ELECTRON DELOCALIZATION IN BINUCLEAR MANGANESE(III IV) COMPLEXES WITHDI-MU-OXO BRIDGES/

Solvent-dependent (solvent; acetonitrile, N,N-dimethylformamide, N,N-d imethylacetamide, dimethylsulfoxide and methanol) solution ESR spectra of binuclear manganese(III/IV) compounds with di-mu-oxo bridges have been studied. The binuclear manganese(III/IV) compounds used in this s tudy [ligand; tris(2-pyridylmethyl)amine, 1,4,8,11-tetraazacyclotetrad ecane, -dimethyl-N,N'-bis(2-pyridylmethyl)ethylenediamine and N,N-bis( 2-pyridylmethyl)glycine] generally exhibit solvent-dependent solution ESR spectra at room temperature; for example, the complex with tris(2- pyridylmethyl)amine shows a 16-line ESR spectrum in acetonitrile at ro om temperature, but a B-line ESR spectrum is observed in the N,N-dimet hylformamide solution. Studies on the temperature dependency of the ES R spectra (range 77-295 K) clearly showed that the 6-line ESR signal o bserved can be attributed to a spin-trapped dimeric species with a di- mu-oxo bridge, rather than a monomeric one, and that the two species, which show 16-line and 6-line ESR signals, are in an equilibrium in th e temperature range studied.