Structural and electronic properties of CuII, CoII, and NiII-containing chelate-based ionic liquids

The interactions of chelate-based ionic liquids: from the perspective of vaporization enthalpy

The vaporization enthalpies of [C_nTPP][Cu(F₆-acac)₃] (n = 14, 16) and [C_nmim][Cu(F₆-acac)₃] (n = 8, 10), a new type of chelate-based ionic liquids (ChILs), were measured by thermogravimetric analysis (ΔglHom(T_av) = 73.2-83.7 kJ mol^-1), which decreased compared to their non-chelate counterparts (difference up to 34.1 kJ mol^-1). This can be explained by the fact that the increase in the polar region size by chelate ions mainly leads to the decrease in Coulomb forces based on the micro-biphasic separation in ionic liquids. Vaporization enthalpies at experimental temperatures were adjusted to a reference temperature by the Verevkin's method, and compared with the data calculated by the Kabo's method, which illustrated clear differences on ChILs. In addition, some physicochemical properties of [C_nTPP][Cu(F₆-acac)₃] (n = 14, 16) were measured including density, viscosity, conductivity, and surface tension.

Special Mixing Behavior of Chelate-based Ionic Liquid with Methanol

Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C₁₀ mim][Cu(hfacac)₃ ]) with methanol was found, indicating the way methanol interacts with ILs might be governed by the special structure of the chelating anion. IR results showed that the v (C2-H) of 1-decyl-3-methylimidazolium hexafluoroacetylacetonate ([C₁₀ mim][hfacac]) blue-shifted more significantly than that of [C₁₀ mim][Cu(hfacac)₃ ], meanwhile the v (C=O) red-shifted in [C₁₀ mim][Cu(hfacac)₃ ], which is contrast with that in [C₁₀ mim][hfacac]. Two-dimensional correlation analysis of the FTIR spectra indicated that the chelating cavity has little effect on the sequence of the ILs sites that interact with methanol. Combined with small angle X-ray scattering (SAXS) results, the picture of mixing processes in these two systems were proposed. Methanol interacts directly with the anion followed by the cation in [C₁₀ mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C₁₀ mim][Cu(hfacac)₃ ] system.