2-Fluoro-N-(2-fluorobenzoyl)-N-(2-pyridyl)benzamide

The title compound, C19H12F2N2O2, a 2:1 product of the reaction of 2-fluorobenzoyl chloride and 2-aminopyridine, crystallizes with a disordered 2-fluorobenzene ring adopting two conformations [ratio of occupancies = 0.930 (4):0.070 (4)] in one of the two independent molecules (differing slightly in conformation) comprising the asymmetric unit. In the crystal structure, C—H⋯O and C—H⋯π(arene) interactions are present.


Comment
Our group is completing a structural systematic study of fluoro-N'-(pyridyl)benzamide isomers (Donnelly et al., 2008) and we are adding to our research with the analogous difluoro-N-(pyridyl)benzamide series (McMahon et al., 2008) (Scheme 1).
In the chemical synthesis of either the mono-or di-fluoro derivatives and when using the ortho-aminopyridine, two products can be isolated as either the 1:1 or 2:1 benzoyl:pyridine components and with yields and ratios depending on the reaction conditions. We have reported on the structure of the 1:1 derivative namely 2,3-difluoro-N-(2-pyridyl)benzamide (Gallagher et al., 2008) and report herein a 2:1 relative of this type of compound, namely 2-fluoro-N-(2-fluorobenzoyl)-N-(2-pyridyl)benzamide (I) (Figs 1, 2).
Compound (I) crystallizes with two independent molecules A and B in the asymmetric unit that differ slightly in conformation as depicted in the overlay diagram, Fig. 3. The interesting differences between molecules A and B in (I) can readily be compared with (II) 3-fluoro-N-(3-fluorobenzoyl)-N-(2-pyridyl)benzamide (Gallagher et al., 2008)  The packing distortions also manifest in the C 6 and C 5 N rings with respect to the central groups to which they are attached.

Experimental
Compound (I) was synthesized via standard condensation procedures and similar to the related syntheses reported by us (Donnelly et al., 2008;McMahon et al., 2008). Separation of the 1:1 and 2:1 derivatives was undertaken by using flash chromatography using CHCl 3 :ethyl acetate. Typical organic workup and washing gave the product (I) in modest yield of 30-40% as a 2:1 component of the mixture. Crystals suitable for X-ray diffraction were grown from CHCl 3 as colourless blocks over a period of 1-2 weeks and gave a melting point of 367-371 K. The compounds gave clean 1 H and 13 C NMR spectra in CDCl 3 solution. IR (ν C=O cm -1 ): 1715, 1688(s, br), (CHCl 3 ); 1710, 1698(s) (KBr).

Refinement
In the final stages of refinement it was observed that there was electron density consistent with a partial occupancy F atom in a position expected for a minor orientation (site) of the F32A F atom position as F36A. This new site only necessitates rotation by 180° about the C2A-C31A axis in a group that is not engaged in strong hydrogen bonding and is relatively free to rotate.
The minor F36A site was treated initially with isotropic displacement values and in the final refinement cycles was restrained by DELU/ISOR restraints of 0.1 (for F32A, F36A). The final refinement cycles gave site occupancy values of 0.930 (4):0.070 (4). As the major and minor sites for the C 6 ring essentially coincide it was decided to retain the major orientation with 100% occupancy for use with the restraints.