Physicochemical properties of the N-methyl-6-hydroxyquinolinium–based protic ionic liquids in the gas and solution media: M06–2X-GD3/6–311 +  + G(d,p) study

The interesting biological activity of N-methyl-6-hydroxyquinolinium salts (6MQc) and their derivatives has made them promising pharmaceutical agents. In this research, the physicochemical properties of N-methyl-6-oxyquinolonium [6MQz]+–based ionic liquids (IL) [6MQc][Y1–6] (Y1–6 = CH3CO2−, CF3CO2−, NTf2−, CF3SO3−, BF4−, and PF6−) were calculated at M06–2X-GD3/6–311 +  + G(d,p) level of theory. It is proposed that the formation of [6MQz] in the [6MQc][Y1] IL makes it sensitively respond to pH variations. The results showed that the degree of association of ions decreases on going from a non-polar solvent to a polar one. Based on electrochemical window values, the studied ILs have no suitable electrochemical stability for use in electrochemical devices. The natural bond orbital (NBO) and atoms-in-molecules (AIM) population analyses were carried out to calculate the atomic charges and electron density properties as well as to characterize the nature of the hydrogen bonding interaction in ion pairs.