Observation of O–O Bond Forming Step of Molecular Co<sub>4</sub>O<sub>4</sub> Cubane Catalyst for Water Oxidation by Rapid-Scan FT-IR Spectroscopy
Hongfei Liu, Heinz Frei
Abstract
Monitoring of water oxidation by the established Co cubane catalyst Co4O4(OAc)4(py)4 (abbrev. Co4O4, OAc = acetate, py = pyridine) by time-resolved rapid-scan ATR FT-IR spectroscopy revealed the O–O bond forming intermediate by its O–O stretch mode at 833 cm–1. The catalysis was either driven in alkaline solution by a visible light sensitizer or in hydroxide (OH–) containing acetonitrile solution using the one-electron oxidized cubane as the sole source of charge. The μ-peroxido structure of the intermediate was established by 18O isotopic labeling, and its catalytic relevancy and role in the O2 evolving cycle were revealed by the kinetic relationship with decreasing cubium ([Co4O4]+) and recovery of the Co4O4 complex.