A NEW MIXED-VALENCE BINUCLEAR COMPLEX CONTAINING THE [MN(IV)(MU-O)2(MU-O2CME)MN(III)]2+ CORE - SYNTHESIS, MAGNETISM, ELECTRON-PARAMAGNETIC RESONANCE AND REDOX PROPERTIES

The complex [Mn2(mu-O)2(mu-O2CMe)L2][ClO4]2.H2O 1 {L = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine} has been synthesised and isolated in the solid state. In MeCN solution complex 1 exhibits absorption spectral features characteristic of the [Mn2(mu-O)2(mu-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 (I = 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 [E1/2 = +1.0 V vs. saturated calomel electrode (SCE)] to the Mn(IV)2 species as well as an irreversible one-electron reduction (E(pc) = -0.10 V vs. SCE) to the Mn(III)2 species. Coulometric or perchloric acid oxidation generates the orange Mn(IV)2 species. The redox stability and the absorption spectral properties of this oxidised species have been investigated.