4-(Dimethylamino)benzohydrazide

The title molecule is essentially flat; in the crystal the molecules are linked by a system of hydrogen bonds formed by the hydrazido group and consisting of chains of fused rings.

The title compound, C 9 H 13 N 3 O, crystallizes in the monoclinic space group C2/c and all non-hydrogen atoms are within 0.1 Å of the molecular mean plane. In the crystal, the hydrogen-bonding pattern results in [001] chains built up from fused R 2 2 (6) and R 2 2 (10) rings; the former consists of N-HÁ Á ÁN bonds and the latter N-HÁ Á ÁO bonds. Electrostatic and dispersion forces are major contributors to the lattice energy, which was estimated by DFT calculations to be À215.7 kJ mol À1 .

Structure description
For decades, there has been an interest in aroyl hydrazides because of their numerous applications, for instance, as synthetic precursors to a large number of potential antimicrobial (Popiołek, 2017) or anticancer (Kumar & Narasimhan, 2013) drugs, in addition to their own anti-tubercular activities (Sah & Peoples, 1954). In our search for inhibitors of bacterial virulence factors (Mossine et al., 2016(Mossine et al., , 2020, we turned our attention to the title compound, which can be viewed as a structural analogue of isoniazid (Andrade et al., 2008) and a potential precursor for pharmacologically active, iron-binding hydrazidehydrazones. We now report its crystal structure.
The title compound crystallizes in the monoclinic space group C2/c, with eight molecules per unit cell. The asymmetric unit contains one molecule of the hydrazide (I), as shown in Fig. 1. All bond lengths and angles are within their expected ranges. The molecule is essentially flat, with the greatest deviation from the average molecular plane, among the non-hydrogen atoms, found for atom N1 at 0.074 (1) Å . The aromatic ring plane is at 1.08 (4) to the molecular plane. The spatial arrangement of the hydrazido group, as defined by the torsion angle H2-N2-N3-H3B = 119.3 (15) , corresponds to the lowest energy conformation that has been calculated for acyl hydrazides (Centore et al., 2010).

data reports
The conventional hydrogen bonding in the extended structure of (I) is limited to two intermolecular heteroatom contacts (Table 1) involving the hydrazido groups only and is shown in Fig. 2. The hydrogen-bonding pattern includes infinite chains that propagate in the [001] direction and consist of fused R 2 2 (10) and R 2 2 (6) rings (Fig. 2a). The R 2 2 (10) motif is formed by pairs of molecules linked by the N3-H3BÁ Á ÁO1 hydrogen bonds related by twofold rotation symmetry, while the R 2 2 (6) motif is formed by centrosymmetric dimers of (I) linked by the N2-H2Á Á ÁN3 hydrogen bonds. In addition, one short intermolecular contact, C6-H6Á Á ÁO1, which satisfies the distance and directionality conditions [C6Á Á ÁO1 iii = 3.4111 (13) Å , C6-H6Á Á ÁO1 iii = 172 ; symmetry code: (iii) x, 1 À y, 1 2 + z], and which is shown in Fig. 3 as a dotted line, may also contribute to the stability of the molecular packing in the crystal. The intermolecular non-polar interactions are dominated by hydrogen-hydrogen contacts between the methyl groups; the shortest of these contacts, H8CÁ Á ÁH9B, is about 0.1 Å less than the sum of the VdW radii. These interactions form a pattern of infinite chains, propagating in the [001] direction, in parallel to the hydrogen-bonded chains ( Fig. 2b and 2c). The crystal structure lacks any strongstacking interactions. However, a short N3-H3AÁ Á ÁCg1 [H3AÁ Á ÁCg1 iv = 2.614 (15) Å ; symmetry code: (iv) x, y À 1, z] contact is present.

Figure 2
Molecular packing and hydrogen bonding in (I). (a) Hydrogen-bonding motifs; (b) and (c) molecular packing views down [001] and [100], respectively. Hydrogen bonds are shown as cyan dotted lines.

Figure 3
Interaction energies in crystal structure of (I). (a) A view of interactions between a central molecule, shown as its Hirshfeld surface, and 13 molecules that share the interaction surfaces with the central molecule. Red areas on the Hirshfeld surface encode the closest intermolecular contacts, which are hydrogen bonds involving the hydrazido groups, a short C-HÁ Á ÁO type contact is shown as a dotted line; (b) Calculated energies (electrostatic, polarization, dispersion, repulsion, and total) of pairwise interactions between the central molecule and those indicated by respective colours.

Figure 1
Atomic numbering and displacement ellipsoids at the 50% probability level for (I).
polarization, and repulsion energies. According to these calculations, the interactions between hydrogen-bonded pairs of molecules contribute about 50% to the lattice energy, with the dispersion energy providing most of the attractive forces between non-hydrogen-bonded molecules of (I) (i.e. E ele = À9.2 kJ mol À1 , E dis = À44.2 kJ mol À1 for symmetry code = x, y, z). To estimate the lattice energy, all total energies of unique pairwise interactions between molecules were summed up, thus yielding E l (l = lattice) = À216 kJ mol À1 for the crystal of (I). The calculated contributions to the overall lattice energy (kJ mol À1 ) are as follows: E ele = À165.3; E pol = À46.0; E dis = À173.9; E rep = 234.1. The spatial distribution of the energetically most significant interactions is illustrated in Fig. 4, showing the interactions energy frameworks as cylinders penetrating the molecular packing of (I). As expected, the most extensive intermolecular interactions occur in the hydrogen-bonded chain direction parallel to [001].

Synthesis and crystallization
A sample of commercial 4-dimethylaminobenzhydrazide was recrystallized from hot 95% ethanol solution, affording colorless needles.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Funding information
Funding for this research was provided by: National Institute of Food and Agriculture (award No. Hatch 1023929); University of Missouri, Agriculture Experiment Station Chemical Laboratories .

Figure 4
Energy frameworks for separate (a) electrostatic and (b) dispersion contributions to the (c) total pairwise interaction energies in (I). The cylinders link molecular centroids, and the cylinder thickness is proportional to the magnitude of the energies (see Fig. 3). For clarity, the cylinders corresponding to energies <5 kJ mol À1 are not shown. The directionality of the crystallographic axes is the same for all three diagrams.  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. The hydrazide H2, H3A, and H3B atoms were located in difference-Fourier maps while all other hydrogen atoms were initially placed in calculated positions with their coordinates constrained to ride on their carrier atoms [C-H(aromatic) = 0.95?Å, C-H(methyl) = 0.98?Å]. The constraint Uiso(H) = 1.2Ueq(carrier) or 1.5Ueq(methyl carrier) was applied in all cases.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )