Assembling an isomer grid: the isomorphous 4-, 3- and 2-fluoro-<i>N</i>′-(4-pyridyl)benzamides
作者:Katie Donnelly、John F. Gallagher、Alan J. Lough
DOI:10.1107/s0108270108012067
日期:2008.6.15
The three title isomers, 4-, (I), 3-, (II), and 2-fluoro-N'-(4-pyridyl) benzamide, (III), all C(12)H(9)FN(2)O, crystallize in the P2(1)/c space group (No. 14) with similar unit-cell parameters and are isomorphous and isostructural at the primary hydrogen-bonding level. An intramolecular C-H center dot center dot center dot O=C interaction is present in all three isomers [C center dot center dot center dot O= 2.8681 (17)-2.884 (2) angstrom and C-H center dot center dot center dot O117-118 angstrom], with an additional N-H center dot center dot center dot F [N center dot center dot center dot F = 2.7544 (15) angstrom] interaction in (III). Intermolecular amide-pyridine N-H center dot center dot center dot N hydrogen bonds link molecules into one-dimensional zigzag chains [ graph set C(6)] along the [ 010] direction as the primary hydrogen bond [N center dot center dot center dot N = 3.022 (2), 3.049 (2) and 3.0213 (17) angstrom]. These are augmented in (I) by C-H center dot center dot center dot pi(arene) and cyclic C-F center dot center dot center dot pi(arene) contacts about inversion centres, in (II) by C-F center dot center dot center dot F-C interactions [C center dot center dot center dot F = 3.037 (2) angstrom] and weaker C-H center dot center dot center dot pi(arene)/C-H center dot center dot center dot F contacts, and in (III) by C-H center dot center dot center dot pi(arene) and C=O center dot center dot center dot O=C interactions, linking the alternating chains into two-dimensional sheets. Typical amide N-H center dot center dot center dot O=C hydrogen bonds [as C(4) chains] are not present [N center dot center dot center dot O = 3.438 (2) angstrom in (I), 3.562 (2) angstrom in (II) and 3.7854 (16) angstrom in (III)]; the C=O group is effectively shielded and only participates in weaker interactions/contacts. This series is unusual as the three isomers are isomorphous (having similar unit-cell parameters, packing and alignment), but they differ in their interactions and contacts at the secondary level.