Structural Studies of the System Na(saccharinate)⋅n H₂O: A Model for Crystallization

Abstract

Not far from a crystal nucleus? The complex crystal structure of sodium saccharin “dihydrate” could be a good model for nucleation (see graphic). The asymmetric unit contains 362 atoms and much water, and the crystal contains ordered and disordered regions. Amazingly, the crystal structure of this metastable compound was not determined for 125 years following its isolation, although it is manufactured in bulk.

Bimodal nanoindentation response of the (001) face in crystalline sodium saccharin dihydrate

“…In other words, some unit cells are fully regular while others are completely irregular. This does not explain the fact that the crystallographic refinement of atoms in the regular region proceeds well for the dihydrate [22].…”

“…While it is difficult to draw firmer conclusions, it is possible that the reported crystal structure, which by definition is a space averaged structure, is not a really accurate representation at lower length scales and that the regular and irregular regions cover much larger domains than would seem to be the case by inspection of the crystal unit cell. In support of such a view, Banerjee et al [22] had noted that the molecular positions and dimensions in the irregular regions vary from crystal to crystal. It is possible therefore that the real structure consists of regular and irregular regions, each of dimensions of at least several tens of m.…”

“…It is of interest to note that this dihydrate was originally characterized by Jovanovski and Kamenar [19][20]. The crystal structure was determined simultaneously and independently by Naumov et al [21] and by Banerjee et al [22] in 2005. Banerjee et al [22] have described this crystal structure in terms of an incipient crystal nucleus, and it is therefore of fundamental mechanistic interest.…”

“…The crystal structure was determined simultaneously and independently by Naumov et al [21] and by Banerjee et al [22] in 2005. Banerjee et al [22] have described this crystal structure in terms of an incipient crystal nucleus, and it is therefore of fundamental mechanistic interest. The structure can be demarcated into -regular‖ and -irregular‖ regions or domains.…”

Unusual co-crystal of isonicotinamide: the structural landscape in crystal engineering

“…Along these lines, Desiraju and co-workers determined the crystal structure of sodium saccharin dihydrate, Na(sac)-(H 2 O) 1.875 , and argued that this heavily hydrated structure is a good model for the nucleus in the crystallization of the lower hydrate Na 3 (sac) 3 (H 2 O) 2 . Essentially, this complex structure resembles a metastable high-energy intermediate [8]. More recently, a Z = 6 structure of phenylacetylene was isolated by Desiraju and co-workers [9].…”