| Title: | Structural systematics and conformational analyses of a 3 × 3 isomer grid of fluoro-N-(pyridyl)benzamides: physicochemical correlations, polymorphism and isomorphous relationships
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| Authors: | Pavle Mocilac, Katie Donnelly, John F. Gallagher, 2012 |
| Abstract: | An isomer grid of nine fluoro-N-(pyridyl)benzamides (Fxx) (x = para-/meta-/ortho-) has been examined to correlate structural relationships between the experimental crystal structure and ab initio calculations, based on the effect of fluorine (Fx) and pyridine N-atom (x) substitution patterns on molecular conformation. Eight isomers form N-HN hydrogen bonds, and only one (Fom) aggregates via intermolecular N-HO=C interactions exclusively. The Fpm and Fom isomers both crystallize as two polymorphs with Fpm_O (N-HO=C chains, P-syn) and Fpm_N (N-HN chains, P-anti) both in P21/n (Z' = 1) differing by their meta-N atom locations (P-syn, P-anti; Npyridine referenced to N-H), whereas the disordered Fom_O is mostly P-syn (Z' = 6) compared with Fom_F (P-anti) (Z' = 1). In the Fxo triad twisted dimers form cyclic R22(8) rings via N-HN interactions. Computational modelling and conformational preferences of the isomer grid demonstrate that the solid-state conformations generally conform with the most stable calculated conformations except for the Fxm triad, while calculations of the Fox triad predict the intramolecular N-HF interaction established by spectroscopic and crystallographic data. Comparisons of Fxx with related isomer grids reveal a high degree of similarity in solid-state aggregation and physicochemical properties, while correlation of the melting point behaviour indicates the significance of the substituent position on melting point behaviour rather than the nature of the substituent. |
| ICHEC Project: | Structural systematics of n x m isomer grids: comparison of structural data (from diffraction) with ab initio calculations |
| Publication: | Acta Crystallographica (2012), B68, pp. 189-203 |
| URL: | http://dx.doi.org/10.1107/S0108768112006799 |
| Keywords: | fluorine; isomerism; grid; chemometric; polymorphism; isomorphous; systematics; conformational analysis |
| Status: | Published |
