A novel mixed-valent Mn III –Mn IV -dimer, [L 2 Mn 2 (µ-O) 2 (µ-MeCO 2 )][BPh 4 ] 2 ·MeCN: crystal structure, magnetic properties, and e.s.r. spectrum (L = 1,4,7-triazacyclononane)

The green mixed-valence dimer [L2Mn2(µ-O)2(µ-MeCO2)][BPh4]2·MeCN (L = 1,4,7-triacacyclononane) is formed on hydrolysis of [L2Mn2(µ-O)(µ-MeCO2)2]2+ in water in the presence of air; characterization by X-ray crystallography showed the presence of the di-µ-acetato-dimanganese(III,IV) core, and temperature dependent magnetic susceptibility measurements indicate an S= 1/2 ground state and very strong intramolecular antiferromagnetic coupling (J–440 cm–1).