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The title compound, C13H9ClOS, crystallizes in the ortho­rhombic system in the non-centrosymmetric space group P212121, with one molecule in the asymmetric unit. The repulsion between two Cl atoms of neighbouring molecules is minimized by a 21 screw arrangement of the asymmetric unit.

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In the title compound, C4H9N2O3+·C6H2N3O7, the two ions are connected by strong asymmetric O—H...O hydrogen bonds. The cation is involved in a Z1 (zigzag) head-to-tail sequence along the b axis. The torsion angle χ21 corresponds to a cis conformation. Hydro­phobic layers across z = {1\over 2} are sandwiched between hydro­philic layers across the z = 0 plane.

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The asymmetric unit of the title compound, C6H13NO2·C6H14NO2+·C6H2N3O7-, contains two unprotonated leucine residues, two protonated leucinium cations and two picrate anions. The leucine residues show a class II hydrogen-bonding scheme and the leucinium residues show a class I hydrogen-bonding scheme. The leucine and leucinium residues form infinite hydrogen-bonded chains running along the a axis.

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In the title compound, [Cu6(CH4N2S)14](ClO4)6, the inter­esting feature of the structure lies in the closely packed Cu–thio­urea core, which is a truncated octa­hedron of two planes and four points at the edges. The octa­hedron is truncated parallel to the (101) plane. The Cu–thio­urea core has pseudo-centrosymmetry about the centre of the octa­hedral void. The structure shows inter- and intra­molecular N—H...S hydrogen bonds.

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The title compound, C4H9N2O3+·NO3-, crystallizes with two asparaginium cations and two nitrate anions in the asymmetric unit. In both asparaginium residues, protonation take place at the carboxyl O atom cis to the amine group. Cation I exists in a trans conformation, whereas cation II exhibits a gauche I conformation. A straight head-to-tail sequence is observed for one of the asparaginium cations. The crystal structure is stabilized by inter- and intra­molecular hydrogen bonding.

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The title compound, C6H11N3O22+·SO42−, crystallizes with two cations and two anions in the asymmetric unit. In both diprotonated histidinium cations, the Cγ atom has a gauche-II conformation with respect to the amine N atom and it is in a trans position to the C atom. An extensive three-dimensional network of inter­molecular N—H...O and O—H...O hydrogen bonds links the histidinium cations and sulfate anions, forming a crystal structure in which zigzag (Z1) head-to-tail sequences are observed for both the cations.

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In the title complex, C6H6NO2+·H2PO4-, the nicotinium cations are sandwiched between layers of dihydrogen­phosphate anions. The structure is held together by extensive hydrogen bonding between the O and N atoms of nicotinium cations and the O atoms of the phosphate anions, and between the O atoms of the phosphate anions themselves. The nicotinium cations are packed in layers, with an inter­layer distance of 3.116 (5) Å.

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The title compound, C6H6NO2+·C6H2N3O7-, is the picrate salt of the nicotinium cation. In the picrate anion, the ortho nitro groups are twisted out of the plane of the ring, whereas the para nitro group lies approximately in the ring plane. Hydrogen bonds from the nicotinate cation link two different picrate anions, forming a straight chain along the b axis. The picrate anions are stacked in columns along [010].

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The title compound, 2C6H5NO2·H+·ClO4, consists of [(nicotinic acid)2H]+ cations and ClO4 anions. Two nicotinic acid zwitterions are linked by a strong symmetric O—H...O hydrogen bond, with the H atom on an inversion center and an O...·O distance of 2.464 (4) Å, forming a cation. The nicotinic acid cation forms hydrogen bonds to adjacent cations, giving two-dimensional layers. The Cl atom of the perchlorate anion lies on a twofold axis.

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In the title complex, 2C6H6NO2+·SO42−, the carboxyl groups of the two nicotinium cations (A and B) are twisted from the pyridinium ring, with dihedral angles of 9.1 (5) and 7.0 (9)°, respectively. Packing involves classical O—H...O and N—H...O hydrogen bonds. Cations A are inter­linked through an O atom of the sulfate anion, forming an infinite chain running along the b axis and leading to cationic layers separated by a distance of 3.106 (4) Å. Cations B form an inversion-related closed hydrogen-bonded loop.
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