Nanoscale PAPER Cite this: DOI: 10.1039/c7nr04373b Received 18th June 2017, Accepted 10th July 2017 DOI: 10.1039/c7nr04373b rsc.li/nanoscale A Waugh type [CoMo 9 O 32 ] 6- cluster with atomically dispersed Co IV originates from Anderson type [CoMo 6 O 24 ] 3- for photocatalytic oxygen molecule activation† Yongdong Chen, a,b Chaolei Zhang, a,b Caoping Yang, a Jiangwei Zhang, * b Kai Zheng, b Qihua Fang b and Gao Li * b An atomically dispersed Waugh type [CoMo 9 O 32 ] 6- cluster is obtained, employing the most flexible struc- ture unit Anderson type [Co(OH) 6 Mo 6 O 18 ] 3- as a precursor. The structure of the [CoMo 9 O 32 ] 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 [CoMo 9 O 32 ] 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, [CoMo 9 O 32 ] 6- can effectively generate 1 O 2 under laser (365 and 532 nm) and sunlight irradiation, detected using a water-soluble DAB probe. Such an n-type multielectron reservoir semi- conductor anionic [CoMo 9 O 32 ] 6- cluster with thermal and electrochemical stability as an effective photo- sensitizer serves as a promising material in solar energy scavenging. Introduction Polyoxometalates (POMs) are an exceptional family of in- organic clusters consisting of early transition metal ions (e.g., Mo, W, V, etc.) in their highest oxidation states with structural versatility and a wide range of properties and applications. 1–4 POMs can be divided into two main categories, i.e., isopoly- anion and heteropolyanion. Isopolyanion is comprised of only one element bridging by O atoms. While, the heteropolyanion incorporates functional heteroatoms (e.g., transition metals, noble metals, and rare earth metals) to make the design of advanced functional materials more accessible and rational. 5,6 Among these heteroatom candidates, the Co element has gained much attention due to its charming intrinsic catalytic applications in energy scavenging, such as water splitting and water–gas shift. 7–10 Since Keggin first reported the X-ray crystal structure of 1 : 12 heteropolyanions in 1934, the basic POM topology structure units of Keggin, Anderson, Dawson, Waugh, Silverton, and Lindqvist have been sequentially discovered, forming six basic structural branches of the POM family. 1 The discovery, exploration, and extension of the basic POM topology structure have always been the frontier and most urgent issue of POM chemistry. The Anderson type POM family stands out as one of the most adaptable and tunable subclasses benefitting from the diversity of the central hetero- atom, which is accessible to many elements, such as transition and noble metals. And recently the direct triol functionali- zation of Anderson clusters 11–15 has been intensively con- ducted and exhibited fascinating properties, such as catalysis, 2 biology applications, and a few to name. 16,17 The species of Waugh type [MnMo 9 O 32 ] 6- clusters isolated with only a single type of heteroatom Mn IV was first reported in 1953. 18 And the further related investigations have been ignored for a very long time until its intrinsic chiral topology and the corresponding spontaneous resolution were recently investigated. 19,20 An obstacle to effectively extend heteroatoms into a Waugh type cluster should be conquered to enrich such an important and unique branch of the fundamental POM topology structure. Two-dimensional (2D) materials (e.g., graphene, transition metal dichalcogenides, and metal oxides) have gained † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c7nr04373b a The Center of New Energy Materials and Technology, College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China b Gold Catalysis Research Center, State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China. E-mail: gaoli@dicp.ac.cn, jwzhang@dicp.ac.cn This journal is © The Royal Society of Chemistry 2017 Nanoscale Published on 12 July 2017. Downloaded by Tsinghua University on 28/07/2017 15:38:05. View Article Online View Journal