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) angstrom 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 (DELTA) sharing corners in order to form infinite chains along [010], with the shorthand notation 3:infinity1(DELTA + 2T). The particular Linkage of the B3O3 rings leads to a new diborate anion {[B2O3(OH)]nn-}, 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.