Optical Outer-Sphere Charge Transfer in Ion Pairs with Peroxoborate as Donor

Abstract

Peroxoborate and the oxidizing cations [Co(NH3)6]3+, [Ru(NH3)6]3+ and N,N′-dimethyl-4,4′- bipyridinium2+ (paraquat2+) form ion pairs in aqueous solutions which display outer-sphere charge transfer (OSCT) bands in their absorption spectra. This CT involves an electronic transition from the peroxo substituents of peroxoborate to the cations. When 10,10′-dimethyl- 9,9′-biacridinium2+ (lucigenin2+, LG2+) is used as an electron acceptor an OSCT absorption is not observed owing to the instability of the ion pair LG2+ peroxoborate which undergoes a chemiluminescent conversion to N-methylacridone.