Electrochemistry of Os Bipyridyl and Phenanthroline Complexes, Comparison with Ru and Fe

Osmium(II) polypyridyl complexes may be useful in H2O and CO(2)photo-catalytic reduction and dye-sensitized solar cell research. Altering substituents on the polypyridyl ligands allows for spectral and electronic tuning of the osmium(II) polypyridyl complexes. The cyclic voltammograms and UV-visible spectra of a series of electronically altered bipyridine and phenanthroline osmium(II) complexes are presented. Os(II/III)experimental oxidation potentials correlate linearly (R-2=0.99) with density functional theory (DFT) implicit solvent model computed ionization potentials and highest occupied molecular orbital (HOMO) energies. The hereby obtained linear relationship provides a theoretical computational tool that may be used for the predetermination of redox potentials of related osmium(II) polypyridyl complexes. Comparison between similar correlations for elements in the same group, namely Fe, Ru and Os, revealed remarkably similar patterns. Of the three, Os(II)bipyridyl is most readily oxidized (0.452 V), followed by Fe-II(0.682 V) and then Ru-II(0.883 V). Spectra of the Os(II)complexes where lambda(max)values range from 392 to 442 nm, were closely simulated by time-dependant DFT computed electronic oscillators. Osmium(II) polypyridyl complex absorbances span almost the entire visible spectrum.