Ionic liquids based on triethanolammonium salts of dicarboxylic acids (oxalic, malonic, succinic). Crystal structure and cation-anion interaction

Abstract

The series of ionic liquids based on triethanolammonium salts of dicarboxylic acids (oxalic, malonic and succinic) was synthesized, characterized by IR and H1, C13 NMR spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Their structure was determined by single-crystal X-ray diffraction. It was found that triethanolammonium [(HOCH2CH2)3NH]+ cations in salts of oxalic (1), malonic (2) and succinic acids (3) containing monoanions [OOC(CH2)nCOOH]− (n = 0–2) have the endo conformation and the ammonium proton (Ham) resides inside the “lampshade” formed by three CH2CH2OH branches connected with nitrogen atom. The asymmetric cell of the second modification of the succinic acid salt (4) includes two triethanolammonium cations and a succinate dianion [(HOCH2CH2)3NH]2+[OOC(CH2)2COO]2 −. In this salt (4) one CH2CH2OH branch of the triethanolammonium cation is rotated around the NC bond (endo-exo conformation) and forms infinite TEA chains. This pattern was firstly found in organic salts of TEA. The obtained results show that different structures of triethanolammonium cations in the salts of dicarboxylic acids have significant influence on the cation-anion interaction.