Verfeinerung der Kristallstruktur des Natriumperchlorats NaClO4

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Abstract
The crystal structure of anhydrous sodium perchlorate NaClO 4 (space group Cmcm — D 17 2 h , anhydrite type) has been refined by the least squares method to R = 0,040, using three dimensional x-ray diffraction data and anisotropic thermal parameters. The cell dimensions at 26°C are: a = 7.085, b = 6.526, c = 7.048 Å. The perchlorate group is slightly stretched along its twofold axis, which lies parallel to the crystallographic b -axis, and has the symmetry C 2 v . The mean Cl—O bond length is 1.435 Å, the mean Na—O distance is 2.54 Å and the average O—O distance between neighboured anions is 3.33 Å. Using the observed anisotropic thermal parameters for the chlorine atom and for the oxygen atoms the rigid-body motion analysis yields r.m.s. amplitudes for the translational motions of the perchlorate group parallel to the crystallographic axes a , b , c of 0.134, 0.127 and 0.129 Å. The components of the librational tensor correspond to oscillations about the principal axes, which are parallel to the crystallographic axes, of 6.2°, 6.8° and 6.9°. The libration causes the apparent Cl—O bond length to be shortened by 0.02 Å.

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