Paramagnetic transition-metal carbonyls and cyanides. Part III. Electron spin resonance studies of manganese pentacarbonyl halides after high-energy irradiation

Abstract

Exposure of the manganese pentacarbonyl halides [Mn(CO)₅X](X = Cl, Br or I), to ⁶⁰Co γ-rays at 77 K gives an S=½ centre having a g ca. 2 and a large hyperfine coupling to ⁵⁵Mn and the halogen nuclei. The results are interpreted in terms of electron addition into a σ* orbital involving mainly the metal d_z² and halide p_z orbitals. A second centre having two apparent g values in the g= 6 region is also formed for all the three complexes. These again exhibit hyperfine coupling to ⁵⁵M and to the halogen nuclei. Various structures are considered, and it is concluded that the most reasonable are cations formed by loss of an electron and one or more carbonyl groups with unpairing of the remaining electrons to give S=5//₂.