In the title isoniazid derivative, C13H11N3O4·2H2O, the Schiff base mol­ecule exists in an E configuration with respect to the acyclic C=N bond. An intra­molecular O—H⋯N hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The essentially planar pyridine ring [maximum deviation = 0.0119 (8) Å] is inclined at a dihedral angle of 7.30 (4)° with respect to the benzene ring. In the crystal, inter­molecular O—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules into two-dimensional arrays lying parallel to the (10) plane. These arrays are further inter­connected into a three-dimensional extended network via O—H⋯O and C—H⋯O hydrogen bonds. A weak inter­molecular π–π inter­action [centroid-to-centroid distance = 3.5627 (5) Å] is also observed.

The asymmetric unit of the title compound, 2C15H9F6N3O·H2O, contains two independent Schiff base mol­ecules and one water mol­ecule. Both Schiff base mol­ecules exist in an E configuration with respect to the C=N double bonds and the dihedral angles between the benzene and the pyridine rings in the two mol­ecules are 17.53 (12) and 20.62 (12)°. In the crystal structure, mol­ecules are linked by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds into infinite one-dimensional chains along the a axis. In addition, inter­molecular O—H⋯N, O—H⋯F, C—H⋯F and C—H⋯O hydrogen bonds further link these chains into a three-dimensional network. Weak π–π inter­actions with centroid–centroid distances in the range 3.6495 (17)–3.7092 (16) Å are also observed.

The asymmetric unit of the title Schiff base compound, C12H15N3O, contains two crystallographically independent mol­ecules, with both existing in an E configuration with respect to the C=N double bonds. In the crystal structure, inter­molecular N—H⋯N and C—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional network.

The title isoniazid derivative, C16H17N3O, exists in an E configuration with respect to the Schiff base C=N bond. The pyridine ring is essentially planar [maximum deviation = 0.009 (3) Å]. The mean plane through the hydrazide unit forms dihedral angles of 38.38 (16) and 39.42 (16)°, respectively, with the pyridine and benzene rings. In the crystal structure, symmetry-related mol­ecules are linked via inter­molecular N—H⋯O hydrogen bonds into chains along [100]. The crystal structure is further stabilized by weak inter­molecular C—H⋯π inter­actions.

The title compound, C20H17N3O2·CH4O·H2O, was synthesized by the condensation reaction of 2-benzyl­oxybenzaldehyde with isoniazid (isonicotinic acid hydrazide). The tricyclic compound displays a trans configuration with respect to the C=N double bond. The central benzene ring makes dihedral angles of 8.83 (7) and 70.39 (8)° with the pyridine ring and the terminal benzene ring, respectively. The dihedral angle between the pyridine ring and the terminal benzene ring is 73.11 (8)°. In the crystal structure, mol­ecules are connected by inter­molecular N—H⋯O, O—H⋯O, O—H⋯(N,N) and C—H⋯O hydrogen bonds, forming a two-dimensional network perpendicular to the a axis.

The asymmetric unit of the title compound, C16H17N3O4·2H2O, contains one Schiff base mol­ecule and two water mol­ecules. The Schiff base mol­ecule exists in an E configuration with respect to the C=N double bond and is essentially planar, the dihedral angle between the benzene and pyridine rings being 5.48 (8)°. The three meth­oxy groups are also coplanar with the benzene ring [C—O—C—C torsion angles = 3.9 (2), 178.51 (15) and 0.8 (2) Å]. In the crystal structure, the water mol­ecules link the mol­ecules into a three-dimensional network via inter­molecular N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds.

In the title compound, C16H17N3O4, the mol­ecule exists in an E configuration with respect to the C=N double bond. The mol­ecule is not planar, the dihedral angle between the pyridine and benzene rings being 71.67 (8)°. In the crystal structure, mol­ecules are linked into chains along the b axis by bifurcated N—H⋯O and C—H⋯O hydrogen bonds. These chains are linked into a three-dimensional network by C—H⋯O and C—H⋯π inter­actions.

In the title compound, C13H11N3O4·1.5H2O, the pyridine ring forms a dihedral angle of 1.50 (6)° with the benzene ring. An intra­molecular O—H⋯N hydrogen bond forms a six-membered ring with an S(6) ring motif. In the crystal structure, one water mol­ecule is disordered over two positions around an inversion centre with site-occupancy factors of 0.5. Inter­molecular O—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds consolidate the structure into a three dimensional network. A π–π stacking inter­action with a centroid–centroid distance of 3.5949 (7) Å is also present.

In the Schiff base mol­ecule of the title compound, C13H8F3N3O·H2O, the benzene ring and the pyridine ring are nearly coplanar, making a dihedral angle of 6.64 (7)°. The mol­ecule exists in an E configuration with respect to the C=N double bond. In the crystal structure, mol­ecules are linked via the water mol­ecules into two-dimensional planes parallel to the ab plane through inter­molecular N—H⋯O, O—H⋯O O—H⋯N and C—H⋯O hydrogen bonds.

In the title compound, C16H15N3O3, the dihedral angle between the pyridine and benzene rings is 7.66 (5)°. The crystal packing is consolidated by inter­molecular C—H⋯O and O—H⋯N inter­actions, which link the mol­ecules into zigzag chains propagating along [010]. The chains are further linked into a three-dimensional network by N—H⋯O, C—H⋯N, C—H⋯O and C—H⋯π inter­actions.

In the title compound, C21H19N3O3, the pyridine ring forms a dihedral angle of 15.25 (6)° with the benzene ring. The dihedral angle between the two benzene rings is 83.66 (7)°. The meth­oxy group is slightly twisted away from the attached ring [C—O—C—C = 7.5 (2)°]. In the crystal structure, mol­ecules are linked into a three-dimensional network by inter­molecular N—H⋯N and C—H⋯O hydrogen bonds. The structure is further stabilized by C—H⋯π inter­actions.

In the title compound, C12H11N3O2S, the pyridine ring is inclined to the thio­phene ring, forming a dihedral angle of 34.96 (7)°. The mean plane through the hydrazide unit forms dihedral angles of 21.57 (8) and 53.08 (8)°, respectively, with the pyridine and thio­phene rings. The two O atoms are twisted away from each other, as indicated by the C—N—N—C torsion angle of −81.27 (15)°. In the crystal structure, mol­ecules are linked into an extended three-dimensional network by inter­molecular N—H⋯N, N—H⋯O and C—H⋯O hydrogen bonds. The crystal structure also features a short S⋯O [3.2686 (10) Å] inter­action and a weak inter­molecular C—H⋯π inter­action.

In the title compound, C13H17N3O2, the mean plane of the cyclo­hexane ring forms a dihedral angle of 33.12 (5)° with the pyridine ring. The two O atoms are twisted away from each other, as indicated by the C—N—N—C torsion angle of −74.97 (9)°. In the crystal structure, mol­ecules are linked into a three-dimensional network by inter­molecular N—H⋯N, N—H⋯O and C—H⋯O hydrogen bonds. The structure is also stabilized by C—H⋯π inter­actions.