Electrochemistry of Zirconium Tetrachloride in the Ionic Liquid N-Butyl-N-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide: Formation of Zr(III) and Exploitation of ZrCl 4 as a Facile Ionic Liquid Drying Agent Chaopeng Fu, a, b Leigh Aldous , a Ninie S. A. Manan, c, d Richard G. Compton* a a Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK tel: + 44 (0) 1865 275 413 ; fax : + 44 (0) 1865 275 410 b College of Chemistry and Chemical Engineering, Hunan University, Changsha, P.R. China c School of Chemistry and Chemical Engineering, The QUILL Centre, Queens University Belfast, Belfast BT95AG, UK d Department of Chemistry, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia *e-mail: richard.compton@chem.ox.ac.uk Received: September 15, 2011; & Accepted: November 16, 2011 Abstract The electrochemistry of zirconium tetrachloride in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluorome- thylsulfonyl)imide has been studied, and the one electron reduction is proved by chronoamperometry. Furthermore, we report the application of ZrCl 4 as a facile and general ionic liquid drying agent for use in voltammetry. Keywords: Zirconium tetrachloride, Electrochemistry, Room temperature ionic liquid, Drying agent DOI: 10.1002/elan.201100513 Room temperature ionic liquids (RTILs) are fascinating, relatively new solvents, composed of a bulky unsymmetri- cal cation and either an organic or an inorganic anion [1], with many unusual or unique combinations of chemical and physical properties [2]. Their wide electrochemical windows and low volatility have led to their widespread application in a variety of areas [3]. Ionic liquids (ILs) are important media for the electrochemical research of species which cannot be studied in aqueous solution. ILs not only have much wider electrochemical windows than regular solvents, often wider than 6 V [2] and thus allow- ing for electrodeposition of various semiconductors and metals [4], but they also can stabilise some compounds that would normally undergo hydrolysis in aqueous solu- tions, allowing for studies on water-sensitive species such as PCl 3 [5]. In this work, we report the electrochemistry of zirconi- um tetrachloride (ZrCl 4 ) in the ionic liquid N-butyl-N- methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C 4 mpyrr][NTf 2 ]. ZrCl 4 is the main source for production of Zr metal and Zr-based alloys [6], which are important materials and have been widely used in applications such as corrosion-resistant materials, as well as catalysts for various processes [7]. Little data on the electrochemistry of ZrCl 4 in ionic liquids has been hitherto reported. This paucity of information likely arises from its volatility and rapid hydrolysis. ZrCl 4 is readily volatile and very sensi- tive to air, which makes it difficult to study electrochemi- cally in any detail. To the best of our knowledge, only Tsuda et al. have reported the electrochemistry of Zr(IV) in aluminium chloride-1-ethyl-3-methylimidazolium chlo- ride (66.7–33.3 mol %, respectively) at 353 K [8]. Howev- er, since more and more air and moisture stable ILs have been synthesized, there is much interest in non-haloalu- minate room temperature ionic liquids. The present study reports not only the electrochemistry of ZrCl 4 but also its application as a facile ionic liquid drying agent. Figure 1 shows the voltammetry of ZrCl 4 in [C 4 mpyrr]- [NTf 2 ], after being dried under vacuum prior to measure- ment. A limiting reduction current with a half-wave po- tential of 0.08 V and an oxidation peak current with a peak potential of 0.70 V are clearly visible. Interestingly, the oxidation peak remains the same size as a function of time under vacuum, while the charge under the peak re- mained constant over a range of scan rates and had a charge characteristic with a monolayer (see below). In contrast the reduction wave steadily decreased over time, since the ZrCl 4 concentrations could not be stabilised in the ionic liquid even if it was put under vacuum for drying for 24 h beforehand, as it both undergoes rapid hy- drolysis and is extremely volatile. Thus additions of vari- ous concentrations of ZrCl 4 resulted in reductive voltam- metry that did not scale with concentration and a white precipitate was always present regardless the concentra- 210  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2012, 24, No. 2, 210 – 213 Short Communication