Paramagnetic transition-metal carbonyls and cyanides. Part 5. Electron spin resonance spectra of cations and anions derived from decacarbonyl-dimanganese and -dirhenium

Abstract

Exposure of [Mn₂(CO)₁₀] and [Re₂(CO)₁₀] to ⁶⁰Co γ rays at 77 K gives paramagnetic species whose e.s.r. spectra show the presence of two strongly coupled metal nuclei. Analysis of the spectra shows that the unpaired electron is located in the metal–metal bond, but this could be σ or σ*. The same centres were formed when solutions in 2-methyltetrahydrofuran containing NNN′N′-tetramethyl-p-phenylenediamine were exposed to u.v. light, and hence the σ* formulation is favoured. A second centre having two sets of features in the g= 6 region has been detected in irradiated [Mn₂(CO)₁₀]. This shows strong hyperfine coupling to one ⁵⁵Mn nucleus and weak coupling to another. This centre is thought to be from a cationic species in which one manganese atom has acquired an S= 5/2 configuration. The structure is similar to that postulated for cationic centres formed from pentacarbonylhalogenomanganese compounds.