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

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 0.89 Å−1. The present study confirms the unusual complexity of the structure comprising a very large primitive unit cell with Z′ = 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 (Z′ = 2) of the 3D superstructure. Therefore, such a superspace approach is desirable to work out this high‐Z′ structure. The displacement and occupational modulation of the saccharinate anions have been studied, as well as their conformational variation along the fourth dimension. [ABSTRACT FROM AUTHOR]