A Waugh type [CoMo9O32]6− cluster with atomically dispersed CoIV originates from Anderson type [CoMo6O24]3− for photocatalytic oxygen molecule activation

Abstract

An atomically dispersed Waugh type [CoMo₉O₃₂]⁶⁻ cluster is obtained, employing the most flexible structure unit Anderson type [Co(OH)₆Mo₆O₁₈]³⁻ as a precursor. The structure of the [CoMo₉O₃₂]⁶⁻ cluster is identified by single crystal X-ray diffraction and also well characterized by FT-IR, ESI-MS, UV-Vis, EA, and TGA spectroscopy. Its 3D framework forms a quasi 2D material and possesses curved edge triangle shape nanopores with a diameter of 8.9 Å. The Co^IV and Mo^VI oxidation states and the related valence band and electronic state of Co are definitely confirmed by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and bond valence sum (BVS). The [CoMo₉O₃₂]⁶⁻ cluster is a typical n-type inorganic semiconductor with a HOMO–LOMO gap of ca. 1.67 eV and exhibits reversible two-electron redox properties, evidenced by UPS, cyclic voltammetric (CV), and Mott–Schottky plot analyses. Furthermore, [CoMo₉O₃₂]⁶⁻ can effectively generate ¹O₂ under laser (365 and 532 nm) and sunlight irradiation, detected using a water-soluble DAB probe. Such an n-type multielectron reservoir semiconductor anionic [CoMo₉O₃₂]⁶⁻ cluster with thermal and electrochemical stability as an effective photosensitizer serves as a promising material in solar energy scavenging.