ESR study of irradiated pentacyanonitrosyl cobaltate II

Abstract An ESR study of γ-irradiated pentacyanonitrosyl cobaltate (II) shows the presence of two paramagnetic species. One, with g∥ =2.005, g∥ =2.172, A∥ 81.3 and A∥ =-26.2 × 10−4 cm−1, is the well-known d 7 species Co(CN)5 3-. The second shows g∥<g∥ and much lower 59Co hyperfine interactions. The ESR parameters are shown to be consistent with those predicted for the species [Co(CN)5 NO]4- with C S symmetry, a bent Co–N–O bond, and a d 7 configuration with the odd electron in an a' orbital formed by mixing the cobalt d x –y 2 and d z 2 orbitals. Theoretical arguments are advanced to show that, in general, small metal hyperfine splittings in low symmetry ions do not necessarily establish that the unpaired electron is in a ligand-dominated orbital.