Electron-Transfer Interactions Of Chloranil Bromanil With Hexacyanometalate (4-), K4[Fe(Cn)6], K4[Ru(Cn)6] And K4[0s(Cn)6]

UV-visible spectrophotometric studies on the interactions of chloranil/bromanil with the hexacyanometalate(4-), [M(CN)6]4- ions, where M = Fe, Ru and Os, in 20-70% (vol./vol.) aqueous dimethyl sulphoxide media at 27-degrees-C demonstrate the formation of the negative semiquinone ion (I) derived from the halonil. New absorption spectral bands are immediately formed after mixing. The positions of the new bands are neither affected by the medium polarity nor by the nature of the metal in the hexacyanometalate (4-) ions. The reaction equilibrium constants and the molar absorptivities of (I) have been calculated. Experimental results indicate that (i) chloranil is the more powerful electron acceptor halonil, (ii) the abilities of the [M(CN)6]4- ions to interact with the halonils depend on their redox potentials and follow the order Fe(II) > Os(II) > Ru(II), and (iii) the reaction equilibrium constants increase greatly with the increasing water content of the medium.