N,N'-(Pyridine-2,6-di-yl)dibenzamide.

The mol-ecule of the title compound, C19H15N3O2, is completed by the application of crystallographic twofold symmetry, with the pyridine N atom lying on the rotation axis. The mol-ecular structure is approximately planar, the dihedral angle between the mean planes of the pyridine and benzene rings being 7.53 (11)°.

(E)-4-Hy-droxy-N'-(2-hy-droxy-5-iodo-benzyl-idene)benzohydrazide methanol monosolvate.

In the title compound, C(14)H(11)IN(2)O(3)·CH(4)O, the dihedral angle between the benzene rings is 33.2 (3)°. The mol-ecule displays trans and anti conformations about the C=N and N-N bonds, respectively.

N'-[(E)-2-Hy-droxy-5-iodo-benzyl-idene]furan-2-carbohydrazide monohydrate.

The organic mol-ecule of the title monohydrate, C(12)H(9)IN(2)O(3)·H(2)O, features a disordered furyl ring with the major component [site occupancy = 0.575 (18)] having the carbonyl O and furyl O atoms syn, and the other conformation having these atoms anti. The mol-ecule is slightly twisted with the dihedral angle between the benzene and furyl rings being 10.

N'-[(2Z)-4-Oxo-4-phenyl-but-2-en-2-yl]pyridine-4-carbohydrazide.

There are significant twists in the title compound, C(16)H(15)N(3)O(2), as seen in the dihedral angle between the benzene and adjacent but-2-enal group [29.26 (4)°] and between the pyridine ring and amide group [24.79 (6)°].

2-[((E)-2-{2-[(E)-2-Hy-droxy-benzyl-idene]hydrazinecarbon-yl}hydrazinyl-idene)meth-yl]phenol.

The mol-ecule of the title compound, C(15)H(14)N(4)O(3), is completed by the application of crystallographic twofold symmetry, with the carbonyl group lying on the rotation axis. The mol-ecule is close to planar: the greatest deviation of a torsion angle from 0° is 7.3 (2)° about the bond linking the phenol ring to the rest of the mol-ecule.

(E)-N'-[(2-Hy-droxy-naphthalen-1-yl)methyl-idene]-4-methyl-benzene-sulfono-hydrazide.

In the title compound, C(18)H(16)N(2)O(3)S, the dihedral angle between the planes of the benzene ring and the naphthyl ring system is 83.37 (10)°. An intra-molecular O-H⋯N hydrogen bond occurs.