Molecular packing modes. Part IX. Crystal and molecular structures of pentafluorobenzoic acid and mesitoic acid

Abstract

The crystal structure of pentafluorobenzoic acid has been solved from 1598 three-dimensional counter data, and refined by least-squares to R 0·04. Crystals are triclinic, space group P, with Z= 2 in a unit cell of dimensions: a= 7·925, b= 8·637, c= 6·262 Å, α= 97·55, β= 89·65, and γ= 121·86°. Values of σ for bond lengths are 0·002 Å. The angle between the planar pentafluorophenyl group and the carboxy-group is 29·8°. The molecules form cyclic hydrogen-bonded dimers (OH ⋯ O 2·668 Å) in which the C–OH and CO bond lengths are 1·278 and 1·221 Å.

The structure of mesitoic acid was refined similarly to R 0·05 for 2060 reflections. Crystals are monoclinic, space group C2/c, Z= 8, in a unit cell of dimensions: a= 15·142(1), b= 7·026(1), c= 17·439(1)Å, β= 89·35(1)°. The mean σ values of the heavy- and hydrogen-atom co-ordinates are 0·001 and 0·03 Å. The angle between the mesityl and carboxy-groups is 48·4°. The molecules form cyclic hydrogen-bonded pairs (OH ⋯ O 2·640 Å) in which the C–O bond lengths are nearly equal (1·275 and 1·248 Å).

The molecular dimensions and the packing arrangements of both structures are discussed.