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Of the 20 dithiolene complexes investigated, only three were effective in the photo-oxidation of water to O2 in the visible region and at the same time sufficiently stable: tris-[1-(4-dimethylaminophenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten, tris-[1-(4-methoxy-phenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten and tris-[1-(4-methoxyphenyl)-1,2-ethylenodithiolenic-S,S′]tungsten. Four more produced oxygen, but were not sufficiently stable for the reaction to be truly catalytic. The three successful catalysts are non-symmetrical and have phenyl rings with para electron-donating substituents. The metals used were W, Mo, Re and Ni. The dithiolene complexes of the first three are trigonal prismatic and of nickel are square planar. The best results in terms of yield and stability were obtained with tungsten, and specifically with tris-[1-(4-dimethylaminophenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′] tungsten; the light storage efficiency for this catalysts was estimated to be better than 9%. As indicated by the oxidation potentials, the excited states of the dithiolenes used were powereful oxidizing agents, sufficient to oxidize water. |
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