A structural systematic study of three isomers of difluoro-N-(4-pyridyl)benzamide
McMahon, Joyce and Anderson, Frankie P. and Gallagher, John F. and Lough, Alan J. (2008) A structural systematic study of three isomers of difluoro-N-(4-pyridyl)benzamide. Acta Crystallographica Section C, 64 (9). pp. 493-497. ISSN 0108-2701
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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...O=C and N-H...F contacts [both with S(6) motifs]. In (I), intermolecular N-H...O=C interactions form one-dimensional chains along  [N...O = 3.0181 (16) Å], with weaker C-H...N interactions linking the chains into sheets parallel to the  plane, further linked into pairs via C-H...F contacts about inversion centres; a three-dimensional herring-bone network forms via C-H...π(py) (py is pyridyl) interactions. In (II), weak aromatic C-H...N(py) interactions form one-dimensional zigzag chains along ; no other interactions with H...N/O/F < 2.50 Å are present, apart from long N/C-H...O=C and C-H...F contacts. In (III), N-H...N(py) interactions form one-dimensional zigzag chains [as C(6) chains] along  augmented by a myriad of weak C-H...π(arene) and O=C...O=C interactions and C-H...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.
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