The ab initio structure determination of Cd₃(OH)₅(NO₃) from X-ray powder diffraction data

The structure of cadmium hydroxide nitrate, Cd₃(OH)₅(NO₃), has been determined directly from conventional powder diffractometry with monochromatic X-rays using no prior structural information. The cell dimensions obtained with an indexing method are a = 3.4203 (3), b = 10.0292 (6), c = 11.0295 (6) Å. The space group is Pmmn, with Z = 2. From pattern-fitting methods, features of integrated intensities, line shapes and breadths were obtained. The powder pattern exhibits anisotropic line broadening with a marked tendency to a Lorentzian character for the peak shapes, due to probable stacking faults. Initial positional parameters for cadmium atoms were obtained from the Patterson function derived from 65 unambiguously indexed reflections. The remaining atoms were located by interpretation of Fourier difference maps. A whole-pattern refinement converged with R_F = 0.049, R_B = 0.059, R_p = 0.061 and R_wp = 0.079. The structure of Cd₃(OH)₅(NO₃) consists of corrugated layers of octahedra sharing edges, connected themselves by hydrogen bonds. The crystal chemistry of this new cadmium hydroxide nitrate, with low nitrate content, is discussed. The JCPDS Diffraction File No. is 40-1491.