Shuang Men

Chlorostannate(II) Ionic Liquids: Speciation, Lewis Acidity, and Oxidative Stability

The anionic speciation of chlorostannate(II) ionic liquids, prepared by mixing 1-alkyl-3-methylimidazolium chloride and tin(II) chloride in various molar ratios, χ(SnCl2), was investigated in both solid and liquid states. The room temperature ionic liquids were investigated by (119)Sn NMR spectroscopy, X-ray photoelectron spectroscopy, and viscometry. Crystalline samples were studied using Raman spectroscopy, single-crystal X-ray crystallography, and differential scanning calorimetry. Both liquid and solid systems (crystallized from the melt) contained [SnCl(3)](-) in equilibrium with Cl(-) when χ(SnCl(2)) < 0.50, [SnCl(3)](-) in equilibrium with [Sn(2)Cl(5)](-) when χ(SnCl(2)) > 0.50, and only [SnCl(3)](-) when χ(SnCl(2)) = 0.50. Tin(II) chloride was found to precipitate when χ(SnCl(2)) > 0.63. No evidence was detected for the existence of [SnCl(4)](2-) across the entire range of χ(SnCl(2)), although such anions have been reported in the literature for chlorostannate(II) organic salts crystallized from organic solvents. Furthermore, the Lewis acidity of the chlorostannate(II)-based systems, expressed by their Gutmann acceptor number, has been determined as a function of the composition, χ(SnCl(2)), to reveal Lewis acidity for χ(SnCl(2)) > 0.50 samples comparable to the analogous systems based on zinc(II). A change of the Lewis basicity of the anion was estimated using (1)H NMR spectroscopy, by comparison of the measured chemical shifts of the C-2 hydrogen in the imidazolium ring. Finally, compositions containing free chloride anions (χ(SnCl(2)) < 0.50) were found to oxidize slowly in air to form a chlorostannate(IV) ionic liquid containing the [SnCl(6)](2-) anion.

X-ray Photoelectron Spectroscopy of Pyridinium-Based Ionic Liquids: Comparison to Imidazolium- and Pyrrolidinium-Based Analogues

Abstract We investigate eight 1‐alkylpyridinium‐based ionic liquids of the form [CnPy][A] by using X‐ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake‐up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic‐liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C8Py][A] and analogues including 1‐octyl‐1‐methylpyrrolidinium‐ ([C8C1Pyrr][A]), and 1‐octyl‐3‐methylimidazolium‐ ([C8C1Im][A]) based samples, where X is common to all ionic liquids.

Tuning the electronic environment of cations and anions using ionic liquid mixtures

Electrostatic interactions are ubiquitous in ionic liquids and therefore, the electronic environment (i.e. the distribution of electron density) of their constituent ions has a determining influence on their properties and applications. Moreover, the distribution of electron density on atoms is at the core of ionic liquid molecular dynamics simulations. In this work, we demonstrate that changing the composition of ionic liquid mixtures can tune the electronic environment of their constituent ions, both anions and cations. The electronic environment of these ions can be monitored by measuring the characteristic electron binding energies of their constituent atoms by X-ray photoelectron spectroscopy (XPS). The possibility to fine tune, in a controlled way, the electronic environment of specific ions provides an invaluable tool to understand ionic liquid properties and allows the design of ionic liquid mixtures towards specific applications. Here, we demonstrate the power of this tool by tuning the electronic environment of a catalytic centre, and consequently its catalytic activity, by the use of ionic liquid mixtures.

An ultra high vacuum-spectroelectrochemical study of the dissolution of copper in the ionic liquid (N-methylacetate)-4-picolinium bis(trifluoromethylsulfonyl)imide

Ultra high vacuum-spectroelectrochemistry was used to investigate the electrochemically generated Cu species in the ionic liquid (N-methylacetate)-4-picolinium bis(trisfluoromethylsulfonyl)imide, [MAP][Tf(2)N]. The diffusion of Cu(+) across the surface of the ionic liquid was monitored in situ by X-ray photoelectron spectroscopy (XPS). A numerical procedure was developed to simulate the surface process from which, the apparent diffusion coefficient of Cu(+) across the surface is estimated to be 3.5 x 10(-5) cm(2) s(-1). Bulk diffusion process of Cu(+) in [MAP][Tf(2)N] was investigated ex situ for comparison with the surface process.

Acidity and basicity of halometallate-based ionic liquids from X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to investigate a series of 1-octyl-3-methylimidazolium halometallate ionic liquids of the general formula (1 − χ)[C8C1Im]Cl–χMCly (where χ is the mole fraction of metal halide and y = 2 or 3). The ionic liquids emitted good photoelectron fluxes allowing the measurement of high quality spectra with good peak resolution. Interrogation of the XPS data has allowed the prediction of trends in solvent parameters for these ionic liquids, including hydrogen bond basicity and Lewis acidity. Clear changes to the shape and energy of metal originated photoelectron peaks, as a function of mole fraction of metal halide, aids the identification of complex polynuclear anions within the ionic liquids.

Directly probing the effect of the solvent on a catalyst electronic environment using X-ray photoelectron spectroscopy

The electronic environment of the metal centre of a catalyst dissolved in ionic liquids has a determining effect on its catalytic efficiency in chemical reactions. However, the electronic environment of the ionic liquid-based metal centres can be influenced by not only their chemical state but also the solute–solvent interaction. In this work, we demonstrate that the anion of an ionic liquid can significantly influence the electronic environment of a metal centre. The metal centre electronic environment can be monitored by measuring the typical electron binding energies by X-ray photoelectron spectroscopy (XPS). The correlation of the electronic environment of the metal centre with reaction performance provides a possibility to design and control a chemical reaction. In this work, we also illustrate a strategy for tuning the electronic environment of metal centres, by the selection of particular ionic liquid anions, to design a catalytic system and consequently to finally control the reaction performance of a model Suzuki cross coupling reaction.