Towards the solution of organic crystal structures by powder diffraction

The solutions of the molecular crystal structures: (I) 2-amino-4,5-dimetoxyacetophenone (C10H13NO3); (II) 1,4-benzenedimethanol (C3H10O2); and (III) 3-aminoquinoline (C9H8N2), were obtained using the simulated annealing technique on synchrotron X-ray powder diffraction patterns. In this procedure we use the knowledge of the molecular geometry which allows to describe trial solutions in the direct space with a few numerical parameters accounting for the position, orientation and conformational degrees of freedom of the molecules in the unit cell. The powder diffraction pattern of (IV) 3-amino-5-mercapto-1,2,4-triazole (C2H4N4S) was indexed in the P2(1)/a space group. It shows anisotropic strain and the structure was not solved yet.