Production of hydrogen by irradiation of metal complexes in aqueous solutions

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Several systems in which molecular hydrogen is produced by photoreduction of protons in aqueous solutions are discussed. One mononuclear system, IrCl2-/3-6, is considered in detail. Ultraviolet irradiation of concentrated HCl solutions of IrCl3-6 yields IrCl2-6 and H2. It is proposed that the reactive excited states are protonated species such as HIrCl2-6 that possess Cl → Ir charge transfer character, and that the photoredox mechanism involves initial release of atomic hydrogen. Irradiation of IrCl2-6 in aqueous HCl solutions over a broad range of wavelengths results in the formation of IrCl3-6 and Cl2. Aqueous HCl is converted to hydrogen and chlorine by coupling the two photoreactions. The possible advantages of using metal cluster complexes to facilitate photochemical hydrogen production are outlined, and related experiments on Mo2X4-8 (X = Cl, Br) and Rh4b6+8 (b = 1,3-diisocyanopropane) are reviewed. Recent experiments have shown that Mo6Cl2-14possesses a long-lived excited state (180 μs in CH3CN; 2eV) that undergoes electron transfer reactions in solutions, and possible extensions of this work aimed at photoreduction of protons are considered. © 1981.

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Inorganica Chimica Acta

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