1-Aryl-3,5-dimethylpyrazolium based tunable protic ionic liquids (TPILs)

A series of new 1-aryl-3,5-dimethylpyrazolium based tunable protic ionic liquids/salts ([Ph(R)Hpz][X], R: -H, -Cl, -Br, -CH3, -OCH3, X: chloride [Cl-] and tetrafluoroborate (BF4-) have been synthesized through acid-base neutralization reactions between 1-aryl-3,5-dimethy1-1H-pyrazoles and the corresponding inorganic acids. The chemical structure of the salts was confirmed by FTIR, H-1 NMR, C-13 NMR, elemental analysis, and F-19 NMR (3a-3e) and the crystal structure of the two salts (2a and 3d) was also elucidated by X-ray analysis of single crystals. Melting points and thermal decomposition temperatures of TPILs (2e and 3b) were determined. The geometries of the cations, anions and ionic salts were optimized, and their molecular electrostatic potentials (MEPs) were assessed by using density functional theory methods (B3LYP and M06-2X). The electrochemical window of the salts was determined both experimentally and theoretically. The correlation coefficient values were also calculated by using theoretical and experimental EW values of the salts