X-Ray and neutron diffraction study of alums
Abstract
The crystal structure of the alums, (NH3CH3)Al(SO4)2 · 12H2O and (NH4)Al(SO4)2 · 12H2O, has been determined and refined from X-ray and neutron diffraction data. The compounds crystallize cubic in space group Pa3 (Z = 4) with a0 = 12.322(3) Å and a0 = 12.242(1) Å respectively. The positional and thermal parameters of all atoms including hydrogens have been refined by full matrix least-squares analysis resulting in Rw values from the X-ray and neutron data of 0.030 and 0.029 respectively for the methylammonium alum and of 0.024 and 0.014 respectively for the ammonium alum.
The atoms of the cation groups (NH3CH3)+ and (NH4)+ are distributed on 8(c) and 24(d) positions in two orientations of equal probability on and around the [111] direction related to each other by an inversion centre. The disorder in the cation groups is explained by a quantized rotation. Disorder in the sulfate groups has been determined to 4.2% for the methylammonium alum and to about 17% for the ammonium alum. The disordered sulfate tetrahedra are distorted and in a reversed orientation along the threefold axis. The system of the hydrogen bonds is discussed.
© 2015 Oldenbourg Wissenschaftsverlag GmbH, Rosenheimer Str. 145, 81671 München
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Articles in the same Issue
- X-Ray and neutron diffraction study of alums
- Complex ion centres in heavily doped NaBr: Tl phosphors
- Distortions of octahedra and octahedral sheets in 1 M micas and the relation to their stability
- Structure of 2-hydroxybenzimidazole
- Structural investigations of synthetic fairchildite, K2Ca(CO3)2
- The crystal and molecular structure of [Co(PO4)(NH3)4] · 3 H2O
- The crystal structure of Benzoic Acid: a redetermination with X-rays at room temperature; a summary of neutron-diffraction work at temperatures down to 5 K
- Modulated structure of a plagioclase An52: Theory and structure determination
- Die Kristallstruktur des Dilithium tetrahydroxo-di-μ-peroxodiborats(Lithiumperoxoborats), Li2[B2(O2)2(OH)4]
- Über Wirkungsbereichsteilungen von kubischer Symmetrie II. Die Typen von Wirkungsbereichspolyedern in den symmorphen kubischen Raumgruppen
- Kristallstrukturen komplexer Alkali-Nickel-Azidhydrate
- Röntgentopographische Untersuchungen an CdTe-Einkristallen
- The crystal structure of synthetic Tl3SbS4
