On the puzzling case of sodium saccharinate 1.875-hydrate : structure description in (3+1)-dimensional superspace

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Rekis, Toms ; Schönleber, Andreas ; van Smaalen, Sander:
On the puzzling case of sodium saccharinate 1.875-hydrate : structure description in (3+1)-dimensional superspace.
In: Acta Crystallographica Section B. Bd. 76 (2020) Heft 1 . - S. 18-27.
ISSN 2052-5206
DOI der Verlagsversion: https://doi.org/10.1107/S2052520619014938

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Abstract

The structure of sodium saccharinate 1.875-hydrate is presented in three- and (3+1)-dimensional space. The present model is more accurate than previously published superstructures, due to an excellent data set collected up to a high resolution of 0.89Å\sp -}1}. The present study confirms the unusual complexity of the structure comprising a very large primitive unit cell with \it Z\prime = 16. A much smaller degree of correlated disorder of parts of the unit cell is found than is present in the previously published models. As a result of pseudo-symmetry, the structure can be described in a higher-dimensional space. The X-ray diffraction data clearly indicate a (3+1)-dimensional periodic structure with stronger main reflections and weaker superstructure reflections. Furthermore, the structure is established as being commensurate. The structure description in superspace results in a four times smaller unit cell with an additional base centring of the lattice, resulting in an eightfold substructure (\it Z\prime = 2) of the 3D superstructure. Therefore, such a superspace approach is desirable to work out this high-\it Z\prime structure. The displacement and occupational modulation of the saccharinate anions have been studied, as well as their conformational variation along the fourth dimension.