Syntheses, Structures, and Ion-Exchange Properties of the Three-Dimensional Framework Uranyl Gallium Phosphates, Cs<sub>4</sub>[(UO<sub>2</sub>)<sub>2</sub>(GaOH)<sub>2</sub>(PO<sub>4</sub>)<sub>4</sub>]·H<sub>2</sub>O and Cs[UO<sub>2</sub>Ga(PO<sub>4</sub>)<sub>2</sub>]
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The reaction of UO2(NO3)2·6H2O with Cs2CO3 or CsCl, H3PO4, and Ga2O3 under mild hydrothermal conditions results in the formation of Cs4[(UO2)2(GaOH)2(PO4)4]·H2O (UGaP-1) or Cs[UO2Ga(PO4)2] (UGaP-2). The structure of UGaP-1 was solved from a twinned crystal revealing a three-dimensional framework structure consisting of one-dimensional [Ga(OH)(PO4)2]4- chains composed of corner-sharing GaO6 octahedra and bridging PO4 tetrahedra that extend along the c axis. The phosphate anions bind the UO22+ cations to form UO7 pentagonal bipyramids. The UO7 moieties edge-share to create dimers that link the gallium phosphate substructure into a three-dimensional [(UO2)2(GaOH)2(PO4)4]4- anionic lattice that has intersecting channels running down the b and c axes. Cs+ cations and water molecules occupy these channels. The structure of UGaP-2 is also three-dimensional and contains one-dimensional [Ga(PO4)2]3- gallium phosphate chains that extend down the a axis. These chains are formed from fused eight-membered rings of corner-sharing GaO4 and PO4 tetrahedra. The chains are in turn linked together into a three-dimensional [UO2Ga(PO4)2]1- framework by edge-sharing UO7 dimers as occurs in UGaP-1. There are channels that run down the a and b axes through the framework. These channels contain the Cs+ cations. Ion-exchange studies indicate that the Cs+ cations in UGaP-1 and UGaP-2 can be exchanged for Ca2+ and Ba2+. Crystallographic data: UGaP-1, monoclinic, space group P21/c, a = 18.872(1), b = 9.5105(7), c = 14.007(1) Å, β = 109.65(3)°, Z = 4 (T = 295 K); UGaP-2, triclinic, space group P1̄, a = 7.7765(6), b = 8.5043(7), c = 8.9115(7) Å, α = 66.642(1)°, β = 70.563(1)°, γ = 84.003(2)°, Z = 2 (T = 193 K).
