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.