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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—H...O inter­actions to form ribbons parallel to [101].

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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—H...O) and a further inter­action (amino–sulfonyl N—H...O) 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).

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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 Br...Br 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 Br...Br contacts is proposed.

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Bis(4-picoline-[kappa]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 Au...Au contacts and C-H...Br hydrogen bonds, and to each other by Br...Br contacts. The corresponding chloride derivative, [Au(C6H7N)2][AuCl2], (II), is isotypic. A previous structure determination of (II), reported in the space group P\overline{1} 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 [gamma] 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.

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The imidazolidin-2-one ring displays a half-chair conformation. N—H...O hydrogen bonds connect the mol­ecules to form R_{2}^{2}(8) rings and thence ribbons parallel to the a and b axes. The crystal was merohedrally twinned.
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