title: Electrochemical probing of the photoreduction of molybdenum and tungsten Dawson-type polyoxometalates in molecular and ionic liquid media using water as an electron donor.
abstract: The photochemistry of the Dawson-type [Bu(4)N](4)[S(2)Mo(18)O(62)] and [Bu(4)N](4)[S(2)W(18)O(62)] polyoxometalates in molecular solvents and [Bmim][BF(4)] and [Bmim][BF(6)] ionic liquids with water present as the electron donor is reported. Irradiation with UV (275-320 nm) or white (275-750 nm) light leads to reduction of the [S(2)Mo(18)O(62)](4-) anion and concomitant oxidation of water to give dioxygen and protons in all media examined. Oxygen gas also is rapidly evolved when solid [Bu(4)N](4)[S(2)Mo(18)O(62)] in contact with water is irradiated with light. In contrast, photoreduction of [S(2)W(18)O(62)](4-) is observed only in "wet" ionic liquids. Reactants and products associated with the photochemical reactions were monitored by a range of electrochemical methods. Substantial shifts in reversible potentials combined with modified structure of water introduced by water-IL interactions are hypothesised to facilitate photooxidation of water in ionic liquid environments. Intriguingly, whilst the polyoxotungstate is preferable as a photosensitizer, the molybdenum analogue is superior for photooxidation of water to dioxygen.
authors: School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
authors: Gianluca
authors: G
authors: Bernardini
authors: Anthony G
authors: AG
authors: Wedd
authors: Chuan
authors: C
authors: Zhao
authors: Alan M
authors: AM
authors: Bond
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry; D055664:Electrochemical Techniques; D004583:Electrons; D052578:Ionic Liquids / Q000737:chemistry*; D008027:Light; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D014414:Tungsten / Q000737:chemistry*; D017973:Tungsten Compounds / Q000737:chemistry*; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry*; D000099294:Polyoxometalates
chemical_list: D056831:Coordination Complexes; D052578:Ionic Liquids; D008982:Molybdenum; D010100:Oxygen; D014414:Tungsten; D017973:Tungsten Compounds; D014867:Water; C102296:polyoxometalate I; D000099294:Polyoxometalates