Influence of the Disposition of the Anisotropy Axes into the Magnetic Properties of Mn^III Dinuclear Compounds with Benzoato Derivative Bridges

Abstract

The two new Mn dinuclear compounds [{Mn(HO)(phen)}(μ-4-CHCHCOO)(μ-O)](ClO)·3CHCN·HO (1·3CHCN·HO) and [{Mn(HO)(phen)}(μ-O)(μ-2-BrCHCOO){Mn(NO)(phen)}]NO (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn 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 Mn ions (D and E) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local D < 0, while compound 2, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state S = 4) and local D > 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.

Assembly of MnIII ions into di-, tetra-, deca-nuclear coordination complexes, zero- to three-dimensional molecular frameworks: molecular spin flop to and short-range bulk magnetic spin flop ordering

“…7, a similar trend of the χT vs. T curve was demonstrated by a weakly coupled anti-ferromagnetic system. 67 The small negative J value is because of the weak anti-ferromagnetic interactions between the Mn III centers, 68 which is consistent with the later mentioned Curie–Weiss fitting data. The large negative D value indicated axial magnetic anisotropy due to the elongated octahedral geometry of the Mn III ions.…”

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn–Teller distortions

“…41,42 The DFT calculations were performed using the unrestricted Kohn-Sham (UKS) approach, with the B3LYP density functional, 43,44 which has been frequently used in calculations of magnetic coupling parameters for Mn III dimers. 7,[12][13][14]45 The def2-TZVP basis set was used for Mn atoms and the def2-SVP basis was used set for all other atoms. [46][47][48] Selecting a larger basis set for metal centres and more reasonable basis sets for the other atoms is a common approach for transition metal compounds.…”

“…10,11 Several reports have found the type and orientation of JT distortion influences the sign and magnitude of magnetic exchange in bridged Mn III dimers. 6,[11][12][13][14] In Mn III dimers with elongated coordination environments, the coupling can range from antiferromagnetic to ferromagnetic, with the relative orientation of the JT axes significantly affecting the magnetic exchange parameter. 12,13 Ferromagnetic coupling has been reported for dimers with both Mn III centres in JT compressed coordination environments.…”