Crystal structures of three N-aryl-2,2,2-tribromoacetamides

Three N-(aryl)-2,2,2-tribromoacetamides show different weak interactions in their crystal structures.


Structural commentary
The molecular structures of (I), (II) and (III) are shown in Figs. 1, 2 and 3, respectively. ISSN 2056-9890 In (I), the conformation of the N-H bond is syn to the 2-fluoro substituent in the benzene ring, similar to that observed in the crystal structures of other ortho substituted compounds (see database survey). Contrast to the above, in (II), the conformation of the N-H bond is anti to the 3-CF 3 substituent.

Figure 2
A view of (II), with displacement ellipsoids drawn at the 50% probability level.
Quite different to the packing in (I) and (II), the molecules in (III) are connected via pairs of C3-H3Á Á ÁF1 interactions ( Fig. 7   Crystal packing of (I), displaying C-BrÁ Á Á and BrÁ Á ÁBr contacts. H atoms are omitted for clarity.
A comparison of the dihedral angle between the benzene ring and the C1-N1-C7(O)-C8 segment in all of the compounds shows that the dihedral angles in the fluorosubstituted compounds are smaller than those observed in chloro-substituted ones, which in turn have smaller values than the methyl-substituted tribromoacetamides ( Table 7). The dihedral angle in the parent (i.e. unsubstituted) compound is closer to those of chloro-substituted ones, thus the order is F < Cl( H) < CH 3 .
The crystal structures of all of the seven compounds [except (Ia)] reported in the literature feature strong N-HÁ Á ÁO hydrogen bonds leading into C(4) chains forming a onedimensional architecture. Compound (Ia) (2-chloro derivative) does not exhibit any conventional intermolecular interactions and therefore exhibits a zero-dimensional supramolecular architecture. However, the packing of molecules in the three structures reported here are very different and are controlled by interactions mainly involving the halogen atoms.

Synthesis and crystallization
All three compounds were prepared according to a literature method (Gowda et al., 2003). The purity of the compounds was checked by determining the melting points. Single crystals of all the compounds used for X-ray diffraction studies were obtained by slow evaporation of an ethanolic solutions of the compound at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 8. H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.93 Å and N-H = 0.86 Å , and with U iso (H) = 1.2U eq (C,N).   N-aryl-2,2,2

(I) 2,2,2-Tribromo-N-(2-fluorophenyl)acetamide
Crystal data  (12) 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq F1 0.3498 (7) 0.6456 (4) 0.5450 (4) 0.0760 (11)     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. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.48 e Å −3 Δρ min = −1.01 e Å −3 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.

sup-8
Acta Cryst. (2015). E71, 1048-1053 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.