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

Inspired by the crystal structure of a Mn^III dinuclear complex we obtained featuring both Jahn-Teller (JT) elongation and compression distortions, we have modelled a series of complex cations based on the disordered crystal formulation; [Mn₂(L1)₂(μ₂-OH)₂)⁴⁺ (1), [Mn₂(L1)(L2)(μ₂-OH)₂)⁴⁺ (2), [Mn₂(L2)(L1)(μ₂-OH)₂)⁴⁺ (3), and [Mn₂(L2)₂(μ₂-OH)₂)⁴⁺ (4) (where L1 = (1E,1'E)-5-tert-butyl-3-(((4-(((5-tert-butyl-2-hydroxy-3-((E)-(hydroxyimino)methyl)benzyl)(methyl)amino)methyl)benzyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde and L2 = 3,3'-(1,4-phenylenebis(methylene))bis(methylazanediyl)bis(methylene)bis(5-tert-butyl-2-hydroxybenzaldehyde)) with different geometries to investigate the effects of the distortions on the magnetic coupling parameter. All computationally modelled dimers had a ferromagnetic interaction between the Mn^III centres, with greater magnetic coupling calculated for complexes with both JT elongation and compression present. The ferromagnetic contribution to the J coupling was ascribed to the orthogonality of the singly occupied magnetic orbitals along with the cross-interaction between the unfilled Mn1(d) and singly occupied Mn2(d) orbitals. Constrained calculations showed that reducing the extent of the compression at Mn2 results in a concomitant increase in the dihedral angle between the JT axes, thereby reducing the relative magnitude of the magnetic coupling between Mn^III centres.