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 d⁷ 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.