Manganese(III) complexes of 1,2-bis(2-pyridinecarboxamido)benzene: synthesis, spectra, and electrochemistry

Abstract

The synthesis and solution properties of the high-spin (µ_eff.= 4.78–4.86 at 298 K) manganese(III) complexes [Mn(bpb)X][X = Cl^–, N₃^–, or SCN^–; H₂bpb = 1,2-bis(2-pyridinecarboxamido)benzene], are described. The brown crystalline complexes display ligand-to-metal charge-transfer transitions at ca. 430 nm, while in the near-infrared region crystal-field transitions are observed. In N,N-dimethylformamide solution the complexes exhibit a quasi-reversible Mn^III–Mn^II couple [E₂₉₈°–0.03 to + 0.03 V vs. saturated calomel electrode (s.c.e.)]. The complexes [Mn(bpb)Cl] and [Mn(bpb)(N₃)] display an additional quasi-reversible Mn^IV–Mn^III couple [E₂₉₈°+0.87 (Cl^–); + 0.49 V (N₃^–)vs. s.c.e.].