3-Fluoro-N-(3-fluorobenzoyl)-N-(2-pyridyl)benzamide

The title compound, C19H12F2N2O2, a 2:1 product of the reaction of 3-fluorobenzoylchloride and 2-aminopyridine crystallizes with a disordered 3-fluorobenzene ring adopting two conformations [ratio of occupancies 0.959 (4):0.041 (4)]. In the crystal structure, there are no classical hydrogen bonds and interactions comprise C—H⋯O in the form 2(C—H)⋯O=C [with motif R 2 1(5)]; C—H⋯π(arene) interactions are also 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).
A search of the literature (Allen, 2002) reveals a structure exhibiting a comparable example of hydrogen bonding and is archived in the CSD (as XOXRIL). However, in this structure the interacting molecules are offset with respect to the C=O···C 2 moiety in the aromatic C 5 N ring. A related search yielded POZWUW ( A related search for C=O···C 2 [in C 6 ] yielded 6 compounds in the same range of C···O from 2.0-3.0 Å but most were disordered, with high R-factors and typically had the solvent benzene as the acceptor; these are listed as BARJUZ10, LAY-DAQ, MERRIK, OGOPUV, SEDLET, XICFEV (Allen, 2002).

Experimental
Compound (I) was synthesized via standard condensation procedures and similar to the related syntheses reported previously (Donnelly et al., 2008;McMahon et al., 2008). Separation of the 1:1 and 2:1 derivatives was undertaken by using flash chromatography. Typical organic workup and washing gave the product (I) in modest yield of 25-35% 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 401-406 K. The compounds gave clean 1 H and 13 C NMR spectra in CDC 3 and infrared spectra (in CHCl 3 solution, and as KBr disks).

Refinement
Molecule (I) crystallized in the triclinic system; space group P1 (No. 2) assumed and confirmed by the refinement and analysis. 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 F33 atom position. This new site only necessitates rotation by 180° about the C2-C31 axis in a group that is not engaged in strong hydrogen bonding.
The minor F35 site was treated initially with isotropic displacement values and in the final refinement cycles was restrained by DFIX values to 1.350 (5) Å, SIMU restraints of 0.2 (F33, F35) and FLAT constraints of 0.1 with the {C31···C36} benzene ring. The final refinement gave site occupancy values of 0.959 (4):0.041 (4). As the major and minor sites for the C 6 ring are essentially coincidental it was decided to retain the major orientation with 100% occupancy for use with the restraints.