Polarity is one of the most important properties of ionic liquids (ILs) and an essential requirement when choosing an IL for a specific industrial application. Up to now, several empirical solvent polarity scales, such as Hildebrand solubility parameter, relative permittivity, the electronic transition energy of the longest-wavelength Vis absorption band of betaine dye no. 30 (E T (30) value) and the hyperfine coupling constant (A N ) etc. have been applied to ILs to provide quantitative evaluation of the polarity of ILs. Among them, the E T (30) value is widely used to reflect the polarity of ILs, however, it cannot be determined for opaque solvents or for solvents in which betaine dye no. 30 is insoluble. To broaden its scope of application and uniform the polarity standard, many approaches were used to predict the values of E T (30). Herein, we managed to apply a modified semiempirical reaction field of molecular solvents to predict the E T (30) and A N values of spin probe in ILs. Based on the experimental and estimated E T (30) values of 791 data entries, 240 ILs, 108 cations, and 34 anions of ILs, an "overall" polarity sequence of ILs can be obtained: primary, secondary, and tertiary alkylammonium salts > heterocyclic salts > quaternary alkylammonium salts ≈ phosphonium salts ≈ guanidinium salts.

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It is considered a more formidable task to precisely control the self-assembled products containing purely covalent components, due to a lack of intrinsic templates such as transition metals to suppress entropy loss during self-assembly. Here, we attempt to tackle this challenge by using directing groups. That is, the self-assembly products of condensing a 1:2 mixture of a tetraformyl and a biamine can be precisely controlled by slightly changing the substituent groups in the aldehyde precursor. This is because different directing groups provide hydrogen bonds with different modes to the adjacent imine units, so that the building blocks are endowed with totally different conformations. Each conformation favors the formation of a specific product that is thus produced selectively, including chiral and achiral cages. These results of using a specific directing group to favor a target product pave the way for accomplishing atom economy in synthesizing purely covalent molecules without relying on toxic transition metal templates.

Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C 10 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 ([C 10 mim][hfacac]) blue-shifted more significantly than that of [C 10 mim][Cu(hfacac) 3 ], meanwhile the v(C=O) red-shifted in [C 10 mim][Cu(hfacac) 3 ], which is contrast with that in [C 10 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 [C 10 mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C 10 mim][Cu(hfacac) 3 ] system.

Systematic measurements (densities, viscosities, conductivities) combined with small-angle X-ray scattering (SAXS) experiments were performed for binary mixtures of Cu IIcontaining chelate-based ionic liquid (ChIL) with linear alcohols. The experimental results were explained by disruption of alcohols to ionic aggregation of the ChILs. Viscosity deviations (Δη) of four binary systems all show negative values, which is because the ion-dipole interactions between the alcohols and the imidazolium ring of the ChIL weakened the hydrogen bonding between cation and anion of ChIL, in turn leading to higher mobility of ions and the decreased viscosity. Excess molar volumes (V E ) of the binary mixtures for the ChIL with methanol/ethanol all exhibit V-shape deviation from that of ideal solution while S-shape from positive to negative values is observed with 1-propanol/1-butanol, which is because the short chain alcohols could enter into the interspace of the ChIL while it is difficult for long chain alcohols.