C-H-π Interactions in 1-n-Butyl-3-methylimidazolium Tetraphenylborate Molten Salt: Solid and Solution Structures

Abstract

The crystal structure of 1-nbutyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H ± p interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H ± p (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 ) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1 H NOESY NMR spectra between the protons of the cation and the anion. The 1 H-NMR spectra of molten salt 1 is almost inde-pendent of its concentration in [D 6 ]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D 6 ]DMSO as a solvent-separated ion pair. In CDCl 3 the 1 H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D 6 ]DMSO. Moreover, the 1 H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl 3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to À 4.5 ppm), an indication of the existence of C-H ± p interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 for a C-H ± p angle of 1808. The apparent volumes for the cation and anion, calculated from the measured 13 C-NMR relaxation times, increase from 38 and 140 3 in [D 6 ]DMSO to 360 and 600 3 in CDCl 3 , respectively; this indicates the formation of floating aggregates of the type (1) n in CDCl 3 via weak hydrogen bonds, with increasing concentration.

Catalytic Applications of Metal Nanoparticles in Imidazolium Ionic Liquids

“…[14,15] The monomeric unit always consists of one imidazolium cation surrounded by at least three anions and in turn each anion is surrounded by at least three imidazolium cations. The three-dimensional arrangement of the imidazolium ionic liquids is generally formed through chains of the imidazolium rings that generates channels in which the anions are generally accommodated as chains ( Figure 2).…”

IR and NMR Properties of Ionic Liquids: Do They Tell Us the Same Thing?

“…Thus, NMR properties, such as proton and carbon chemical shifts, 13 C relaxation times, and diffusion coefficients, can be measured. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] IR spectroscopy is applied to study the structure of ILs, in particular the strength of the interactions between anions and cations. [19][20][21] However, there is no available systematic study of the structural and dynamical properties by using NMR and IR spectroscopy.…”

AuPd/Fe3O4-based three-dimensional electrochemical system for efficiently catalytic degradation of 1-butyl-3-methylimidazolium hexafluorophosphate

“…The a was not stable and apt to be was further oxidized. Reports [37,38] have proven that N1-C2 and C2 -N3 bonds in the ring of BMIM can be treated as 'one-and-an-half' N-C bond, the bond lengths of which is much shorter than that of N3-C4 and N1-C5 in the imidazolium ring of BMIM. Thus the N1-C2 and C2-N3 bonds were in less energy and better stability.…”