Porous Uranyl Borophosphates with Unique Three-Dimensional Open-Framework Structures.

Two novel alkali-metal uranyl borophosphates have been prepared and characterized for the first time, namely, K5 (UO2 )2 [B2 P3 O12 (OH)]2 (OH)(H2 O)2 and K2 (UO2 )12 [B(H2 PO4 )4 ](PO4 )8 (OH)(H2 O)6 denoted as KUPB1 and KUPB2, respectively. KUPB1 was obtained hydrothermally at 220 °C and crystallizes in a monoclinic structure in the chiral space group P21 . 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) Å3 . It features a unique three-dimensional (3D) open-framework structure, composed of two corner-sharing linked one-dimensional (1D) anionic borophosphates (BP), [B2 P3 O13 ]5- , along the a axis and uranyl phosphate (UP), [(UO2 )(PO4 )3 ]7- , chains along the c axis, further bridged by PO4 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 {4.84 .10}{42 .6}2 {43 .62 .83 .102 }{82 .10}. By modification of the synthetic conditions of KUPB1 through an increase in the amount of H3 BO3 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) Å3 . KUPB2 crystallizes in a tetragonal structure in the polar space group I4̅2m, and its structure is based on a highly complex 3D framework, {(UO2 )12 [B(PO4 )4 ](PO4 )8 }9- , in which 1D 8-R UP [(UO2 )(PO4 )]- tubes can be observed along the c axis. The [(UO2 )(PO4 )]- tubes consist of three uranyl chains along the c axis, which are linked alternately by [PO4 ]3- tetrahedra. Those isolated 1D [(UO2 )(PO4 )]- tubes are further bridged through [(UO2 )4 B(PO4 )4 ]- clusters, forming an exceptional 3D open-framework structure. Its simplified cation network is a new 5-nodal net topological type such as {32 .43 .5.62 .7.8}8 {34 .45 .54 .62 }8 {4.62 .83 }4 {42 .6}4 {44 .62 }. Their facile hydrothermal synthetic routes, porous structure topology, thermal stability, and Raman spectroscopy properties are reported and discussed.