Alexander Shaplov - Extremely short C-H...F contacts in the crystal of 1-methyl-3-propyl-imidazolium SiF6 – the reason of unexpected high melting point for ionic "liquid"

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  D.G. Golovanov, K.A. Lyssenko, M.Yu. Antipin, Ya.S. Vygodskii,   E.I. Lozinskaya, A.S.   Shaplov. Cryst. Eng. Comm.,   2005, v. 7, no. 6, P. 53-56.


  The synthesis and XRD investigation of hexafluorosilicate salt   with 1-propy-3-methylimidazolium   ([Pmim]+) cation is described.   Analysis of crystal packing has revealed that unexpectedly high   m.p. (210oC) of salt is resulted from the presence of   extremely short interionic C(Im)H…F contacts in the crystal (1.94   – 2.42Å). The absence of strong C-H…F interaction for alkyl   radicals lead to high mobility of substituents and resulted to   phase transition of the order-disorder type. The total energy of   the CH…F interactions in the hypothetical   [SiF6(Pmim)6]+4 cluster   according to DFT calculation and topological analysis of the   electron density distribution attains ca. 33 kcal/mole.

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