EPR of Spin-52 Mn(II) Complexes with Very Large Ligand-Field Splittings

An unusual manganese complex has been constructed in which the Mn(II) is in a spin-52 state with large ligand-field splitting. The angular dependence of the EPR spectrum indicates significant mixing of |M〉 states (i.e., those differing in electronic quantization along the z axis) by terms such as 12(− 3 sinθ cosθ)b20 × [(S+′ + S−′)Sz′ + Sz(S+′ + S−′(] and B(S+I− + S−I+). This mixing causes an unusual angular dependence of EPR transitions that occur near magnetic fields where two levels cross. When water is removed from the crystal, the Mn(II) ligand-field splitting becomes greater such that only one EPR transition is observed for most orientations of the crystal in the magnetic field. Magnetic susceptibility measurements indicate that the Mn(II) is still in a spin-52 state. This is the only Mn(II) complex known by us in which the Mn(II) has a single-line EPR spectrum while in a spin-52 state. The g factor of the dehydrated complexes is larger than the free-spin value indicating strong covalent coupling of the Mn(II) d states with low-lying ligand states.