Syntheses, Structures And Magnetic Properties Of[Mo（CN）₇]^4--based Molecular Magnets

[Mo(CN)7]4-unit plays an important role in the field of molecular magnets. It has strong magnetic exchange which can build molecule-based magnets with high critical temperatures; and it has strong anisotropy which is good for high anisotropic molecular magnets, including single-molecule magnets and single-chain magnets. Meanwhile, Due to its sensitivity to oxygen, its high negative charges and its large number of cyanides, the chemistry based on [Mo(CN)7]4-is very difficult and it usually leads to high dimensional mangets. In this work, We intend to tackle the problems in the field of molecular magnets based on the [Mo(CN)7]4-and a series of new molecular magnets, especially low dimensional materials, were carefully designed and synthesized. Their structures and magnetic properties were determined with the following details.First, as a demonstration of a concept, we achieved the construction of three zero-dimensional compounds,([Fe(LDAPSC)(H2O)]2[Mo(CN)7]·6H2O (1),[Co(LDAPSC)(H2O)]2[Mo(CN)7]·6H2O (2), and [Mn(L3-2-3)]2[Mo(CN)7]·7H2O (3) All of them were trinuclear clusters with two MnII centers connected to MoⅢ by the two CN-groups of [Mo(CN)7]4-. For the compounds1and2, M2+were connected by two equatorial cyanides of [Mo(CN)7]4-unit, while for compound3, Mn2+ions were connected to Mo3+by one equatorial cyanide and one axial cyanide ligand of [Mo(N)7]4-ion. Ferromagnetic interaction through the CN bridges were found between FeⅡ/Con centers and MoⅢ for compounds1and2and antiferromagnetic interaction was found for the Mn-Mo pair for compound3. No SMM behavior was observed for compounds1-3.Then, we synthesized the first SMM based on the [Mo(CN)7]4-unit. Three zero-dimensional compounds4-6,[Mn(LN5Me)(H2O)]2[Mo(CN)7]·6H2O (4)、[MnLN3O2(H2O)]2[Mo(CN)7]·7H2O (5)、[Mn(LDAPSC)(H2O)[Mo(CN)7]·6H2O·CH3CN (6) were prepared and their structures and magnetic properties were studied. All of these compounds were also trinuclear clusters with two MnⅡ capping groups and one MoⅢ ion connected via two CN-groups. The primary difference is the relative positions of the two Mn units on the pentagonal bipyramid of [Mo(CN)7]4-. In4, the two Mn units are bound to the Mo ion through the axial CN-groups wheras in the compound5-6are connected to the equatorial CN-groups. Compound4showed SMM behavior with an energy barrier Ueff=40.5cm-1, which constituted a new record for the cyanide-bridged SMMs. Detailed magnetic measurement on one oriented single crystal revealed the highly distinct hysteresis loops at up to3.2K. Obvious step-like features corresponding to resonant quantum tunnelling between opposite spin states were observed too. The blocking temperature of4(3.2K) is very close to the one of the classical [Mn12ac] SMMs. Theoretical analyses revealed the vital importance of the anisotropic magnetic interaction between the MnⅡ and MoⅢ for their magnetic behaviors. The magnetic interaction was found to be Ising-like (Jz=-34and Jxy=-11cm-1) for4and XY type for compounds5and6. The calculated spin flipping energy barrier Ueff is47cm-1, which is very close to the experimental results. Furthermore, the spin energy spectrum of4was constructed and the calculated resonance field (1.99and2.32T) were also very close to the experimental values (1.83and2.25T).Following these results, four one-dimensional compounds7-10,[Mn(LN5C6)H2O]2[Mn(LN5C6)][Mo(CN)7]·5H2O·CH3CN (7)、[Mn(LN5en)H2O]2[Mn(LN5en)][Mo(CN)7]·2H2O (8).[MnLN5C10]2[Mo(CN)7]-2H20(9)、[Ni(L12-N-4)]2[Mo(CN)7]-5H20(10) were synthesized. For7, frequency-dependent ac susceptibilities were observed at low temperatures, indicating slow magnetic relaxation for a single-chain magnet. Strong antiferromagnetic interaction through the CN bridges between MnⅡ and MoⅢ were observed for8and9, and ferromagnetic interaction was observed bet ween NiⅡ and MoⅢ in10.Finally, two-dimensional compounds,[Fe(LN3O2)H2O][Fe(LN3O2)]3[Mo(CN)7]2·28H2O (11) and [NiCyclam]4[Mo(CN)7]2·12H2O (12) and one three-dimensional compound [NiC12N4H25]2[Mo(CN)7]·0.5H2O·3CH3CN (13) were studied. Ferromagnetic interactions were observed in both compounds11-12. Long-range magnetic ordering was observed for11.