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In the crystal structure of the title compound, C4H5N2 +·C6HCl2O4 −, there are three crystallographically independent 1,2-diazinium cations and hydrogen chloranilate anions. The anions are held together by pairs of O—H⋯O hydrogen bonds to form two types of dimers, one of which is centrosymmetric. The 1,2-diazinium cations are linked on both sides of each dimer via bifurcated N—H⋯O hydrogen bonds to give two kinds of 2–2 cation–anion associations. The 2–2 associations are linked by inter­molecular C—H⋯O and C—H⋯N hydrogen bonds, forming a mol­ecular tape along the [230] direction. The tapes are further connected by C—H⋯O hydrogen bonds, forming a three-dimensional network.

The asymmetric unit of the title compound, C5H6N3O2 +·ClO4 −·2C5H5N3O2·H2O, comprises two symmetry-independent zwitterions, one cation, one perchlorate anion and one water mol­ecule. In the crystal, the three different types of organic entities are linked by N—H⋯O and N—H⋯N hydrogen bonds, forming undulating sheets parallel to (1-10). These sheets are in turn connected by O—H⋯N and O—H⋯O hydrogen bonds involving perchlorate anions and water mol­ecules, forming a three-dimensional network. Intra­molecular N—H⋯O and weak inter­molecular C—H⋯O hydrogen bonds are also present.

In the title hydrated salt, C16H12Cl2N3 +·Cl−·H2O, there is a small twist in the cation as seen in the torsion angle linking the benzene ring to the rest of the mol­ecule [171.96 (17)°]. In the crystal, the quinolinium H atom forms a hydrogen bond to the lattice water mol­ecule, which also forms hydrogen bonds to two Cl− anions. Each Cl− ion also accepts a hydrogen bond from the hydrazine H atom. The three-dimensional architecture is also stabilized by π–π inter­actions between centrosymmetrically related quinoline residues [centroid–centroid distance = 3.5574 (11) Å].

In the title compound, C4H6N3 +·C6HCl2O4 −·H2O, anions, cations and water mol­ecules are linked by inter­molecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds into one-dimensional tapes along [111]. These tapes are further linked by weak Cl⋯Cl inter­actions [Cl⋯Cl = 3.394 (2) Å], forming sheets parallel to the (10) plane.

The asymmetric unit of the title compound, (C4H5N2O)2[Cu2Cl6(C4H4N2O)2]·2H2O, consists of one cation, one half of a centrosymmetric dianion and one water mol­ecule. The centrosymmetric dianion formed by dimerization in the crystal structure has neutral pyrimidin-2-one ligands coordinated to each copper(II) centre through Cu—N bonds. The Cu atoms each have a distorted trigonal bipyramidal geometry, with the N atom of the pyrimidin-2-one ligand in an axial position, and dimerize by sharing two equatorial Cl atoms. N—H⋯Cl, O—H⋯Cl and N—H⋯O hydrogen bonds connect the anions, cations and water mol­ecules, forming a three-dimensional network.

The title compound, (C4H7N4O)2[Bi2Cl9(C4H7N4O)]·H2O, was prepared by the reaction of bis­muth trichloride and 5-amino-1H-imidazole-4-carboxamide in a dilute HCl medium. The asymmetric unit contains two 5-amino-4-amino­carbonyl-1H-imidazol-3-ium cations, one edge-shared non-centrosymmetric biocta­hedral [Bi2C19(C4H7N4O)]2− dianion and a water mol­ecule. In the dianion, the planar 5-amino-4-amino­carbonyl-1H-imidazol-3-ium ligand occupies an equatorial site and is inclined at an angle of 75.7 (2)° to the Bi2(μ-C1)2 plane. The salt forms a three-dimensional network arising from hydrogen bonds between cations, anions and water mol­ecules.

In the crystal structure of the title compound (systematic name: triethyl­ammonium 2,5-dichloro-4-hy­droxy-3,6-dioxo­cyclo­hexa-1,4-dien-1-olate), C6H16N+·C6HCl2O4 −, two hydrogen chloranilate anions are connected by a pair of bifurcated O—H⋯O hydrogen bonds into a dimeric unit. The triethyl­ammonium cations are linked on both sides of the dimer via bifurcated N—H⋯O hydrogen bonds into a centrosymmetric 2:2 aggregate. The 2:2 aggregates are further linked by inter­molecular C—H⋯O hydrogen bonds.

In the crystal structure of the title compound, C4H10NO+·C6HCl2O4 −·CH4O, the components are held together by bifurcated O—H⋯(O,O), O—H⋯(O,Cl) and N—H⋯(O,O) hydrogen bonds into a centrosymmetric 2+2+2 aggregate. The aggregates are further connected by another bifurcated N—H⋯(O, O) hydrogen bond, forming a double-tape structure along the b axis. A weak C—H⋯O inter­action is observed between the tapes.

In the title salt hydrate, C5H6NO+·C6HCl2O4 −·H2O, the three components are held together by O—H⋯O and N—H⋯O hydrogen bonds, as well as by C—H⋯O contacts, forming a double-tape structure along the c axis. Within each tape, the pyridinium ring and the chloranilate ring are almost coplanar, forming a dihedral angle of 2.35 (7)°.

In the title mol­ecular salt, C8H13N2O+·C7H3N2O7 −·H2O, the pyrimidinium cation is essentially planar, with a maximum deviation of 0.009 (1) Å. The cation undergoes an enol–keto tautomerism during the crystallization. In the crystal, the ion pairs and water mol­ecules are connected via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming two-dimensional networks parallel to the bc plane. There is an intra­molecular O—H⋯O hydrogen bond in the 3,5-dinitro­salicylate anion, which generates an S(6) ring motif.

In the title compound, alternatively called xylazine hydro­chloride monohydrate, C12H17N2S+·Cl−·H2O, the six-membered thia­zine ring is in a half-chair conformation. In the crystal structure, six component centrosymmetric clusters are formed via inter­molecular O—H⋯Cl, N—H⋯O and N—H⋯Cl hydrogen bonds involving xylazine cations, chloride anions and water mol­ecules.

In the crystal structure of the title compound, C4H7N4O+·Cl−·2H2O, adjacent cations are connected to one another through N—H⋯O hydrogen bonds, forming infinite chains along the b axis. These chains are further hydrogen bonded to the chloride anions and water mol­ecules, resulting in a three-dimensional network. The pyrimidine rings of adjacent mol­ecules are arranged in an anti­parallel manner above each other with centroid–centroid distances of 3.435 (1) Å, indicative of π–π inter­actions.

In the title structure, C7H9N3O2·H2O, there are two formula units in the asymmetric unit. The mol­ecule is a zwitterion, containing a quaternary N atom and a deprotonated carboxyl group, with C—O distances in the range 1.256 (2)–1.266 (3) Å. The two independent mol­ecules form a hydrogen-bonded R 2 2(16) dimer about an approximate inversion center via N—H⋯O hydrogen bonds, with N⋯O distances of 2.766 (2) and 2.888 (2) Å. O—H⋯O hydro­gen bonds involving the water mol­ecules and additional N—H⋯O hydrogen bonds link these dimers, forming double chains.

The asymmetric unit of the title compound, 2C9H12N3 +·2Cl−·H2O, comprises two mol­ecules, two chloride anions and one mol­ecule of crystal water. In the imidazolinium ring, the protonation contributes to delocalization of the positive charge over the two C—N bonds. Both chloride anions are acceptors of four hydrogen bonds in a flattened tetra­hedron environment. The donors are NH2 groups, the NH groups of the imidazolinium rings and the water mol­ecule. These hydrogen bonds and N—H⋯O(H2O) hydrogen bonds form a three-dimensional network.

In the title compound, 2C3H5N4O2 +·H2PO4 −·NO3 −·C3H4N4O2, three independent 5-amino-1H-1,2,4-triazol-3-carb­oxy­lic acid moieties are observed. Two are in the form of cations, while the third is in the zwitterionic form. The triazole rings in the two cations are almost coplanar, making an angle of 4.11 (7)°. Layers parallel to the (20-1) plane, resulting from hydrogen bonding of the organic mol­ecules and the nitrate anions, are linked via H2PO4 − infinite zigzag chains running parallel to the c axis. The crystal studied was an inversion twin, with refined components of 0.33 (7) and 0.67 (7).

The organic mol­ecule in the title monohydrate, C6N6O5·H2O, presents an almost planar configuration, the greatest deviation from the least-squares plane through the atoms being 0.061 (1) Å for the O atom within the seven-membered ring. Each water H atom is bifurcated, one forming two O—H⋯N hydrogen bonds and the other forming O—H⋯N,O hydrogen bonds. The result of the hydrogen bonding is the formation of supra­molecular layers with a zigzag topology that stack along [001].

The two-dimensional crystal packing of the title compound, C3H5N4O2 +·NO2 −·H2O, results from the stacking of well separated layers (i.e. with nothing between the layers) parallel to the (-113) plane in which adjacent cations adopt a head-to-head arrangement such that two –COOH groups are linked via two water mol­ecules (the water O atom behaves simultaneously as donor and acceptor of hydrogen bonds) and two –NH2 groups are linked through two nitrate anions. This arrangement leads to alternating hydro­philic and hydro­phobic zones in which O—H⋯O and N—H⋯O hydrogen bonds, respectively, are observed.

The asymmetric unit of the triclinic polymorph of the title compound (systematic name: 4-cyano­pyridinium 2,5-dichloro-4-hy­droxy-3,6-dioxocyclo­hexa-1,4-dien-1-olate), C6H5N2 +·C6HCl2O4 −, consists of two crystallographically independent cation–anion units, in each of which the cation and the anion are linked by an N—H⋯O hydrogen bond. In the units, the dihedral angles between the cation and anion rings are 78.43 (11) and 80.71 (11)°. In the crystal, each unit independently forms a chain through N—H⋯O and O—H⋯N hydrogen bonds; one chain runs along the c axis while the other runs along [011]. Weak C—H⋯O, C—H⋯N and C—H⋯Cl inter­actions are observed between the chains.

In the title compound, C8H10N2O4·H2O, the imidazole N atom is protonated and one of the carboxyl­ate groups is deprotoned, forming a zwitterion. An intra­molecular O—H⋯O hydrogen bond occurs. The crystal structure is stabilized by inter­molecular N—H⋯O and O—H⋯O hydrogen bonds. In addition, inter­molecular N—H⋯O and O—H⋯O hydrogen bonds link the mol­ecules into two-dimensional networks parallel to (10).

In the crystal structure of the title compound, C6H4N2·C6H2Cl2O4, two chloranilic acid (systematic name: 2,5-dichloro-3,6-dihydr­oxy-1,4-benzoquinone) mol­ecules are connected by O—H⋯O hydrogen bonds to form a dimeric unit. The pyridine-4-carbonitrile mol­ecules are linked on both sides of the dimer via N⋯H⋯O hydrogen bonds to give a centrosymmetric 2:2 complex of pyridine-4-carbonitrile and chloranilic acid. The H atom in the N⋯H⋯O hydrogen bond is disordered over two positions with approximately equal occupancies. The pyridine ring makes a dihedral angle of 61.54 (14)° with the chloranilic acid plane. The 2:2 units are further linked by inter­molecular C—H⋯O and C—H⋯Cl hydrogen bonds. This determination presents a siginficantly higher precision crystal structure than the previously published structure [Tomura & Yamasshita (2008 ▶). X-ray Struct. Anal. Online, 24, x31–x32].

The asymmetric unit of the title compound, C14H18N3O+·Cl−·H2O, comprises a substituted amido–naphthyridine cation, a chloride anion and a water mol­ecule of crystallization. Intra­molecular C—H⋯O hydrogen bonds generate six-membered rings, producing an S(6) ring motif. The amido group is twisted from the naphthyridine ring, making a dihedral angle of 17.65 (7)°. The crystal structure is stabilized by inter­molecular N—H⋯O, N—H⋯Cl, O—H⋯Cl (× 2), and C—H⋯O (× 2) hydrogen bonds. These inter­actions linked neighbouring mol­ecules into chains along the a and b axes of the crystal, thus forming mol­ecular sheets parallel to the (001) plane.

In the crystal of the title compound, C16H17N2 +·NO3 −·H2O, the tetra­methyl-1,10-phenanthrolinium cations, nitrate anions and lattice water mol­ecules are all located on a mirror plane with the methyl H atoms of the cation equally disordered over two sites about the mirror plane. The cation, anion and water mol­ecule are linked by O—H⋯O and N—H⋯O hydrogen bonds into a sheet parallel to the bc plane. π–π stacking between phenanthroline ring systems is observed in the crystal structure, the centroid–centroid distance being 3.4745 (6) Å.

In the title compound, C5H9N2 +·0.5C2O4 2−·C2H2O4·H2O, the anions, cations and water mol­eculars are linked by N—H⋯O and O—H⋯O hydrogen bonds which define a tightly bound three-dimensional structure. The title compound is a layered structure as viewed along the a or c axis; one layer contains water and oxalic acid mol­ecules, the other the imidazolium cation. The C atoms of the ethyl group of the 2-ethyl­imidazolium cation are disordered over two positions of equal occupancy.

The title compound, (C4H5N2O)5[Cd3Cl11], was obtained from the reaction of 2-hydroxy­pyrimidine hydro­chloride and cadmium(II) chloride in concentrated HCl solution. The crystal structure consists of planar 2-oxo-1,2-dihydro­pyrimidin-3-ium cations with both N atoms protonated and the O atom unprotonated, and a complex trinuclear [Cd3Cl11]5− anion of approximately D 3h symmetry, which has a triangle of three octa­hedrally coordinated CdII centres bonded to 11 chloride ions. Three of the chloride ions bridge adjacent Cd atoms, two cap the faces of the Cd3 triangle and the remaining six are terminally bonded and act as hydrogen-bond acceptors. Various N—H⋯Cl hydrogen bonds connect the anions and cations and, in addition, inter­molecular N—H⋯O hydrogen bonds contribute to the formation of a three-dimensional network.

In the title crystal structure, C13H9N4 +·ClO4 −·H2O, cations, anions and water mol­ecules are linked through inter­molecular N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds, forming layers parallel to (001). In addition, there are weak π–π stacking inter­actions between the layers, involving the cations and with centroid–centroid distances in the range 3.584 (2)–3.662 (2) Å, forming a three-dimensional network.