From Two-Dimensional Layers to Three-Dimensional Frameworks: Expanding the Structural Diversity of Uranyl Compounds by Cation–Cation Interactions

Two uranyl tungstates, Cs<sub>4</sub>[(UO<sub>2</sub>)<sub>4</sub>­(WO<sub>5</sub>)­(W<sub>2</sub>O<sub>8</sub>)­O<sub>2</sub>] (<b>CsUW-1</b>) and Cs<sub>4</sub>[(UO<sub>2</sub>)<sub>7</sub>­(WO<sub>5</sub>)<sub>3</sub>O<sub>3</sub>] (<b>CsUW-2</b>), were obtained via the high-temperature solid-state synthesis method by reacting uranyl nitrate with WO<sub>3</sub> in the presence of cesium nitrate. <b>CsUW-1</b> crystallizes in space group <i>P</i>2<sub>1</sub><i>/n</i>, adopting a two-dimensional (2D) sheet structure. <b>CsUW-2</b> forms a three-dimensional (3D) framework constructed by complex 2D sheets linked by cation–cation interactions of UO<sub>2</sub><sup>2+</sup> groups. The cation–cation interactions fragment presented in <b>CsUW-2</b> involves the 2D → 3D transformation of the uranyl tungstate network and acts as an intermediate part by bridging the structures of <b>CsUW-1</b> and <b>CsUW-2</b>. We demonstrate that the chemical and structural transformation from <b>CsUW-1</b> to <b>CsUW-2</b> is possible via adding a suitable amount of UO<sub>3</sub> oxide. In addition, the differential scanning calorimetry-thermogravimetric technique was carried out to gain insight into the thermal behavior of the synthesized compounds. Raman spectra of titled compounds were obtained and analyzed for signature peaks.