It was recently discovered that mono-nuclear ruthenium complexes serve as a competitive prototype to other artificial photosynthetic catalysts including its predecessor the ruthenium blue dimer.  Using UB3LYP, with the LACV3P relativistic effective core potential in continuum aqueous solvent, we have determined that the water oxidation mechanism occurs through 3 PCETs, 1 ET, 1 atom proton transfer (APT), and 1 ligand exchange (LE) and involves a metal(V)-oxo catalytically competent species similar to other substrate activation processes in materials science and biochemistry.  The APT and LE steps were found to be rate limiting with large free energy barriers of 19.27 and 19.53 kcal/mol which is in excellent agreement with the ~20 kcal/mol barrier obtained from experimental rate constants using classical transition state theory.  Automated database tools applied to ground state multiplicities, spin-crossover and spin-splitting energetics, redox potentials, ligand removal enthalpies, etc. reveal correctable error patterns in the B3LYP functional. B3LYP calculations employing the recently developed set of d-block localized orbital correction (DBLOC) parameters provide accurate insight about the relative properties of ruthenium and other transition metal complexes created from a congeneric series of ligand substitutions.  Faster DFT methods in combination with the DBLOC empirical correction scheme, which is of negligible additional cost, can in principle be used to tune the catalytic time scales of water oxidation.

Mechanistic investigation of 2H2O (aq) → 2H2 (g) + O2 (g) catalysis by mono-nuclear ruthenium complexes using empirical correction schemes to DFT for transition metal containing systems

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.