Research conducted by Zhu Yunqing from the School of Environmental Science at Shaanxi University of Science and Technology, along with Dr. He Peilei from Ningbo Institute of Materials Technology, Chinese Academy of Sciences, and Associate Professor Chen Weichao from Northeast Normal University, focused on titanium-substituted Keggin-type polyoxometalate clusters. By employing a strategy of non-stoichiometric ion exchange, they managed to regulate the spatial distribution of ligands on the surface of polyoxometalate clusters, constructing subnanometer assembly units with rhombic dodecahedral structures. Subsequently, inducing their assembly in a dual-solvent system led to the construction of micrometer-scale rhombic dodecahedral superstructures. This recent achievement has been published in Angewandte Chemie International Edition.
The study involved stoichiometric and non-stoichiometric ion exchange between titanium-substituted polyoxometalate clusters and tetra-n-butylammonium bromide. Molecular dynamics simulations indicated that stoichiometric ion exchange resulted in disordered subnanometer units, while non-stoichiometric ion exchange yielded rhombic dodecahedral subnanometer units containing bromide ions. By inducing assembly in a dual-solvent system, microscale spherical or rhombic dodecahedral assemblies were obtained from these two assembly units, respectively. Through non-stoichiometric ion exchange and assembly, bromide ions were introduced, enhancing Lewis acid-base properties and the adsorption of carbon dioxide. This makes the assembled structure potentially capable of catalyzing the cycloaddition reaction between carbon dioxide and epoxides without the need for a cocatalyst.
Ultimately, the micrometer-scale rhombic dodecahedral superstructure exhibited excellent catalytic performance and good cycling stability in the cycloaddition of carbon dioxide without a cocatalyst. By tuning the spatial distribution of surface ligands, this work achieved control over the structure and symmetry of assembly units, providing a new strategy for constructing superstructures with novel properties.
