The Role of the -OH Groups within Mn₁₂ Clusters in Electrocatalytic Water Oxidation

The formidable reactivity of the oxygen-evolving center near photosystem II is largely based on its protein environment that stabilizes it during catalysis. Inspired by this concept, the water-soluble Mn₁₂ clusters Mn₁₂ O₁₂ (O₂ CC₆ H₃ (OH)₂ )₁₆ (H₂ O)₄ (3,5DHMn₁₂ ) and Mn₁₂ O₁₂ (O₂ CC₆ H₃ (OH)₃ )₁₆ (H₂ O)₄ (3,4,5THMn₁₂ ) were developed as efficient electrocatalysts for water oxidation. In this work, the role of the -OH groups in the electrocatalytic process was explored by describing the structural and electrocatalytic properties of two new Mn₁₂ clusters, 3,4DHMn₁₂ and 2,3DHMn₁₂ , having one -OH group in the meta position relative to the benzoate-Mn moiety, and one at the para or ortho position, respectively. The Mn centers in 3,4DHMn₁₂ were discovered to have lower oxidation potential compared with those in 2,3DHMn₁₂ , and thus, 3,4DHMn₁₂ can catalyze water oxidation with higher rate and TON than 2,3DHMn₁₂ . Hence, the role of the -OH groups in the electrocatalysis was established, being involved in electronic stabilization of the Mn centers or in proton shuttling.