Crystal structure of lepidocrocite FeO(OH) from the electron-diffractometry data

The crystal structure of lepidocrocite gamma -FeO(OH) with the lattice parameters a = 3.072(2), b = 12.516(3), c = 3.873(2) Angstrom, sp. gr. Cmcm has been refined by the electron-diffractometry data for 135 crystallo-graphically nonequivalent reflections up to R = 0.048. Using the difference syntheses of the Fourier potential, we established, for the first time, the anisotropy in the distribution of the electrostatic potential of hydrogen and the statistical occupancy (with the probability of 1/2) by hydrogen atoms of two positions in the in plane normal to the a-axis at a distance of 0.27 Angstrom from the twofold axis. The O-H distance equals 0.97(3) Angstrom, the O-H . . .O angle, 135 degrees. The average Fe-O distance in octahedra is 2.022 Angstrom. (C) 2001 MAIK Nauka/Interperiodica.