Synthesis, characterization, and study of the photophysics and photocatalytic properties of the photoinitiated electron collector [{(phen)2Ru(dpp)}2RhBr2](PF6)5

The heterometallic photoinitiated electron collector [{(phen)(2)Ru(dpp)}(2)RhBr2](PF6)(5) (phen=1,10-phenanthroline, dpp=2,3-bis(2-pyridyl)pyrazine) has been synthesized and studied by spectroscopic, photophysical, electrochemical, and photochemical techniques. Substitution of chloride with bromide in the previously reported [{(phen)(2)Ru(dpp)}(2)RhCl2](PF6)(5) complex presents a new photoinitiated electron collector which can assist in understanding the functioning of our supramolecular systems [{(TL)(2)Ru(BL)}(2)RhX2](PF6)(5) (TL=terminal ligand, BL=bridging ligand, X=halide) in the photoinitiated electron collection and generation of hydrogen through the reduction of water and a detailed comparison is presented. Both the bromide and chloride analogues of these supramolecular complexes contain low energy, emissive nnetal-to-ligand charge transfer ((MLCT)-M-3) excited states that populate lower lying metal-to-metal charge transfer ((MMCT)-M-3) excited states. The electrochemistry of these complexes showed an impact on the reduction of the central Rh-III upon halide substitution with the bromide analogue [{(Phen)(2)Ru(dpp)}(2)RhBr2](PF6)(5) having a slightly lower reduction potential than the corresponding chloride counterpart. The more positive reduction of Rh-III to generate the Rh-I species in the bromide analogue impacts the photocatalytic properties upon photolysis in the presence of a sacrificial electron donor. The trimetallic complex [{(phen)(2)Ru(dpp)}(2)RhBr2](PF6)(5) generates hydrogen through the reduction of water with higher yields than the chloride [{(phen)(2)Ru(dpp)}(2)RhCl2](PF6)(5) analogue under the same conditions. Despite the longer lived (MLCT)-M-3 state of both [(TL)(2)Ru(dpp)](2+) and [{(TL)(2)Ru}(2)(dpp)](4+) when TL=phen vs. bpy (bpy=2,2'-bipyridine), the phen trimetallics with X=Cl- or Br- do not display longer lived (MLCT)-M-3 states and show lower H-2 yields than the analogous bpy trimetallic systems. (C) 2009 Published by Elsevier B.V.