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 Mn-12 clusters Mn12O12(O2CC6H3(OH)(2))(16)(H2O)(4) (3,5DHMn(12)) and Mn12O12(O2CC6H3(OH)(3))(16)(H2O)(4) (3,4,5THMn(12)) 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 Mn-12 clusters, 3,4DHMn(12) and 2,3DHMn(12), 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 3,4DHMn(12) were discovered to have lower oxidation potential compared with those in 2,3DHMn(12), and thus, 3,4DHMn(12) can catalyze water oxidation with higher rate and TON than 2,3DHMn(12). 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.

Automated summary

This study investigates the role of -OH groups in water oxidation catalysis by comparing two new Mn-12 clusters, revealing that Mn centers with -OH groups in meta positions have lower oxidation potential and higher catalytic rates. This establishes the involvement of -OH groups in electronic stabilization of the Mn centers or in proton shuttling during electrocatalysis.