Artificial model of photosynthetic oxygen evolving complex: Catalytic O-2 production from water by di-mu-oxo manganese dimers supported by clay compounds

Adsorption of [(OH2)(terpy)Mn(mu-O)(2)Mn(terpy)(OH2)](3+) (terpy=2,2':6',2 ''-terpyridine) (1) onto montmorillonite K10 (MK10) yielded catalytic dioxygen (O-2) evolution from water using a Ce-IV 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-mu-oxo Mn-2 core could be Mn-III-Mn-IV. 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 O-2 evolution showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on MK10. The reaction of the [(bpy)(2)Mn(mu-O)(2)Mn(bpy)(2)](3+) (bpy=2,2'-bipyridine) (2)/MK10 hybrid with a Ce-IV oxidant evolved O-2. 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 O-2 production by photosynthetic oxygen evolving complex is discussed based on catalytic O-2 evolution by 1 adsorbed on MK10. (c) 2006 Elsevier B.V. All rights reserved.