Photolysis of <i>cis</i>(benzimidazole)(chloro)- bis(ethylenediamine)cobalt(III) in aqueous solution-Part 3^†

393-395The photolysis of cis(benzimidazole)(chloro)bis- (ethylenediamine)cobalt(llI) at 254 nm yields Co(II) and Cl- as the major products. The quantum yield (φ)for Cl- and Co(II) are pH dependent and a small period of irradiation dependence is observed. The zero time (extrapolated) values of φ0 (Co2 +) and φ0 (Cl- )are maximized at pH= 0.8 and 1 respectively. φ0 (Cl-) exceeds φ0(Co2+) at pH> 0.5 indicating prevalence of photoaquation and photoreduction. At pH≤0.5, φ0(Cl-) is less than φ0 (Co2+) which is presumed to be due to the solvent caged radical pair [Co(en)2(bzmH) ....Cl]2+ undergoing CI substitution in the benzimidazole nucleus with cobalt(II) production