What controls the magnetic interaction in bis-μ-alkoxo Mn(III) dimers? A combined experimental and theoretical exploration

The synthesis and magnetic characterisation of a series of bis-μ-alkoxide bridged Mn(III) dinuclear complexes of general formula [Mn(III)(2)(μ-OR)(2)(biphen)(2)(ROH)(x)(L)(y)] (where R = Me, Et; H(2) biphen = 2,2'-biphenol and L = terminally bonded N-donor ligand) is described, doubling the literature basis set for this type of complex. Building on these findings we have categorised all known μ-OR bridged Mn(III) dinuclear complexes into one of three classifications with respect to their molecular structures. We have then employed DFT and MO calculations to assess all potential magneto-structural correlations for this class of compound in order to identify the structural requirements for constructing ferromagnetic family members. Our analysis indicates that the most influential parameter which governs the exchange interaction in this class of compounds is the relative orientation of the JT axes of the Mn(III)  atoms. A perpendicular orientation of the JT axes leads to a large ferromagnetic contribution to the exchange. These results also suggest that a large ferromagnetic interaction and a large anisotropy are unlikely to co-exist in such structural types.