organic compounds
Asarinin, C20H18O6, was isolated as a racemate from the shrub Zanthoxylum alatum. Both forms of the enantiomerically pure substance, (+)- and (−)-asarinin, have been the subject of a total of five previous structure determinations that are essentially identical except for the absolute stereochemistry. However, there seems to be some confusion in the literature concerning these structure determinations of asarinin and also those of its stereoisomer sesamin. The molecular structure of racemic asarinin differs from that of the pure enantiomers in the orientation of one ring system. In the packing of the racemate, molecules are linked by C—HO interactions to form ribbons parallel to [101].
organic compounds
The title compound, C10H11N3O3S, (I), crystallizes as the NH tautomer. The two rings subtend an interplanar angle of 72.54 (4)°. An intramolecular hydrogen bond is formed from the NH2 group to a sulfonyl O atom. The molecular packing involves layers of molecules parallel to the bc plane at x ≃ 0, 1 etc., with two classical linear hydrogen bonds (amino–sulfonyl and pyrazoline–carbonyl N—HO) and a further interaction (amino–sulfonyl N—HO) completing a three-centre system with the intramolecular contact. The analogous phenyl derivative, (II) [Elgemeie, Hanfy, Hopf & Jones (1998). Acta Cryst. C54, 136–138], crystallizes with essentially the same unit cell and packing pattern, but with two independent molecules that differ significantly in the orientation of the phenyl groups. The space group is P21/c for (I) but P21 for (II), which is thus a pseudosymmetric counterpart of (I).
organic compounds
The title compound, C8H12Br4, displays crystallographic inversion symmetry, so that the cyclobutane ring is exactly planar. The ring C—C bond with eclipsed substituents is lengthened somewhat to 1.572 (5) Å. The packing can be described in terms of three BrBr contacts; two of these combine to form layers of molecules parallel to the ac plane, while the third crosslinks the layers in the third dimension. A simple topological descriptor for systems involving BrBr contacts is proposed.
metal-organic compounds
Bis(4-picoline-N)gold(I) dibromidoaurate(I), [Au(C6H7N)2][AuBr2], (I), crystallizes in the monoclinic space group P21/n, with two half cations and one general anion in the asymmetric unit. The cations, located on centres of inversion, assemble to form chains parallel to the a axis, but there are no significant contacts between the cations. Cohesion is provided by flanking anions, which are connected to the cations by short AuAu contacts and C-HBr hydrogen bonds, and to each other by BrBr contacts. The corresponding chloride derivative, [Au(C6H7N)2][AuCl2], (II), is isotypic. A previous structure determination of (II), reported in the space group P with very similar axis lengths to those of (I) [Lin et al. (2008). Inorg. Chem. 47, 2543-2551], might be identical to the structure presented here, except that its angle of 88.79 (7)° seems to rule out a monoclinic cell. No phase transformation of (II) could be detected on the basis of data sets recorded at 100, 200 and 295 K.
organic compounds
The imidazolidin-2-one ring displays a half-chair conformation. N—HO hydrogen bonds connect the molecules to form (8) rings and thence ribbons parallel to the a and b axes. The crystal was merohedrally twinned.