A new Pt(ii)-based metalloviologen analog, [PtCl(Mepytpy)] 2+ (abbreviated as PV 2+; Mepytpy + = 4′-(4-methyl- pyridinio)-2,2′:6′,2′′-terpyridine), was synthesized and its spectroscopic and electrochemical properties were investigated. The structures of Mepytpy + and PV 2+ were solved by single-crystal X-ray diffraction analysis. Electrochemical studies in DMF (N,N-dimethylformamide) revealed that both the first and second reduction potentials of PV 2+ (E11/2 = -0.87 V vs. Fc/Fc + for PV 2+/PV +; E21/2 = -1.31 V vs. Fc/Fc + for PV +/PV 0) are nearly consistent with those of methylviologen (N,N′-dimetyl-4,4′-bipyridinium, MV 2+) (E11/2 = -0.90 V vs. Fc/Fc + for MV 2+/MV +; E21/2 = -1.28 V vs. Fc/Fc + for MV +/MV 0), where the first reduction of PV 2+ is assigned as the reduction at the Mepytpy + ligand bound to the Pt(ii) ion. Upon the addition of a reducing agent Na 2S 2O 4 into an aqueous acetate buffer solution (pH = 5.0) of PV 2+, the generation of one-electron-reduced radical species (PV +) was spectrophotometrically observed and was assigned based on the time-dependent density functional theory (TD-DFT) calculations. The H 2-evolving activity of PV 2+ was evaluated in the presence of a sacrificial electron donor (EDTA) in an aqueous acetate buffer solution (pH = 5.0). It was found that the stability of the metalloviologen PV 2+ during the photolysis is much higher than that of the parent compound [PtCl(tpy)] +.
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