel(II) complex [Ni(tsc-difo)PPh3] and a homodinuclear zinc(II) complex [Zn2(tsc-hydra)(OAc)2] were synthesized with the single Schiff-base precursor ligand H2tsc-difo and the double Schiff-base ligands H2tsc-hydra, respectively. Both complexes crystallized in the monoclinic space group P21/n. For [Ni(tsc-difo)PPh3] a square-planar geometry is found for nickel(II) ion with H2tsc-difo acting as a tridentate ligand. Whereas the structure of complex [Zn2(tsc-hydra)(OAc)2] reveals two zinc(II) ions in distinctly different coordination geometry, one in distorted octahedral coordination located in the bispyridine based binding pocket with [N4O2] donor set and the other zinc(II) ion in a distorted square-pyramidal coordination given by the thiosemicarbazone based binding pocket with [NO3S] donor set.

Synthesis, Theoretical Study and Catalytic Application of Oxidometal (Mo or V) Complexes: Unexpected Coordination Due to Ligand Rearrangement through Metal-Mediated CC Bond Formation

Co-reporter:Sagarika Pasayat;Michael Böhme;Sarita Dhaka;Subhashree P. Dash;Sudarshana Majumder;Mannar R. Maurya;Werner Kaminsky;Rupam Dinda

European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 10) pp:1604-1618

Publication Date(Web):

DOI:10.1002/ejic.201501465

Abstract

Two novel dioxidomolybdenum(VI) complexes [MoO₂L′¹] (1) and [MoO₂L′²] (2) containing the MoO₂²⁺ motif with unexpected coordination motifs due to ligand rearrangement through Mo-mediated interligand C–C bond formation are reported. The ligands (H₂L′^1–2) are tetradentate C–C-coupled O₂N₂-donor systems formed in situ during synthesis of the complexes by reaction of [Mo^VIO₂(acac)₂] with Schiff base ligands of 2-aminophenol with 2-pyridinecarbaldehyde (HL¹) and 2-quinolinecarbaldehyde (HL²). To confirm that the ligand rearrangement is assisted by molybdenum, the corresponding vanadium complexes [VO₂L¹] (3) and [VO₂L²] (4) containing original Schiff base ligand (HL^1,2) are also reported here. All complexes 1–4 are characterized by several physicochemical techniques and the structural features of 1 and 2 have been solved by X-ray crystallography. The proposed mechanism of molybdenum-mediated interligand C–C bond formation is supported by DFT calculations including the comparisons with the synthesized vanadium analogues. The catalytic potentials of 1–4 for the epoxidation of styrene and cyclohexene have also been explored.

A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State

Co-reporter:Eike T. Spielberg; Aksana Gilb; Daniel Plaul; Daniel Geibig; David Hornig; Dirk Schuch; Axel Buchholz; Arzhang Ardavan

Inorganic Chemistry 2015 Volume 54(Issue 7) pp:3432-3438

Publication Date(Web):March 23, 2015

DOI:10.1021/ic503095t

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2′-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = −324 cm–1). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = 1/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

Palladium(II) complexes bearing 2-(1H-imidazol/oxazol-2-yl)-pyridines: Synthesis, structures and ligand effects in Suzuki–Miyaura cross-coupling

Co-reporter:Abiodun Omokehinde Eseola, Daniel Geibig, Helmar Görls, Wen-Hua Sun, Xiang Hao, Joseph Anthony Orighomisan Woods, Winfried Plass

Journal of Organometallic Chemistry 2014 Volume 754() pp:39-50

Publication Date(Web):15 March 2014

DOI:10.1016/j.jorganchem.2013.12.041

•Synthesis and characterization of palladium complexes with hemilabile azole ligands.•Investigation of catalytic efficiency of the pre-catalysts in C–C cross-coupling.•Determination of ligand effects on the cross-coupling reaction.A series of dichloropalladium(II) complexes (Pd1–Pd4ox) based on derivatives of the hemilabile 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands were synthesized and characterized. The ligands were designed to introduce a variety of electronic and structural features and crystal structures of Pd1, Pd1Me, Pd3, and Pd3Me were determined. Pd1 and Pd1Me both crystallize in the monoclinic space group C2/c. Pd3 crystallizes in the monoclinic space group P21/c while Pd3Me crystallizes in the orthorhombic space group P212121. All complexes were utilized as pre-catalysts in a comparative study to probe relevant features of the palladium active species during high temperature Suzuki–Miyaura cross-coupling catalysis. Relatively higher catalytic activities were obtained for complexes bearing the bidentate ligands that possess weaker azole donor arms. Results obtained suggest that ligand dissociation steps may be important for generating active species with high efficiency. In particular, the observed ligand effects in the investigated series indicate that higher catalyst efficiencies were observed with complexes for which the coordination of the ligand at the palladium center could readily be converted into a monodentate mode.Dichloropalladium(II) complexes with bidentate 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands were used as catalyst in Suzuki–Miyaura cross-coupling. Higher catalytic activities were observed for complexes with ligands possessing weaker azole donors. This suggests the preference of monodentate ligand coordination in the active species.

Vanadium complexes with side chain functionalized N-salicylidene hydrazides: Hydrogen-bonding relays as structural directive for supramolecular interactions

Co-reporter:Axel Buchholz, Simona Nica, Robert Debel, Annika Fenn, Hergen Breitzke, Gerd Buntkowsky, Winfried Plass

Inorganica Chimica Acta 2014 420() pp: 166-176

Publication Date(Web):

DOI:10.1016/j.ica.2014.03.037

Chiral vanadium(V) complexes with 2-aminoglucose Schiff-base ligands and their solution configurations: synthesis, structures, and DFT calculations

Co-reporter:Gholamhossein Mohammadnezhad, Michael Böhme, Daniel Geibig, Anja Burkhardt, Helmar Görls and Winfried Plass

Dalton Transactions 2013 vol. 42(Issue 33) pp:11812-11823

Publication Date(Web):16 May 2013

DOI:10.1039/C3DT50890K

The sugar-modified Schiff-base ligands derived from benzyl 2-deoxy-2-salicylideneamino-α-D-glucopyranoside (H2L5-Br and H2L3-OMe) were used to prepare the chiral oxidovanadium(V) complexes [VO(L5-Br)(OMe)] (1) and [VO(L3-OMe)(OMe)] (2) which can be isolated from a methanol solution as the six-coordinate complexes with an additional methanol ligand [VO(L5-Br)(OMe)(MeOH)] (1–MeOH) and [VO(L3-OMe)(OMe) (MeOH)] (2–MeOH). Both complexes crystallize in the orthorhombic space group P212121 together with two solvent molecules of methanol as 1–MeOH·2MeOH and 2–MeOH·2MeOH. In both crystal structures, only diastereomers with A configuration at the chiral vanadium centre (OC-6-24-A) are observed which corresponds to an cis configuration of the oxido group at the vanadium centre and the benzyl group at the anomeric carbon of the sugar backbone. Upon recrystallization of 2–MeOH from chloroform, the five-coordinate complex 2 was obtained which crystallizes in the monoclinic space group P21 with one co-crystallized chloroform molecule (2·CHCl3). For the chiral vanadium centre in 2·CHCl3, a C configuration (SPY-5-43-C) is observed which corresponds to an trans structure as far as the orientations of the oxido and benzyl groups are concerned. 1H and 51V NMR spectra of 1 and 2 indicate the presence of two diastereomers in solution. Their absolute configurations can be assigned based on the magnetic anisotropy effect of the oxidovanadium group. This effect leads to significant differences for the 1H NMR chemical shifts of the H-2 (1.1 ppm) and H-3 protons (0.3 ppm) of the glucose backbone of the two diastereomers, with the downfield shift observed for the H-2 proton of the C-configured and the H-3 proton of the A-configured diastereomer at the vanadium centre. For 1 and 2 the difference between the 51V NMR chemical shifts of the two diastereomers is 30 and 28 ppm, respectively. Also in the 13C NMR significant chemical shift differences between the two diastereomers are observed for the carbon atoms C2 (2 ppm) and C3 (4 ppm). DFT calculations of the NMR chemical shift parameters have been performed which are in good agreement with the experimental data. Moreover, the isomerization mechanism between the diastereomers is analysed on the basis of DFT calculations which indicate the required presence of methanol molecules as protic donors.

Chiral and supramolecular model complexes for vanadium haloperoxidases: Host–guest systems and hydrogen bonding relays for vanadate species

Co-reporter:Winfried Plass

Coordination Chemistry Reviews 2011 Volume 255(19–20) pp:2378-2387

Publication Date(Web):October 2011

DOI:10.1016/j.ccr.2011.04.014

AbstractSupramolecular interactions and hydrogen bonding play a fundamental role in determining both structure and function of vanadate in enzymatic systems and in particular for the active site of vanadium haloperoxidases. Vanadium complexes with N-salicylidene hydrazide ligands provide a versatile approach towards molecular model systems with hydrogen bonding interactions. The variation of the side chains within these hydrazone ligands provides the ability to introduce chirality in molecular model complexes by the utilization of appropriate carbohydrate fragments. Moreover, the synthetic potential and the transformation reactions found for dioxidovanadium(V) complexes with N-salicylidene hydrazide ligands are reminiscent of what is usually observed for carboxylates and can therefore be regarded as their inorganic counterpart. The anisotropy effect of the oxido groups in vanadium complexes is a valuable tool that allows for the configurational and conformational analysis of structures with corresponding chelate rings. Utilizing appropriate vanadium complexes it is possible to generate inclusion compounds with cyclodextrins. The dependence of solid state and solution structures on the ring size of the cyclodextrin is discussed.

Copper(II) and Zinc(II) Complexes with a Photoactive Bridging Ligand Based on Carbazole: Synthesis, Structures, Electronic and Magnetic Properties

Co-reporter:Eike T. Spielberg

European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 6) pp:826-834

Publication Date(Web):

DOI:10.1002/ejic.201000970

Abstract

The synthesis of the new Schiff base ligand N-(4-methoxyphenyl)-3,4-bis(salicylidenimino)carbazole (H₂SalCarbOMe) is described. It readily reacts with copper(II) andzinc(II) ions to form metallacycles of the general formula [M₂(SalCarbOMe)₂] (M = Cu, Zn). Their structures are determined by X-ray crystallography and show significant differences for the coordination at the metal ion with a nearly tetrahedral arrangement for Zn^II, but a considerable distortion towards square-planar geometry for Cu^II. This in turn leads to substantial differences for the dihedral angles observed between the salicylidene and carbazole moieties. As a consequence different arrangements in the unit cell are observed, which becomes particularly obvious when the additional solvent molecules of crystallization are considered. For the Zn^II compound this leads to the incorporation of a chloroform and a methanol molecule in fixed positions, whereas in the structure of the Cu^II compound a higher number of solvent molecules (chloroform, methanol, and water) in highly disordered crystallographic positions is observed. The optical and magnetic properties have been characterized for both complexes. They both show two band fluorescence in the visible region with emission maxima at 531 and 586 nm for the Zn^II compound and 488 and 580 nm in the Cu^II complex. The electronic properties have been further elucidated by quantum chemical calculations. For the two copper(II) ions an antiferromagnetic interaction through the carbazole bridging ligand with an exchange coupling constant of J = –3.1 cm^–1 is observed. ESR spectroscopy reveals a rhombic signal with g values [g_x, g_y, g_z] = [2.057, 2.125, 2.200] consistent with the distorted coordination geometry around the copper(II) ions.

Phloroglucinol-bridged trinuclear complexes with three paramagnetic octahedral nickel(II) ions: Syntheses, crystal structures, and magnetic properties

Co-reporter:Daniel Plaul, Winfried Plass

Inorganica Chimica Acta 2011 Volume 374(Issue 1) pp:341-349

Publication Date(Web):1 August 2011

DOI:10.1016/j.ica.2011.03.018

Three new C3-symmetric tritopic ligands with a central phloroglucinol bridging unit have been synthesized and characterized. The ligands are accessible through Schiff-base condensation of 2,4,6-triformylphloroglucinol with 2-aminomethylpyridine (H3tfpg-ampy), N,N-bis(pyridin-2-ylmethyl)-ethylenediamine (H3tfpg-unspenp), and benzhydrazide (H6tfpg-bhy). These ligands differ in nature and number of the donor atoms within the resulting binding pockets. Based on these ligands the synthesis of the first trinuclear phloroglucinol-bridged nickel(II) complexes with three octahedrally coordinated nickel centers is reported. The ligands H3tfpg-ampy and H6tfpg-bhy, which provide tridentate binding pockets, react with nickel(II) perchlorate in the presence of bis(pyridin-2-ylethyl)-amine (bpea) as an additional tridentate capping ligand leading to the formation of the trinuclear complexes [Ni3(tfpg-ampy)(bpea)3](ClO4)3 and [Ni3(tfpg-bhy)(bpea)3](ClO4)3, respectively. Due to the pentadentate binding pocket in ligand H3tfpg-unspenp, no additional coligand is needed and a water molecule occupies the sixth coordination site at the nickel(II) ion resulting in the complex [Ni3(tfpg-unspenp)(H2O)3](ClO4)3. Temperature-dependent magnetic measurements reveal overall weak antiferromagnetic exchange interactions within the trinuclear complex together with a rather strong zero-field splitting (ZFS) for the nickel(II) ions. The observed isotropic coupling constants for the three complexes are in the range of 0.14 < − J < 0.37 cm−1, whereas for the zero-field splitting parameter ∣D∣∣D∣ values between 1.8 and 5.5 cm−1 are found. This is indicative for competitive spin-polarization and superexchange mechanisms, with the latter prevailing the interaction between the nickel(II) ions through the meta-phenylene-linkage for the complexes reported.Graphical abstractThree new tritopic Schiff-base ligands with a central phloroglucinol unit have been synthesized. The first phloroglucinol-bridged trinuclear high-spin nickel(II) complexes with three paramagnetic ions have been obtained in a directed synthetic approach. The temperature-dependent magnetic measurements indicate small antiferromagnetic interactions between the nickel(II) ions.Highlights► New C3- symmetric phloroglucinol-based bridging ligands. ► Trinuclear complexes with paramagnetic octahedral high-spin nickel(II) ions. ► Weak antiferromagnetic exchange interactions are observed through the bridging ligands. ► Rather large zero-field splitting is observed for the nickel(II) ions. ► Competitive spin-polarization and superexchange mechanisms are observed, with the latter prevailing.

2,4,6-Triacetylphlorogucinol as Threefold Symmetric Bridging Ligand: Synthesis, Structure and Magnetic Properties of the Copper Complex

Co-reporter:Eike T. Spielberg

European Journal of Inorganic Chemistry 2010 Volume 2010( Issue 20) pp:3093-3096

Publication Date(Web):

DOI:10.1002/ejic.201000341

Abstract

It is shown that 2,4,6-triacetylphlorogucinol (H₃tapg) can be utilized as C₃-symmetric tritopic bridging ligand, that can be regarded as an annulated threefold acetylacetonate. Together with 2-[bis(2-hydroxyethyl)amino]ethylamine (H₂bhea) as capping ligand the corresponding trinuclear copper complex [Cu₃(tapg)(H₂bhea)₃](ClO₄)₃ has been synthesized as the first example. The compound crystallizes in the trigonal space group R3c with the complex cation located on a threefold rotation axis. Magnetic measurements reveal a ferromagnetic coupling between the copper centers, which are transmitted through the bridging tapg^3– ligand by a spin-polarization mechanism.

Electronic and magnetic structure of a triacetylphlorogucinol-bridged -symmetric trinuclear copper complex: Magnetic characterization, ESR spectroscopy, and DFT calculations

Co-reporter:Eike T. Spielberg, Maria Fittipaldi, Daniel Geibig, Dante Gatteschi, Winfried Plass

Inorganica Chimica Acta 2010 Volume 363(Issue 15) pp:4269-4276

Publication Date(Web):10 December 2010

DOI:10.1016/j.ica.2010.08.017

For the trinuclear copper complex [Cu3(tapg)(H2bhea)3](ClO 4)3 based on the tritopic bridging ligand 2,4,6-triacetylphlorogucinol (H3tapg) and the capping ligand 2-[bis-(2-hydroxyethyl)amino]ethylamine (H2bhea) a detailed study on the magnetic and electronic properties is presented. The C3C3-symmetric structure of the molecular assembly is preserved in the solid state structure of the compound which crystallizes in the space group R3cR3c with a threefold rotation axis passing through the center of the molecule. Susceptibility measurements show weak ferromagnetic interactions with a coupling constant J=1.10(4)cm-1 mediated by a spin-polarization mechanism. This is confirmed by DFT calculations according the broken symmetry approach at B3LYP/def2-TZVP level of theory. Extended characterization by ESR spectroscopy both in X- and W-band confirm an exchange-coupled system with axial symmetry with g⊥=2.0633(4)g⊥=2.0633(4), g‖=2.2303(4)g‖=2.2303(4) and an effective axial hyperfine constant A‖,eff=64G.Graphical abstractFor the C3C3-symmetric trinuclear copper complex depicted the ferromagnetic exchange coupling through the bridging annulated threefold acetylacetonate ligand is investigated.

Structural variety and magnetic properties of polynuclear assemblies based on 2-aminoglucose and tritopic triaminoguanidine ligands

Co-reporter:Winfried Plass

Coordination Chemistry Reviews 2009 Volume 253(19–20) pp:2286-2295

Publication Date(Web):October 2009

DOI:10.1016/j.ccr.2008.12.002

Structural features of molecular assemblies determine their magnetic properties. This has been expressed in several qualitative and quantitative magnetostructural correlations. Herein two classes of ligands and there structural and magnetic properties will be discussed. 2-Aminoglucose ligands are 2-aminoalcohols derived from a sugar backbone and therefore provide specific structural and chemical properties which can be used as structural directives. Hence, this allows to control the magnetic properties of related polynuclear complexes. On the other hand, triaminoguanidine derivatives as tritopic ligands preset an equilateral triangular arrangement of metal ions with preferentially antiferromagnetic interactions. This can be utilized to generate higher nuclearity complexes and coordination polymers.

Cyclodextrin inclusion compounds of vanadium complexes: Structural characterization and catalytic sulfoxidation

Co-reporter:Ines Lippold, Kristin Vlay, Helmar Görls, Winfried Plass

Journal of Inorganic Biochemistry 2009 Volume 103(Issue 4) pp:480-486

Publication Date(Web):April 2009

DOI:10.1016/j.jinorgbio.2008.12.014

Reaction of potassium vanadate with the hydrazone ligand derived from Schiff-base condensation of salicylaldehyde and biphenyl-4-carboxylic acid hydrazide (H2salhybiph) in the presence of two equivalents α-cyclodextrin (α-CD) in water yields the 1:2 inclusion compound K[VO2(salhybiph)@(α-CD)2]. Characterization in solution confirmed the integrity of the inclusion compound in the polar solvent water. The inclusion compound crystallizes together with additional water molecules as K[VO2(salhybiph)@(α-CD)2] · 18H2O in the monoclinic space group P2(1). Two α-CD rings forming a hydrogen bonded head to head dimer are hosting the hydrophobic biphenyl side chain of the complex K[VO2(salhybiph)]. The supramolecular aggregation of the inclusion compound in the solid state is established through hydrogen bonding interactions among adjacent α-CD hosts and with vanadate moieties of the guest complexes as well as ionic interactions with the potassium counterions. In contrast the supramolecular structure of the guest complex K[VO2(salhybiph)] without the presence of CD host molecules is governed by π–π-stacking interactions and additional CH/π interactions. The new inclusion complex K[VO2(salhybiph)@(α-CD)2] and the analogous 1:1 inclusion compound with β-CD were tested as catalyst in the oxidation of methyl phenyl sulfide (thioanisol) using hydrogen peroxide as oxidant in a water/ethanol mixture, under neutral as well as acidic conditions.

Heterometallic 3d–4f coordination polymers: Synthesis, characterization and magnetic properties of 1D zigzag chains containing samarium and terbium

Co-reporter:Adrian E. Ion, Eike T. Spielberg, Lorenzo Sorace, Axel Buchholz, Winfried Plass

Solid State Sciences 2009 Volume 11(Issue 4) pp:766-771

Publication Date(Web):April 2009

DOI:10.1016/j.solidstatesciences.2008.05.019

Reaction of the copper precursor [Cu(MeOsaltn)(H2O)] (H2MeOsaltn = N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane) with Ln(NO3)3·6H2O (Ln = Sm and Tb) and pyrazine-2,3-dicarboxylic acid (H2pyrdic) results in the formation of 1D zigzag chains with the general formula of [Cu(MeOsaltn)Ln(NO3)(pyrdic)]n·nDMF. X-ray crystal structures reveal that the samarium and terbium compounds are isostructural and crystalize in the orthorhombic space group Pbcn. The chains are composed of heterodinuclear copper–lanthanide building blocks which are linked by the pyrazine-2,3-dicarboxylate bridging units. Temperature-dependent susceptibility measurements indicate antiferromagnetic exchange interactions for the samarium–copper chain whereas for the terbium–copper compound ferromagnetic interactions are observed.

Mono- and dinuclear copper(II) complexes with meta-phenylene-bridging ligands: Synthesis, structure and magnetic properties

Co-reporter:Daniel Plaul, Daniel Geibig, Helmar Görls, Winfried Plass

Polyhedron 2009 28(9–10) pp: 1982-1990

Publication Date(Web):

DOI:10.1016/j.poly.2008.11.039

Chiral oxovanadium(V) complexes with a 6-amino-6-deoxyglucopyranoside-based Schiff-base ligand: Catalytic asymmetric sulfoxidation and structural characterization

Co-reporter:Ines Lippold, Jana Becher, Dieter Klemm, Winfried Plass

Journal of Molecular Catalysis A: Chemical 2009 Volume 299(1–2) pp:12-17

Publication Date(Web):18 February 2009

DOI:10.1016/j.molcata.2008.10.005

Two new chiral oxovanadium(V) complexes [VO(OMe)(L)] (1) and [VO(Osal)(L)] (2) derived from the Schiff-base ligand 6-N-[(3,5-di-tert-butyl-salicylidene)amino]-6-deoxy-1,2,3-tri-O-methyl-α-d-glucopyranose (H2L) were synthesized via two different routes. The reaction of the Schiff-base ligand H2L with ammonium metavanadate in hot methanol as well as with tris(isopropoxy)oxovanadium(V) in diethyl ether at room temperature leads to a mixture of complexes 1 and 2, which can be isolated by means of fractional crystallization. The complexes were characterized with elemental analysis, 51V, 1H and 13C NMR, IR spectroscopy, MS and in case of 1 by X-ray diffraction. Complex 1 crystalizes in the orthorhombic space group P212121 with a distorted trigonal bipyramidal geometry at the vanadium center (τ = 0.58). Under hydrolytic conditions 1 forms the cis-dioxovanadium(V) complex [VO2(MeOH)(HL)] (3) which can be monitored by NMR spectroscopy. Complexes 1 and 2 were tested as catalysts for sulfoxidation of different sulfide substrates PhSR (R = Me, Bz) utilizing hydrogen peroxide or tert-butyl hydroperoxide (TBHPO) as oxidant in dichloromethane as solvent. The yield as well as the enantiomeric excess were found to strongly depend on the catalyst, substrate and oxidant used.Vanadium(V) complexes with carbohydrate-based functionalized Schiff-base ligands have been synthesized and structurally characterized. These complexes have been tested for the catalytic oxidation of sulfides.

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis, Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2-Aminoglucose Ligand

Co-reporter:Anja Burkhardt Dr.;EikeT. Spielberg;Sascha Simon;Helmar Görls Dr.;Axel Buchholz Dr. Dr.

Chemistry - A European Journal 2009 Volume 15( Issue 5) pp:1261-1271

Publication Date(Web):

DOI:10.1002/chem.200800670

Abstract

The reaction of benzyl 2-amino-4,6-O-benzylidene-2-deoxy-α-D-glucopyranoside (HL) with the metal salts Cu(ClO₄)₂⋅6 H₂O and Ni(NO₃)₂⋅6 H₂O affords via self-assembly a tetranuclear μ₄-hydroxido bridged copper(II) complex [(μ₄-OH)Cu₄(L)₄(MeOH)₃(H₂O)](ClO₄)₃ (1) and a trinuclear alcoholate bridged nickel(II) complex [Ni₃(L)₅(HL)]NO₃ (2), respectively. Both complexes crystallize in the acentric space group P2₁. The X-ray crystal structure reveals the rare (μ₄-OH)Cu₄O₄ core for complex 1 which is μ₂-alcoholate bridged. The copper(II) ions possess a distorted square-pyramidal geometry with an [NO₄] donor set. The core is stabilized by hydrogen bonding between the coordinating amino group of the glucose backbone and the benzylidene protected oxygen atom O4 of a neighboring {Cu(L)} fragment as hydrogen-bond acceptor. For complex 2 an [N₄O₂] donor set is observed at the nickel(II) ions with a distorted octahedral geometry. The trinuclear isosceles Ni₃ core is bridged by μ₃-alcoholate O3 oxygen atoms of two glucose ligands. The two short edges are capped by μ₂-alcoholate O3 oxygen atoms of the two ligands coordinated at the nickel(II) ion at the vertex of these two edges. Along the elongated edge of the triangle a strong hydrogen bond (244 pm) between the O3 oxygen atoms of ligands coordinating at the two relevant nickel(II) ions is observed. The coordinating amino groups of the these two glucose ligands are involved in additional hydrogen bonds with O4 oxygen atoms of adjacent ligands further stabilizing the trinuclear core. The carbohydrate backbones in all cases adopt the stable ⁴C₁ chair conformation and exhibit the rare chitosan-like trans-2,3-chelation. Temperature dependent magnetic measurements indicate an overall antiferromagnetic behavior for complex 1 with J₁=−260 and J₂=−205 cm⁻¹ (g=2.122). Compound 2 is the first ferromagnetically coupled trinuclear nickel(II) complex with J_A=16.4 and J_B=11.0 cm⁻¹ (g_1,2=2.183, g₃=2.247). For the high-spin nickel(II) centers a zero-field splitting of D_1,2=3.7 cm⁻¹ and D₃=1.8 cm⁻¹ is observed. The S=3 ground state of complex 2 is consistent with magnetization measurements at low temperatures.

Chiral Tetranuclear μ3-Alkoxo-Bridged Copper(II) Complex with 2 + 4 Cubane-Like Cu4O4 Core Framework and Ferromagnetic Ground State

Co-reporter:Anja Burkhardt ; Eike T. Spielberg ; Helmar Görls

Inorganic Chemistry 2008 Volume 47(Issue 7) pp:2485-2493

Publication Date(Web):March 4, 2008

DOI:10.1021/ic701777t

The sugar-modified Schiff base ligand benzyl 2-deoxy-2-salicylideneamino-α-d-glucopyranoside H2L, prepared by condensation of salicylaldehyde and the monomeric chitosan analogue benzyl 2-deoxy-2-amino-α-d-glucopyranoside, reacts with copper(II) acetate to form a self-assembled, alkoxo-bridged tetranuclear homoleptic copper(II) complex [{Cu(L)}4] (4) with Cu4O4 heterocubane core. The chiral complex 4 crystallizes in the space group P212121. The tetranuclear complex 4 is composed of two dinuclear {Cu(L)}2 entities linked by the four μ3-bridging C-3 alkoxide oxygen atoms of the sugar backbone. The preorganization of the dimeric {Cu(L)}2 entities is enforced by strong hydrogen bonds between the phenolate oxygen atom and the C-4 hydroxy group of the two constituting chiral monomeric building blocks. Therefore the Cu4O4 core can be classified as a type I or 2 + 4 cubane. The chirality of the structure is confirmed by circular dichroism (CD) spectra, which reveal a significant dichroism associated with the copper centered transitions at around 600 nm. Temperature dependent magnetic susceptibility measurements indicate ferromagnetic exchange interactions in complex 4. Fitting of the experimental data with a two J model based on the 2 + 4 topology leads to exchange coupling constants of J1 = 64 and J2 = 4 cm−1. The observed ferromagnetic coupling can be attributed to the very small Cu−O−Cu bridging angles within the Cu2O2 core of the constituting dimeric entities, which are a result of the conformational requirements introduced by the sugar backbone. 4 is not only the first example of an alkoxo-bridged tetranuclear copper(II) complex with Cu4O4 core representing the 2 + 4 cubane class with ferromagnetic ground state but also a rare example for the class of molecules combining a ferromagnetic ground state with optical activity. The ferromagnetic S = 2 ground state of 4 is confirmed by magnetization measurements and ESR spectroscopy.

Mixed-Ligand Oxidovanadium(V) Complexes with N-Salicylidenehydrazides: Synthesis, Structure, and 51V Solid-State MAS NMR Investigation

Co-reporter:Simona Nica;Axel Buchholz;Manfred Rudolph;Annika Schweitzer;Maria Wächtler;Hergen Breitzke;Gerd Buntkowsky

European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 14) pp:2350-2359

Publication Date(Web):

DOI:10.1002/ejic.200800063

Abstract

The synthesis and spectroscopic characterization of a series of three oxidovanadium(V) complexes with 8-hydroxyquinoline and Schiff-base ligands derived from salicylaldehyde and ω-hydroxy-functionalized carbohydrazides with different chain lengths are reported. The complex with the hydrazone ligand containing the shortest chain length was crystallographically characterized. This complex crystallizes in the triclinic space group P with two structurally similar but crystallographically independent oxidovanadium(V) complexes. Each vanadium atom is six-coordinate in a distorted-octahedral geometry. The two molecules are assembled through hydrogen-bonding interactions between the hydroxyl groups of the side-chain substituted Schiff-base ligand and the oxido group of one of the two complexes. Electrochemical measurements performed in acetonitrile solution reveal two reversible one-electron reduction steps. The observed pre-wave feature of the second reduction step indicates the presence of dissociation equilibria related to the 8-hydroxyquinoline coligand. Magic-angle spinning solid-state ⁵¹V NMR spectroscopy allowed to characterize the full series of complexes with alkyl and hydroxy alkyl-substituted hydrazone ligands that were used. The quadrupolar coupling constants are small with a value of about 4 MHz and show little variation within the series. The asymmetry of the chemical shift tensor indicates a rather axial symmetric environment around the vanadium(V) center. The isotropic chemical shifts observed in the solid state occur at about 30 ppm, which is in the same order of magnitude as the solvent induced variations, about 10 ppm, found for different solvents.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Modeling the coordination chemistry of chitosan: Synthesis and characterization of a nickel(II) complex with a 2-aminoglucose Schiff-base ligand

Co-reporter:Anja Burkhardt, Winfried Plass

Inorganic Chemistry Communications 2008 Volume 11(Issue 3) pp:303-306

Publication Date(Web):March 2008

DOI:10.1016/j.inoche.2007.12.006

Based on the sugar-modified Schiff-base ligand derived from salicylaldehyde and benzyl 2-deoxy-2-amino-α-d-glucopyranoside (H2salagluc) the new mixed-ligand nickel(II) complex [Ni(Hsalagluc)(tptz)]ClO4 has been synthesized (tptz = 2,4,6-tri-(2-pyridyl)-1,3,5-triazine). The X-ray crystal structure reveals a distorted octahedral geometry at the nickel(II) center with the rare 2,3-chelation of the trans-configured donor atoms of the carbohydrate backbone. Intermolecular hydrogen bonding leads to dimeric units of the complex cations. The supramolecular assembly of these units by π-stacking of the tptz coligands affords one-dimensional chains along the two fold screw axis. O–H⋯π(Ar) hydrogen bonding is observed for a methanol molecule of crystallization. Magnetic susceptibility measurements are consistent with a high-spin nickel(II) ion with a zero-field-splitting of D = −11.5 cm−1 (g = 2.311).The first nickel(II) complex with a 2-aminoglucose Schiff-base ligand representing a monomeric chitosan model with trans-configured 2,3-chelation by the sugar backbone is reported. The complex shows extensive hydrogen bonding and π-stacking in the crystal lattice. The distorted octahedral geometry at the nickel(II) ions leads to a rather large zero-field-splitting.

Directed Synthesis of a Heterobimetallic Complex Based on a Novel Unsymmetric Double-Schiff-Base Ligand: Preparation, Characterization, Reactivity and Structures of Hetero- and Homobimetallic Nickel(II) and Zinc(II) Complexes

Co-reporter:Arne Roth;Axel Buchholz Dr.;Manfred Rudolph Dr.;Eileen Schütze;Erika Kothe Dr. Dr.

Chemistry - A European Journal 2008 Volume 14( Issue 5) pp:1571-1583

Publication Date(Web):

DOI:10.1002/chem.200701124

Abstract

A series of bimetallic zinc(II) and nickel(II) complexes based on the novel dinucleating unsymmetric double-Schiff-base ligand benzoic acid [1-(3-{[2-(bispyridin-2-ylmethylamino)ethylimino]methyl}-2-hydroxy-5-methylphenyl)methylidene]hydrazide (H₂bpampbh) has been synthesized and structurally characterized. The metal centers reside in two entirely different binding pockets provided by the ligand H₂bpampbh, a planar tridentate [ONO] and a pentadentate [ON₄] compartment. The utilized ligand H₂bpampbh has been synthesized by condensation of the single-Schiff-base proligand Hbpahmb with benzoic acid hydrazide. The reaction of H₂bpampbh with two equivalents of either zinc(II) or nickel(II) acetate yields the homobimetallic complexes [Zn₂(bpampbh)(μ,η¹-OAc)(η¹-OAc)] (ZnZn) and [Ni₂(bpampbh)(μ-H₂O)(η¹-OAc)(H₂O)](OAc) (NiNi), respectively. Simultaneous presence of one equivalent zinc(II) and one equivalent nickel(II) acetate results in the directed formation of the heterobimetallic complex [NiZn(bpampbh)(μ,η¹-OAc)(η¹-OAc)] (NiZn) with a selective binding of the nickel ions in the pentadentate ligand compartment. In addition, two homobimetallic azide-bridged complexes [Ni₂(bpampbh)(μ,η¹-N₃)]ClO₄ (NiNi(N₃)) and [Ni₂(bpampbh)(μ,η¹-N₃)(MeOH)₂](ClO₄)_0.5(N₃)_0.5 (NiNi(N₃)(MeOH)₂) were synthesized. In all complexes, the metal ions residing in the pentadentate compartment adopt a distorted octahedral coordination geometry, whereas the metal centers placed in the tridentate compartment vary in coordination number and geometry from square-planar (NiNi(N₃)) and square-pyramidal (ZnZn and NiZn), to octahedral (NiNi and NiNi(N₃)(MeOH)₂). In the case of complex NiNi(N₃) this leads to a mixed-spin homodinuclear nickel(II) complex. All compounds have been characterized by means of mass spectrometry as well as IR and UV/Vis spectroscopies. Magnetic susceptibility measurements show significant zero-field splitting for the nickel-containing complexes (D=2.9 for NiZn, 2.2 for NiNi(N₃), and 0.8 cm⁻¹ for NiNi) and additionally a weak antiferromagnetic coupling (J=−1.4 cm⁻¹) in case of NiNi. Electrochemical measurements and photometric titrations reveal a strong Lewis acidity of the metal center placed in the tridentate binding compartment towards external donor molecules. A significant superoxide dismutase reactivity against superoxide radicals was found for complex NiNi.

Carboxylate-Bridged Dinuclear Active Sites in Oxygenases: Diiron, Dimanganese, or is Heterodinuclear Better?

Co-reporter:Arne Roth Dr. Dr.

Angewandte Chemie International Edition 2008 Volume 47( Issue 40) pp:7588-7591

Publication Date(Web):

DOI:10.1002/anie.200802366

Carboxylatverbrckte Zweikernzentren in Oxygenasen: Dieisen, Dimangan oder doch besser heterozweikernig?

Co-reporter:Arne Roth Dr. Dr.

Angewandte Chemie 2008 Volume 120( Issue 40) pp:7700-7703

Publication Date(Web):

DOI:10.1002/ange.200802366

New Aspects for Modeling Supramolecular Interactions in Vanadium Haloperoxidases: β-Cyclodextrin Inclusion Compounds of cis-Dioxovanadium(V) Complexes

Co-reporter:Ines Lippold;Helmar Görls

European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 11) pp:

Publication Date(Web):6 MAR 2007

DOI:10.1002/ejic.200601225

The reaction of potassium vanadate and the hydrazone ligand derived from Schiff base condensation of salicylaldehyde and biphenyl-4-carboxylic acid hydrazide (H₂salhybiph) in the presence of β-cyclodextrin (β-CD) in water yields the 1:1 inclusion compound K[VO₂(salhybiph)@ β-CD]. The characterization in solution confirmed the integrity of the inclusion compound in different polar solvents such as DMSO and water. The inclusion compound crystallizes with additional water molecules in the triclinic space group P1. The supramolecular aggregation of the inclusion compound in the solid state is established through hydrogen bonding interactions between adjacent β-CD hosts and the π–π stacking ability of the ligand side chain of the guest complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Triaminoguanidine derivatives as supports to construct magnetic assemblies: Synthesis and characterization of trinuclear nickel(II) complexes

Co-reporter:Adrian E. Ion, Eike T. Spielberg, Helmar Görls, Winfried Plass

Inorganica Chimica Acta 2007 Volume 360(Issue 13) pp:3925-3931

Publication Date(Web):1 October 2007

DOI:10.1016/j.ica.2007.04.014

The synthesis of two nickel(II) complexes based on a central bridging triaminoguanidine scaffold and a capping ligand per metal ion is reported. When 2,2′-bipyridine (bipy) is utilized as co-ligand the complex [Ni3LBr(bipy)3(H2O)3]NO3 · 9H2O · 1.5DMF (1) is obtained which crystallizes in the hexagonal space group P63/mP63/m. Complex 1 shows an interesting supramolecular structure pattern with alternating hydrophilic and hydrophobic layers characterized by extensive hydrogen-bonding and π–π-stacking, respectively. With 2,4,6-(2-pyridyl)-1,3,5-triazine (tptz) as capping ligand, complex [Ni3LBr(tptz)3]ClO4 · 7H2O · 1.5DMF (2) is obtained. The magnetic susceptibility data can be fitted using an equilateral triangle model (H^=-J(S^1S^2+S^2S^3+S^1S^3)) with an isotropic coupling constant of J=-31.0±0.6J=-31.0±0.6 for 1 and J=-30.9±0.3cm-1 for 2.Triaminoguanidine ligands provide a C3 symmetric core fragment for the generation of trinuclear metal complexes with interesting magnetic and supramolecular features.

Structural characterization and electrochemical behavior of oxovanadium(V) complexes with N-salicylidene hydrazides

Co-reporter:Simona Nica, Manfred Rudolph, Helmar Görls, Winfried Plass

Inorganica Chimica Acta 2007 Volume 360(Issue 5) pp:1743-1752

Publication Date(Web):1 April 2007

DOI:10.1016/j.ica.2006.09.018

The hydrazone ligands derived from salicylaldehyde and aliphatic carbonic acid hydrazides react with equimolecular amounts of ammonium metavanadate and 8-hydroxyquinoline in refluxing methanol to yield oxovanadium(V) complexes. The synthesis can alternatively be performed starting from [VO(acac)2] followed by aerial oxidation to form the corresponding oxovanadium(V) complexes. The molecular structures determined by X-ray crystallography feature in all cases a oxovanadium(V) moiety in an distorted octahedral arrangement with an oxygen and nitrogen rich environment. The obtained compounds posses very good solubility in organic solvents, permitting electrochemical investigation. Square wave voltammetric measurements revealed two reversible one-electron reduction steps at 0.355 and −1.638 V. The reduction of the oxovanadium(V) complexes to the corresponding vanadium(IV) species occurs at relatively positive potential, which is independently verified by ESR spectroscopy. While the second reduction step appears to be accompanied by a pre-wave exhibiting an unusual frequency dependence which can be attributed to ligand addition/elimination equilibria related to the 8-hydroxyquinoline coligand. The oxovanadium(V) complexes can be converted into the corresponding cis-dioxovanadium(V) compounds by reaction with aqueous NaOH. 51V NMR monitoring of this reaction reveals that one equivalent of base results in a full conversion with the cis-dioxovanadium(V) complex being the only species present in solution.Two different routes lead to mixed-ligand oxovanadium(V) complexes [VO(salhyn)(Q)] derived from N-salicylidene hydrazide ligands and 8-hydroxyquinoline with interesting electrochemical properties.

Synthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2-Substituted Glucopyranoside Schiff Base Ligand

Co-reporter:Anja Burkhardt;Axel Buchholz;Helmar Görls

European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 17) pp:

Publication Date(Web):27 JUL 2006

DOI:10.1002/ejic.200600404

Condensation of a derivatized 2-aminoglucose fragment with salicylaldehyde affords the new sugar-based Schiff base ligand benzyl 4,6-O-benzylidene-2-deoxy-2-salicylideneamino-α-D-glucopyranoside (H₂L). The reaction of the dibasic ligand H₂L with [Cu(CH₃COO)₂]·H₂O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)}₄] (3) by a self-assembly process. The X-ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P2₁2₁2₁ revealed for all copper atoms a NO₃ coordination environment with a square-planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3-coordination of the trans-configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan-derived polysaccharide ligands can act as a chiral support for transition-metal complexes. The C-3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight-membered Cu₄O₄ ring with a boat-like conformation. Temperature-dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = –130 cm^–1.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A New Coordination Polymer Architecture with (10,3)-a Network Containing Chiral Hydrophilic 3-D Channels

Co-reporter:Aksana Zharkouskaya;Axel Buchholz

European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 24) pp:

Publication Date(Web):7 NOV 2005

DOI:10.1002/ejic.200500652

The triaminoguanidine-based Schiff-base ligand H₅L^OH reacts with copper(II) ions to afford a three-dimensional coordination polymer with (10,3)-a topology which is solely assembled by a single trigonal molecular building block {Cu₃L^OH}⁺. The unusual bridging mode of the phenolate oxygen atoms between the trigonal building blocks leads to a dihedral angle between the interlinked {Cu₃L^OH}⁺ units of 71°. The (10,3)-a topology of the singular network results in a rather large void space of about 56 % that is established by interpenetrated chiral channels with a diameter limited by pseudo-tetrahedral cavities defined by non-coordinating phenolate hydroxy groups of the ligand. Additional information to establish the composition is derived from elemental analysis and TGA measurements. For the coordination polymer an overall antiferromagnetic behavior is observed. The spin-frustrated trinuclear building blocks {Cu₃L^OH}⁺ are antiferromagnetically coupled via the bis(phenoxide)-bridged dinuclear copper(II) moieties for which a dihedral angle of 132° is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Vanadium(V) Oxoperoxo Complexes with Side Chain SubstitutedN-Salicylidenehydrazides: Modeling Supramolecular Interactions inVanadium Haloperoxidases

Co-reporter:Simona Nica;Axel Pohlmann

European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 11) pp:

Publication Date(Web):2 MAY 2005

DOI:10.1002/ejic.200401060

The Schiff-base ligand derived from salicylaldehyde and γ-hydroxybutanoic acid hydrazide (H₂Salhyhb) reacts with potassium metavanadate and hydrogen peroxide in a water/methanol solution with a pH value of around two to yield the corresponding vanadium(V) oxoperoxo complex [VO(O₂)HSalhyhb(H₂O)] (1). Complex 1 crystallizes with one molecule of water as 1·H₂O in the monoclinic space group P2₁/n. For the vanadium atom a pentagonal-bipyramidal coordination geometry is observed, with a side-on bonded peroxo ligand in the equatorial plane. The hydroxy side chain of the hydrazide ligand is involved in a hydrogen-bond network with the peroxo ligand at the vanadium atom. This network shows some similarities with the hydrogen-bonding scheme found for the peroxo form of vanadium haloperoxidases. The stoichiometric reaction of 1 with 1,3,5-trimethoxybenzene (TMB) in the presence of tetrabutylammonium bromide leads to the formation of 1-bromo-2,4,6-trimethoxybenzene (Br-TMB), thus mimicking the oxidative halogenation function of the native enzyme. Complex 1 is also capable of oxidizing triphenylphosphane and methylphenylsulfane, yielding a cis-dioxovanadium(V) complex and the corresponding phosphane or sulfane oxide, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)