Hydrogen-bonding patterns in cis-4-ammoniocyclohexanecarboxylate hemihydrate

In the title compound, C7H13NO2.0.5H(2)O, cis-4-aminocyclohexanecarboxylic acid exists as a zwitterion and co-crystallizes with water molecules in a 2: 1 amino acid - water ratio. The cyclohexane ring adopts a chair conformation, with the carboxylate and ammonium groups in axial and equatorial positions, respectively. The basic motif in the crystal structure is a sandwich structure, formed by two amino acid units linked by head-to-tail hydrogen bonds. Hydrogen bonds of the type N+ - H ... O - C - O- link these motifs, forming helicoidally extended chains running along the c axis. The water molecule lies on a twofold axis and interacts with the chains by means of O - H ... O hydrogen bonds.