Direct Space Structure Solution Applications

The crystal structures of 2,4,6-triisopropylbenzenesulfonamide, 1,2,3-trihydroxybenzene-hexamethylenetetramine (1/1), 5-bromonicotinic acid and chlorothalonil form II have been solved from x-ray powder diffraction data, by application of a direct space structure solution approach using the Monte Carlo method and confirmed by Rietveld refinement. In the sulfonamide, the molecules are linked by N-H⋯O hydrogen bonds into two-dimensional sheets built from alternating eight and twenty-membered rings. In the cocrystal, the molecules are linked by O-H⋯N hydrogen bonds to form puckered molecular ribbons that are in turn linked into a continuous 3D framework by C-H⋯π (arene) interactions. 5-bromonicotinic acid also displays atypical hydrogen-bonding behaviour by formation of dimers through a self-complementary acid-acid hydrogen-bond motif that are connected into antiparallel ribbons by C-H⋯O and C-H⋯N hydrogen bonds. Structure determination of the cocrystal and the bromonicotinic acid was successful despite the presence of preferred orientation in the data, whereas the distortion of the chlorothalonil data was so severe that structure solution was only possible when the effects of preferred orientation were minimized. Both the disordered structure, and an ordered structural approximation of chlorothalonil form II have been determined and rationalized.