editorial
organic compounds
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A low-temperature redetermination of the title compound, C12H16N2O3, more commonly known as hexobarbitone, is reported, with significantly improved precision. The crystal packing reveals an infinite hydrogen-bonded hexobarbitone chain linked by a single N—HO interaction, an extremely rare motif in barbiturate crystal packing. Unlike some other barbiturate crystal structures, there is no phase transition on cooling to 150 K.
metal-organic compounds
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In the title complex, [CdCl2(C4H6N2S)2], the Cd atom has a distorted tetrahedral coordination geometry, with two Cl− and two monodentate neutral thione ligands bonded through S. There are intramolecular N—HCl and intermolecular N—HS hydrogen bonds, generating centrosymmetric dimers.
organic compounds
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The title compound, 2-p-tolyl-5,6,7,8-tetrahydrobenzo[d]imidazo[2,1-b]thiazole, C16H16N2S, is a condensation product of pifithrin-α, which has been previously reported as an inhibitor of the tumour suppressor protein p53. The molecule contains a planar fused pair of heterocyclic five-membered rings and the attached p-tolyl substituent is also essentially coplanar.
metal-organic compounds
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In the title complex, (C16H36N)[WCuO2S2(C3H6N2S)], the W and Cu atoms have tetrahedral and trigonal-planar coordination, respectively. Two sulfide ligands bridge the two metal centres; tungsten is additionally coordinated by two terminal oxo ligands and copper by the exocyclic S atom of imidazolidine-2-thione. There is an intramolecular N—HS hydrogen bond in the anion, and anions are linked into chains by N—HO intermolecular hydrogen bonds. The more loosely held cation is disordered.
organic compounds
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The asymmetric unit of the title compound, C6H16N22+·2(HO)2(O)PCH2P(O)2(OH)-, contains two singly charged diphosphonate anions and two half-cations, each doubly charged cation lying on an inversion centre. Single deprotonation of methylenediphosphonic acid to give a salt with an organic amine is unprecedented, double deprotonation being normal. All N-H and O-H groups act as hydrogen-bond donors in the crystal structure, with unprotonated O atoms as the acceptors, giving a three-dimensional network.
organic compounds
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A tetragonal polymorph of malonamide, C3H6N2O2, is reported. The unit-cell dimensions, crystallographic symmetry and some aspects of the molecular geometry are significantly different from those of the known monoclinic form [Chieh et al. (1970). J. Chem. Soc. A, pp. 179-184]. An R33(12) hydrogen-bonding motif links molecules together into a three-dimensional network.
organic compounds
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An orthorhombic polymorph of malonamide, C3H6N2O2, is reported. The unit-cell dimensions, crystallographic symmetry and some aspects of the molecular geometry are significantly different from those of the known monoclinic form [Chieh et al. (1970). J. Chem. Soc. A, pp. 179-184] and of the tetragonal form described in the previous paper [Nichol & Clegg (2005). Acta Cryst. E61, o3424-o3426]. A simple R42(8) motif links the molecules together and the symmetry of the molecule means that this extends into a three-dimensional network.
organic compounds
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A second monoclinic polymorph of the title compound, neocuproine dihydrate, C14H12N2·2H2O, is reported. Unlike the first polymorph [Baggio, Baggio & Mombrú (1998). Acta Cryst. C54, 1900–1902], in which the phenanthroline ring system was constrained to lie in a crystallographic mirror plane, here there is no such imposed symmetry. Consequently, the molecule shows small deviations from planarity, the outer rings being twisted slightly in opposite directions from the plane of the central ring. The hydrogen-bonding motifs remain essentially the same as in the first polymorph, involving small rings of four water molecules and large rings containing four water molecules and two neocuproine molecules, but with no H-atom disorder for the water molecules in this case. There are also aromatic π–π stacking interactions.
organic compounds
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A redetermination at 150 K of the structure of violuric acid monohydrate, C4H3N3O4·H2O, confirms that the space group is non-centrosymmetric Cmc21, despite indications from the intensity statistics and possible molecular symmetry that it could be centrosymmetric Cmcm. Issues raised in the original reports [Craven & Mascarenhas (1964). Acta Cryst. 17, 407-414; Craven & Takei (1964). Acta Cryst. 17, 415-420] suggested either a disordered model or an ordered one with high thermal motion. The redetermination shows that an ordered model is correct, and the low-temperature data collection leads to normal displacement parameters. The precision of the structure is significantly improved in this new study. The violuric acid molecule is entirely planar, and every atom in the structure lies on a crystallographic mirror plane. Violuric acid and water molecules form hydrogen-bonded sheets.