Arene-Perfluoroarene-Anion Stacking and Hydrogen Bonding Interactions in Imidazolium Salts for the Crystal Engineering of Polarity

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• 作者：Hanan I. Althagbi ; Alison J. Edwards ; Brian K. Nicholson ; Daniel A. Reason ; Graham C. Saunders ; Sophie A. Sim ; Danielle A. van der Heijden
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：January 6, 2016
• 年：2016
• 卷：16
• 期：1
• 页码：174-188
• 全文大小：1011K
• ISSN：1528-7505

文摘

The crystal structure of 1-(2,3,5,6-tetrafluoropyridyl)-3-benzylimidazolium bromide possesses C₆H₅···C₅F₄N···Brp>–p> interactions that link the cations into chains, N(C)C–H···Brp>–p> interactions that link the chains into sheets, and N₂C–H···Brp>–p> interactions that link the sheets to one another. As a consequence of these, it is polar (Pna2₁). Density functional theory calculations indicate that the strength of the interaction between a cation and a bromide anion lies in the order N₂C–H···Brp>–p> > N(C)C–H···Brp>–p> > C₆H₅···C₅F₄N···Brp>–p>. Prevention of the N₂C–H···Brp>–p> interaction by substitution of the hydrogen atom with a methyl group leads to dimers linked by two C₆H₅···C₅F₄N···Brp>–p> interactions. Prevention of the N(C)C–H···Brp>–p> interaction by substitution of the hydrogen with a methyl group permits chains of cations, but because the N₂C–H···Brp>–p> interactions link the chains there are no strong interactions between the sheets. Chains of cations linked by Ar···C₅F₄N···Brp>–p> interactions also arise when the benzyl group is replaced by 3-phenylbenzyl and 2-naphthylmethyl groups. The former also contains N₂C–H···Brp>–p> and N(C)C–H···Brp>–p> interactions and is centrosymmetric. The latter does not contain N(C)C–H···Brp>–p> interactions and is chiral and polar (P2₁). Exchanging the positions of the aryl and polyfluoroaryl groups results in a crystal structure with no π–π stacking between the aryl and polyfluoroaryl groups although N₂C–H···Brp>–p> and N(C)C–H···Brp>–p> interactions persist.