Artificial model of photosynthetic oxygen evolving complex: Catalytic O2 production from water by di-μ-oxo manganese dimers supported by clay compounds

Adsorption of [(OH2)(terpy)Mn(μ-O)2Mn(terpy)(OH2)]3+ (terpy = 2,2′:6′,2ʺ-terpyridine) (1) onto montmorillonite K10 (MK10) yielded catalytic dioxygen (O2) evolution from water using a CeIV oxidant. The Mn K-edge X-ray absorption near edge structure (XANES) of the 1/MK10 hybrid suggested that the oxidation state of the di-μ-oxo Mn2 core could be MnIII–MnIV. However the pre-edge peak in the XANES spectrum of 1 adsorbed on MK10 is different from the neat 1 powder. The kinetic analysis of O2 evolution showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on MK10. The reaction of the [(bpy)2Mn(μ-O)2Mn(bpy)2]3+ (bpy = 2,2′-bipyridine) (2)/MK10 hybrid with a CeIV oxidant evolved O2. However, the turnover number value was less than unity for 2/MK10, showing that 2 adsorbed on MK10 does not work as a catalyst. The terminal water ligands could be an important for the catalysis by adsorbed 1. The mechanism of O2 production by photosynthetic oxygen evolving complex is discussed based on catalytic O2 evolution by 1 adsorbed on MK10.