Pyridine-4-carbaldehyde 4-phenylsemicarbazone

In the title compound, C13H12N4O, the semicarbazone fragment links a benzene and a pyridine ring in the structure. The crystal packing is stabilized by strong intermolecular N—H⋯O hydrogen bonds, which connect two molecules to form a synthon unit, and by N—H⋯N hydrogen bonds and weak C—H⋯π interactions. The molecular conformation is stabilized by intramolecular N—H⋯N and C—H⋯O interactions.

In the title compound, C 13 H 12 N 4 O, the semicarbazone fragment links a benzene and a pyridine ring in the structure. The crystal packing is stabilized by strong intermolecular N-HÁ Á ÁO hydrogen bonds, which connect two molecules to form a synthon unit, and by N-HÁ Á ÁN hydrogen bonds and weak C-HÁ Á Á interactions. The molecular conformation is stabilized by intramolecular N-HÁ Á ÁN and C-HÁ Á ÁO interactions.
The configuration of (I) is E with respect to the C6═N2 bond. The pyridine and benzene rings are conected by a semicarbazone fragment (C6/N2/N3/C7/O1/N4). The values of the dihedral angles between the aromatic rings and the semicarbazone fragnent are 23.99 (7)° and 42.15 (7)° for the benzene and pyridine rings, respectively. This indicates the lack of planarity.
The crystal packing is stabilized by a pair of strong intermolecular N-H···O hydrogen bonds conecting two molecules to form a centrosymmtric unit (synthon), and by an N-H···N hydrogen bond (Fig. 2), which extends the packing along the c axis (Fig 3). The crystal is also stabilized by intermolecular C-H···π interactions (Fig. 4). This type of interaction affects the conformation of the molecule, specifically the torsion angle between the benzene ring and the semicarbazone moeity.
From the centroid-centroid distance between two pyridine rings [4.0085 (2)Å] and the angle between the normal of the aromatic plane and the centroid-centroid vector [35.13 (5)°], we conclude that there is no significant π-π stacking interaction between the pyridine rings.

Experimental
A solution of 4-pyridine carboxaldehyde (1.0711 g, 0.01 mol) and 4-phenylsemicarbazide (1.5117 g, 0.01 mol) in absolute methanol (50 ml) was refluxed for 4 h in the presence of p-toluenesulfonic acid as catalyst, with continuous stirring. On cooling to room temperature the precipitate was filtered off, washed with copious cold methanol and dried in air (m.p. 493.15 K). White single crystals of compound (I) were obtained after recrystallization from a solution in methanol.

Refinement
The NH and Schiff base CH H-atoms were found in difference Fourier maps and were freely refined: N3-H = 0.93 (2) Å, N4-H = 0.91 (2) Å and C6-H=0.99 (2) Å. All other C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 Å for aromatic CH with U iso (H) = 1.2 × U eq (C). At the end of the refinement the highest peak in the electron density was 0.20 eÅ -3 , while the deepest hole was -0.17 eÅ -3 .

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.