Electron addition to [Mn2(CO)10] and [Mn2(CO)8(PR3)2] induced by ionizing radiation: an electron spin resonance study

Exposure of dilute solutions of the title compounds to 60Co γ-rays at 77 K gave the corresponding anions. Analyses of the e.s.r. spectra show that the excess electron is accommodated in the metal-metal σ* orbital. A small extra splitting for two equivalent 31P nuclei for the [Mn2(CO)8(PR3)2]- anion shows that delocalisation of electron density on to the axial ligands is small (ca.1%). This unexpectedly low value may account for the absence of any 13C splitting for the anion derived from [Mn2(CO)10] enriched with 13C in the axial ligands. These results are compared with those for the cobalt anion, [Co2(CO)6(PR3)2]-, which has been reported elsewhere to have a far higher spin density on the phosphine ligands (ca.23%). (author)