Water oxidation catalysts and pH sensors based on azo-conjugated iridium/rhodium motifs

Abstract

Herein we report the molecular structures and electronic properties of ionic, hydrophobic half-sandwich complexes with formula [η⁵-Cp*Ir(L)(Cl)](OTf) (1), [η⁵-Cp*Rh(L)(Cl)](OTf) (2), [η⁵-Cp*Ir(L)(H₂O)](OTf)₂ (3) and [η⁵-Cp*Rh(L)(H₂O)](OTf)₂ (4), where L is 1-(2-pyridylazo)-2-naphthol. The electrochemical properties of these complexes have been investigated, and they displayed good electronic properties for use as water oxidation catalysts. Interestingly, the color of their solutions is unambiguously transformed from brown to green at pH = 12; the color changes of 1, 2 and 4 are especially apparent. For this reason, their use as pH sensors for detecting solution pH values can be explored.