Effects of big planar anions on the spin transition of a mononuclear manganese(III) complex with a hexadentate schiff-base ligand

Two new ion-pair complexes [Mn(3-MeO-sal-N-1,5,8,12)][Ni(dmit)₂] (1) and [Mn(3-MeO-sal-N-1,5,8,12)][Pt(mnt)₂]·2CH₃CN (2), based on the known six-coordinate mononuclear Schiff-base manganese(III) spin-crossover complex [Mn(3-MeO-sal-N-1,5,8,12)]NO₃, have been synthesized and structurally characterized. Their crystal structures indicate that increasing the size of the anion from NO₃^- to [Pt(mnt)₂]^- and [Ni(dmit)₂]^- leads to the dimerization of the cations and formation of alternating cation-anion stacks with loss of the most effective cation-anion interactions; only weak short contacts exist between the cations and anions. Magnetic measurements and variableerature single-crystal X-ray crystallography analysis provided firm evidence for spin-crossover (SCO) effects in 1. The magnetic susceptibility of compound 2 is typical of a simple paramagnet, and the manganese(III) complex cations remain in the high-spin state in the temperature range 2-300 K. Spin-crossover in d⁴ ions is a most rare event. Changing the size of the anion from NO₃^- to [Pt(mnt)₂]^- and [Ni(dmit)₂]^- leads to significant changes in the overall crystal packing of Mn ion-pair complexes and furthermore in the spin state of the Mn^III center.