title: New water oxidation chemistry of a seven-coordinate ruthenium complex with a tetradentate polypyridyl ligand.
abstract: The mononuclear ruthenium(II) complex [Ru](2+) (Ru = Ru(dpp)(pic)2, where dpp is the tetradentate 2,9-dipyrid-2'-yl-1,10-phenanthroline ligand and pic is 4-picoline) reported by Thummel's group (Inorg. Chem. 2008, 47, 1835-1848) that contains no water molecule in its primary coordination shell is evaluated as a catalyst for water oxidation in artificial photosynthesis. A detailed theoretical characterization of the energetics, thermochemistry, and spectroscopic properties of intermediates allowed us to interpret new electrochemical and spectroscopic experimental data, and propose a mechanism for the water oxidation process that involves an unprecedented sequence of seven-coordinate ruthenium complexes as intermediates. This analysis provides insights into a mechanism that generates four electrons and four protons in the solution and a gas-phase oxygen molecule at different pH values. On the basis of the calculations and corroborated substantially by experiments, the catalytic cycle goes through [(2)Ru(III)](3+) and [(2)Ru(V)(O)](3+) to [(1)Ru(IV)(OOH)](3+) then [(2)Ru(III)(···(3)O2)](3+) at pH 0, and through [(3)Ru(IV)(O)](2+), [(2)Ru(V)(O)](3+), and [(1)Ru(IV)(OO)](2+) at pH 9 before reaching the same [(2)Ru(III)(···(3)O2)](3+) species, from which the liberation of the weakly bound O2 might require an additional oxidation to form [(3)Ru(IV)(O)](2+) to initiate further cycles involving all seven-coordinate species.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973-5000, United States.
authors.forename: James T
authors.initials: JT
authors.lastname: Muckerman
authors.forename: Marta
authors.initials: M
authors.lastname: Kowalczyk
authors.forename: Yosra M
authors.initials: YM
authors.lastname: Badiei
authors.forename: Dmitry E
authors.initials: DE
authors.lastname: Polyansky
authors.forename: Javier J
authors.initials: JJ
authors.lastname: Concepcion
authors.forename: Ruifa
authors.initials: R
authors.lastname: Zong
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
authors.forename: Etsuko
authors.initials: E
authors.lastname: Fujita