Small imperfection causes a very small molecule to pack in a very large cell: Sodium saccharinate 1.875 hydrate with unit cell of 15.6 nm3

ICYS, National Institute for Materials Science* Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, Skopje, Macedonia** Department of Inorganic Chemistry, University of Zagreb, Zagreb, Croatia*** Australian National University, Caberra, Australia**** Department of Chemistry, University of Malaya, Malaysia*****
â—‹Pance Naumov* Gligor Jovanovski** Orhideja Grupce** Branko Kaitner*** David A. Rae**** Seik Weng Ng*****

The structure of the common artificial sweetener sodium saccharinate, with one of the largest unit cells for a small, nearly planar organic anion such as the saccharinate, was determined for the first time from laboratory X-ray diffraction data. The formally 15/8 hydrate crystal is composed of 64 formula units and represents an eight-fold occupational and displacive modulation of a C2/m parent structure with 8 formula units. The lack of one water molecule in the hypothetical dihydrate crystal Na(C7H4NO3S).2H2O and the respective structural misfit result in eight-fold expansion of the aperiodicity and the formula Na64(C7H4NO3S)64.120H2O. Due to the extensive disorder, the compound can be considered a frozen intermediate state between complete disorder of a concentrated solution of the salt and the completely ordered triclinic Na(C7H4NO3S).2/3H2O, which crystallizes as stable hydrate from ethanol.

Ref.: P. Naumov, G. Jovanovski, O. Grupce, B. Kaitner, A. D. Rae, S. W. Ng, Angew. Chem., Int. Ed. Engl. 2005, 44, 1251.