Nicotinohydrazide

In the title compound (alternative name: pyridine-3-carbohydrazide, C6H7N3O), the asymmetric unit contains a single molecule. In contrast with nicotinic acid and nicotinamide, the C=O bond is found to be oriented cis with respect to the Cipso C N fragment in the pyridine ring. The pyridine ring and the hydrazide group make a dihedral angle of 34.0 (2)°. In the crystal structure, molecules are associated into a three-dimensional framework by a combination of N—H⋯N and three-centre N—H⋯O hydrogen bonds.

In the title compound (alternative name: pyridine-3-carbohydrazide, C 6 H 7 N 3 O), the asymmetric unit contains a single molecule. In contrast with nicotinic acid and nicotinamide, the C O bond is found to be oriented cis with respect to the C ipso . . . C . . . N fragment in the pyridine ring. The pyridine ring and the hydrazide group make a dihedral angle of 34.0 (2) . In the crystal structure, molecules are associated into a threedimensional framework by a combination of N-HÁ Á ÁN and three-centre N-HÁ Á ÁO hydrogen bonds.

Comment
As a part of a more general study of multiple-hydrogen-bonding N -heterocyclic systems as potential supramolecular reagents (Portalone, 2007;Portalone & Colapietro, 2007), we report here the structure of the title compound (I, Fig. 1). The asymmetric unit of (I) comprises one independent molecule, and the angle between the mean planes of the acid hydrazine group and the pyridine ring is 34.0 (2)°. Noteworthy, in contrast to nicotinic acid (Kutoglu & Scheringer, 1983) and nicotinamide (Miwa et al., 1999), the C═O bond is oriented cis with respect to the C2-C3 bond.
Analysis of the crystal packing of (I) shows that, at variance with isonicotinohydrazide (Bhat et al., 1974), for which the crystal structure is stabilized by a network of N-H···N hydrogen bonds, in compound (I) two of the three independent N-H bonds act as donor in three-centre N-H···O systems (Table 1, entries 2 and 3), and the third is involved in a N-H···N interaction ( Table 1, entry 1). These hydrogen bonds delineate patterns in which rings are the most prominent features (Fig.   2). Two small rings with descriptor R 2 2 (10) (Etter et al., 1990;Bernstein et al., 1995;Motherwell et al., 1999) are then formed by NH 2 functionalities and two symmetry-related carbonyl O atoms [O1 ii and O1 iii , symmetry codes: (ii) x + 1/2, −y + 1/2, −z; (iii) x − 1/2, −y + 1/2, −z]. The formation of the N-H···N hydrogen bonds between the N-H groups and the pyridyl N atoms [N1 i , symmetry code: (i) −x + 1, y + 1/2, −z + 1/2] leads to the formation of larger R 6 6 (30) rings.
Experimental 1 mmol of the title compound (purchased from Sigma-Aldrich at 97% purity) was dissolved in a mixture benzene/ethanol (8:1, 50 ml) and refluxed for 1 h. After cooling the solution to ambient temperature, a colorless precipitate was formed, which was collected by filtration and washed with benzene/ethanol (8:1). Crystals suitable for single-crystal X-ray diffraction were grown from a benzene solution, by slow evaporation of the solvent.

Refinement
Diffraction from the very small crystals was weak; nevertheless, these data gave good structural results, albeit with a lower data/parameter ratio than usual. All H atoms were detected in a difference map, after the first cycles of the isotropic refinement. The final full-matrix least-squares refinement was carried out on F 2 with anisotropic non-H atoms and isotropic H atoms. C-bonded H atoms were positioned with idealized geometry and refined using a riding model, with C-H bond lengths fixed to 0.95 Å and U iso (H) = 1.2U eq (carrier C). H atoms bonded to N atoms were refined freely with U iso (H) = 1.2U eq (carrier N). In the absence of significant anomalous scattering in this light-atom study, measured Friedel pairs were merged.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.   (4)