Optical outer-sphere charge transfer in aqueous ion pairs with sulfidic anions as donors

Various sulfidic anions and the oxidizing cations [Ru(NH3)6]3+ and N,N′-dimethyl-4,4′-bipyridinium2+ (paraquat2+) form ion pairs in aqueous solutions which display outer-sphere charge-transfer (CT) absorptions. The CT energies are used to establish a series of sulfidic anions with increasing CT donor strength: SCN−