A Novel Cesium Pentaborate with Ribbon-Type Anionic Radical

Abstract

A novel hydrated cesium hydroxypentaborate is synthesized from boric acid flux at 180°С, and its crystal structure is determined by X-ray diffraction. The compound crystallizes in the triclinic system, sp. gr. P\(\bar {1}\), with the parameters a = 7.8107(5) Å, b = 9.1929(8) Å, c = 12.3553(11) Å, α = 98.98(1)°, β = 106.32(1)°, γ = 91.10(1)°, V = 839.1(1) ų, Z = 4. The structure is refined to R₁ = 5.8% with anisotropic displacement parameters for all nonhydrogen atoms, with allowance for the non-merohedral twinning by a twofold axis coinciding with the b axis. The twin components were 0.546(1) and 0.454(1). The features of the hydrogen bonds in Cs[B₅O₇(OH)₂] · 0.5H₂O are analyzed in comparison with isostructural rubidium analogue. The unit-cell parameters a and c of A[B₅O₇(OH)₂] · 0.5H₂O pentaborates are found to systematically increase with an increase in the radius of A cation in the NH₄ → Rb → Cs series; the small variation in the b parameter is due to the rigidity of the pentaborate chains elongated along this direction.