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, Fe ^II ions, and three pentadentate N ₃ O ₂ ligands, namely {[Fe ₂ H ₃ (dapab) ₂ ][Mo(CN) ₆ ]} _n ·2H ₂ O·3.5MeCN ( 1 ), [Fe(H ₂ dapb)(H ₂ O)][Fe(Hdapb)(H ₂ O)][Mo(CN) ₆ ]·4H ₂ O·3MeCN ( 2 ), and [Fe(H ₂ dapba)(H ₂ O)] 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 Fe ^II ions are bridged by the in situ generated [Mo ^III (CN) ₆ ] ^3- unit through two trans -cyanide groups into trinuclear Fe ₂ ^II Mo ^III clusters that are further linked by the amino of the ligand into an infinite chain. Complexes 2 and 3 are cyano-bridged Fe ₂ ^II Mo ^III trinuclear clusters with two Fe ^II 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 Fe ^II and Mo ^III 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.