Thermophysical properties of ionic liquid, 1-hexyl-3-methylimidazolum bromide + N-N′bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base + N,N-dimethylformamide solutions

Effect of N-N′bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base on thermodynamic properties of ionic liquid, 1-hexyl-3-methylimidazolium bromide ([HMIm]Br) in N,N-dimethylformamide (DMF) solutions were determined at T = 298.15–313.15 K. The standard partial molar volumes, Vϕ0, partial molar volumes of transfer, ΔtrVϕ0 have been calculated using the measured density data. The cosphere overlap model was used to interpretate the partial molar volumes of transfer, ΔtrVϕ0. The calculated Hepler's constants, ∂2Vϕ0/∂2T, indicate that the BPIE and ionic liquid have structure-breaking (chaotropic) tendency. Ion association constants, Ka, and limiting molar conductivities, Λ0, viscosity B-coefficients and molar refractions, RD, have been used to confirm the conclusions obtained from the volumetric properties. The results were interpreted in terms of various solute–solvent interactions occuring in the investigated solutions and indicating an enhancement in the nonpolar–nonpolar interactions between the BPIE Schiff base and the ionic liquid with increasing BPIE concentration.

► Thermodynamic properties of ionic liquids + BPIE Schiff base + DMF were studied.
► There are preferential interactions between ionic liquid and BPIE molecules.
► The nonpolar–nonpolar interactions are dominant interactions between BPIE and ionic liquid.