Effect of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane Schiff base (BPIE) on the thermodynamic properties of the ionic liquid 1-hexyl-3-methylimidazolium chloride in N,N-dimethylacetamide solvent at T = 298.15 K

Densities, viscosities, and refractive indices of ternary mixtures of ionic liquid 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) + Schiff base, N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE), a mixture of cis- and trans-isomers, + N,N-dimethylacetamide (DMA) were measured at T = 298.15 K. From the obtained data, apparent molar volumes (Vϕ), corresponding experimental slopes (Sv), standard partial molar volumes (Vϕ0), transfer volumes (ΔtVϕ0), viscosity B-coefficients, solvation numbers (Sn), and molar refractions (RD) were calculated and discussed on the basis of (solute + solvent), and (solute + cosolute) interactions. As stated by cosphere overlap model (Yan et al., 2009), the negative transfer volumes obtained here show the dominance of (polar + nonpolar) interactions between the polar group of BPIE and the nonpolar alkyl chain of [HMIm]Cl and (nonpolar + nonpolar) interactions between the nonpolar groups of BPIE and the alkyl chain of [HMIm]Cl. The values of solvation numbers (Sn) were obtained as Sn > 2.5 and decrease as the concentration of BPIE in the mixtures increases. The Sn > 2.5 means that the IL is solvated in the mixtures, but the decreasing the Sn values indicates that the solvation of the ions of the ionic liquid decreases at higher concentrations of the Schiff base.