Structural and Spectroscopic Characterization of Reaction Intermediates Involved in a Dinuclear Co-Hbpp Water Oxidation Catalyst

Abstract

<p> An end-on superoxido complex with the formula {[Co^III(OH₂)(trpy)][Co^III(OO^&bull;)(trpy)](&mu;-bpp)}⁴⁺ (<strong>3</strong>⁴⁺) (bpp^&ndash; = bis(2-pyridyl)-3,5-pyrazolate; trpy = 2,2&prime;;6&prime;:2&Prime;-terpyridine) has been characterized by resonance Raman, electron paramagnetic resonance, and X-ray absorption spectroscopies. These results together with online mass spectrometry experiments using ¹⁷O and ¹⁸O isotopically labeled compounds prove that this compound is a key intermediate of the water oxidation reaction catalyzed by the peroxido-bridged complex {[Co^III(trpy)]₂(&mu;-bpp)(&mu;-OO)}³⁺ (<strong>1</strong>³⁺). DFT calculations agree with and complement the experimental data, offering a complete description of the transition states and intermediates involved in the catalytic cycle.</p>