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

Two uranyl tungstates, Cs₄[(UO₂)₄­(WO₅)­(W₂O₈)­O₂] (CsUW-1) and Cs₄[(UO₂)₇­(WO₅)₃O₃] (CsUW-2), were obtained via the high-temperature solid-state synthesis method by reacting uranyl nitrate with WO₃ in the presence of cesium nitrate. CsUW-1 crystallizes in space group P2₁/n, adopting a two-dimensional (2D) sheet structure. CsUW-2 forms a three-dimensional (3D) framework constructed by complex 2D sheets linked by cation–cation interactions of UO₂²⁺ groups. The cation–cation interactions fragment presented in CsUW-2 involves the 2D → 3D transformation of the uranyl tungstate network and acts as an intermediate part by bridging the structures of CsUW-1 and CsUW-2. We demonstrate that the chemical and structural transformation from CsUW-1 to CsUW-2 is possible via adding a suitable amount of UO₃ 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.