Crystal structure determination by combined synchrotron powder X-ray diffraction and crystal structure prediction: 1: 1 L-ephedrine D-tartrate

The crystal structure of the diastereomeric salt 1 : 1 L-ephedrine D-tartrate (1 : 1 LD, C10H16NO+center dot C4H5O6-) was determined from high-resolution synchrotron powder X-ray diffraction (PXRD) data using global optimization in direct space (parallel tempering) together with computational modelling to locate hydrogen positions and refined by the Rietveld method. The structure is monoclinic, space group P2(1), with a = 18.82810(3) angstrom, b = 7.19429(2) angstrom, c = 5.73035(1) angstrom, beta = 95.9613(1)degrees, V = 772.006(3) angstrom(3), and Z = 2. Computational prediction of organic salt structures, especially hydrogen positions, is a valuable complementary technique to PXRD for the final stages of structure determination.