Phase Behaviour and FTIR Spectra of Ionic Liquids: The Mixtures of 1-Butyl-1-methylpyrrolidinium Chloride and TaCl₅

Abstract

A series of ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr 14 Cl) and TaCl 5 at molar ratios of Pyr 14 Cl in the range of 0.85 - 0.20 was synthesized. They exhibit potential application as electrolytes for the electrochemical deposition of tantalum. The thermal behaviour of the Pyr 14 Cl-TaCl 5 mixtures was investigated, using differential scanning calorimetry (DSC) to estimate the range of thermal stability and to determine the optimal compositions for electrochemical trials. The Pyr 14 Cl-TaCl 5 mixtures formed stoichiometric 3 : 2 and 2 : 3 crystalline phases with melting points of 70 °C and 130 °C, respectively, characterized by entropies of fusion of 13.6 JK −1 mol −1 and 10.1 JK −1 mol −1 . The mixtures with molar fractions of Pyr 14 Cl equal to 0.60 and 0.40 were clear and transparent liquids and had the lowest viscosity; they were the most suitable for electrochemical applications. FTIR spectra of the Pyr 14 Cl-TaCl 5 mixtures allowed to get insight into inter-ionic interactions and the nature of formation of these ionic liquids as a function of the molar ratio of the components.