Structure−Property Relationships in Lithium, Silver, and Cesium Uranyl Borates.

Four new uranyl borates, Li[UO2B5O9]·H2O (LiUBO-1), Ag[(UO2)B5O8(OH)2] (AgUBO-1), α-Cs[(UO2)2B11O16(OH)6] (CsUBO-1), and β-Cs[(UO2)2B11O16(OH)6] (CsUBO-2) were synthesized via the reaction of uranyl nitrate with a large excess of molten boric acid in the presence of lithium, silver, or cesium nitrate. These compounds share a common structural motif consisting of a linear uranyl, UO22, cation surrounded by BO3triangles and BO4tetrahedra to create an UO8hexagonal bipyramidal environment around uranium. The borate anions bridge between uranyl units to create sheets. Additional BO3triangles extend from the polyborate layers, and are directed approximately perpendicular to the sheets. In Li[(UO2)B5O9]·H2O, the additional BO3triangles connect these sheets together to form a three-dimensional framework structure. Li[UO2)B5O9]·H2O and β-Cs[(UO2)2B11O16(OH)6] adopt noncentrosymmetric structures, while Ag[(UO2)B5O8(OH)2] and α-Cs[(UO2)2B11O16(OH)6] are centrosymmetric. Li[(UO2)B5O9]·H2O, which can be obtained as pure phase, displays second-harmonic generation of 532 nm light from 1064 nm light. Topological relationships of all actinyl borates are developed. [ABSTRACT FROM AUTHOR]