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Porous Uranyl Borophosphates with Unique Three-Dimensional Open-Framework Structures
35
Citations
41
References
2017
Year
Two novel alkali-metal uranyl borophosphates have been prepared and characterized for the first time, namely, K<sub>5</sub>(UO<sub>2</sub>)<sub>2</sub>[B<sub>2</sub>P<sub>3</sub>O<sub>12</sub>(OH)]<sub>2</sub>(OH)(H<sub>2</sub>O)<sub>2</sub> and K<sub>2</sub>(UO<sub>2</sub>)<sub>12</sub>[B(H<sub>2</sub>PO<sub>4</sub>)<sub>4</sub>](PO<sub>4</sub>)<sub>8</sub>(OH)(H<sub>2</sub>O)<sub>6</sub> denoted as KUPB1 and KUPB2, respectively. KUPB1 was obtained hydrothermally at 220 °C and crystallizes in a monoclinic structure in the chiral space group P2<sub>1</sub>. The unit cell parameters of KUPB1 are a = 6.7623(2) Å, b = 19.5584(7) Å, c = 11.0110(4) Å, α = γ = 90°, β = 95.579(3)°, and V = 1449.42(8) Å<sup>3</sup>. It features a unique three-dimensional (3D) open-framework structure, composed of two corner-sharing linked one-dimensional (1D) anionic borophosphates (BP), [B<sub>2</sub>P<sub>3</sub>O<sub>13</sub>]<sup>5-</sup>, along the a axis and uranyl phosphate (UP), [(UO<sub>2</sub>)(PO<sub>4</sub>)<sub>3</sub>]<sup>7-</sup>, chains along the c axis, further bridged by PO<sub>4</sub> tetrahedra. Multi-intersectional channels can be observed within the structure, in which the largest 11-ring (11-R) tunnel size is ∼7.0 Å × 8.8 Å. Its simplified framework can be described as a new 4-nodal net topological type with a point symbol of {4.8<sup>4</sup>.10}{4<sup>2</sup>.6}<sub>2</sub>{4<sup>3</sup>.6<sup>2</sup>.8<sup>3</sup>.10<sup>2</sup>}{8<sup>2</sup>.10}. By modification of the synthetic conditions of KUPB1 through an increase in the amount of H<sub>3</sub>BO<sub>3</sub> as flux 4-fold and a reduction of water as the reaction medium, the novel compound KUPB2 is generated. The unit cell parameters of KUPB2 are a = b = 21.8747(3) Å, c = 7.0652(2) Å, α = β = γ = 90°, and V = 3380.72(12) Å<sup>3</sup>. KUPB2 crystallizes in a tetragonal structure in the polar space group I4̅2m, and its structure is based on a highly complex 3D framework, {(UO<sub>2</sub>)<sub>12</sub>[B(PO<sub>4</sub>)<sub>4</sub>](PO<sub>4</sub>)<sub>8</sub>}<sup>9-</sup>, in which 1D 8-R UP [(UO<sub>2</sub>)(PO<sub>4</sub>)]<sup>-</sup> tubes can be observed along the c axis. The [(UO<sub>2</sub>)(PO<sub>4</sub>)]<sup>-</sup> tubes consist of three uranyl chains along the c axis, which are linked alternately by [PO<sub>4</sub>]<sup>3-</sup> tetrahedra. Those isolated 1D [(UO<sub>2</sub>)(PO<sub>4</sub>)]<sup>-</sup> tubes are further bridged through [(UO<sub>2</sub>)<sub>4</sub>B(PO<sub>4</sub>)<sub>4</sub>]<sup>-</sup> clusters, forming an exceptional 3D open-framework structure. Its simplified cation network is a new 5-nodal net topological type such as {3<sup>2</sup>.4<sup>3</sup>.5.6<sup>2</sup>.7.8}<sub>8</sub>{3<sup>4</sup>.4<sup>5</sup>.5<sup>4</sup>.6<sup>2</sup>}<sub>8</sub>{4.6<sup>2</sup>.8<sup>3</sup>}<sub>4</sub>{4<sup>2</sup>.6}<sub>4</sub>{4<sup>4</sup>.6<sup>2</sup>}. Their facile hydrothermal synthetic routes, porous structure topology, thermal stability, and Raman spectroscopy properties are reported and discussed.
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