Raman Spectroscopy of the Mixtures (x)1-Butyl-1-methylpyrrolidinium Chloride-(1 − x)TaCl5 in Solid and Molten States

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2008-09, Vol.112 (36), p.8288-8294
• Main Authors: Babushkina, Olga B, Ekres, Silvia, Nauer, Gerhard E
• Format: Article
• Language: English
• Subjects: A: Kinetics, Spectroscopy
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp8026176

A series of novel ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl) and TaCl5 were obtained in a wide range of molar compositions for electrochemical application. Raman spectroscopy was used to investigate the complex formation of tantalum(V) in the mixtures of (x)Pyr14Cl−(1 − x)TaCl5 (x = 0.80−0.30) over the temperature range 20−160 °C. Depending on the molar composition, different species of tantalum (V) were identified. In the basic and neutral mixtures of (x)Pyr14Cl−(1 − x)TaCl5 (x = 0.80−0.50), tantalum(V) exists in the form of octahedral [TaCl6]− in both solid and molten states. In acidic ionic liquids (x = 0.45−0.30), [Ta2Cl10] units are the main species of tantalum(V) identified in the solid state. As the temperature rose, the gradual degradation of [Ta2Cl10] units was observed in the solid state, accompanied by the formation of [TaCl6]− and [Ta2Cl11]− anions. In the molten state, in the range between 130 and 160 °C, the latter two species exist in equilibrium and are the dominant species of tantalum(V). The formation of oxochloride species of tantalum(V) was investigated in mixtures of Pyr14Cl−TaCl5−Na2O (x = 0.65) at various O/Ta mole ratios, and the formation of the oligomeric species with Ta−O−Ta bridging bonds was determined.