A series of novel ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr(14)Cl) 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)Pyr(14)Cl-(1 - x)TaCl5 (x = 0.90-0.30) 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)Pyr(14)Cl-(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 reose, the gradual degradation of [Ta2Cl10] units was observed in the solid state, accompanied by temperature rose, the g 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 Pyr(14)Cl-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.