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In the title compound, [Ag(BF(4))(C(14)H(12)N(2)O(4))](n), the coordination of the Ag(+) ion is trigonal-bipyramidal with the N atoms of two ethane-1,2-diyl bis-(pyridine-3-carboxyl-ate) ligands in the apical positions and three F atoms belonging to different tetra-fluorido-borate anions in the equatorial plane. The material consists of infinite chains of [Ag(C(14)H(12)N(2)O(4))] units running along [001], held together by BF(4) (-) bridging anions.

The title compound, [Cu(C(5)H(3)N(2)O(2))(0.88)(C(6)H(4)NO(2))(1.12)](n), is characterized by disorder of the anion, resulting from a statistical occupation in a 0.44 (3):0.56 (3) ratio of pyrazine-2-carboxylate and pyridine-2-carboxylate. The compound was isolated during attempts to synthesize a mixed-ligand coordination polymer by solvothermal reaction between copper(II) nitrate and equimolar mixtures of pyrazine-2-carboxylic acid and pyridine-2-carb-oxy-lic acid in a mixture of water and EtOH. The difference in the two components of the compound is due to substitutional disorder of a CH group for one of the N atoms of the pyrazine ring which share the same site in the structure. In the crystal structure, the Cu(II) atom lies on an inversion centre and is six-coordinated in a distorted N(2)O(4) geometry. The carboxyl-ate group carbonyl O atoms are weakly coordinated to an equivalent Cu(II) atom that is translated one unit cell in the a-axis direction, thus forming a polymeric chain through carboxyl-ate bridges.

The title compound, C(16)H(14)O(5)·2H(2)O [systematic name: 5-hy-droxy-2-(4-hy-droxy-phen-yl)-7-meth-oxy-chroman-4-one dihydrate], is a natural phytoalexin flavone isolated from the native chilean species Heliotropium taltalense and crystallizes with an organic mol-ecule and two water mol-ecules in the asymmetric unit. The 5-hy-droxy group forms a strong intra-molecular hydrogen bond with the carbonyl group, resulting in a six-membered ring. In the crystal, the components are linked by O-H⋯O hydrogen bonds, forming a three-dimensional network. The 4-hy-droxy-phenyl benzene ring is bonded equatorially to the pyrone ring, which adopts a slightly distorted sofa conformation. The title compound is the hydrated form of a previously reported structure [Shoja (1990 ▶). Acta Cryst. C46, 1969-1971]. There are only slight variations in the mol-ecular geometry between the two compounds.

The structure of the title compound, (C(15)H(15)N(2)O(4))[AgI(2)], consists of an organic 4-[3-(isonicotino-yloxy)propoxycarbon-yl]pyridinium cation which has a gauche-gauche (O/C/C/C-O/C/C/C or GG') conformation and lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, and an inorganic [AgI(2)](-) anion. In the complex anion, the Ag(+) cation is bound to two I(-) anions in a linear geometry. The anion was modelled assuming disorder around a crystallographic inversion centre near the location of the Ag(+) cation. The crystal packing is stabilized by a strong inter-molecular N-H⋯N hydrogen bond, which links the cations into zigzag chains with graph-set notation C(16) running along the face diagonal of the ac plane. The N-bound H atom is disordered over two equally occupied symmetry-equivalent sites, so that the mol-ecule has a pyridinium ring at one end and a pyridine ring at the other.

In the title compound, [Cd(C(6)H(5)N(2)O(2))(2)(H(2)O)(2)], the Cd(II) ion is coordinated in a severely distorted octa-hedral geometry. The N atoms are cis to each other, while the water O atoms and ligand O atoms are mutually trans. The crystal structure is stabilized by a network of O-H⋯O, O-H⋯N and C-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distances = 3.730 (3) and 3.652 (3) Å] between the 5-methyl-pyrazine-2-carboxyl-ate ligands. The structure is isotypic with the manganese analog.

The asymmetric unit of the title compound, C(3)H(12)N(2) (2+)·2C(6)H(4)NO(2) (-)·H(2)O, consists of half of a doubly protonated propane-1,3-diammonium dication, a pyridine-4-carboxyl-ate anion and half of a solvent water mol-ecule; the dication and the solvent water are located on a twofold rotation axis which passes through the central C atom of the dication and the water O atom. The carboxyl-ate group of the anion appears to be delocalized on the basis of the C-O bond lengths. In the crystal, the components are linked by inter-molecular N-H⋯O, N-H⋯N and O-H⋯O hydrogen bonds.

In the title compound, C(15)H(14)N(2)O(4), (I), the mol-ecule lies on a twofold rotation axis which passes through the central C atom of the aliphatic chain, giving one half-mol-ecule per asymmetric unit. The structure is a monoclinic polymorph of the triclinic structure previously reported [Brito, Vallejos, Bolte & López-Rodríguez (2010). Acta Cryst. E66, o792], (II). The most obvious difference between them is the O/C/C/C-O/C/C/C torsion angle [58.2 (7)° in (I) and 173.4 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively]. Another important difference is observed in the dihedral angle between the planes of the aromatic rings [86.49 (7)° for (I) and 76.4 (3)° for (II)]. The crystal structure features a weak π-π inter-action [centroid-centroid distance = 4.1397 (10)Å]; this latter kind of inter-action is not evident in the triclinic polymorph.

The title compound, C(28)H(24)N(4)O(4)·H(2)O, crystallizes with two organic mol-ecules and two solvent water mol-ecules in the asymmetric unit. The most obvious difference between the mol-ecules is the torsion angles between the isoxazole ring and the benzene and phenyl rings [47.0 (2)/56.4 (2) and 33.3 (2)/11.0 (2)°, respectively]. Another important difference is observed in the rotation of the nitro group with respect to the phenyl groups [3.5 (6) and 31.1 (6)°]. The pyrrolidinone fragment is cis oriented with respect to the 4-nitro-phenyl fragment. In the crystal, mol-ecules are linked into centrosymmetric R(4) (2)(8) and R(4) (4)(20) motifs by O-H⋯O and N-H⋯O inter-actions.

The title compound. C(15)H(14)N(2)O(4), (I), has a gauche-gauche (O/C/C/C-O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis-(pyridine-3-carboxyl-ate), (II). The mol-ecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-mol-ecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C-O/C/C/C torsion angles [56.6 (2)° in (I) and 174.0 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3 (10)° in (I) and 76.5 (3)° in (II)]. The crystal structure is stabilized by weak C-H⋯ N and C-H⋯ O hydrogen bonding.

The title compound, C(14)H(12)N(2)O(4), has twofold imposed crystallographic symmetry in the solid state. The asymmetric unit contains one half-mol-ecule. An intra-molecular C-H⋯O hydrogen bond is formed between the carboxyl-ate O group and one H atom of the aromatic ring such that a five-membered ring is formed. The angle between the planes of symmetry-related aromatic rings is 44.71 (19)°.

The title compound, C(15)H(22)O(4), consists of two trans-fused six-membered rings and a trans-fused five-membered γ-lactone. The ep-oxy and hydroxyl groups are α-oriented. The cyclo-hexane rings adopt half-chair and chair conformations and the lactone ring is in an envelope conformation. The mol-ecular structure is stabilized by one O-H⋯O and three C-H⋯O intra-molecular hydrogen bonds.

In the title compound, C(16)H(17)NO(2), the isoxazole ring makes a dihedral angle of 14.81 (13)° with the 4-methoxy-phenyl ring. Two atoms of the cyclo-hexene ring are disordered over two almost equally occupied positions [0.526 (13)/0.474 (13)]. The mol-ecular structure features a short intra-molecular C-H⋯O contact.

The mol-ecule of the title compound, C(20)H(32)O(4), is built up from three fused five-membered, six-membered and seven-membered rings. The five-membered ring has an envelope conformation, whereas the six- and seven-membered rings have chair conformations. The crystal structure is stabilized by strong inter-molecular O-H⋯O hydrogen bonds, forming a three-dimensional network. The absolute configuration was assigned on the basis of earlier chemical studies.

The mol-ecule of the title compound, C(23)H(34)O(6), is built up from three fused carbocycles, one five-membered, one six-membered and one seven-membered. The five-membered ring has an envelope conformation, whereas the six-membered ring has a perfect chair conformation and the seven-membered ring has a boat conformation. Intra-molecular C-H⋯O hydrogen bonds together with van der Waals inter-actions stabilize the mol-ecular conformation.

In the title disulfide, C(12)H(8)N(6)O(2)S(2), all bond lengths and angles are within normal ranges, and the molecules are linked into centrosymmetric R(2)(2)(20) dimers by simple C-H...N interactions. Weak intermolecular C-H...pi(arene) and pi-pi interactions, involving the benzene CH groups and the benzene rings, and the pyridine rings, respectively, further stabilize and reinforce the crystal structure.

The structure of title compound, C6H16N+.C14H8N3O7S-, comprises discrete ions which are interconnected by N-H...O- and N-H+...O- hydrogen bonds, leading to a neutral one-dimensional network along [100]. These hydrogen bonds appear to complement the Coulombic interaction and help to stabilize the structure further.

The title compound, C27H19NO2S, contains chains of fused R(2)(2) (19) rings formed by intermolecular C-H...O=C hydrogen bonds and running along the [011] and [0-11] directions. These chains are linked through short intermolecular C-H...pi contacts, giving rise to sheets. The conformation of the title compound is dominated primarily by the nearly orthogonal lone-pair orbitals on the N and S atoms.