X-Ray Investigations of Ammines of Alkaline Earth Metal Halides. I. The Structures of CaCl2(NH3)8, CaCl2(NH3)2 and the Decomposition Product CaClOH.

The Unusual Coordination Sphere in the Octaammine Calcium(II) Ions of [Ca(NH3)8]Br2 and [Ca(NH3)8]I2 and the Thermal Decomposition of the Iodide to [Ca(NH3)6]I2

“…He described a colorless voluminous product of the composition "CaBr · 3 NH 3 " (sic!). By tensieudiometric measurements in the CaBr 2 /NH 3 system Hüttig discussed compounds with the compositions CaBr 2 · 8 NH 3 , CaBr 2 · 6 NH 3 and CaBr 2 · 2 NH 3 [2]. He also studied the CaCl 2 -NH 3 system and described the corresponding products.…”

“…For the CaI 2 -NH 3 system he discovered compounds with the composition CaI 2 · x NH 3 (x = 8, 6, 2, and 1). The first crystallographic evidence of a calcium ammine complex was obtained by Westman and coworkers on the compound "CaCl 2 (NH 3 ) 8 ", of which they elucidated the structure from powder X-ray patterns and consecutive Rietveld refinements [3]. The cell parameters of this chloride (a = 12.1143, b = 7.3076, c = 15.0829 Å, V = 1335,24 Å 3 , T = 298 K) are quite similar to the ones reported here, and the space group is the same (Pnma).…”

Structure determination by use of pattern decomposition and the Rietveld method on synchrotron X-ray and neutron powder data; the structures of Al2Y4O9and T2O4

“…Similarly, high-resolution data from a Guinier-H~igg camera can be used to determine the heavy-atom positions by Patterson methods followed by Rietveld refinement and identification of light atoms from difference Fourier maps, and examples of this are the structure analyses of CaCI2(NH3) 8 and CaCI2(NH3) 2 (Westman, Werner, Schuler & Raldow, 1981) and of (NH4)4[(MoO2)4Oa](C4H3Os)2.H20 (Berg & Werner, 1977). For sufficiently complicated structures overlap is, however, unavoidable, and some technique is then needed to decompose the pattern into individual Bragg components without any reference to a structural model.…”

Solving Crystal Structures from Powder Diffraction Data

“…A rather limited number of complex crystal structures has been solved from powder diffraction data alone. Examples are the structures of CaC1 2 (NH 3 )s and CaC1 2 (NH 3 )2 (Westman et al 1981) and of (NH4M(Mo02)403](C4H30sh,H20 (Berg and Werner 1977), solved from Guinier photographs by Patterson methods, and the structure of ,a-oxalic acid solved from a neutron diffraction powder pattern by direct methods (A. W. Hewat, personal communication).…”