A Family of Layered Phosphates Crystallizing in a Rare Geometrical Isomer of the Phosphuranylite Topology: Synthesis, Characterization, and Computational Modeling of A4[(UO2)3O2(PO4)2] (A = Alkali Metal) Exhibiting Intralayer Ion Exchange

Single crystals of eight new layered uranyl phosphates were grown from alkali chloride fluxes: Cs1.4K2.6­[(UO2)3O2(PO4)2], Cs0.7K3.3­[(UO2)3O2(PO4)2], Rb1.4K2.6­[(UO2)3O2(PO4)2], K4­[(UO2)3O2(PO4)2], K2.9Na0.9Rb0.2­[(UO2)3O2(PO4)2], K2.1Na0.7Rb1.2­[(UO2)3O2(PO4)2], Cs1.7K4.3­[(UO2)5O5(PO4)2], and Rb...

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Published in:Inorganic chemistry 2018-04, Vol.57 (8), p.4726-4738
Main Authors: Juillerat, Christian A, Moore, Emily E, Kocevski, Vancho, Besmann, Theodore, zur Loye, Hans-Conrad
Format: Article
Language:English
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Summary:Single crystals of eight new layered uranyl phosphates were grown from alkali chloride fluxes: Cs1.4K2.6­[(UO2)3O2(PO4)2], Cs0.7K3.3­[(UO2)3O2(PO4)2], Rb1.4K2.6­[(UO2)3O2(PO4)2], K4­[(UO2)3O2(PO4)2], K2.9Na0.9Rb0.2­[(UO2)3O2(PO4)2], K2.1Na0.7Rb1.2­[(UO2)3O2(PO4)2], Cs1.7K4.3­[(UO2)5O5(PO4)2], and Rb1.6K4.4­[(UO2)5O5(PO4)2]. All structures crystallize in the monoclinic space group, P21/c and contain uranyl phosphate layers with alkali metals located between the layers for charge balance. Ion exchange experiments on Cs0.7K3.3[(UO2)3O2(PO4)2], Rb1.4K2.6[(UO2)3O2(PO4)2], and K4[(UO2)3O2(PO4)2] demonstrated that Cs and Rb cations cannot be exchanged for K cations; however, K cations can be readily exchanged for Na, Rb, and Cs. Enthalpies of formation were calculated from density functional theory (DFT) and volume-based thermodynamics (VBT) for all six structures. A value for the enthalpy of formation of the phosphuranylite sheet, [(UO2)3O2(PO4)2]4–, was derived using single-ion additive methods coupled with VBT. DFT and VBT calculations were used to justify results of the ion exchange experiments. Cs0.7K3.3­[(UO2)3O2(PO4)2], Rb1.4K2.6­[(UO2)3O2(PO4)2], and K4­[(UO2)3O2(PO4)2] exhibit typical luminescence of the uranyl group.
ISSN:0020-1669
1520-510X
DOI:10.1021/acs.inorgchem.8b00434