Two cyanide-bridged compounds based on the FeII cation and the anisotropic [MoIII(CN)7]4– anion, namely, {Fe2(H2O)5[Mo(CN)7]·5H2O}n (1) and {[NH2(CH3)2]2Fe5(H2O)10[Mo(CN)7]3·8H2O}n (2), have been prepared. Single crystal X-ray analyses revealed that their structures exhibit different three-dimensional topologies as a result of the addition of [NH2(CH3)2]+ during the synthesis of 2. For both 1 and 2, the geometry of the [Mo(CN)7]4– unit is a slightly distorted capped trigonal prism; all FeII centers are hexacoordinate and adopt a distorted octahedral configuration. Compound 1 is a three-nodal 3,4,7-connected net with the point symbol of {4.62}{45.6}{46.612.83}, while compound 2 is a five-nodal 4,4,4,6,7-connected net with the point symbol of {44.62}{45.6}4{46.67.82}{49.611.8}2. Magnetic studies revealed that both compounds exhibit magnetic ordering below 65 K. Apart from the plethora of MnII–[Mo(CN)7]4– compounds documented in the literature, these two FeII–[Mo(CN)7]4– compounds are the only other [Mo(CN)7]4– extended structures to be characterized by single crystal structures to date.

Crystal structures and magnetic properties of three one-dimensional (1D) azido-bridged cobalt(II) chains with different amide ligands (L), [Co2(N3)4(DMF)3] (1), [Co4(N3)8(DEF)5] (2), and [Co2(N3)4(DIPF)2] (3) (DMF = N,N-dimethylformamide, DEF = N,N-diethylformamide, and DIPF = N,N-diisopropylformamide), are reported to investigate the influence of L on their structures and magnetic properties. Single-crystal X-ray crystallographic analysis revealed that, although 1–3 all consist of cobalt chains bridged by end-on (EO) azides, the coordination geometry of the CoII ions and the repeating units of the 1D structures are quite different. As the size of L increases, the ratio of L to CoII decreases from 6:4 in 1 to 5:4 and 4:4 in 2 and 3, respectively. In 1, two [CoN5O1] and two [CoN4O2] distorted octahedra form the {[CoN5O1][CoN4O2]2[CoN5O1]} tetramers (denoted as Co4A), which are linked to each other by sharing the N–N edge to form the chain. Similarly, the chain structure of 3 is constructed from a similar tetramer unit {[CoN5][CoN4O2]2[CoN5]} (denoted as Co4B), where half of the CoII centers are in the [CoN5] trigonal bipyramid because of the larger steric effect of the DIPF ligand, while, for compound 2 of the medium-sized amide, it has the transition structure between those of 1 and 3. The chain is composed of two different repeating units: Co4A unit similar to that in 1 and Co4B unit similar to that in 3. Because of their similar structures, compounds 1–3 exhibit analogical magnetic properties. Direct-current magnetic measurements demonstrated that all compounds show intrachain ferromagnetic coupling through the EO azides and interchain anti-ferromagnetic interactions. Alternating-current data revealed the slow magnetic relaxation in the anti-ferromagnetic ordered phases. While compound 1 exhibits spin glass behavior, compounds 2 and 3 behave as the single-chain magnets. This difference might come from the interference of the anti-ferromagnetic ordering on the magnetic dynamic of the magnetic chain.

Dynamic molecular crystals are of high interest due to their potential applications. Herein we report the reversible on–off switching of single-molecule magnet (SMM) behavior in a [Mo(CN)7]4– based molecular compound. Upon dehydration and rehydration, the trinuclear Mn2Mo molecule [Mn(L)(H2O)]2[Mo(CN)7]·2H2O (1) undergoes reversible crystal-to-crystal transformation to a hexanuclear Mn4Mo2 compound [Mn(L)(H2O)]2[Mn(L)]2[Mo(CN)7]2 (2). This structural transformation involves the breaking and reforming of coordination bonds which leads to significant changes in the color and magnetic properties. Compound 1 is an SMM with an energy barrier of 44.9 cm–1, whereas 2 behaves as a simple paramagnet despite its higher ground state spin value. The distortion of the pentagonal bipyramidal geometry of [Mo(CN)7]4– in 2 disrupts the anisotropic exchange interactions that lead to SMM behavior in 1.

Field-induced slow magnetic relaxation was observed in a cyano-bridged coordination nanotube constructed from a pentagonal bipyramidal CoII building block and a hexacyanocobaltate(III) anion, which represents the first example of a coordination nanotube displaying field-induced single-molecule magnet behaviour.

Two seven-coordinate compounds with pentagonal bipyramidal YbIII centers, namely, [Yb(H3Bmshp)(DMF)2Cl2]·DMF·1.5H2O (1) and [Yb(H3Bmshp)(DMF)2Cl2]·H4Bmshp (2) (H4Bmshp = (2,6-bis[(3-methoxysalicylidene)hydrazinecarbonyl]-pyridine)) were synthesized by changing the molar ratio of reactants in DMF. The structures of compounds 1 and 2 are very similar, except for the existence of different lattice molecules: one DMF and one and a half water molecules in 1, and one neutral uncoordinated ligand in 2. The coordination geometries of both the pentagonal bipyramidal YbIII centers (YbCl2N1O4) in compounds 1 and 2 are also very similar with only slight differences. Magnetic data analyses revealed that the subtle structure variations result in remarkable different slow magnetic relaxation properties of compounds 1 and 2. To further understand their magnetic behaviors, ab initio calculations were performed for both compounds 1 and 2. The calculated results indicate that the magnetic anisotropies of compounds 1 and 2 are significantly different: easy-plane magnetic anisotropy for 1 and easy-axis magnetic anisotropy for 2. To the best of our knowledge, these compounds are the first YbIII-based SIMs of pentagonal bipyramidal geometry.

Four 2p–4f LnIII-radical complexes, [(NIT-2-Pm)Ln(hfac)3]·0.5C7H16 (NIT-2-Pm = 2-pyrimidyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide, hfac = hexafluoroacetylacetonato, Ln = Tb (1), Dy (2), Ho (3) and Er (4)), and four 4f–2p–4f LnIII-radical-LnIII complexes, [(μ-NIT-2-Pm)Ln2(hfac)6(H2O)2]·0.5C7H16 (Ln = Tb (5), Dy (6), Ho (7) and Er (8)) have been synthesized and characterized structurally and magnetically. These compounds can be selectively obtained by controlling the reaction ratio of Ln(hfac)3·2H2O to the radical ligand NIT-2-Pm. The crystal structures show that in the former four complexes 1–4, the NIT-2-Pm radical acts as a terminal bidentate ligand chelating to one LnIII ion, while in 5–8, the NIT-2-Pm acts as a bridging ligand linking two LnIII ions to form a binuclear three-spin system. Magnetic studies revealed that complexes 1–4 and 6 show frequency-dependent ac magnetic susceptibilities, suggesting a possible single-molecule magnet behavior. To the best of our knowledge, complexes 3 and 4 are the first Ho-NIT and Er-NIT compounds showing slow magnetic relaxation. Compounds 5–8 represent a rare family of compounds showing the NIT bridged 4f–2p–4f three-spin motif, while complex 6 is a rare NIT bridged multinuclear lanthanide compound possessing SMM-like behaviour. Ab initio calculations were performed on all these complexes. The fitting of the magnetic susceptibilities of these compounds suggests weak antiferromagnetic coupling between the LnIII and NIT radical in 1–8 and weak ferromagnetic LnIII–LnIII interactions in 5–8.

A bicomponent ion-pair molecule compound [Co(Brphterpy)2][Co(NCS)4]·2MeCN was designed and prepared for the construction of multistable functional materials. Due to the different coordination geometries of the cationic and anionic CoII ions, this compound exhibits both thermally induced spin crossover (SCO) and field-induced single-ion magnetism (SIM). This represents a rare example of a two-component system with the coexistence of SIM and SCO behaviors and suggests a simple, yet very efficient strategy for the construction of multistable molecular materials.

We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal CoII unit [Co(TODA)]2+ and two hexacyanometallates, namely [MIII(CN)6]2[CoII(TODA)]3·9H2O (M = Cr (1), Co (2), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)]2+ units are bridged by the [MIII(CN)6]3− groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the CrIII and CoII centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1. A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr–Co molecular magnets. For compound 2 containing the diamagnetic [CoIII(CN)6]3− unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm−1 by PHI and 26.5 cm−1 by Anisofit2.0) was deduced for hepta-coordinated CoII centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.

The reaction of Cu(valdmpn) (H2valdmpn = N,N′-bis-(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane), LnCl3·nH2O (Ln = La(1), Ce (2), Pr(3), Nd(4), Sm(5), Eu(6), Gd(7), Tb(8), Dy(9), Ho(10), Er(11), Tm(12), Yb(13), Lu(14)) and NaN3 in methanol led to a whole series of heterometallic CuII–LnIII complexes. The basic structural components of these complexes are the [CuII(valdmpn)LnIII] units with a compartmental Schiff-base ligand. These [CuIILnIII] units were then further connected by the end-on (EO) azides between the Ln3+ centers to form tetranuclear {[CuLn](μ-N3)n[LnCu]} motifs, where n is 3 for the complexes of larger radii lanthanides (1CuLa to 5CuSm) and 2 for the complexes of smaller radii lanthanides (6CuEu to 14CuLu). While compounds 6CuEu to 14CuLu remain isolated tetranuclear clusters, compounds 1CuLa to 5CuSm are one-dimensional chains where tetranuclear motifs are further connected by end-to-end (EE) azides between CuII and LnIII centers. Direct current (dc) magnetic susceptibilities have been measured in the range of 1.8–300 K for all complexes, revealing the different nature of magnetic interactions between the spin centers. Among them, dominant ferromagnetic interactions were found in compounds 7CuGd, 8CuTb and 9CuDy. Alternating current (ac) magnetic measurements performed on 8CuTb, 9CuDy, and 10CuHo demonstrated the presence of slow magnetic relaxation under zero applied dc field. The spin relaxation barrier Ueff was determined to be 19.54 cm−1 (28.12 K) and 10.34 cm−1 (14.87 K) for compounds 8CuTb and 9CuDy. The SMM behavior of 8CuTb was further confirmed by the presence of magnetic hysteresis loops; while no hysteresis loop was observed for 9CuDy and 10CuHo. These results demonstrated that azido-bridged copper(II)–lanthanide(III) complexes could be synthesized successfully despite the generally weak azido–lanthanide interaction.

A new bis-bidentate nitronyl nitroxide radical with a pyrimidyl substituent group and two Co(II) complexes of this ligand were synthesized and characterized. Field-induced single-molecule magnet behavior was firstly observed in the nitronyl nitroxide radical-bridged complexes.

We herein reported the synthetic, structural, computational, and magnetic studies of four air-stable heptacoordinated mononuclear cobalt(II) complexes, namely, [CoII(tdmmb)(H2O)2][BF4]2 (1), [CoII(tdmmb)(CN)2]·2H2O (2), [CoII(tdmmb)(NCS)2] (3), and [CoII(tdmmb)(SPh)2] (4) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[[3](2,6)pyridino[3](2,9)-1,10-phenanthrolinophane-2,10-diene; SPh– = thiophenol anion). Constrained by the rigid pentadentate macrocyclic ligand tdmmb, the CoII centers in all of these complexes are in the heptacoordinated pentagonal-bipyramidal geometry. While the equatorial environments of these complexes remain very similar to each other, the axial ligands are systematically modified from C to N to O to S atoms. Analyses of the magnetic data and the ab initio calculations both reveal large easy-plane magnetic anisotropy (D > 0) for all four complexes. While the experimentally obtained D values do not show any clear tendency when the axial coordinated atoms change from C to N to O atoms (complexes 1–3), the largest value is for the heavier and softer S-atom-coordinated complex 4. Because of significant magnetic anisotropy, all four complexes are field-induced single-ion magnets. This work represents a delicate modification of the magnetic anisotropy by tuning the chemical environment of the metal centers.

Self-assembly of the [MoIII(CN)7]4– anion and the MnII unit with a macrocyclic ligand results in the first example of a one-dimensional (1D) chain compound based on the heptacyanomolybdate, [Mn(LN5C10)]2[Mo(CN)7]·2H2O (LN5C10 = 1,4,7,10,13-pentaazacyclopentadecane). Because of the existence of the interchain magnetic coupling, long-rang magnetic ordering was observed in this compound.

Starting from the pentagonal bipyramidal single-ion magnet [Co(tdmmb)(H2O)2][BF4]2 and a series of linear bridging ligands of different lengths, three new cobalt(II) one-dimensional (1D) coordination polymers, [Co(tdmmb)(pyz)][BF4]2·CH3CN·H2O (1), [Co(tdmmb)(apy)][BF4]2·2CH3CN (2), and [Co(tdmmb)(bpe)][BF4]2·3CH3CN (3) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetra-aza[3](2,6)pyridino[3](2,9)-1,10-phenanthrolinophan-2,10-diene) (pyz = pyrazine) (apy = 4-aminopyridine) (bpe = 1,2-di(4-pyridyl)ethane)), have been synthesized and characterized structurally and magnetically. Symmetric ligands pyz and bpe result in the nearly linear chains in 1 and 3, while the asymmetric ligand apy leads to the zig-zag chain in 2. As the length of the ligands increases, the intrachain Co⋯Co distance also increases, i.e. 7.56, 7.70, and 13.85 Å for 1–3, respectively. Magnetic investigation revealed the gradual decrease in the magnetic interactions between the Co2+ ions from 1 to 3, along with the increase in the intrachain Co–Co distances. Due to the existence of the weak antiferromagnetic (AF) interaction, the SIM behavior of the starting material is surpressed in compounds 1 and 2, and they show a simple paramagnetic behavior. While for 3, field-induced slow magnetic relaxation was observed at a low temperature with an energy barrier of Ueff = 19 K. This observation suggests that the magnetic interaction between the Co2+ centers in 3 is negligible, consistent with the very long Co–Co distance in 3. These 1D compounds are rare chain compounds composed of metal centers with a nearly D5h symmetry. Notably, compound 3 is the second example of a 1D Co(II) chain compound displaying a SIM behaviour. These studies illustrated that the magnetic interaction between the SIMs can be used to tune slow magnetic relaxation.

Magneto-structural relationships were studied experimentally and theoretically for two enantiomorphic tetranuclear [CuTb]2 SMMs. For the first time, the determination of the magnetic anisotropy axis of an individual magnetic ion, Tb3+, was achieved in a polynuclear Tb3+-based SMM.

Spin canting, antiferromagnetic ordering, metamagnetism and single-chain magnetism were verified in a cyano-bridged FeII compound synthesized from the pentagonal bipyramidal FeII starting material in the presence of excessive BF4− anions.

Three mononuclear spin crossover (SCO) compounds [Fe(2-pic)3]·A2·Solv (A = m-ABS–, Solv = MeOH, 1; A = p-ABS–, 2; A = OTf–, 3) were prepared and characterized magnetically and structurally (2-pic = 2-picolylamine, m-HABS = m-aminobenzenesulfonic acid, p-HABS = p-aminobenzenesulfonic acid, HOTf = trifluoromethanesulfonic acid). Single-crystal X-ray analyses show that they are constructed from the charge-assisted hydrogen bonds between the 2-pic donors and the organosulfonate acceptors, forming the hydrogen-bonded three-dimensional networks for 1 and 2 and one-dimensional columns for 3. While the [Fe(2-pic)3]2+ cations in compounds 1 and 2 are in the meridional (mer-) configuration, it has a facial (fac-) configuration in complex 3. Magnetic susceptibility measurements revealed the SCO transitions and the SCO properties in all three complexes are quite different. Compound 1 undergoes an abrupt SCO with critical temperatures T1/2↓ = 100 K and T1/2↑ = 103 K, while compound 2 exhibits a gradual SCO with T1/2 = 218 K. Compound 3, with the fac-configuration, has an abrupt SCO transition accompanied by the structural phase transition with critical temperatures T1/2↓ = 333 K and T1/2↑ = 343 K. The SCO transitions were further confirmed by the detailed structural analyses of the coordination environments of the FeII centers in both spin states and also by differential scanning calorimetry. Compared to the famous [Fe(2-pic)3]·A2·Solv compounds in the literature, compound 2 has the highest transition temperature for the mer-[Fe(2-pic)3]2+-containing compounds, while compound 3 represents the first example of the structurally characterized compound of the fac-[Fe(2-pic)3]2+ motif showing SCO behavior. These results show that the organosulfonate anions are very promising to adjust the hydrogen-bonded structures of the SCO compounds and improve the SCO properties of those structures.

Four one-dimensional heterobimetallic coordination polymers {Fe(pic)2[M(CN)4]}n (M = PdII (1) and PtII (2), pic = 2-picolylamine), and {Fe(pypz)2[M(CN)4]}n (M = PdII (3) and PtII (4), pypz = 2-(1H-pyrazol-3-yl)pyridine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, magnetic measurements and differential scanning calorimetry (DSC). Single-crystal X-ray analyses show that all the compounds are 1D neutral zigzag chain structures in which the planar [M(CN)4]2− anion acts as a μ2-bridging ligand, and the two pic/pypz molecules as chelating coligands. Examination of the intermolecular contacts in compounds 1–4 reveals the existence of the hydrogen bonding interactions involving the hydrogen donor groups of the pic and pypz ligands and the nitrogen atoms of the non-bridging cyanide groups of the [M(CN)4]2− anions. Weak π–π interactions were also found to be important for the formation of the 3D structures of compounds 3 and 4. The SCO properties of all compounds were confirmed by the detailed structural analyses of the coordination environments of the FeII centres, DSC analyses, and magnetic susceptibility measurements. Compounds 1 and 2 exhibit complete SCO behaviour with very narrow thermal hysteresis loops centred near the room temperature (T1/2↓ = 270 K and T1/2↑ = 272 K for 1 and T1/2↓ = 272 K and T1/2↑ = 274 K for 2), whereas 3 and 4 exhibit abrupt SCO at 186 and 180 K, respectively. Compared to the mononuclear species of the pic and pypz ligands, the SCO temperatures are adjusted by the different ligand field strength of the [M(CN)4)]2− units. The cooperativity from both the coordination bonds and supramolecular interaction leads to the observation of the hysteresis loops in the Fe–pic systems and the abrupt SCO transition in the Fe–pypz systems. Furthermore, the light-induced excited-spin-state trapping (LIESST) effect was observed for 2.

With three pentadentate macrocyclic ligands, three new [Mn(CN)6]3− based complexes, [Mn(LN3O2)(H2O)]2[Mn(CN)6](ClO4)·3H2O (1), {[Mn(LN5)]3[Mn(CN)6]2}n (2) and {[Mn(LN5Me)]3[Mn(CN)6]2}n·10nH2O (3) (LN3O2 = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, LN5 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene, LN5Me = 2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]-pyridine), have been synthesized and characterized structurally and magnetically. The structure of 1 was found to be a linear MnII2MnIII trinuclear cluster with two MnII capping groups and one MnIII ion connected via two trans-cyano groups. In contrast, compounds 2 and 3 are cyano-bridged 2D networks. Magnetic investigation revealed antiferromagnetic coupling between the MnIII and MnII ions via the bridging cyanide groups. Complex 1 showed paramagnetic behavior down to 2.0 K with no sign of SMM behavior. The magnetic coupling constant of J = −1.63 cm−1 with the Hamiltonian H = −2J(SMn(III)·SMn(II)1 + SMn(III)·SMn(II)2) was obtained from the fitting of the magnetic susceptibility. For 2 and 3, ferrimagnetic ordering was observed with magnetic phase transition temperatures (Tc) being 7.5 K and 7.0 K, respectively. These compounds are rare examples of a small number of [Mn(CN)6]3− based magnetic materials.

Two one-dimensional (1-D) chain complexes with pentagonal bipyramidal DyIII centers have been synthesized and magnetically characterized. Field-induced single molecule magnet behavior has been revealed in both compounds, which is still rarely reported in a lanthanide compound with a pentagonal bipyramidal coordination geometry. Their crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation.

Three trinuclear Mn2Mo molecules based on the orbitally degenerate [Mo(CN)7]4– anion were prepared, one of which is the first single-molecule magnet (SMM) based on heptacyanomolybdate. The blocking temperature and the energy barrier (U = 40.5 cm–1) are records for a cyanide-based SMM. Wide hysteresis loops and sharp quantum tunneling steps were observed from single-crystal measurements.

A series of end-to-end azido-bridged perovskite-type compounds [(CH3)nNH4–n][Mn(N3)3] (n = 1–4) were synthesized and characterized. Structural phase transitions indicating the general lattice flexibility were observed and confirmed by the crystal structures of different phases. These materials show cation-dependent magnetic ordering at up to 92 K and magnetic bistability near room temperature.

Four tetranuclear 3d–4f complexes with the 4f centers bridged solely by end-on azide bridges were reported. The [CuTb]2 compound displays single-molecule-magnet behavior with hysteresis loops observed at up to 2.4 K.

A series of discrete complexes, [Ni8(BTC4A)2(μ6-CO3)2(μ-CH3COO)4(dma)4]·H2O (1), [Ni8(BTC4A)2(μ6-CO3)2(μ-Cl)2(μ-HCOO)2(dma)4]·2DMF·2CH3CN (2), [Ni8(PTC4A)2 (μ6-CO3)2(μ-CH3COO)4(dma)4]·DMF (3), and [Ni8(PTC4A)2(μ6-CO3)2(μ-OH)(μ-HCOO)3 (dma)4] (4) (p-tert-butylthiacalix[4]arene = H4BTC4A, p-phenylthiacalix[4]arene = H4PTC4A, dma = dimethylamine, and DMF = N,N′-dimethylformamide), have been prepared under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, powder XRD, and IR spectroscopy. These four complexes are stacked by dumbbell-like building blocks with one chairlike octanuclear-nickel(II) core, which is capped by two thiacalix[4]arene molecules and connected by two in situ generated carbonato anions and different auxiliary anions. This work implied that not only the solvent molecules but also the upper-rim groups of thiacalix[4]arenes have significant effects on the self-assembly of the dumbbell-like building blocks. The magnetic properties of complexes 1–4 were examined, indicating strong antiferromagnetic interactions between the nickel(II) ions in the temperature range of 50–300 K.

Spin canting, antiferromagnetic ordering, metamagnetism and single-chain magnetism were verified in a cyano-bridged FeII compound synthesized from the pentagonal bipyramidal FeII starting material in the presence of excessive BF4− anions.

Four one-dimensional heterobimetallic coordination polymers {Fe(pic)2[M(CN)4]}n (M = PdII (1) and PtII (2), pic = 2-picolylamine), and {Fe(pypz)2[M(CN)4]}n (M = PdII (3) and PtII (4), pypz = 2-(1H-pyrazol-3-yl)pyridine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, magnetic measurements and differential scanning calorimetry (DSC). Single-crystal X-ray analyses show that all the compounds are 1D neutral zigzag chain structures in which the planar [M(CN)4]2− anion acts as a μ2-bridging ligand, and the two pic/pypz molecules as chelating coligands. Examination of the intermolecular contacts in compounds 1–4 reveals the existence of the hydrogen bonding interactions involving the hydrogen donor groups of the pic and pypz ligands and the nitrogen atoms of the non-bridging cyanide groups of the [M(CN)4]2− anions. Weak π–π interactions were also found to be important for the formation of the 3D structures of compounds 3 and 4. The SCO properties of all compounds were confirmed by the detailed structural analyses of the coordination environments of the FeII centres, DSC analyses, and magnetic susceptibility measurements. Compounds 1 and 2 exhibit complete SCO behaviour with very narrow thermal hysteresis loops centred near the room temperature (T1/2↓ = 270 K and T1/2↑ = 272 K for 1 and T1/2↓ = 272 K and T1/2↑ = 274 K for 2), whereas 3 and 4 exhibit abrupt SCO at 186 and 180 K, respectively. Compared to the mononuclear species of the pic and pypz ligands, the SCO temperatures are adjusted by the different ligand field strength of the [M(CN)4)]2− units. The cooperativity from both the coordination bonds and supramolecular interaction leads to the observation of the hysteresis loops in the Fe–pic systems and the abrupt SCO transition in the Fe–pypz systems. Furthermore, the light-induced excited-spin-state trapping (LIESST) effect was observed for 2.

Magneto-structural relationships were studied experimentally and theoretically for two enantiomorphic tetranuclear [CuTb]2 SMMs. For the first time, the determination of the magnetic anisotropy axis of an individual magnetic ion, Tb3+, was achieved in a polynuclear Tb3+-based SMM.

With three pentadentate macrocyclic ligands, three new [Mn(CN)6]3− based complexes, [Mn(LN3O2)(H2O)]2[Mn(CN)6](ClO4)·3H2O (1), {[Mn(LN5)]3[Mn(CN)6]2}n (2) and {[Mn(LN5Me)]3[Mn(CN)6]2}n·10nH2O (3) (LN3O2 = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, LN5 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene, LN5Me = 2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]-pyridine), have been synthesized and characterized structurally and magnetically. The structure of 1 was found to be a linear MnII2MnIII trinuclear cluster with two MnII capping groups and one MnIII ion connected via two trans-cyano groups. In contrast, compounds 2 and 3 are cyano-bridged 2D networks. Magnetic investigation revealed antiferromagnetic coupling between the MnIII and MnII ions via the bridging cyanide groups. Complex 1 showed paramagnetic behavior down to 2.0 K with no sign of SMM behavior. The magnetic coupling constant of J = −1.63 cm−1 with the Hamiltonian H = −2J(SMn(III)·SMn(II)1 + SMn(III)·SMn(II)2) was obtained from the fitting of the magnetic susceptibility. For 2 and 3, ferrimagnetic ordering was observed with magnetic phase transition temperatures (Tc) being 7.5 K and 7.0 K, respectively. These compounds are rare examples of a small number of [Mn(CN)6]3− based magnetic materials.

A new bis-bidentate nitronyl nitroxide radical with a pyrimidyl substituent group and two Co(II) complexes of this ligand were synthesized and characterized. Field-induced single-molecule magnet behavior was firstly observed in the nitronyl nitroxide radical-bridged complexes.

Two one-dimensional (1-D) chain complexes with pentagonal bipyramidal DyIII centers have been synthesized and magnetically characterized. Field-induced single molecule magnet behavior has been revealed in both compounds, which is still rarely reported in a lanthanide compound with a pentagonal bipyramidal coordination geometry. Their crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation.

The reaction of Cu(valdmpn) (H2valdmpn = N,N′-bis-(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane), LnCl3·nH2O (Ln = La(1), Ce (2), Pr(3), Nd(4), Sm(5), Eu(6), Gd(7), Tb(8), Dy(9), Ho(10), Er(11), Tm(12), Yb(13), Lu(14)) and NaN3 in methanol led to a whole series of heterometallic CuII–LnIII complexes. The basic structural components of these complexes are the [CuII(valdmpn)LnIII] units with a compartmental Schiff-base ligand. These [CuIILnIII] units were then further connected by the end-on (EO) azides between the Ln3+ centers to form tetranuclear {[CuLn](μ-N3)n[LnCu]} motifs, where n is 3 for the complexes of larger radii lanthanides (1CuLa to 5CuSm) and 2 for the complexes of smaller radii lanthanides (6CuEu to 14CuLu). While compounds 6CuEu to 14CuLu remain isolated tetranuclear clusters, compounds 1CuLa to 5CuSm are one-dimensional chains where tetranuclear motifs are further connected by end-to-end (EE) azides between CuII and LnIII centers. Direct current (dc) magnetic susceptibilities have been measured in the range of 1.8–300 K for all complexes, revealing the different nature of magnetic interactions between the spin centers. Among them, dominant ferromagnetic interactions were found in compounds 7CuGd, 8CuTb and 9CuDy. Alternating current (ac) magnetic measurements performed on 8CuTb, 9CuDy, and 10CuHo demonstrated the presence of slow magnetic relaxation under zero applied dc field. The spin relaxation barrier Ueff was determined to be 19.54 cm−1 (28.12 K) and 10.34 cm−1 (14.87 K) for compounds 8CuTb and 9CuDy. The SMM behavior of 8CuTb was further confirmed by the presence of magnetic hysteresis loops; while no hysteresis loop was observed for 9CuDy and 10CuHo. These results demonstrated that azido-bridged copper(II)–lanthanide(III) complexes could be synthesized successfully despite the generally weak azido–lanthanide interaction.

We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal CoII unit [Co(TODA)]2+ and two hexacyanometallates, namely [MIII(CN)6]2[CoII(TODA)]3·9H2O (M = Cr (1), Co (2), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)]2+ units are bridged by the [MIII(CN)6]3− groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the CrIII and CoII centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1. A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr–Co molecular magnets. For compound 2 containing the diamagnetic [CoIII(CN)6]3− unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm−1 by PHI and 26.5 cm−1 by Anisofit2.0) was deduced for hepta-coordinated CoII centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.

We herein report the syntheses, crystal structures, and magnetic properties of two complexes based on the anisotropic pentagonal bipyramidal FeII starting material [Fe(LN3O2)]2+, namely [Fe(LN3O2)(H2O)2][MQ]2·H2O (1) and [Fe(LN3O2)(CN)][ABSA]·3H2O (2) (LN3O2 = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene; MQ− = methyl orange anion; ABSA− = 4-aminoazobenzene-4′-sulfonic anion). Compound 1 is a mononuclear material where the [Fe(LN3O2)(H2O)2]2+ cations form a one-dimensional (1D) chain by the hydrogen bonds between the bulky MQ− anions and the coordinated water molecules. With a slightly different anion, ABSA−, a cyano-bridged FeII chain is formed for compound 2. This chain has a similar structure as that in our recently reported compound [Fe(LN5)(CN)][BF4] (Chem. Commun., 2015, 51, 4360). However, compared with the reported result where the chains interact with each other through the π⋯π interactions, the chains in 2 are well isolated by the bulky ABSA− anions with the shortest interchain Fe⋯Fe distances around 12.0 Å. Magnetic investigation on 1 reveals the easy-axis magnetic anisotropy of the mononuclear FeII centre (zero-field splitting parameter D = −3.7 cm−1), which leads to the field-induced slow magnetic relaxation. For compound 2, the Fe2+ spins are antiferromagnetically coupled through the cyano bridges with a coupling constant of J = −4.13(2) cm−1 with the Hamiltonian H = −J∑Si·Si+1. AC magnetic measurements revealed the pure single-chain magnetic (SCM) behaviour of these isolated chains with an effective energy barrier of 26.1(5) K. This system represents a good example showing that the structures and magnetic properties, such as field-induced single-ion magnets, SCMs, and SCM-based magnets, can be selectively prepared by anion modification.