Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered manganese complexes of the general formula [Mn_3O(O_2CR)_6L_3]~(z+) (R = Me, Et, Ph, CH_2Cl;L = 3-metnylpyridine or water z = 1, 0)

摘要

Preparation and magnetic properties of the trinuclear oxo-centered manganese complexes [Mn_3O(O_2CR)_6L_3]~(z+) (1, R = Me, L = 3-methylpyridine, z = 1; 2, R = Et, L = 3-methylpyridine, z = 1; for 1 and 2 the counteranion is ClO_4~-; 3, R = Ph, L = 3-methylpyridine and water, z = 0; 4, R = CH_2Cl, L = 3-methylpyridine and water, z = 0), prepared by N-n-Bu_4MnO_4 with appropriate reagents in ethanol and 3-methelpyrdine, are reported. The crystal structures of complexes 1 and 2 have been determined. It is shown that complexes 1 and 2 possess an oxo-centered Mn_3O unit with peripheral ligands provided by bridging carboxylate and terminal 3-methylpyridine groups, and an approximate three-fold symmetry axis for the whole cluster. The variable temperature magnetic susceptibility of the four title complexes in the range 1.5-300 K has been interpreted in terms of the Kambe vector-coupling method and Van Vleck equation, and the J' (cm~(-1)) and g values are found to be-12.87, 2.22 for complex 1 and -12.31, 2.12 for complex 2, respectively. For complexes 3 and 4 the J (cm~(-1)), J' (cm~(-1)), g values are found to magnitude, both |J| and |J'| < 9 cm~(-1) where J characterizes the Mn~(II)-Mn~(III) interaction and J' characterizes the Mn~(III)-Mn~(III) interaction. Magnetization measurements up to 65 kG at 1.5 K show the ground state S = 3/2 for complexes 3 and 4. These results indicate a weakly antiferromagnetic exchange coupling among the manganese ions. The effects of the bridging and terminal ligands on J and J' values are discussed briefly.