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

A series of ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl) and TaCl5 at molar ratios of Pyr14Cl 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 Pyr14Cl-TaCl5 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 Pyr14Cl-TaCl5 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 Pyr14Cl 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 Pyr14Cl-TaCl5 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.