Syntheses, Structures, and Magnetic Properties of Three Cyano-Bridged Fe^II-Mo^III Single-Molecule Magnets

Three new cyano-bridged Fe-II-Mo(III )complexes assembled from the [Mo-III(CN)(7)](4- )unit, FeII ions, and three pentadentate N3O2 ligands, namely {[Fe2H3(dapab)(2)][Mo(CN)(6)]}n. 2H(2)O.3.5MeCN (1), [Fe(H(2)dapb)(H2O)][Fe(Hdapb)(H2O)][Mo-(CN)(6)].4H(2)O.3MeCN (2), and [Fe(H(2)dapba)(H2O)](2)[Mo(CN)(7)]. 6H(2)O (3) (H(2)dapab = 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone), H(2)dapb = 2,6-diacetylpyridine bis(benzoylhydrazone), H(2)dapba = 2,6-diacetylpyridine bis(4-aminobenzoylhydrazone)), have been synthesized and characterized. Single-crystal structure analyses suggest that complex 1 contains a one-dimensional (1D) chain structure where two FeII ions are bridged by the in situ generated [Mo-III(CN)(6)](3-) unit through two trans-cyanide groups into trinuclear (Fe2MoIII)-Mo-II clusters that are further linked by the amino of the ligand into an infinite chain. Complexes 2 and 3 are cyano-bridged (Fe2MoIII)-Mo-II trinuclear clusters with two FeII ions connected by the [Mo-III(CN)(6)](3)- and [Mo-III(CN)(7)](4-) units, respectively. Direct current magnetic studies confirmed the ferromagnetic interactions between the cyano-bridged FeII and MoIII centers and significant easy-axis magnetic anisotropy for all three complexes. Furthermore, complexes 1-3 exhibit slow magnetic relaxation under a zero dc field, with relaxation barriers of 42.3, 21.6, and 14.4 K, respectively, making them the first examples of cyano-bridged Fe-II-Mo-III single-molecule magnets.