Photophysics and Photochemistry of Hexachlororhenate(IV) and Hexabromorhenate(IV)

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A study of the solution photophysical and photoredox properties of ReCl62- and ReBr62- is reported. The solutions are phosphorescent at room temperature, with emission maxima (lifetimes) of 1340 nm (80 ns) and 1380 nm (40 ns) for (Bu4N)2[ReCl6] and (Bu4N)2[ReBr6], respectively, in CH3CN. The phosphorescences are assigned to the Г8(2T1g) → Г8(4A2g) transition. Although the ions also phosphoresce from upper excited states when they are doped into host crystals, no such phosphorescence is observed for the pure solids or for solutions, either at room temperature or at 77 K. Both ions undergo one-electron oxidation on irradiation in the presence of 2, 3, 5, 6-tetrachloro- (chloranil) and 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone (DDQ); with ReCl62-, this process is reversible, and back-electron-transfer reactions are essentially diffusion-controlled. Photochemical reactions with some acceptors, such as tetracyanoethylene, are complicated by the formation of charge-transfer complexes. Irradiation of ReCl62- with C(NO2)4 in CH3CN or CH2Cl2 yields ReO4-, along with NOCl (produced by reaction of NO2 with ReCl62- or Cl-) and C(NO2)3-. © 1991, American Chemical Society. All rights reserved.

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Inorganic Chemistry

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