Various thermophysical properties, densities, electrical conductances, viscosities, and refractive indices of two ionic liquids, 1-pentyl-3-methylimidazolium bromide ([PnMIm]Br) and 1-propyl-3-methylimidazolium bromide ([PMIm]Br, in the presence of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in N,N-dimethylformamide (DMF) solutions have been measured at 298.15 K. These data have been used to calculate the standard partial molar volumes, V
ϕ
0, partial molar volumes of transfer, Δtr
V
ϕ
0, ion association constants, K
a, limiting molar conductivities, Λ0, viscosity B-coefficients, and molar refractions, R
D, for the solutions studied. These parameters decrease with increasing BPIE concentration and increase with increasing alkyl chain length of ionic liquids. The results were interpreted in terms of cosphere overlap model and solute–solvent interactions. In general, it is concluded that there is an enhancement in the nonpolar–nonpolar interactions between the BPIE Schiff base and the ionic liquid.
Schiff bases and their metal complexes in the mixtures of ionic liquid (IL) + organic solvent have shown great potential in attractive oxidation catalytic processes. The efficiency of such a process is strongly dependent on the various molecular interactions occurring between components. Thermodynamic properties of these systems can provide valuable information about structural interactions. Therefore, in this work, the interactions of the IL 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) with Schiff bases in organic solvents were studied through the measurements of density, viscosity, and electrical conductivity. The effect of solvent on the interactions was examined by the solutions of IL + BPIC Schiff base + solvent (C2H6O-C3H8O-C4H10O). Moreover, the influence of Schiff base ligand and Schiff base complex structures was probed by the solutions of IL + DMA + ligand (salcn/salpr/salen) and IL + DMA + complex (VO(3-OMe-salen)/VO(salophen)/VO(salen)), respectively. Using the experimental data, some important thermodynamic properties, such as standard partial molar volume (V(0)(φ,IL)), experimental slope (Sv), viscosity B-coefficient, solvation number (B/V(0)(φ,IL) and limiting molar conductivity (Λ0) were calculated and discussed in terms of solute-solvent (IL-DMF/alcohol) and solute-cosolute (IL-Schiff base) interactions.
The
effect of some imidazolium based ionic liquids including 1-propyl-3-methylimidazolium
bromide ([PMIm]Br), 1-pentyl-3-methylimidazolium bromide ([PnMIm]Br),
1-hexyl-3-methylimidazolium bromide ([HMIm]Br), and 1-hexyl-3-methylimidazolium
chloride ([HMIm]Cl) on the volumetric and viscometric properties of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane
Schiff base (BPIE) in acetonitrile (CH3CN) solutions was
studied at T = (298.15 to 313.15) K. The measured
densities were used to calculate apparent molar volumes (V
ϕ) which were utilized to obtain standard partial
molar volumes (V
ϕ
0) of the ionic liquids. The temperature
dependence of the V
ϕ
0 values was examined by determination
of partial molar expansivity (E
ϕ
0 = (∂V
ϕ
0/∂T)
P
) and thermal expansion coefficient
at infinite dilution (α = E
ϕ
0/V
ϕ
0)). Moreover,
the pair (V
SIL) and triplet (V
SSIL) interaction coefficients were estimated based on
McMillan and Mayer’s theory. The calculated Helper’s
constants ((∂2
V
ϕ
0/∂T
2)
P
) indicate that the ionic
liquids being studied behave as a structure-breaker in the solutions.
To confirm the volumetric results, viscosities of the solutions were
measured using an Ubbelohde-type viscometer. The viscosity values
were used to calculate viscosity B-coefficients by
the Jones–Dole equation and the solvation numbers (B/V
ϕ
0) of the ionic liquids in the solutions. The
effect of anion and cation size of ionic liquids on the calculated
parameters was also examined. The results were used to deduce various
interactions in the ternary solutions. It is concluded that the Schiff
base–IL interactions are strengthened as the Schiff base concentration
increases in the solution.
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