In the title hydrate, C16H19N3O3·1.5H2O, both water mol­ecules are disordered: one over two adjacent sites in a 0.498 (5):0.502 (5) ratio and one lying near a crystallographic twofold axis. The dihedral angle between the pyridine rings of the organic moleucle is 1.47 (6)°. In the crystal, the components are linked by N—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds, forming sheets lying parallel to the ac plane.

The asymmetric unit of the title compound, C9H7N3O2, is composed of two independent mol­ecules. The crystal structure is stabilized by C—H⋯O and C—H⋯N hydrogen bonds, forming a three-dimensional network. The crystal structure also features pyrazine–pyrazine π–π inter­actions [centroid–centroid distance = 3.6994 (5) Å] and also pyridine–pyrazine π–π inter­actions [centroid–centroid distance = 3.6374 (5) Å].

In the title compound, C18H17N3, the dihedral angles between the central pyrimidine ring and its directly-bonded and N-bonded pendant phenyl rings are 25.48 (6) and 80.33 (6)°, respectively. The dihedral angle between the phenyl rings is 79.66 (6)°. In the crystal, inversion dimers linked by pairs of N—H⋯N hydrogen bonds generate R 2 2(8) loops. The crystal structure also features weak π–π [centroid–centroid separation = 3.6720 (7) Å] and C—H⋯π inter­actions.

In the title compound, C20H21N3, the pyrimidine ring is inclined at dihedral angles of 51.57 (4) and 2.49 (4)° to the two phenyl rings. The dihedral angle between the two terminal phenyl rings is 50.44 (4)°. In the crystal, adjacent mol­ecules are linked via a pair of N—H⋯N hydrogen bonds, forming an inversion dimer with an R 2 2(8) ring motif. Furthermore, the crystal structure is stabilized by a weak π–π inter­action, with a centroid–centroid distance of 3.6065 (5) Å.

In the title salt (systematic name: 6-amino-9H-purin-1-ium perchlorate), C5H6N5 +·ClO4 −, the adeninium cation is essentially planar, with a maximum deviation of 0.038 (1) Å. The whole of the perchlorate anion is disordered over two sets of sites with an occupancy ratio of 0.589 (13):0.411 (13). In the crystal, the adeninium cations are linked by pairs of N—H⋯N hydrogen bond into inversion dimers. The dimers and the anions are further inter­connected into a three-dimensional supra­molecular structure via inter­molecular N—H⋯O, C—H⋯O and C—H⋯N hydrogen bonds.

In the title complex, [CuBr2(C6H4N2Se)2], the CuII ion is tetra­coordinated by two bromide anions and two N atoms in a distorted square-planar geometry. The two essentially planar 2,1,3-benzoselenadiazole ligands [maximum deviations = 0.012 (2) and 0.030 (2) Å] are approximately coplanar [dihedral angle = 6.14 (6)°]. In the crystal, short inter­molecular Se⋯Br, Se⋯N and N⋯N inter­actions are observed. These short inter­actions and inter­molecular C—H⋯Br hydrogen bonds link the complex mol­ecules into two-dimensional arrays parallel to the ac plane.

The title compound, C18H8Cl4N4, exists in a cis configuration with respect to the bridging C=C bond. The two essentially planar quinoxaline ring systems [maximum deviations = 0.012 (1) and 0.022 (1) Å] are inclined at an angle of 59.84 (3). In the crystal, adjacent mol­ecules are linked into chains propagating along [001] via inter­molecular C—H⋯N hydrogen bonds. Weak inter­molecular π–π [centroid–centroid distance = 3.6029 (7)°] and C—H⋯π inter­actions are also observed.

The title acetamide compound, C8H9BrN2O, crystallizes with three crystallographically independent mol­ecules (A, B and C) in the asymmetric unit. In mol­ecule A, the mean plane through the acetamide unit is inclined at a dihedral angle of 4.40 (11)° with respect to the pyridine ring [10.31 (12) and 2.27 (11)°, respectively, for mol­ecules B and C]. In the crystal structure, mol­ecules are inter­connected into sheets parallel to the ac plane by N—H⋯O, C—H⋯Br, C—H⋯O and C—H⋯N hydrogen bonds. The structure is further stabilized by weak inter­molecular C—H⋯π inter­actions.

The title compound, C22H30N4O2, lies about a crystallographic inversion center. The whole mol­ecule is disordered over two positions with a refined occupancy ratio of 0.636 (10):0.364 (10). The pyridine rings are approximately planar, with maximum deviations of 0.033 (10) and 0.063 (17) Å for the major and minor components, respectively. The mean planes of the pyridine rings form dihedral angles of 17 (2)° in the major component and 18 (2)° in the minor component with the respective formamide groups attached to them. In the crystal packing, inter­molecular N—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules into two-dimensional networks parallel to the ab plane.

The asymmetric unit of the title compound, C12H8N2·0.5C2H4N2S2, contains one 1,10-phenanthroline mol­ecule and a half-mol­ecule of dithio­oxamide, which lies across a crystallographic inversion center. The 1,10-phenanthroline unit is not strictly planar, with dihedral angles between the central benzene ring and the pyridine rings of 1.42 (10) and 1.40 (10)°. In the crystal structure, two 1,10-phenanthroline mol­ecules are linked together by one dithio­oxamide via inter­molecular N—H⋯N hydrogen bonds.

In the title compound, C15H19N3, the pyrimidine ring is approximately planar [maximum deviation = 0.007 (1) Å] and forms a dihedral angle of 3.15 (6)° with the benzene ring. In the crystal packing, inter­molecular N—H⋯N hydrogen bonds link pairs of neighbouring mol­ecules into dimers with R 2 2(8) ring motifs. These dimers are stacked along the b axis.

The complete mol­ecule of the title compound, C10H4Cl6N2, is generated by crystallographic twofold symmetry, with two C atoms lying on the rotation axis; the 1,8-naphthyridine ring is almost planar with an r.m.s. deviation of 0.0002 Å. In the crystal structure, the mol­ecules are stacked in an anti­parallel manner along [001]. Short Cl⋯Cl [3.3502 (4)] and Cl⋯N [3.2004 (11)–3.2220 (10) Å] contacts are observed in the crystal structure.

In the title compound, guanidinium chloridotrioxidochrom­ate(VI), (CH6N3)[CrClO3], both the cation and anion are generated by crystallographic mirror symmetry, with one O and one N atom and the Cr, Cl and C atoms lying on the mirror plane. The bond lengths in the guanidinium cation are inter­mediate between normal C—N and C=N bond lengths, indicating significant delocalization in this species. In the crystal structure, inter­molecular N—H⋯Cl inter­actions generate R 2 1(6) ring motifs. These ring motifs are further inter­connected by inter­molecular N—H⋯O hydrogen bonds into infinite chains along [010].

The asymmetric unit of the title compound, C14H6Cl6N2, contains two crystallographically independent mol­ecules, each of which is slightly twisted from planarity. The dihedral angles between the central ring and the two outer rings are 3.81 (7) and 4.30 (7)° in one mol­ecule, and 4.13 (8) and 4.10 (7)° in the other. In the crystal structure, mol­ecules are inter­linked by C—Cl⋯Cl inter­actions into sheets parallel to the ac plane. These sheets are stacked along the b axis in such a way that the mol­ecules are anti­parallel; they are further connected into a supra­molecular network. There are no classical hydrogen bonds. C⋯Cl [3.637 (2) Å], Cl⋯Cl [3.5639 (5)–3.6807 (8) Å] and Cl⋯N [3.3802 (15)–3.4093 (15) Å] short contacts and π–π inter­actions, with centroid–centroid distances in the range 3.5868 (9)–3.7844 (9) Å, are observed.

In the title compound, C9H5N3, the quinoxaline ring is essentially planar, with a maximum deviation of 0.012 (1) Å. Short inter­molecular distances between the centroids of the 2,3-dihydro­pyrazine and benzene rings [3.6490 (5) Å] indicate the existence of π⋯π inter­actions. In the crystal packing, the mol­ecules are linked via two pairs of inter­molecular C—H⋯N inter­actions, forming R 2 2 (8) and R 2 2 (10) ring motifs; these mol­ecules are further linked into a two-dimensional network parallel to (1 0 2) via another C–H⋯N inter­action.

The asymmetric unit of the title compound, C10H10N2, contains one half-mol­ecule with the two shared C atoms lying on a twofold rotation axis. The 1,8-naphthyridine is almost planar with a dihedral angle of 0.42 (3)° between the fused pyridine rings. In the crystal, mol­ecules are linked into infinite chains along the c axis by inter­molecular C—H⋯N hydrogen bonds, generating R 2 2(8) ring motifs. In addition, the crystal structure is further stabilized by C—H⋯π inter­actions.

The asymmetric unit of the title compound, C14H23N5O3·2H2O, contains two crystallographically independent 6-amino-2,5-bis­(pivaloylamino)pyrimidin-4(3H)-one mol­ecules (A and B) with similar geometry and four water mol­ecules. In both independent mol­ecules, one of the amide groups is almost coplanar with the pyrimidine ring [dihedral angle of 12.85 (9) in A and 12.30 (10)° in B], whereas the other amide group is significantly twisted away from it [dihedral angle is 72.18 (7) in A and 71.29 (7)° in B]. In each independent mol­ecule, an intra­molecular N—H⋯O hydrogen bond generates an S(6) ring motif. Mol­ecules A and B are linked into chains along the a axis by N—H⋯O and C—H⋯O hydrogen bonds. Adjacent chains are linked into a two-dimensional network parallel to the ac plane by water mol­ecules via N—H⋯O and O—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C20H17N3, contains two crystallographically independent mol­ecules (A and B). In mol­ecule A, the two benzene rings form dihedral angles of 74.12 (7) and 7.83 (7)° with the pyridine ring, while in mol­ecule B these angles are 77.48 (7) and 21.50 (7)°. The seven-membered heterocyclic ring adopts a boat conformation in both mol­ecules. In the crystal structure, each of the independent mol­ecules forms a centrosymmetric R 2 2(8) dimer linked by paired N—H⋯N hydrogen bonds. The crystal structure is further stabilized by inter­molecular C—H⋯N hydrogen bonds and C—H⋯π inter­actions.

In the mol­ecular structure of the title compound, C11H14Br2N2O, the dimethyl­propionamide substituent is twisted slightly with respect to the pyridine ring, the inter­planar angle being 12.3 (2)°. The dibromo­methyl group is orientated in such a way that the two Br atoms are tilted away from the pyridine ring. In the crystal structure, mol­ecules are associated into supra­molecular chains by weak C—H⋯O inter­actions. The crystal is further stabilized by weak N—H⋯Br and C—H⋯N inter­actions.

The title compound, C20H14N2, comprises two crystallographically independent centrosymmetric mol­ecules (A and B) with different conformations due to the disorder of molecule B. The whole of mol­ecule B is disordered over two sets of positions, corresponding to a 180° rotation of the molecule, with a site-occupancy ratio of 0.780 (6):0.220 (6). The minor component of the disordered part in B has the same configuration as mol­ecule A, but the major component is different. The dihedral angle between the planes of mol­ecule A and mol­ecule B (major component) is 63.22 (3)°. The crystal structure is stabilized by inter­molecular C—H⋯π inter­actions.

The nitro group in the title compound, C10H11NO2S2, is almost coplanar with the benzene ring, making a dihedral angle of 3.42 (8)°. The 1,3-dithiane ring adopts a chair conformation. The crystal structure is stabilized by inter­molecular C—H⋯O and C—H⋯π [C⋯Cg = 3.4972 (10) Å] inter­actions.

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 title compound, C13H15NO2S2, the nitro group is coplanar with the benzene ring to which it is attached, forming a dihedral angle of 1.07 (14)°. The dithiane ring adopts a chair conformation. In the crystal structure, mol­ecules are linked through C—H⋯O and C—H⋯π [C⋯Cg = 3.7164 (15) Å] inter­actions. The crystal studied was an inversion twin with an 0.134 (5):0.866 (5) domain ratio.

The asymmetric unit of the title compound, C9H14OS4, comprises two crystallographically independent mol­ecules with similar conformations. In each mol­ecule, an intra­molecular C—H⋯O hydrogen bond generates a six-membered ring, producing an S(6) ring motif. All of the six-membered dithia­cyclo­hexane rings adopt chair conformations. The crystal structure is stabilized by four inter­molecular C—H⋯O and one C—H⋯S inter­action.

In the title compound, C6H6Cl2N2, intra­molecular N–H⋯Cl and C—H⋯Cl contacts generate five-membered rings, producing S(5) ring motifs. Pairs of inter­molecular N—H⋯N hydrogen bonds link neighbouring mol­ecules into dimers with R 2 2(8) ring motifs. In the crystal structure, these dimers are connected by N—H⋯Cl inter­actions and are packed into columns.