Probing the Local Structure of Pure Ionic Liquid Salts with Solid‐ and Liquid‐State NMR

Abstract

Room-temperature ionic liquids (RTILs) are gaining increasing interest and are considered part of the green chemistry paradigm due to their negligible vapour pressure and ease of recycling. Evidence of liquid-state order, observed by IR and Raman spectroscopy, diffraction studies, and simulated by ab initio methods, has been reported in the literature. Here, quadrupolar nuclei are used as NMR probes to extract information about the solid and possible residual order in the liquid state of RTILs. To this end, the anisotropic nature and field dependence of quadrupolar and chemical shift interactions are exploited. Relaxation time measurements and a search for residual second-order quadrupolar coupling were employed to investigate the molecular motions present in the liquid state and infer what kind of order is present. The results obtained indicate that on a timescale of approximately 10(-8) sec or longer, RTILs behave as isotropic liquids without residual order.

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

“…Experimental 35/37 Cl and 43 Ca SSNMR observations and analysis for CaCl 2 The 35 Cl EFG tensor parameters reported previously 46 for CaCl 2 appeared to be inconsistent with the trends observed for other group 2 metal halides, 12,44 prompting us to reinvestigate this system using SSNMR spectroscopy. Chlorine-35 SSNMR spectra were obtained for CaCl 2 at two applied fields (B 0 = 11.75 and 21.1 T), and analytical modeling of all observed line shapes resulted in identical EFG and CS tensor parameters (Fig.…”

“…32 Calcium-43 SSNMR spectra were referenced to a 2 mol/dm 3 aqueous solution of CaCl 2 (d iso = 0 ppm). 48 Chlorine and calcium pulse widths were established using the 35/37 Cl and 43 Ca SSNMR signals of solid KCl and saturated CaCl 2 (aq), respectively. Central transition (CT) selective (i.e., "solid p/2") pulse widths were determined by scaling the p/2 pulse widths measured for the above standards by 1/ (I + 1/2) (i.e., 1/2 for 35/37 Cl and 1/4 for 43 Ca).…”

“…The 37 Cl and 43 Ca SSNMR spectra of anhydrous CaCl 2 are also discussed. The results of GIPAW DFT computations on CaCl 2 and its known crystalline hydrates (i.e., CaCl 2 ·2H 2 O, (a/b/g)-CaCl 2 ·4H 2 O, and CaCl 2 ·6H 2 O) are discussed in an attempt to understand the prior 35 Cl SSNMR measurements for CaCl 2 , to refine the hydrogen positions for CaCl 2 ·2H 2 O, and to complement our experimental SSNMR data.…”

“…Probe ringing and second-order QI line shape broadening are both reduced by performing the SSNMR experiments in as high an applied magnetic field (B 0 ) as available. A variety of chlorine environments have been probed using 35/37 Cl SSNMR spectroscopy at "ultrahigh" B 0 , including (i) group 4 organometallic 40,41 and group 13 inorganic materials, 31 (ii) amino acid hydrochlorides, 34,36 (iii) ionic liquids, 42,43 (iv) group 2 metal chlorides, 44 and (v) pharmaceutical hydrochlorides. 45 As a result of these recent studies, a number of trends in the halogen SSNMR parameters have been observed and rationalized.…”

Pulsed-field gradient 1H NMR study of diffusion and self-aggregation of long-chain imidazolium-based ionic liquids

“…therein]. However, the recent nuclear magnetic resonance (NMR) relaxation (T 1 and T 2 ) studies indicate that some of imidazolium-based RTILs behave as isotropic liquids without residual order on the timescale of the inverse Larmor frequency~1/ω, i.e.~0 −8 s or longer [11,12]. The T 1 /T 2 values of 1.07-2.93 were determined for the series of the neat [C n mim][X] with n = 2, 4, and 10 and X = Cl and Br close to their melting points.…”