MANGANESE(III) COMPLEXES WITH MNIIIN3O3 (S = 2) COORDINATION BY SEXIDENTATE SCHIFF-BASE LIGANDS - SYNTHESIS, SPECTRA AND ELECTROCHEMISTRY

Complexes of high-spin manganese(III) (mu-eff = 4.79-5.30 at 298 K) with a closely related group of sexidentate Schiff-base ligands have been prepared and their solution properties thoroughly investigated. The brown to green crystalline complexes display ligand-to-metal charge-transfer transitions in the range 330-400 nm in addition to a crystal-field transition in the range 560-600 nm. The solution stereochemistry has been determined by paramagnetically shifted H-1 NMR spectroscopy. Unlike the C-3 symmetry in the solid-state structure, in solution the Mn(III)N3O3 co-ordination sphere is severely distorted (almost-equal-to C1 symmetry). Cyclic voltammetric studies in dimethylformamide solution reveal an irreversible Mn(III)-Mn(II) couple [E(pc) in the range -0.62 to -0.05 V vs. saturated calomel electrode (SCE)] and a quasi-reversible Mn(IV)-Mn(III) couple (E(t) in the range +0.42 to +0.86 V vs. SCE).