The tetraruthenium polyoxometalate {Ru^IV(H₂O)₄(μ-OH)₂(μ-O)₄[SiW₁₀O₃₆]₂}¹⁰⁻ (Ru₄POM) shows multiple oxidative proton coupled electron transfer (PCET) events in a [Ru(bpy)₃]²⁺/S₂O₈²⁻ photochemical cycle for catalytic water oxidation, with electrons conveyed to the photogenerated [Ru(bpy)₃]³⁺ oxidant and protons transferred to aqueous bases. As shown by laser flash photolysis, in aqueous phosphate buffer the consumption of the [Ru(bpy)₃]³⁺ oxidant by Ru₄POM shows bi-exponential kinetics with a fast component and a slow component that feed the Ru₄POM catalyst with up to 6 oxidative equivalents through PCET in ca. 50 ms. The apparent rates of both the fast and slow components depend linearly on HPO₄²⁻ and on the pH of the aqueous medium, suggesting the involvement of the buffer base, of water and of OH⁻ in assisting removal of the protons from Ru₄POM. In particular, the beneficial role of HPO₄²⁻ is reflected in a proportional improvement in the oxygen evolution activity, reaching quantum efficiency approaching 14%, although an excessive increase of buffer concentration is detrimental to the [Ru(bpy)₃]³⁺ stability and leads to the abatement of the O₂ evolution.

中文翻译：

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光化学水氧化中四钌多金属氧酸盐的连续质子耦合电子转移事件

多金属氧酸四钌 {Ru ^IV (H ₂ O) ₄ (μ-OH) ₂ (μ-O) ₄ [SiW ₁₀ O ₃₆ ] ₂ } ¹⁰⁻ (Ru ₄ POM) 显示多个氧化质子耦合电子转移 (PCET) 事件在催化水氧化的[Ru(bpy) ₃ ] ²⁺ /S ₂ O ₈ ²⁻光化学循环中，电子传递至光生[Ru(bpy) ₃ ] ³⁺氧化剂，质子传递至碱水溶液。如激光闪光光解所示，在磷酸盐缓冲液中，Ru _{4 POM 对 [Ru(bpy) 3} ] ³⁺氧化剂的消耗表现出双指数动力学，其中快速组分和慢速组分向 Ru ₄ POM 催化剂供给通过 PCET，大约可达到 6 氧化当量。50 毫秒快组分和慢组分的表观速率与 HPO ₄ ²⁻和水介质的 pH 值线性相关，表明缓冲碱、水和 OH ^{−参与帮助从 Ru} ₄ POM中去除质子。特别是，HPO ₄ ²⁻的有益作用体现在析氧活性的成比例改善，达到接近 14% 的量子效率，尽管缓冲液浓度的过度增加对 [Ru(bpy) ₃ ] ^{3+是不利的。稳定性并导致 O} ₂释放的减少。