Crystal structures of 3-fluoro-N-[2-(trifluoromethyl)phenyl]benzamide, 3-bromo-N-[2-(trifluoromethyl)phenyl]benzamide and 3-iodo-N-[2-(trifluoromethyl)phenyl]benzamide

The crystal structures of three N-[2-(trifluoromethyl)phenyl]benzamides are reported. The 3-fluorobenzamide crystallized with two independent molecules in the asymmetric unit; the dihedral angles between the two benzene rings are 43.94 (8) and 55.66 (7)°. In the 3-bromobenzamide and the 3-iodobenzamide, this dihedral angle is much smaller, viz. 10.40 (12) and 12.5 (2)°, respectively.


Chemical context
Amides are very common in nature, and are easily synthesized and provide structural rigidity to various molecules (Gowda et al., 2003). Furthermore, N-arylamides show a broad spectrum of pharmacological properties, including antibacterial (Manojkumar et al., 2013a), antitumor (Abdou et al., 2004), antioxidant, analgesic and antiviral activity (Manojkumar et al., 2013b). In view of their importance, the title N-(2-trifluoromethylphenyl)benzamides (I)-(III) were synthesized and we report herein on their crystal structures. ISSN 2056-9890

Structural commentary
The molecular structure of compound (I) is illustrated in Fig. 1. It crystallizes with two independent molecules (A and B) in the asymmetric unit, which slightly differ in their molecular conformations, as shown in the AutoMolFit diagram ( Fig. 2; Spek, 2009). In both molecules, the 3-fluoro substituent on the benzoic acid ring and the 2-CF 3 substituent on the aniline ring are anti to one another, and the 3-fluoro substituent is anti to the N-H bond in the central -C ar -C( O)-N-C ar -(ar = aromatic) segment of the molecules. The dihedral angle between the two benzene rings is 43.94 (8) in molecule A, while in molecule B it is larger, being 55.66 (7) . The torsion angle of the central -C ar -C( O)-N-C ar -segment is 176.74 (12) in molecule A and À179.58 (12) in molecule B.
The molecular structures of compounds (II) and (III) are illustrated in Figs. 3 and 4, respectively. Here, the 3-bromo and 3-iodo substituents on the benzoic acid ring and the 2-CF 3 substitution on the aniline ring are anti to one another, and the 3-bromo and 3-iodo substituents are anti to the N-H bond in the central -C ar -C( O)-N-C ar -segment of the molecules, similar to situation observed in (I). The dihedral angle between the two benzene rings is 10.40 (12) in (II) and 12.5 (2) in (III), which is much less than observed for molecules A and B of compound (I). The torsion angle of the central -C ar -C( O)-N-C ar -segment is À175.5 (2) in (II) and 174.8 (3) in (III), again similar to that in molecules A and B of compound (I).

Supramolecular features
In the crystal of (I), strong N1-H1Á Á ÁO2 and N2-H2Á Á ÁO1 hydrogen bonds link the molecules to form -A-B-A-B-C(4) chains running along the a-axis direction (Table 1 and  A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the molecular fit of molecules A (black) and B (red) of compound (I).

Figure 3
A view of the molecular structure of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.
The crystal structure of (III), features similar characteristics to that of (II). Strong N1-H1Á Á ÁO1 hydrogen bonds link the molecules into C(4) chains running parallel to the b axis (Table 3 and  From the above observations, it can be concluded that the bromo and iodo substitutions on the meta position of the benzoic acid ring have a similar effect on the molecular conformations and the supramolecular architectures exhibited by this class of compounds, whereas the fluoro substitution has a very different influence. For instance, there are two molecules in the asymmetric unit of (I) compared to one molecules in those of (II) and (III). Also, the dihedral angle between the two benzene rings is much larger in the two  Table 2 Hydrogen-bond geometry (Å , ) for (II). (2) 2.00 (2) 2.835 (2) 156 (3) Symmetry code: (i) x; y À 1; z.

Figure 8
A view along the b axis of the crystal packing of compound (III). The N-HÁ Á ÁO hydrogen bonds (see Table 3) and the IÁ Á ÁI contacts are shown as dashed lines.

Figure 5
A view along the c axis of the crystal packing of compound (I). The N-HÁ Á ÁO hydrogen bonds are shown as dashed lines (see Table 1).

Figure 7
A view along the b axis of the crystal packing of compound (II). The N-HÁ Á ÁO hydrogen bonds (see Table 2) and the BrÁ Á ÁBr contacts are shown as dashed lines.
molecules (A and B) of (I), compared to the values observed in (II) and (III). Furthermore, the crystal structures of both (II) and (III) feature short halogenÁ Á Áhalogen contacts, in addition to the N-HÁ Á ÁO hydrogen bonds, resulting in onedimensional structures, whereas in (I), in the absence of FÁ Á ÁF contacts, C-HÁ Á ÁO hydrogen bonds andinteractions are observed, in addition to the strong N-HÁ Á ÁO hydrogen bonds, resulting in a two-dimensional architecture.  (Hathwar et al., 2014) and LASHOE in space group P4 1 (Panini & Chopra, 2012), and 2-(trifluoromethyl)-N-(2-(trifluoromethyl)phenyl)benzamide (LASKAT; Panini & Chopra, 2012). In compounds LASHOE and LASKAT, the 2-CF 3 group in the aniline ring is nearly syn to the N-H bond in the central amide segment of the molecule, as observed in the title compounds. In LASHOE (Panini & Chopra, 2012), the dihedral angle between the two benzene rings is 41.3 (1) , and the torsion angle of the central -C ar -N-C( O)-C ar -segment is 175.1 (5) , which is very close to the values observed for the two independent molecules in compound (I). This shows that introducing a fluorine atom into the meta position of the benzoyl ring, as in compound (I), has little effect on the molecular conformation of this class of compounds.

Synthesis and crystallization
The different substituted benzoic acids (3 mmol) were dissolved in phosphorous oxychloride taken in a 250 ml round-bottomed flask. The mixtures were refluxed for an hour and later cooled to 273 K. An equimolar amount of 2-(trifluoromethyl)aniline was added dropwise to these mixtures with continuous stirring. After completion of the addition, the reaction mixtures were brought to room temperature and stirring was continued for 1 h. The reaction mixtures were poured into ice-cold water. The solids that separated were washed thoroughly with water, followed by washing with dilute hydrochloric acid, water, aqueous sodium hydrogen carbonate solution and again with water.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 4. In all three compounds the NH H atoms were located in difference Fourier maps and refined with a distance restraint: N-H = 0.90 (4) Å . The C-bound H atoms were positioned with idealized geometry and refined using a riding model: C-H = 0.95 Å , with U iso = 1.2U eq (C). In the final cycles of refinement of compound (III), a bad reflection (4 2 2) was omitted, which lead to an improvement in the values of R1, wR2, and GOF. For all compounds, data collection: APEX2 (Bruker, 2009); cell refinement: APEX2 and SAINT-Plus (Bruker, 2009); data reduction: SAINT-Plus and XPREP (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).  Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.

(II) 3-Bromo-N-[2-(trifluoromethyl)phenyl]benzamide
Crystal data 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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq H1 1.167 (2) 0.262 (5) 0.0800 (14) 0.022 (7) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.