Effect of Spin−Orbit Coupling on Reduction Potentials of Octahedral Ruthenium(II/III) and Osmium(II/III) Complexes

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• 作者：Martin Srnec ; Jakub Chalupský ; Miroslav Fojta ; Lucie Zendlová ; Ludě ; k Havran ; Michal Hocek ; Mojmí ; r Ký ; vala ; Lubomí ; r Rulí ; š ; ek
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：August 20, 2008
• 年：2008
• 卷：130
• 期：33
• 页码：10947-10954
• 全文大小：282K
• 年卷期：v.130,no.33(August 20, 2008)
• ISSN：1520-5126

文摘

Reduction potentials of several M^2+/3+ (M = Ru, Os) octahedral complexes, namely, [M(H₂O)₆]^2+/3+, [MCl₆]^4−/3−, [M(NH₃)₆]^2+/3+, [M(en)₃]^2+/3+ [M(bipy)₃]^2+/3+, and [M(CN)₆]^4−/3−, were calculated using the CASSCF/CASPT2/CASSI and MRCI methods including spin−orbit coupling (SOC) by means of first-order quasi-degenerate perturbation theory. It was shown that the effect of SOC accounts for a systematic shift of approximately −70 mV in the reduction potentials of the studied ruthenium (II/III) complexes and an approximately −300 mV shift for the osmium(II/III) complexes. SOC splits the sixfold-degenerate ²T_2g ground electronic state (in ideal octahedral symmetry) of the M³⁺ ions into the E_(5/2)g Kramers doublet and G_(3/2)g quartet, which were calculated to split by 1354−1573 cm⁻¹ in the Ru³⁺ complexes and 4155−5061 cm⁻¹ in the Os³⁺ complexes. It was demonstrated that this splitting represents the main contribution to the stabilization of the M³⁺ ground state with respect to the closed-shell ¹A_1g ground state in M²⁺ systems. Moreover, it was shown that the accuracy of the calculated reduction potentials depends on the calculated solvation energies of both the oxidized and reduced forms. For smaller ligands, it involves explicit inclusion of the second solvation sphere into the calculations, whereas implicit solvation models yield results of sufficient accuracy for complexes with larger ligands. In such cases (e.g., [M(bipy)₃]^2+/3+ and its derivatives), very good agreement between the calculated (SOC-corrected) values of the reduction potentials and the available experimental values was obtained. These results led us to the conclusion that especially for Os^2+/3+ complexes, inclusion of SOC is necessary to avoid systematic errors of ∼300 mV in the calculated reduction potentials.