The water oxidation half-reaction is considered the bottleneck in the development of technological advances to replace fossil fuels with sustainable and economically affordable energy sources. In natural photosynthesis, water oxidation occurs in the oxygen evolving complex (OEC), a manganese-oxo cluster {Mn₄CaO₅} with a cubane-like topology that is embedded within a redox-active protein environment located in photosystem II (PS II). Therefore, the preparation of biomimetic manganese-based compounds is appealing for the development of efficient and inexpensive water oxidation catalysts. Here, we present the water oxidation catalytic activity of a high-nuclearity mixed-metal manganese-strontium cluster, [Mn^III₁₂Mn^II₆Sr(μ₄-O₈)(μ₃-Cl)₈(HL^Me)₁₂(MeCN)₆]Cl₂∙15MeOH (Mn₁₈Sr) (HL^Me = 2,6-bis(hydroxymethyl)-p-cresol), in neutral media. This biomimetic mixed-valence cluster features different cubane-like motifs and it is stabilized by redox-active, quinone-like organic ligands. The complex displays a low onset overpotential of 192 mV and overpotentials of 284 and 550 mV at current densities of 1 mA cm⁻² and 10 mA cm⁻², respectively. Direct O₂ evolution measurements under visible light-driven water oxidation conditions demonstrate the catalytic capabilities of this cluster, which exhibits a turnover frequency of 0.48 s⁻¹ and a turnover number of 21.6. This result allows for a direct comparison to be made with the structurally analogous Mn-oxo cluster [Mn^III₁₂Mn^II₇(µ₄-O)₈(µ₃-OCH₃)₂(µ₃-Br)₆(HL^Me)₁₂(MeOH)₅(MeCN)]Br₂·9MeCN·MeOH (Mn₁₉), the water oxidation catalytic activity of which was recently reported by us. This work highlights the potential of this series of compounds towards the water oxidation reaction and their amenability to induce structural changes that modify their reactivity.

中文翻译：

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通过高核锰氧簇 [Mn18M] (M = Sr2+, Mn2+) 的结构改性来调节催化水氧化活性

水氧化半反应被认为是用可持续和经济实惠的能源替代化石燃料的技术进步发展的瓶颈。在自然光合作用中，水氧化发生在析氧复合物 (OEC) 中，这是一个锰氧簇 {Mn ₄ CaO ₅ }，具有类似立方烷的拓扑结构，嵌入位于光系统 II (PS II) 的氧化还原活性蛋白质环境中）。因此，仿生锰基化合物的制备对于开发高效且廉价的水氧化催化剂具有吸引力。在这里，我们展示了高核混合金属锰-锶簇的水氧化催化活性，[Mn ^III ₁₂ Mn ^II ₆Sr(μ ₄ -O ₈ )(μ ₃ -Cl) ₈ (HL ^Me ) ₁₂ (MeCN) ₆ ]Cl ₂ ∙15MeOH ( Mn ₁₈ Sr ) (HL ^Me = 2,6-双(羟甲基)-对甲酚)，在中性媒体中。这种仿生混合价簇具有不同的类立方基序，并由具有氧化还原活性的类醌有机配体稳定。该复合物在电流密度为 1 mA cm ^-2和 10 mA cm ^-2时分别显示出 192 mV 的低起始过电位和 284 和 550 mV 的过电位。直接O ₂在可见光驱动的水氧化条件下的演化测量证明了该簇的催化能力，其周转频率为 0.48 s ^-1，周转数为 21.6。该结果允许与结构类似的 Mn-oxo 簇 [Mn ^III ₁₂ Mn ^II ₇ (µ ₄ -O) ₈ (µ ₃ -OCH ₃ ) ₂ (µ ₃ -Br) ₆ (HL ^Me ) ₁₂ (MeOH) ₅ (MeCN)]Br ₂ ·9MeCN·MeOH ( Mn ₁₉)，我们最近报道了其水氧化催化活性。这项工作突出了这一系列化合物对水氧化反应的潜力及其诱导结构变化的适应性，从而改变其反应性。