Density functional theory methods in combination with vibrational spectroscopy are used to investigate possible variants of molecular structure of the ion pairs of several imidazolium-based ionic liquids (ILs). Multiple stable structures are determined with the anion positioned (a) near to the C2 atom of the imidazolium ring, (b) between N1 and C5, (c) between N3 and C4, and (d) between C4 and C5. Chloride and bromide anions in vacuum also occupy positions above or below the imidazolium ring, but in the condensed state these positions are destabilized. In comparison with the halides that almost equally occupy the positions (a-d), tetrafluoroborate and hexafluorophosphate anions strongly prefer position (a). The position and the type of the anion influence the conformation of the side chains bound to the imidazolium N1 atom, which are able to adopt in vacuum all usual staggered or eclipsed conformations, although in the liquid state some of the conformations are present only as minor forms if at all. Vibrations of the cations depend both on the conformational changes and on the association with the anion. The formation of the ion pairs influences mainly stretching and out-of-plane vibrations of the imidazolium C-H groups and stretching vibrations of the perfluoroanions. Other modes of the ions retain their individuality and practically do not mix. This allows "interionic" vibrations to be separated and to regard the couple of the ions as an anharmonic oscillator. Such a model correlates the molecular structure of various ILs and their melting points without involving the energy of the interaction between the cations and anions but explains structure-melting point correlations on the grounds of quasy-elastic properties.

The IR and Raman spectra and conformations of the ionic liquid 1-ethyl-3-methyl-1H-imidazolium tetrafluoroborate, [EMIM] [BF 4 ] (6), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM ¥ BF À 4 ion pair closely resemble those of the isolated ions EMIM and BF À 4 , except for the antisymmetric BF stretching vibrations of the anion, and the out-of-plane and stretching vibrations of the HÀC(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion-pair formation is the H-bonding between HÀC(2) and BF À 4 . However, these weak H-bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD 2 Cl 2 solutions. According to the −gas-phase× computations, in these associates, the BF À 4 anion is positioned over the imidazolium ring of the EMIM cation and has short contacts not only with the HÀC(2) of the latter, but also with a proton of the MeÀN(3) group.

Relative infrared (IR) intensities and relative Raman activities have been computed for vibrations of test molecules, including from two to nine heavy atoms, using second-order Moller-Plesset perturbation theory (MP2), and three hybrid density functionals (B3LYP, M05, and M05-2X). The basis set convergence of vibrational properties is discussed. Our results demonstrate that B3LYP offers the most cost-effective choice for the prediction of molecular vibrational properties, but the predictions of another two tested hybrid functionals are very similar and in very good agreement with experimental data. MP2 shows good performance for the IR intensities, whereas the quality of prediction of the relative Raman activities should be characterized as only moderate. B3LYP calculations of the relative IR intensities using highly compact Sadlej's Z3PolX basis set retain the high accuracy of the more CPU expensive Sadlej's pVTZ and much more expensive aug-cc-pVTZ calculations. Relative Raman activities are more sensitive to basis set effects and require at least Sadlej's pVTZ to obtain quantitative results.

The cycloaddition of CO 2 into epoxides catalyzed by imidazolium and related salts continues to attract attention due to the industrial importance of the cyclic carbonate products. The mechanism of the imidazolium-catalyzed transformation has been proposed to require the participation of the acidic C2 proton. However, other simple salts without acidic protons, such as N,N,N,N-tetrabutylammonium chloride, are also efficient catalysts for the reaction. Hence, we decided to investigate the role of the ring protons of imidazolium salts in this reaction. To this end, we systematically studied the catalytic activity of a series of methylsubstituted imidazolium cations, in the presence of various halide anions, both by experiment and in silico. Our results demonstrate that, while stabilization of intermediates by C2, C4, or C5 protons in imidazolium salts takes place, it is the nucleophilicity of the anion that governs the overall activity, which is intimately related to the strength of the interactions between the cation and anion. Consequently, the reactivity of the halide anion strongly depends on the nature of the cation and cosolvents. This study completes the (known) mechanism and should facilitate the development of highly efficient catalysts.

We describe a catalytic system composed of rhodium nanoparticles immobilized in a Lewis acidic ionic liquid. The combined system catalyzes the hydrogenation of quinolines, pyridines, benzofurans, and furan to access the corresponding heterocycles, important molecules present in fine chemicals, agrochemicals, and pharmaceuticals. The catalyst is highly selective, acting only on the heteroaromatic ring, and not interfering with other reducible functional groups.

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DFT methods in combination with NMR spectroscopy are used to investigate possible variants of the molecular structure of the ion pairs of the ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF(4)], in dichloromethane. According to the computations of the chemical shifts, experimental NMR spectra can be rationalized by an equilibrium between ca. 70-80% of structures with the anion positioned near to the C2 atom of the imidazolium ring and ca. 20-30% of structures with the anion close to the C5 and/or C4 atoms. The content of the latter structures, according to the computed Gibbs free energies, does not exceed 10%. Both the computations and the experimental NMR data suggest that the ratio of the two above-mentioned types of structures of the imidazolium-based ILs is influenced by the concentration/polarity of their dichloromethane solutions.

Possible stable structures of various 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) complexes, [Ni(bpy)(3)](2+), [Co(bpy)(3)](2+), [Fe(bpy)(3)](2+) and Fe(phen)(2)(NCS)(2), were optimized for different spin states of the metals, and the spectra computed for every form were compared with the experimental IR spectra of the compounds. It is demonstrated that the changes in spin states of the metals influence both geometry and vibrational spectra of the complexes. Spectral changes are predicted not only in the low frequency range, corresponding to metal-ligand vibrations, but also in the mid-IR range, where ligand vibrations are active. Detailed computational analysis in combination with the corresponding spectroscopic experiment shows that the spectral changes are of a similar character for complexes with the same ligands independent on the central metal and can be used as spectroscopic markers of the electronic state of the latter. Found spectral markers have been validated at a number of complexes of Fe(II), Ni(II), Co(II), Zn(II) and Cu(II) with bpy and phen ligands.