A new mixed-valence binuclear complex containing the [Mn^IV(μ-O)₂(μ-O₂CMe)Mn^III]²⁺ core: synthesis, magnetism, electron paramagnetic resonance and redox properties

Abstract

The complex [Mn₂(μ-O)₂(μ-O₂CMe)L₂][ClO₄]₂·H₂O 1{L = methyl[2-(2-pyridyl)ethyl](2-pyridyl-methyl)amine} has been synthesised and isolated in the solid state. In MeCN solution complex 1 exhibits absorption spectral features characteristic of the [Mn₂(μ-O)₂(μ-O₂CMe)]²⁺ core. Variable-temperature (19.8-300 K) solid-state magnetic susceptibility data are consistent with a doublet ground state with J=-144 cm^-1. The X-band EPR spectrum at 77 K exhibits a sixteen-line pattern centred at g= 2. This spectrum is attributed to the overlap of hyperfine splitting of two chemically distinct manganese nuclei (l= 5/2) with one hyperfine coupling constant being roughly twice the magnitude of the other. Cyclic voltammetry of 1 shows a quasi-reversible one-electron oxidation [E_½=+1.0 V vs. saturated calomel electrode (SCE)] to the Mn^IV₂ species as well as an irreversible one-electron reduction (E_pc=-0.10 V vs. SCE) to the Mn^III₂ species. Coulometric or perchloric acid oxidation generates the orange Mn^IV₂ species. The redox stability and the absorption spectral properties of this oxidised species have been investigated.