Electronic structure of oxidized complexes derived from cis-[Ru <sup>II</sup>(bpy) <inf>2</inf>(H <inf>2</inf>O) <inf>2</inf>] <sup>2+</sup> and its photoisomerization mechanism

Nora Planas, Laura Vigara, Clyde Cady, Pere Miró, Ping Huang, Leif Hammarström, Stenbjörn Styring, Nils Leidel, Holger Dau, Michael Haumann, Laura Gagliardi, Christopher J. Cramer, Antoni Llobet

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The geometry and electronic structure of cis-[Ru II(bpy) 2(H 2O) 2] 2+ and its higher oxidation state species up formally to Ru VI have been studied by means of UV-vis, EPR, XAS, and DFT and CASSCF/CASPT2 calculations. DFT calculations of the molecular structures of these species show that, as the oxidation state increases, the Ru-O bond distance decreases, indicating increased degrees of Ru-O multiple bonding. In addition, the O-Ru-O valence bond angle increases as the oxidation state increases. EPR spectroscopy and quantum chemical calculations indicate that low-spin configurations are favored for all oxidation states. Thus, cis-[Ru IV(bpy) 2(OH) 2] 2+ (d 4) has a singlet ground state and is EPR-silent at low temperatures, while cis-[Ru V(bpy) 2(O)(OH)] 2+ (d 3) has a doublet ground state. XAS spectroscopy of higher oxidation state species and DFT calculations further illuminate the electronic structures of these complexes, particularly with respect to the covalent character of the O-Ru-O fragment. In addition, the photochemical isomerization of cis-[Ru II(bpy) 2(H 2O) 2] 2+ to its trans-[Ru II(bpy) 2(H 2O) 2] 2+ isomer has been fully characterized through quantum chemical calculations. The excited-state process is predicted to involve decoordination of one aqua ligand, which leads to a coordinatively unsaturated complex that undergoes structural rearrangement followed by recoordination of water to yield the trans isomer. © 2011 American Chemical Society.
Original languageEnglish
Pages (from-to)11134-11142
JournalInorganic Chemistry
Issue number21
Publication statusPublished - 7 Nov 2011


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