Photoredox chemistry of iron(III) chloride and iron(III) perchlorate in aqueous media was investigated in the wavelength range 250-425 nm. The effects of incident intensity, iron(III) and iron(II) concentrations, wavelength of irradiation, chloride concentration, radical scavengers, pH, time of irradiation, and temperature on product quantum yields were investigated. The primary photoreaction is postulated to be Fe3+-OH--Fe2+ 4--OH in iron (III) chloride and iron(III) perchlorate solutions; secondary reactions of • affect the product quantum yields. From the variation of quantum yields with the wavelength of irradiation the OH--*• Fe(III) charge-transfer excited state is concluded to be the one responsible for photoreduction. Under identical conditions, the product quantum yield ( 2+) for the photoreduction of iron(III) chloride is less than that of iron(III) perchlorate.

Investigation of the photoreduction of copper(II) to copper(I) in methanolic solutions of copper(II) chloride and copper(II) bromide indicates the halide-to-copper(II) charge-transfer (CT) responsible for the photoreduction. Quantum yields for the formation of copper(I) as a function of irradiating wavelength and copper(II) halide concentration show that [Cu(CH3OH)5Cl]+ and [Cu(CH3OH)4Cl2] have identical photoreaction efficiency, while [Cu(CH3OH)4Br2] is more photoreactive than [Cu(CH3OH)5Br]+. In the copper(II) chloride system the chloride-to-copper(II) CT band centered around 272 nm appears to be responsible for the photoreaction, while the bromide-to-copper(II) CT band centered around 245 nm effects the photoreaction in copper(II) bromide system.

A study of the photoreduction of iron(II1) to iron(I1) in aqueous iron(m) chloride as a function of hydrochloric acid and chloride ion concentrations indicates that Fe3fOH-, and not Fe3+Cl-, is the photoactive species.

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