Structural analysis of 2-iodobenzamide and 2-iodo-N-phenylbenzamide

The molecular and crystal structures of 2-iodo benzamide and 2-iodo-N-phenylbenzamide are reported. In both crystals, N—H⋯O hydrogen bonds and C—I⋯π(ring) interactions stabilize the packing with additional C—H⋯π(ring) contacts found in the latter.

The title compounds, 2-iodobenzamide, C 7 H 6 INO (I), and 2-iodo-N-phenylbenzamide, C 13 H 10 INO (II), were both synthesized from 2-iodobenzoic acid. In the crystal structure of (I), N-HÁ Á ÁO and hydrogen bonds form two sets of closed rings, generating dimers and tetramers. These combine with C-IÁ Á Á(ring) halogen bonds to form sheets of molecules in the bc plane. For (II), N-HÁ Á ÁO hydrogen bonds form chains along the a-axis direction, while inversion-related C-IÁ Á Á(ring) contacts supported by C-HÁ Á Á(ring) interactions generate sheets of molecules along the ab diagonal.

Chemical context
Aromatic amides can be found in a wide range of aromatic molecules and they also serve as intermediates in the production of many pharmaceutical compounds (Suchetan et al., 2016). Aromatic amides and N-aryl amides display a wide spectrum of pharmacological properties and are used as antibacterial (Ragavan et al., 2010), analgesic (Starmer et al., 1971), antiviral (Hu et al., 2008), anti-inflammatory (Kalgutkar et al., 2000) and anti-cancer (Pradidphol et al., 2012) agents. Furthermore, N-aryl amides are known to act as anti-tumor agents against a broad spectrum of human tumors (Abdou et al., 2004). In view of their potential importance, the title compounds (I) and (II) were synthesized and we report herein a comparison of their structures.
orthogonal with an angle of 79.84 (6) between them. The iodobenzene ring plane is inclined to the O1/C1/N1 amide plane by 52.01 (1) , somewhat similar to the inclination found for (I), while the phenyl ring of the amide is inclined by 28.45 (5) to this plane.

Supramolecular features
In the crystal structure of compound (I), strong classical N1-H1AÁ Á ÁO1 and N1-H1BÁ Á ÁO1 hydrogen bonds, Table 1, arrange the molecules in two linked sets of closed rings, forming both dimers with an R 2 2 (8) graph-set motif and tetramers that enclose R 2 4 (8) rings (Etter et al., 1990). These contacts form chains of molecules along the a-axis direction (Fig. 3). In addition, C3-I1Á Á ÁCg1 halogen bonds, Table 1, combine with the previously mentioned inversion dimers to generate sheets of molecules in the bc plane (Fig. 4).
For compound (II), the absence of a second H atom on the N1 amine nitrogen atom limits the formation of classical hydrogen bonds to N1-H1Á Á ÁO1 contacts that generate C(4) molecular chains along the a-axis direction (Fig. 5, Table 2). Additional weak inversion-related C3-I1Á Á ÁCg2 interactions (Table 2), in this instance also supported by C6-H6Á Á ÁCg2 contacts that also lie about an inversion centre, form sheets of molecules along the ab diagonal (Fig. 6 Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 1
The molecular structure of (I) showing the atom numbering with ellipsoids drawn at the 50% probability level.

Figure 2
The molecular structure of (II) showing the atom numbering with ellipsoids drawn at the 50% probability level.

Figure 3
Chains of molecules of (I) along the a-axis direction, showing the dimers and tetramers formed by N-HÁ Á ÁO hydrogen bonds.

Figure 4
N-HÁ Á ÁO and C-IÁ Á Á(ring) contacts forming sheets of molecules of (I) in the bc plane.

Database survey
A search for the crystal structures of 2-iodobenzamide and 2-iodo-N-phenylbenzamide was carried out in the Cambridge Structural Database (Conquest Version 1.17; CSD Version 5.39, last update November 2017; Groom et al., 2016). Compound (I) was found to have been previously reported from film data (IBNZAM; Nakata et al., 1976), but there were no hits for compound (II). Four other related structures were observed: two fluorine-substituted 2-iodobenzamides, FAHSAK and FAHSIS (Nayak et al., 2012) and two nitro substituted 2-iodobenzamides, TAQBIX (Garden et al., 2005) and WAWMAJ .

Synthesis and crystallization
The synthesis of the title compounds was carried out using a reported procedure (Jursic & Zdravkovski, 1993;Kavala et al., 2012;Mao et al., 2012). Single crystals for both compounds were grown by the slow evaporation method from dichloromethane and hexane (v/v 1:1) at low temperature for (I), whereas those for compound (II) were obtained from aceto- N-HÁ Á ÁO hydrogen bonds forming chains of molecules of (II) along the a-axis direction.

2-Iodobenzamide (I)
Crystal data Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0170 (5) 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.

2-Iodo-N-phenylbenzamide (II)
Crystal data 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq I1 −0.30400 (