Microphase separation upon crystallization of small amphiphilic molecules: ‘low’ temperature form II of sodium benzoate (E 211)

A so far unknown low temperature polymorph (form II crystallized at 350 °C) of the common food preservative sodium benzoate (NaBz; E 211) could be crystallized by annealing (7 days) of the poorly crystalline technical material. Its crystal structure was solved by indexing a tiny single crystal by electron diffraction followed by structure solution and refinement applying powder X-ray diffraction (PXRD). The new polymorph shows many structural similarities to form I (crystallized at 420 °C). Both form I and II are the result of a microphase separation: the structures consist of pseudo-hexagonal packings of rod-shaped micelles where the core consists of sodium cations being coordinated by the…