Solid-State Analysis of Low-Melting 1,3-Dialkylimidazolium Hexafluorophosphate Salts (Ionic Liquids) by Combined X-ray Crystallographic and Computational Analyses

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• 作者：W. Matthew Reichert ; John D. Holbrey ; Richard P. Swatloski ; Keith E. Gutowski ; Ann E. Visser ; Mark Nieuwenhuyzen ; Kenneth R. Seddon ; Robin D. Rogers
• 刊名：Crystal Growth & Design
• 出版年：2007
• 出版时间：June 2007
• 年：2007
• 卷：7
• 期：6
• 页码：1106 - 1114
• 全文大小：641K
• 年卷期：v.7,no.6(June 2007)
• ISSN：1528-7505

文摘

The interactions of ions in the solid state for a series of representative 1,3-dialkylimidazolium hexafluorophosphatesalts (either ionic liquids or closely related) have been examined by crystallographic analysis, combined with the theoretical estimationof crystal-packing densities and lattice-interaction energies. Efficient close-packing of the ions in the crystalline states is observed,but there was no compelling evidence for specific directional hydrogen-bonding to the hexafluorophosphate anions or the formationof interstitial voids. The close-packing efficiency is supported by the theoretical calculation of ion volumes, crystal lattice energies,and packing densities, which correlated well with experimental data. The crystal density of the salts can be predicted accuratelyfrom the summation of free ion volumes and lattice energies calculated. Of even more importance for future work, on these andrelated salts, the solid-state density of 1,3-dialkylimidazolium hexafluorophosphate salts can be predicted with reasonable accuracypurely on the basis of on ab initio free ion volumes, and this allows prediction of lattice energies without necessarily requiring thecrystal structures.