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Structural systematics and conformational analyses of a 3x3 isomer grid of fluoro-N-(pyridyl)benzamides: physicochemical correlations, polymorphism and isomorphous relationships

Mocilac, Pavle and Donnelly, Katie and Gallagher, John F. (2012) Structural systematics and conformational analyses of a 3x3 isomer grid of fluoro-N-(pyridyl)benzamides: physicochemical correlations, polymorphism and isomorphous relationships. Acta Crystallographica. Section B: Structural Science, 68 . pp. 189-203. ISSN 0108-7681

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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—H...N hydrogen bonds, and only one (Fom) aggregates via intermolecular N—H...O=C interactions exclusively. The Fpm and Fom isomers both crystallize as two polymorphs with Fpm_O (N—H...O=C chains, P-syn) and Fpm_N (N— H...N chains, P-anti) both in P21/n (Z0 = 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—H...N 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— H...F 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.

Item Type:Article (Published)
Refereed:Yes
Uncontrolled Keywords:fluorine; isomerism; grid; chemometric; polymorphism; isomorphous; systematics; conformational analysis
Subjects:Physical Sciences > Chemistry
Physical Sciences > Crystallography
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Chemical Sciences
Publisher:Blackwell Publishing
Official URL:http://dx.doi.org/10.1107/S0108768112006799
Copyright Information:©2012 International Union of Crystallography
Use License:This item is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 3.0 License. View License
ID Code:16884
Deposited On:11 Apr 2012 11:11 by Fran Callaghan. Last Modified 20 Aug 2013 09:36

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