A comparative study of two polymorphs of L-aspartic acid hydrochloride.

Two polymorphs of l-aspartic acid hydrochloride, C4H8NO4+center dot Cl-, were obtained from the same aqueous solution. Their crystal structures have been determined from single-crystal data collected at 100 K. The crystal structures revealed three-and two-dimensional hydrogen-bonding networks for the triclinic and orthorhombic polymorphs, respectively. The cations and anions are connected to one another via N-H center dot center dot center dot Cl and O-H center dot center dot center dot Cl interactions and form alternating cation-anion layer-like structures. The two polymorphs share common structural features; however, the conformations of the l-aspartate cations and the crystal packings are different. Furthermore, the molecular packing of the orthorhombic polymorph contains more interesting interactions which seems to be a favourable factor for more efficient charge transfer within the crystal.