3-Fluorobenzoic acid–4-acetylpyridine (1/1) at 100 K

In the title compound, C7H5FO2·C7H7NO, a moderate-strength hydrogen bond is formed between the carboxyl group of one molecule and the pyridine N atom of the other. The benzoic acid molecule is observed to be disordered over two positions with the second orientation only 4% occupied. This disorder is also reflected in the presence of diffuse scattering in the diffraction pattern.

In the title compound, C 7 H 5 FO 2 ÁC 7 H 7 NO, a moderatestrength hydrogen bond is formed between the carboxyl group of one molecule and the pyridine N atom of the other. The benzoic acid molecule is observed to be disordered over two positions with the second orientation only 4% occupied. This disorder is also reflected in the presence of diffuse scattering in the diffraction pattern.

Comment
The structure of a molecular complex of 3-fluorobenzoic acid with 4-acetylpyridine (C 7 H 5 O 2 F C 7 H 7 NO) at 100 K is reported ( Fig. 1). The molecular geometry of the 4-acetylpyridine is generally unremarkable. However the F atom in the 3fluorobenzoic acid molecule is seen to be disordered over two positions in a 96:4% ratio. The majority component is found to lie on the same side of the molecule as the carbonyl C═O and this is consistent with the reported crystal structure of the pure material (Taga et al., 1985). The minority component was identified using a Fourier difference map which shows a peak height of greater than 1 electron bonded to C6, at a distance longer than characteristic for a C-H bond. The inclusion of a disorder model even at the 4% level improves the model significantly. Diffuse scattering was also observed in the diffraction images supporting the presence of disorder in this material. The minor component F atom was modelled isotropically and with constraints on the C-F distance. The thermal ellipsoids of both the carboxylic acid group and the methyl-keto group are slightly larger than those of their corresponding aromatic rings, indicating the possible presence of a small amount of libration in these groups.
A moderate strength hydrogen bond [O···N = 2.6428 (14) Å] is formed between the carboxylic acid group and the pyridine N atom. There is no indication of disorder of the carboxylic H atom at this temperature although the H atom isotropic thermal parameter is large as is often observed in the presence of a hydrogen bond. The two molecules lie almost exactly co-planar with each other.
These dimers are packed in an offset planar arrangement, as shown in Figs. 2 and 3. All the molecules are approximately co-planar with the (103) plane. The reason that this offset occurs may be due to the optimization of two close contacts from the methyl group. These contacts comprise a C-H···O interaction between the methyl group of the 4-acetylpyridine and the C═O of the carboxylic acid between planes, which induces an attractive tilt upwards in the acetylpyridine towards this acid molecule. Equally, the C-H···F interaction within the plane causes an attractive tilt in the adjacent molecule, giving rise to this offset packing arrangement.

Experimental
Crystals of the title material were grown by slow evaporation of solvent from a 1:1 solution of the two component molecules in ethanol.