No abstract

We report on molecular dynamics simulations of the ionic liquid [bmim][BF 4] and its mixtures with water, from zero up to 0.5 mol fraction of water. All of the simulations are carried out with two published force fields. The results are compared with each other and with published as well as new NMR data on the same mixtures, whenever possible. We perform extensive analyses of structural quantities, such as pair correlation functions, nearest-neighbor analysis and size distribution of the water clusters formed at higher concentrations. We show that the water clusters are formed almost exclusively by linear chains of hydrogen-bonded molecules. There is a nanoscale structuring of the mixtures but no macroscopic phase separation among the components, in agreement with experiment. Roughly, we identify two solvation regimes. At low water content, the ions are selectively coordinated by individual water molecules, but their ionic network is largely unperturbed. At high water content, the ionic network is somewhat disrupted or swollen in a nonspecific way by the water clusters.

Experimental Details: NMR Measurements. The 1 H-NMR spectrum was measured at room temperature on a Varian Gemini 200 MHz spectrometer. Deuterated acetonitrile (CD 3 CN, 99.8 atom% D, containing 1% v/v TMS) was used as the solvent. 1 H-NMR data for the clear, colorless PY 15 TFSI (Figure S-1) salt indicate that the IL is of high purity (>99%). Elemental Analysis. Elemental analysis data for PY 15 TFSI, collected by Atlantic Microlab, Inc., are shown in Table S-1. Single-Crystal Structure of (1-x) PY 14 TFSI-(x) LiTFSI (x = 0.67). Schematic views of the ion coordination of the 1/2 PY 14 TFSI/LiTFSI structure are shown in Figure S-2. The structure is isostructural with the 1/2 PY 15 TFSI/LiTFSI structure (Figure S-3 or Figure 3), but this structure contains significant disorder amongst the ions (both cations and anions). The 1/2 IM 102 TFSI/LiTFSI structure is also reproduced here for comparison Figure S-4 or Figure 3). Raman Spectroscopic Measurements. Figure S-5 shows two Raman plots of the same (1-x) PY 15 TFSI-(x) LiTFSI (x = 0.50) sample which has been crystallized using different procedures. The data suggests that significant variations occur in the anion coordination for this sample based upon its thermal history. The DSC results (Figure 1) indicate that a new metastable phase may form for this composition which would explain the variability of the anion Raman bands. Figures S-6 to S-8 show variable-temperature Raman data of (1-x) PY 15 TFSI-(x) LiTFSI mixtures (dark line indicate where the samples melt).

Lithium salts dissolved in ionic liquids (ILs) are interesting alternatives to the commonly used electrolytes for Li-ion batteries. In this study, the solution of Li [bis-(trifluoromethanesulfonyl)imide] (LiTFSI) in N-butyl-N-methylpyrrolidinium TFSI (PYR14TFSI) ionic liquid in the 0.1:0.9 molar ratio is studied by heteronuclear NOE and NMR diffusion measurements. The main purpose is to spot on the interions organization and mobility. NOE data support the existence of strongly coordinated Li+ species, whereas variable temperature measurements of the self-diffusion coefficients D show large, selective, and unexpected enhancement of Li+ mobility with T. The measured activation energy for Li+ diffusion is significantly larger than those of TFSI− and PYR14 +. These findings can be related to the mechanism of Li+ diffusion in ILs based on disruption formation of the coordination shells of Li+ with TFSI anions rather than on the Brownian motion of the whole Li+ coordinated species.

A new heteroditopic receptor for alkali metal halides has been designed and synthesized. It is comprised of a well-established motif for cation binding and a motif for halogen-bonding-based anion recognition processes. The single-crystal X-ray structure of the complex between the heteroditopic receptor and sodium iodide is reported. Thanks to the cooperativity of metal coordination and the strong I-...I halogen bonding, the ion pair is fully separated. The boosting effect of the binding of the anion through halogen bonding on the coordination of the cation by the receptor has been proved also in solution by NMR experiments. The selectivity of the new heterotopic receptor toward different alkali metal halides has been tested by ESI mass experiments.