Despite their technological importance for water splitting, the reaction mechanisms of most water oxidation catalysts (WOCs) are poorly understood. This paper combines theoretical and experimental methods to reveal mechanistic insights into the reactivity of the highly active molecular manganese vanadium oxide WOC [Mn₄V₄O₁₇(OAc)₃]³⁻ in aqueous acetonitrile solutions. Using density functional theory together with electrochemistry and IR-spectroscopy, we propose a sequential three-step activation mechanism including a one-electron oxidation of the catalyst from [Mn₂³⁺Mn₂⁴⁺] to [Mn³⁺Mn₃⁴⁺], acetate-to-water ligand exchange, and a second one-electron oxidation from [Mn³⁺Mn₃⁴⁺] to [Mn₄⁴⁺]. Analysis of several plausible ligand exchange pathways shows that nucleophilic attack of water molecules along the Jahn–Teller axis of the Mn³⁺ centers leads to significantly lower activation barriers compared with attack at Mn⁴⁺ centers. Deprotonation of one water ligand by the leaving acetate group leads to the formation of the activated species [Mn₄V₄O₁₇(OAc)₂(H₂O)(OH)]⁻ featuring one H₂O and one OH ligand. Redox potentials based on the computed intermediates are in excellent agreement with electrochemical measurements at various solvent compositions. This intricate interplay between redox chemistry and ligand exchange controls the formation of the catalytically active species. These results provide key reactivity information essential to further study bio-inspired molecular WOCs and solid-state manganese oxide catalysts.

中文翻译：

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分子锰钒氧化物水氧化催化剂中的氧化和配位交换活化

尽管它们对水分解具有重要的技术意义，但大多数水氧化催化剂 (WOC) 的反应机制仍知之甚少。本文结合理论和实验方法，揭示了高活性分子锰钒氧化物WOC [Mn ₄ V ₄ O ₁₇ (OAc) ₃ ] ^3-在乙腈水溶液中的反应性的机理见解。使用密度泛函理论以及电化学和红外光谱，我们提出了一个连续的三步活化机制，包括催化剂从 [Mn ₂ ³⁺ Mn ₂ ⁴⁺ ] 到 [Mn ³⁺ Mn ₃的单电子氧化⁴⁺ ]，乙酸盐到水的配体交换，以及从 [Mn ³⁺ Mn ₃ ⁴⁺ ] 到 [Mn ₄ ⁴⁺ ]的第二次单电子氧化。对几种可能的配体交换途径的分析表明，与在 Mn ⁴⁺中心的攻击相比，水分子沿 Mn ³⁺中心的 Jahn-Teller 轴的亲核攻击导致显着更低的激活势垒。一个水配体被离去的乙酸酯基团去质子化导致形成活性物质 [Mn ₄ V ₄ O ₁₇ (OAc) ₂ (H ₂ O)(OH)] ^-以一个 H _{2 为特征}O 和一个 OH 配体。基于计算中间体的氧化还原电位与各种溶剂组成下的电化学测量非常一致。氧化还原化学和配体交换之间的这种错综复杂的相互作用控制着催化活性物质的形成。这些结果为进一步研究受生物启发的分子 WOC 和固态氧化锰催化剂提供了关键的反应性信息。