Electron Paramagnetic Resonance and Optical Spectra of Pentacyanocobaltate(II)

Electron paramagnetic resonance (EPR) and optical spectral studies have been carried out on the pentacyanocobaltate(II) ion in ethylene glycol–water solutions, and in electron‐irradiated powder samples of K₃Co(CN)₆. Both EPR and optical spectra observed for the ion in the powder samples are essentially similar to those obtained from the ethylene glycol–water solutions. There was no observable linewidth variation with nuclear spin states $M_I$ , no dependence on the different solvent media used, and no dependence on the concentration ratio Co²⁺/CN⁻, in both X‐band and K‐band spectra. The results indicate that the structure of Co(CN)₅³⁻ in solutions and in polycrystalline media is a slightly distorted square pyramid with no solvent bound in the sixth coordination site. The two strong hyperfine components with exceptionally large spacings occurring at the low‐field end of the X‐band spectrum are identified as the so‐called angular anomalies. An effective method of simulation of the first‐derivative EPR spectra of polycrystalline samples has also been developed.