A 1-Phenylbiguanide-iodine Complex — An Imino π–Cation Radical of Guanidines —

1-Phenylbiguanide in the solid state was oxidized by iodine, and a π-cation radical was observed as a charge-transfer complex. The dark-brown powder exhibited a charge-transfer band in the near-UV region. The electron spin resonance (ESR) spectra of the complex exhibited Lorentzian peaks with g = 2.007–2.008, which suggested an imino-centered, monocation radical. Regardless of the imino fragment with a σ lone-pair, the cationic species was characterized as a π-radical conjugated with the phenyl group. This is the first observation of π-cation radical complexes of guanidine derivatives in the solid state. 1-Phenylbiguanide was oxidized by iodine to form an imino-centered cation radical as a charge-transfer complex. The cationic state was characterized as π-radical, and is the first observation of imino π-cation radical species at room temperature in the solid state.