A new mixed-valence binuclear complex containing the [MnIV(µ-O)2(µ-O2CMe)MnIII]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 [E½=+1.0 V vs. saturated calomel electrode (SCE)] to the MnIV2 species as well as an irreversible one-electron reduction (Epc=–0.10 V vs. SCE) to the MnIII2 species. Coulometric or perchloric acid oxidation generates the orange MnIV2 species. The redox stability and the absorption spectral properties of this oxidised species have been investigated.