Structural studies of triglycine sulphate part i: Low radiation dose (structure a)

The crystal structure of ferroelectric triglycine sulphate has been determined from single-crystal X-ray diffractometer data. A single-domain crystal was used and the X-ray dose was minimized in order to reduce the effects of radiation damage. The crystals are monoclinic, with unit cell dimensions a = 9.419(1), b = 12.647(1), c = 5.727(1) å, β= 110.32°, space group P21, Z = 1. Least-squares refinement using 1270 independent reflections has reached R 0.041.The structure consists of three independent glycine molecules and a sulphate ion connected by a three-dimensional hydrogen bonding network. One of the three glycine molecules, glycine I, is a non-planar glycinium ion. The other two, glycines II and III, are both planar, but one is a glycinium ion and the other a glycine zwitterion. Anomalous scattering effects have been used to determine the absolute configuration. The major displacement in ferroelectric switching is 0.9 A for the nitrogen atom of glycine I, while for glycine II and III relatively small displacements are required.