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Chlorostannate(II) ionic liquids: speciation, Lewis acidity, and oxidative stability
Matthew Currie1, Julien Estager, Peter Licence
1QUILL, The Queen's University of Belfast, Belfast BT9 5AG, United Kingdom.
Inorganic Chemistry
|June 9, 2012
Summary
This study reveals the anionic speciation of tin(II) chloride ionic liquids, identifying key species like [SnCl3](-) and Cl(-). It also quantifies their Lewis acidity and notes oxidation to tin(IV) compounds.
Area of Science:
- Materials Chemistry
- Ionic Liquids
- Coordination Chemistry
Background:
- Ionic liquids (ILs) are salts that are liquid at room temperature, offering unique solvent properties.
- Chlorostannate(II) ILs are of interest due to tin's versatile coordination chemistry.
- Understanding anionic speciation is crucial for predicting and controlling IL properties.
Purpose of the Study:
- To investigate the anionic speciation of chlorostannate(II) ionic liquids.
- To determine the influence of tin(II) chloride molar ratio on speciation and properties.
- To assess the Lewis acidity and basicity of these ionic liquids.
Main Methods:
- Synthesis of 1-alkyl-3-methylimidazolium chloride and tin(II) chloride mixtures.
- Characterization using (119)Sn NMR, X-ray photoelectron spectroscopy, viscometry, Raman spectroscopy, single-crystal X-ray crystallography, and differential scanning calorimetry.
- Lewis acidity determination via Gutmann acceptor number and Lewis basicity via (1)H NMR spectroscopy.
Main Results:
- Identified anionic species: [SnCl3](-), Cl(-), and [Sn2Cl5](-) in equilibrium depending on SnCl2 molar ratio (χ(SnCl2)).
- Observed precipitation of SnCl2 at χ(SnCl2) > 0.63.
- Found no evidence for [SnCl4](2-) but noted Lewis acidity comparable to Zn(II) systems for χ(SnCl2) > 0.50.
- Demonstrated slow air oxidation of Cl(-)-containing compositions to tin(IV) ionic liquids ([SnCl6](2-)).
Conclusions:
- The anionic speciation of chlorostannate(II) ILs is highly dependent on the SnCl2 molar ratio.
- The Lewis acidity of these ILs can be tuned by composition.
- The potential for oxidation to tin(IV) species must be considered during handling and application.
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