GEMINATE RECOMBINATION IN THE LIGAND-FIELD PHOTOCHEMISTRY OF PENTACYANOFERRATE(II) COMPLEXES WITH 1,2-DIAMINOETHANE AND 1,3-DIAMINOPROPANE

The continuous photolysis in aqueous solution of pentacyanoferrate(II) complexes with bidentate diamine ligands, [Fe(CN)5(N and N)]3-, where N and N is 1,2-diaminoethane (en) or 1,3-diaminopropane (tn) was inve stigated with emphasis on the effect of the excitation energy and the solvent properties. The quantum yields obtained for the ring closure p rocess were found to be strongly dependent on the excitation wavelengt h, ranging from 0.022 to 0.236. The quantum yield variation over the s pectral region of irradiation exhibited a systematic trend towards hig her values for shorter wavelengths, indicating that cyanide photosubst itution takes place from more than one channel. In glycerol-water solu tions, the quantum yields for the photoprocess decreased with the incr ease in glycerol concentration. The magnitudes of the quantum yields s howed a good correlation with the physical properties of the mixed sol vents, such as viscosity and dielectric constant. The results showed t he presence of an efficient cage effect and that the influence of phys ical parameters, such as medium properties, can interfere in the quant um yield values of a determined process.