Solar energy conversion via water splitting to produce H₂ fuel is an attractive alternative energy source. Complexes that both absorb solar light and photocatalytically split water are difficult to design as a delicate balance between steric and electronic effects must be struck.

Karen J. Brewer and colleagues, Virginia Tech, USA, have studied the known complex 1 and report the new Ru,Rh bimetallic complexes 2 and 3 (see figure). They find that complex 1 can photoreduce but does not catalyze H₂O reduction, dimerizing upon Rh(I) formation instead. Increasing the steric bulk to ^tBu₂bpy, complex 2, stopped dimerization but also increased electron density at Rh, preventing photocatalytic function.

The complex 3 achieved the correct balance of steric and electronic factors, undergoing photoinitiated electron collection and photocatalytically generating H₂ from H₂O, one of only a few motifs known to display both functions.

^{Figure 1. bpy = 2,2′-bipyridine, dpp = 2,9-diphenyl-1,10-phenanthroline, phen = phenanthroline.}

• Discovering the Balance of Steric and Electronic Factors Needed To Provide a New Structural Motif for Photocatalytic Hydrogen Production from Water
  T. A. White, B. N. Whitaker, K. J. Brewer,
  J. Am. Chem. Soc. 2011.
  DOI: 10.1021/ja206782k