Acta Crystallographica Section C

Volume 65, Part 7 (July 2009)

organic compounds

sk3328 scheme

Acta Cryst. (2009). C65, o345-o351 [ doi:10.1107/S010827010902215X ]

A structural systematic study of four isomers of difluoro-N-(3-pyridyl)benzamide

J. McMahon, J. F. Gallagher, F. P. Anderson and A. J. Lough

Abstract: The four isomers 2,4-, (I), 2,5-, (II), 3,4-, (III), and 3,5-difluoro-N-(3-pyridyl)benzamide, (IV), all with formula C₁₂H₈F₂N₂O, display molecular similarity, with interplanar angles between the C₆/C₅N rings ranging from 2.94 (11)° in (IV) to 4.48 (18)° in (I), although the amide group is twisted from either plane by 18.0 (2)-27.3 (3)°. Compounds (I) and (II) are isostructural but are not isomorphous. Intermolecular N-HO=C interactions form one-dimensional C(4) chains along [010]. The only other significant interaction is C-HF. The pyridyl (py) N atom does not participate in hydrogen bonding; the closest HN_py contact is 2.71 Å in (I) and 2.69 Å in (II). Packing of pairs of one-dimensional chains in a herring-bone fashion occurs via [pi] -stacking interactions. Compounds (III) and (IV) are essentially isomorphous (their a and b unit-cell lengths differ by 9%, due mainly to 3,4-F₂ and 3,5-F₂ substitution patterns in the arene ring) and are quasi-isostructural. In (III), benzene rotational disorder is present, with the meta F atom occupying both 3- and 5-F positions with site occupancies of 0.809 (4) and 0.191 (4), respectively. The N-HN_py intermolecular interactions dominate as C(5) chains in tandem with C-HN_py interactions. C-HO=C interactions form R₂²(8) rings about inversion centres, and there are [pi] - [pi] stacks about inversion centres, all combining to form a three-dimensional network. By contrast, (IV) has no strong hydrogen bonds; the N-HN_py interaction is 0.3 Å longer than in (III). The carbonyl O atom participates only in weak interactions and is surrounded in a square-pyramidal contact geometry with two intramolecular and three intermolecular C-HO=C interactions. Compounds (III) and (IV) are interesting examples of two isomers with similar unit-cell parameters and gross packing but which display quite different intermolecular interactions at the primary level due to subtle packing differences at the atom/group/ring level arising from differences in the peripheral ring-substitution patterns.

Formula: Four isomers of C₁₂H₈F₂N₂O


	Structure factor file (CIF format) (111.6 kbytes) [ doi:10.1107/S010827010902215X/sk3328Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (107.3 kbytes) [ doi:10.1107/S010827010902215X/sk3328IIsup3.hkl ] Contains datablock II

	Structure factor file (CIF format) (118.6 kbytes) [ doi:10.1107/S010827010902215X/sk3328IIIsup4.hkl ] Contains datablock III

	Structure factor file (CIF format) (115.5 kbytes) [ doi:10.1107/S010827010902215X/sk3328IVsup5.hkl ] Contains datablock IV

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