CRYSTAL-STRUCTURE REFINEMENT AND ELECTRON-DENSITY DISTRIBUTION IN DIASPORE

Diaspore from Dilln, Hungary, AlOOH, is orthorhombic with space group Pbnm, a=4.4007(6), b=9.4253(13), c=2.8452(3) Å, and Z=4. The crystal structure and electron distribution have been refined from 791 graphite-monochromatized Mo Kα data (maximum 2θ=130°) to R=0.035 (Rw=0.029). Difference maps show substantial electron density ascribed to covalent bonding in the hydroxyl group, O(2)-H, but no residual density is observed along the Al-O(1,2) bonds. An analysis of the charge distribution implies net charges of +1.47(26), -1.08(16), -0.59(13) and +0.20(5) for Al, O(1), O(2) and H respectively. Semi-empirical molecular orbital calculations of the Hückel type agree with the experimentally determined atomic charge distribution and also allow a rationalization of the observed bond length variations. © 1979 Springer-Verlag.