Raman spectroscopy of the mixtures (x)1-butyl-1-methylpyrrolidinium chloride-(1 - x)TaCl5 in solid and molten states

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 degrees 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 degrees 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.