Crystal structure determination of lithium diborate hydrate, LiB₂O₃(OH).H₂O, from X-ray powder diffraction data collected with a curved position-sensitive detector

The crystal structure of lithium diborate hydrate, LiB₂O₃(OH).H₂O, has been solved ab initio and refined by the Rietveld method from powder diffraction data collected with a curved position-sensitive detector (INEL CPS120) using Debye–Scherrer diffraction geometry with monochromatic X-rays. In the first stage the indexing of the powder pattern was performed by the successive dichotomy method from data collected with a diffractometer using Bragg–Brentano geometry. The lattice parameters are a = 9.7984 (10), b = 8.2759 (7) and c = 9.6138 (8) Å and the space group is Pnna. The structural model was obtained from direct methods and two difference Fourier maps. The Rietveld refinement converged to final crystal structure and profile indicators R_F = 0.05, R_B = 0.05, R_p = 0.03 and R_wp = 0.04. The structure consists of BO₄ tetrahedra (T) and BO₂(OH) triangles (Δ) sharing corners in order to form infinite chains along [010], with the shorthand notation 3:∞¹(Δ + 2T). The particular linkage of the B₃O₃ rings leads to a new diborate anion {[B₂O₃(OH)]ⁿ⁻_n}, in which two tetrahedral B atoms have an occupation factor of 0.5. Li atoms, tetrahedrally surrounded by four O atoms, three belonging to separate chains and one to a water molecule maintain the cohesion of the structure.