Influence of the Disposition of the Anisotropy Axes into the Magnetic Properties of MnIII Dinuclear Compounds with Benzoato Derivative Bridges.

The two new MnIII dinuclear compounds [{Mn(H2O)(phen)}2(μ-4-CH3C6H4COO)2(μ-O)](ClO4)2·3CH3CN·H2O (1·3CH3CN·H2O) and [{Mn(H2O)(phen)}(μ-O)(μ-2-BrC6H4COO)2{Mn(NO3)(phen)}]NO3 (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the MnIII ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the MnIII ions (DMn and EMn) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local DMn < 0, while compound 2, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state S = 4) and local DMn > 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Δ, in absolute value is increased.