Topological investigations of binary mixtures containing ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate and pyridine or isomeric picolines

Abstract

The densities, ρ, speeds of sound, u of {1-ethyl-3-methylimidazolium tetrafluoroborate (i)+pyridine or α- or β- or γ-picoline (j)} at T/K=(293.15, 298.15, 303.15, and 308.15) and excess molar enthalpies, HE of the same set of mixtures at T/K=(298.15) have been measured over entire mole fraction range using DSA-5000 and 2-drop microcalorimeter. Excess molar volumes, VE and excess isentropic compressibilities, κSE values have been predicted by utilizing the measured densities and speeds of sound data. It has been observed that VE, HE, and κSE values for the studied mixtures are negative over entire composition. The connectivity parameter of third degree of a molecule, 3ξ (which in turn depends upon its topology) have been applied to predict (i) state of components of ionic liquid mixtures in their pure and mixed state; (ii) nature and extent of interactions existing in mixtures; and (iii) VE, HE, and κSE values. The analysis of VE data in terms of Graph theory (which deals with topology of a molecule) suggest that while 1-ethyl-3-methylimidazolium tetrafluoroborate is characterised by electrostatic forces of attraction and exist as monomer; α- or β- or γ-picoline exist as associated molecular entities. Further, (i+j) mixtures are characterized by interactions between nitrogen and florine atoms of 1-ethyl-3-methylimidazolium tetrafluoroborate with nitrogen and carbon atoms of pyridine or isomeric picolines to form 1:1 molecular complex. The IR studies also support to this view point. The VE, HE, and κSE values predicted by Graph theory compare well with experimental values.