Interaction of I(-) and I(3)(-) with a redox-stable Cr(III)-based structural surrogate for photo-oxidized "N3 Dye".

A series of [Cr (L)(2)(NCS)(2)]X complexes, where L = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb) and X(-) is I(-), I(3)(-), or NO(3)(-), have been prepared for study as redox-inactive surrogates for diisothiocyanatobis(2,2'-bipyridine-4,4'-dicarboxylic acid)ruthenium(III) ("N3(+)"). Dilute solution spectra in dichloromethane or acetonitrile of the I(-) and NO(3)(-) salts are the same, but the I(-) salts show clear evidence of a charge-transfer interaction between the cation and anion in the solid state and in concentrated I(-) solutions in acetonitrile. X-ray structural determination of the dmb complex shows that this interaction is between the I(-) and one of the dmb ligands. X-ray structural determination of the bpy complex as the I(3)(-) salt indicates a similar interaction between one of the bpy ligands and one of the terminal iodine atoms of the anion. These results have potential implications in the reduction mechanism of photo-oxidized N3 dye used as a sensitizer in nanocrystalline TiO(2)-based photogalvanic cells.