A structural systematic study of three isomers of difluoro-N-(4-pyridyl)-benzamide

The isomers 2,3-, (I), 2,4-, (II), and 2,5-difluoro-N-(4-pyridyl)-benzamide, (III), all with formula C12H8F2N2O, all exhibit intramolecular C-H center dot center dot center dot O=C and N-H center dot center dot center dot F contacts [both with S(6) motifs]. In (I), intermolecular N-H center dot center dot center dot O=C interactions form one-dimensional chains along [010] [N center dot center dot center dot O = 3.0181 (16) A], with weaker C-H center dot center dot center dot N interactions linking the chains into sheets parallel to the [001] plane, further linked into pairs via C-H center dot center dot center dot F contacts about inversion centres; a three-dimensional herring-bone network forms via C-H center dot center dot center dot pi(py) (py is pyridyl) interactions. In (II), weak aromatic C-H center dot center dot center dot N(py) interactions form one-dimensional zigzag chains along [001]; no other interactions with H center dot center dot center dot N/O/F < 2.50 angstrom are present, apart from long N/C-H center dot center dot center dot O=C and C-H center dot center dot center dot F contacts. In (III), N-H center dot center dot center dot N (py) interactions form one-dimensional zigzag chains [as C(6) chains] along [010] augmented by a myriad of weak C-H center dot center dot center dot pi(arene) and O=C center dot center dot center dot O=C interactions and C-H center dot center dot center dot O/N/F contacts. Compound (III) is isomorphous with the parent N-(4-pyridyl) benzamide [Noveron, Lah, Del Sesto, Arif, Miller & Stang (2002). J. Am. Chem. Soc. 124, 6613-6625] and the three 2/3/4 fluoro-N-(4-pyridyl) benzamides [Donnelly, Gallagher & Lough (2008). Acta Cryst. C64, o335-o340]. The study expands our series of fluoro(pyridyl) benzamides and augments our understanding of the competition between strong hydrogen-bond formation and weaker influences on crystal packing.