In the title compound, C14H13N3O2·2H2O, the hydrazone mol­ecule adopts an E conformation with respect to the C=N bond. The dihedral angle between the benzene and pyridine rings is 8.55 (10)°. The methyl­idene–hydrazide [–C(=O)–N–N=C–] fragment is essentially planar, with a maximum deviation of 0.0375 (13) Å. The mean planes of the benzene and pyridine rings make dihedral angles of 2.71 (14) and 11.25 (13)°, respectively, with mean plane of the methyl­idene-hydrazide fragment. In the crystal, the benzohydrazide and water mol­ecules are linked by N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds into a three-dimensional network.

In the title hydrated compound, C15H15N3O3·H2O, the nicotinohydrazide mol­ecule adopts a trans conformation with respect to the C=N double bond. The dihedral angle between the benzene and pyridine rings is 5.10 (14)°. In the crystal, the solvent water mol­ecule acts as an acceptor, forming an N—H⋯O hydrogen bond supported by two C—H⋯O contacts. It also acts as a donor, forming bifurcated O—H⋯(O,O) and O—H⋯N hydrogen bonds that combine with the former contacts to form zigzag chains of mol­ecules along the c-axis direction. An additional O—H⋯O donor contact completes a set of six hydrogen bonds to and from the water mol­ecule and connects it to a third nicotinohydrazide mol­ecule. This latter contact combines with weaker C—H⋯O hydrogen bonds supported by a C—H⋯π contact to stack mol­ecules along b in a three-dimensional network.

In the title compound, C17H22N2O6, the di­hydro­pyrimidine ring adopts a flattened boat conformation. The dihedral angle between the benzene ring and the mean plane of the di­hydro­pyrimidine ring is 75.25 (6)°. In the crystal, mol­ecules are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif which are linked through N—H⋯O and weak C—H⋯O hydrogen bonds. These, together with π–π ring inter­actions [centroid–centroid distance = 3.7965 (10) Å], give an overall three-dimensional structure.

Key indicators: single-crystal X-ray study; T = 293 K; mean (C-C) = 0.004 Å; R factor = 0.033; wR factor = 0.075; data-to-parameter ratio = 16.6.In the title compound, C 19 H 13 Br 2 NO, the dihedral angle between the rings of the biphenyl group is 53.59 (14) . The ring of the benzamide group is inclined to the phenyl rings of the biphenyl group by 23.87 (15) and 75.89 (15) . There are no significant intermolecular interactions in the crystal structure. Related literature

The title compound, C12H7Br2NO2, a biphenyl derivative, displays a twisted conformation with the two benzene rings making a dihedral angle of 55.34 (14)°. The dihedral angle between the nitro group and its parent benzene ring is 26.8 (2)°. The crystal structure is stabilized by inter­molecular C—H⋯Br and C—H⋯O inter­actions, which lead to the formation of chains propagating along the c-axis direction.