Observation of the Same New Sheet Topology in Both the Layered Uranyl Oxide-Phosphate Cs₁₁[(UO₂)₁₂(PO₄)₃O₁₃] and the Layered Uranyl Oxyfluoride-Phosphate Rb₁₁[(UO₂)₁₂(PO₄)₃O₁₂F₂] Prepared by Flux Crystal Growth

We report single crystals of four new layered uranyl phosphates, including three oxyfluoride-phosphates, were synthesized by molten flux methods using alkali chloride melts, and their structures were determined by single-crystal X-ray diffraction. Cs₁₁[(UO₂)₁₂(PO₄)₃O₁₃] (1) and Rb₁₁[UO₂)₁₂(PO₄)₃O₁₂F₂] (2) contain uranyl phosphate layers exhibiting a new sheet topology that can be related to that of β-U₃O₈, while Cs_4.4K_0.6[(UO₂)₆O₄F(PO₄)₄(UO₂)] (3) and Rb_4.4K_0.6[(UO₂)₆O₄F(PO₄)₄(UO₂)] (4) contain layers of a known isomer of the prominent phosphuranylite topology. The location of the fluorine in structures 2-4 is discussed using bond valence sums. First principles calculations were used to explore why a pure oxide structure is obtained for the Cs containing phase (1) and in contrast an oxyfluoride phase for the Rb containing phase (2). Ion exchange experiments were performed on 1 and 2 and demonstrate the ability of these structures to exchange approximately half of the parent alkali cation with a target alkali cation in an aqueous concentrated salt solution. Optical measurements were performed on 1 and 2 and the UV-vis and fluorescence spectra show features characteristic of the ${\text{UO}}_2^{2+}$ uranyl group.