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

Abstract

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.

Probing the electronic environment of binary and ternary ionic liquid mixtures by X-ray photoelectron spectroscopy

“…A typical Cl 2p spectrum is composed of a doublet peak with a spin-orbital coupling energy difference of 1.6 eV [22] and area ratio of 2p3/2 : 2p1/2 is 2:1.…”

“…A satisfactory fitting could be achieved by setting the area ratio of the two different environments to 3:1 and both chlorine environments with spin-orbital coupling energy gap of 1.6 eV [22]. [SnCl3] -and Cl -, which leads to both of the Sn centre and the Cl centre being less negatively charged and thus show higher binding energy.…”

Synthesis of chlorostannate(ii) ionic liquids and their novel application in the preparation of high-qualityl-lactide

“…Thirdly, chlorostannate(II) ionic liquids are more inexpensive than those incorporating gallium(III) or indium(III) and less sensitive toward moisture than those based on aluminum(III) and gallium(III). 29 In this study, the imidazolium-based ionic liquids incorporating stannum(II) were successfully prepared. The structure, thermal stability, and acidity of these synthesized ILs were experimentally determined and systematically analyzed.…”

Phosphonium Chloromercurate Room Temperature Ionic Liquids of Variable Composition

“…67 This information can be used to design metal recovery processes with increased extraction efficiency. Simple and fast approaches to quantification of the dissolved metal are also of interest.…”