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)2Ru(dpp)}2RhBr2](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)2Ru(dpp)}2RhCl2](PF6)5 complex presents a new photoinitiated electron collector which can assist in understanding the functioning of our supramolecular systems [{(TL)2Ru(BL)}2RhX2](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 metal-to-ligand charge transfer (3MLCT) excited states that populate lower lying metal-to-metal charge transfer (3MMCT) excited states. The electrochemistry of these complexes showed an impact on the reduction of the central RhIII upon halide substitution with the bromide analogue [(phen)2Ru(dpp)}2RhBr2](PF6)5 having a slightly lower reduction potential than the corresponding chloride counterpart. The more positive reduction of RhIII to generate the RhI species in the bromide analogue impacts the photocatalytic properties upon photolysis in the presence of a sacrificial electron donor. The trimetallic complex [{(phen)2Ru(dpp)}2RhBr2](PF6)5 generates hydrogen through the reduction of water with higher yields than the chloride [{(phen)2Ru(dpp)}2RhCl2](PF6)5 analogue under the same conditions. Despite the longer lived 3MLCT state of both [(TL)2Ru(dpp)]2+ and [{(TL)2Ru}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 3MLCT states and show lower H2 yields than the analogous bpy trimetallic systems.