Manganese(III) complexes with Mn^IIIN₃O₃(S=2) co-ordination by sexidentate schiff-base ligands: synthesis, spectra and electrochemistry

Abstract

Complexes of high-spin manganese(III)(μ_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 ¹H NMR spectroscopy. Unlike the C₃ symmetry in the solid-state structure, in solution the Mn^IIIN₃O₃ co-ordination sphere is severely distorted (≈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_f in the range +0.42 to +0.86 V vs. SCE).