Abstract
Water oxidation is critically important for the development of energy solutions based on the concept of artificial photosynthesis. In order to gain deeper insight into the mechanism of water oxidation, the catalytic cycle for the first designed water oxidation catalyst, cis,cis-[(bpy)&sub2;(H&sub2;O)RuIIIORuIII(OH&sub2;)(bpy)&sub2;]4+ (bpy is 2,2-bipyridine) known as the blue dimer (BD), is monitored in D&sub2;O by combined application of stopped flow UV-Vis, electron paramagnetic resonance (EPR) and resonance Raman spectroscopy on freeze quenched samples. The results of these studies show that the rate of formation of BD[4,5] by Ce(IV) oxidation of BD[3,4] (numbers in square bracket denote oxidation states of the ruthenium (Ru) centers) in 0.1 M HNO&sub3;, as well as further oxidation of BD[4,5] are slower in D&sub2;O by 2.1-2.5. Ce(IV) oxidation of BD[4,5] and reaction with H&sub2;O result in formation of an intermediate, BD[3,4]', which builds up in reaction mixtures on the minute time scale. Combined results under the conditions of these experiments at pH 1 indicate that oxidation of BD[3,4]' is a rate limiting step in water oxidation with the BD catalyst.