Xiaopeng Xuan

Vibrational spectroscopic studies on ion solvation of lithium perchlorate in propylene carbonate+N,N-dimethylformamide mixtures

The infrared (IR) and Raman spectra are reported for solutions of lithium perchlorate in propylene carbonate (PC), N,N-dimethylformamide (DMF) and PC + DMF mixtures. The band splittings of symmetric ring deformation for PC and O=CN deformation for DMF suggest that there is a strong interaction between lithium cations and solvent molecules. The solvent molecules have been assigned to two types, the free and complexed molecules. By a comparison of the intensity for the corresponding bands, it has been concluded that Li+ cations are preferentially solvated by DMF molecules in the LiClO4/PC-DMF solutions. This has been explained by the difference in values of donor number.

Theoretical study on cation-anion interaction and vibrational spectra of 1-allyl-3-methylimidazolium-based ionic liquids.

In order to deepen the understanding of the cation-anion interaction in ionic liquids, the structures of cation, anions, and cation-anion ion-pairs of 1-allyl-3-methylimidazolium-based ionic liquids are optimized using density functional theory (DFT), and their most stable geometries are discussed. The structural parameters, hydrogen bonds and interaction energies of 1-allyl-3-methylimidazolium dicyanamide ([Amim]DCA), 1-allyl-3-methylimidazolium chloride ([Amim]Cl), 1-allyl-3-methylimidazolium formate ([Amim]FmO) and 1-allyl-3-methylimidazolium acetate ([Amim]AcO) ion pairs are studied. The vibrational frequencies of [Amim]DCA and [Amim]Cl have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes.

Synthesis, crystal structure, vibrational spectra and theoretical calculation of 1-carboxymethyl-3-methylimidazolium chloride

In this paper, the structure of 1-carboxymethyl-3-methylimidazolium chloride was studied by X-ray diffraction, density functional theory, and FT-IR and Raman spectroscopic techniques for the first time. Title compound crystallizes in the orthorhombic space group Pca2(1) with the cell dimensions a=13.445 (6) Å, b=6.382 (3) Å, c=9.727 (5) Å and V=834.6 (7) Å(3). All the geometrical parameters have been calculated using by B3LYP with 6-311G++(d,p) basis set. Optimized geometries have been compared with the experimental data, and the hydrogen bond and short contact interactions were discussed. The vibrational frequencies, infrared intensities and Raman scattering activities of the title compound were calculated at the same level. The observed bands were assigned based on the theoretical calculations. The scaled vibrational frequencies seem to coincide with the experimental data with acceptable deviations.

The Enhanced Dissolution of β-Cyclodextrin in Some Hydrophilic Ionic Liquids†

Beta-cyclodextrin (beta-CD) is difficult to dissolve in water and in many common solvents and searching for the proper solvents is the key step to expand its application. In this work, six kinds of hydrophilic ionic liquids 1-n-butyl-3-methylimidazolium chloride, 1-(2-hydroxyethyl)-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-n-butyl-3-methylimidazolium dicyanamide, 1-(2-hydroxyethyl)-3- methylimidazolium dicyanamide and 1-allyl-3-methyl-imidazolium dicyanamide have been prepared. The solubilities of beta-cyclodextrin in these ionic liquids have been determined in the temperature range from 333.2 to 363.2 K with 5 K intervals. The solution thermodynamic parameters of beta-cyclodextrin have been calculated from the solubility data. It was shown that solubility of beta-cyclodextrin was remarkable in ionic liquids, it was as high as 125.0 g in 100 g of [Amim][N(CN)(2)] at 348.2 K. The dissolution process was unfavorable thermodynamically and controlled by the enthalpic term. (1)H NMR and IR spectroscopic measurements were used to study the enhanced dissolution of beta-cyclodextrin in the ionic liquids. The results indicated that 1:1 inclusion complexes were formed between beta-cyclodextrin and imidazolium cations of the ionic liquids. The differences in the solubility of beta-cyclodextrin have been discussed from the interionic interaction between cation and anion of the ionic liquids and the inclusion interaction of the cations of the ionic liquids into the cavities of beta-cyclodextrin. The strength of the interionic interactions was found to be predominant for the dissolution of beta-cyclodextrin. It is expected that such information may find application in the molecular design of the stationary phases in gas chromatography.

Hydrogen bonds in the crystal structure of hydrophobic and hydrophilic COOH-functionalized imidazolium ionic liquids

The crystal structures of six COOH-functionalized imidazolium ionic liquids (ILs) were determined, and different hydrogen bonds were found in the hydrophobic and hydrophilic ionic liquids. For the hydrophilic COOH-functionalized ILs based on halide anions, the classic O–H⋯Cl− or O–H⋯Br− hydrogen bond was observed by single crystal X-ray diffraction, whereas the carboxyl group dimer was present for the hydrophobic COOH-functionalized ILs based on the (CF3SO2)2N− (TFSI) and PF6− anions. Parallel vibrational spectroscopic studies and DFT calculations have also demonstrated the difference in the hydrogen bond structures. The relationship between the solubility of the ionic liquids in water and their structures was discussed.

Quantum chemical studies of FT-IR and Raman spectra of methyl 2,5-dichlorobenzoate.

In this paper, experimental and theoretical studies on the molecular structure and vibrational spectra of methyl 2,5-dichlorobenzoate (MDCB) are presented. Fourier transform infrared and Raman spectra of the title molecule in the solid phase were recorded and analyzed. The geometrical parameters were calculated using DFT (B3LYP) with 6-311G(d,p) and 6-311++G(d,p) basis sets, and compared with the experimental data. The vibrational frequencies, infrared intensities and Raman scattering activities were also reported. The detailed assignments were given based on the total energy distribution of the vibrational modes, calculated with scaled quantum mechanics method. The observed and calculated frequencies are found to be in good agreement.

A VIBRATIONAL SPECTROSCOPIC STUDY OF ION SOLVATION IN LITHIUM PERCHLORATE/PROPYLENE CARBONATE ELECTROLYTE

Abstract The infrared (IR) and Raman spectra of propylene carbonate (PC) containing various concentrations of LiClO4 have been measured and analyzed. The difference in spectra of PC with and without LiClO4 was attributed to the interaction of the PC molecules and lithium ions. This interaction occurs mainly on the carbonyl oxygen atom of the PC molecule. The ring deformation, symmetric ring deformation, carbonyl stretching and stretching of ring oxygens for PC are sensitive to this interaction. The solvation number of Li+ is also calculated. On the other hand, the structure of the ClO− 4 is also affected by PC molecule, forming the solvent separated ion pairs.

Ion solvation and association in LiClO4/sulfolane solution: a vibrational spectroscopic and molecular orbital study.

Solvation interaction and ion association in solutions of lithium perchlorate/sulfolane have been studied by using infrared and Raman spectra as a function of concentration of lithium perchlorate. The band changes of antisymmetric OSO stretch, antisymmetric CSC stretch, -SO2 wag and twist suggest that there is an interaction between Li+ and sulfolane molecules, and the site of solvation is the oxygen atom of -SO2 group. The molecular orbital calculation supports this suggestion. On the other hand, the apparent solvation number was calculated, and the band fitting for the ClO4- band reveals the presence of contact ion pair, solvent separated ion pair and free ClO4- anion in the concentrated solutions.

Theoretical study of molecular structure and vibrational spectra of 1,4-dihydroxyanthraquinone

Molecular structure and vibrational spectra of 1,4-dihydroxyanthraquinone (1,4-DAQ) are studied theoretically and experimentally. FT-infrared and Raman spectra of 1,4-DAQ are recorded in solid phase in regions of 4000-400 and 3500-100 cm(-1), respectively. The geometry of 1,4-DAQ is optimized by B3LYP and B3PW91 methods, and the most stable structure with C2v point group is found. The harmonic vibration frequencies, infrared intensities, and the Raman scattering activities of the compound are calculated, analyzed, and compared with experimental data. Our calculated frequencies agree well with the experimental results.

Density functional theory calculations of structure, FT-IR and Raman spectra of S-phenyl thioacetate

The infrared (4000-400 cm(-1)) and Raman spectra (3700-100 cm(-1)) of liquid S-phenyl thioacetate have been recorded. Molecular geometry, vibrational frequencies and the corresponding assignments were performed by density funtional theory (DFT) using the 6-311++G(d,p) basis set. Two conformers have been identified. One is syn form where the carbonyl group is on the same side of the phenyl ring and the other is the anti form. The energy difference between these two configurations is about 1.63 kcal mol(-1) at B3LYP/6-311++G(d,p) level. By utilizing the more stable syn conformer, a complete assignment of the observed frequencies is given according to the total energy distribution of the vibrational modes. The general agreements between the observed and the calculated frequencies are shown.