Sergey A. Katsyuba

Ab Initio and DFT Predictions of Infrared Intensities and Raman Activities

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 Sadlejs Z3PolX basis set retain the high accuracy of the more CPU expensive Sadlejs pVTZ and much more expensive aug-cc-pVTZ calculations. Relative Raman activities are more sensitive to basis set effects and require at least Sadlejs pVTZ to obtain quantitative results.

Scaled quantum mechanical computations of vibrational spectra of organoelement molecules, containing the atoms P, S, and Cl

Abstract Density functional theory has been used for the calculation of vibrational force fields of organoelement molecules. Optimal scaling factors for various stretching and bending force constants are derived from a training set of 12 molecules, containing H, C, N, O, P, S, and Cl atoms, and used to scale force constants for further 14 molecules. These 13 scaling factors, applied to B3LYP force fields, allow compute the 310 frequencies of 26 molecules with the total standard deviation of about 11 cm −1 for 6-31G* and 6-31+G* basis sets, the latter set being preferable for computations of Raman spectra.

Enhanced Conversion of Carbohydrates to the Platform Chemical 5‐Hydroxymethylfurfural Using Designer Ionic Liquids

5-Hydroxymethylfurfural (HMF) is a key platform chemical that may be obtained from various cellulosic (biomass) derivatives. Previously, it has been shown that ionic liquids (ILs) facilitate the catalytic conversion of glucose into HMF. Herein, we demonstrate that the careful design of the IL cation leads to new ionic solvents that enhance the transformation of glucose and more complex carbohydrates into HMF significantly. In Situ NMR spectroscopy and computational modeling pinpoint the key interactions between the IL, catalyst, and substrate that account for the enhanced reactivities observed.

Structural studies of the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate in dichloromethane using a combined DFT-NMR spectroscopic approach.

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.

A Rhodium Nanoparticle–Lewis Acidic Ionic Liquid Catalyst for the Chemoselective Reduction of Heteroarenes

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.

Mass spectrometric and theoretical study of polyiodides: the connection between solid state, solution, and gas phases.

Polyiodides have been transferred intact from acetonitrile solution to the gas phase and analyzed by mass spectrometry. A range of ions were observed, including [I(11)](-), [I(13)](-), and [I(15)](-), which have higher iodine/iodide ratios than any previously characterized ions. Theoretical calculations show that branched structures are strongly favored, a result which is in excellent agreement with with gas phase fragmentation studies (MS/MS) and also previous solid state studies. This study demonstrates the utility of mass spectrometry to provide structural information in the absence of other spectroscopic handles.

Phosphonium ionic liquids based on bulky phosphines: synthesis, structure and properties

A series of new ionic liquids based on sterically hindered decyl(tri-tert-butyl)phosphonium (DTBP) or decyl(tricyclohexyl)phosphonium (DCHP) cations were prepared using quaternisation of tri-tert-butyl- or tricyclohexylphosphine with decylbromide and subsequent bromide exchange with the weakly-coordinating anions BF(4)(-), PF(6)(-), SO(3)CF(3)(-), N(SO(2)CF(3))(2)(-). The salts obtained melt below 100 degrees C and possess a broad electrochemical window. Density functional theory combined with X-ray crystallography, IR and Raman spectroscopy has been used to analyze the molecular and supramolecular structures of the compounds obtained and their possible influence on their physical properties.

Cooperative intramolecular hydrogen bond and conformations of thiocalix[4]arene molecules

The joint FTIR spectroscopic study and ab initio quantum-chemical calculations (HF/3-21G and PBE/TZ2P methods) showed that thiocalix[4] arene molecules adopt the cone conformation in CCl4 solutions. The weakening of the cooperative intramolecular H bond in thiocalix[4]arenes compared to the corresponding calix[4]arenes can be due to the larger thiocalixarene macrocycle, bifurcated hydrogen bond in it, and electron density transfer from the bridging S atom to the benzene ring.

Complex Formation of d-Metal Ions at the Interface of TbIII-Doped Silica Nanoparticles as a Basis of Substrate-Responsive TbIII-Centered Luminescence

The complex formation of d-metal ions at the interface of Tb(III)-doped silica nanoparticles modified by amino groups is introduced as a route to sensing d-metal ions and some organic molecules. Diverse modes of surface modification (covalent and noncovalent) are used to fix amino groups onto the silica surface. The interfacial binding of d-metal ions and complexes is the reason for the Tb(III)-centered luminescence quenching. The regularities and mechanisms of quenching are estimated for the series of d-metal ions and their complexes with chelating ligands. The obtained results reveal the interfacial binding of Cu(II) ions as the basis of their quantitative determination in the concentration range 0.1-2.5 μM by means of steady-state and time-resolved fluorescence measurements. The variation of chelating ligands results in a significant effect on the quenching regularities due to diverse binding modes (inner or outer sphere) between amino groups at the interface of nanoparticles and Fe(III) ions. The applicability of the steady-state and time-resolved fluorescence measurements to sense both Fe(III) ions and catechols in aqueous solution by means of Tb(III)-doped silica nanoparticles is also introduced.

Rationalization of Solvation and Stabilization of Palladium Nanoparticles in Imidazolium-Based Ionic Liquids by DFT and Vibrational Spectroscopy

A combined DFT/vibrational spectroscopy approach is used to determine the interactions of the 1,3-dimethylimidazolium ([Mmim](+)) and 1-ethyl-3-methylimidazolium ([Emim](+)) cations and [BF(4)](-) anions with each other in the liquid state and with Pd nanoparticles (NPs) immersed in ionic liquids (ILs) composed of these ions. Formation of aggregates of the counter-ions in the liquid does not have a strong influence on the interaction energy of the IL components with the palladium clusters used to model NPs, which is smaller than the energy of addition of a Pd atom to the cluster. Stronger Pd-Pd interactions in comparison to the interactions of the palladium cluster with the IL suggest kinetic stabilisation of Pd-NPs in 1,3-dialkylimidazolium tetrafluoroborates rather than thermodynamic stabilisation. Moreover, the palladium clusters interact more strongly with the anions than with the cations, and this suggests an important role of the anions in formation and stabilisation of Pd-NP in ILs. At the same time, binding between an isolated Pd atom and [Mmim](+) cation is stronger than Pd-[BF(4)](-) binding. IR and Raman spectral simulations reveal that surface-enhanced Raman spectroscopy is much less sensitive to interactions of Pd-NPs with the [BF(4)](-) anion compared to interactions with [Mmim](+) cations. In contrast, IR spectroscopy is better suited to study the anion-metal interactions, whereas IR spectral manifestations of the cation-metal interactions are rather modest. The splitting of the strong ν(as)(BF(4)(-)) IR band into three components appears to be a convenient spectroscopic marker for Pd-[BF(4)](-) interactions, which is confirmed by actual spectra of Pd-NPs stabilised by [Emim][BF(4)]. The IR spectra and their assignment with quantum chemical computations suggest that both the anions and cations of [Emim][BF(4)] interact with the Pd-NP surface in the IL. The cation ring orientation close to the surface normal appears to be the dominant interaction. The anion is bound to the surface through either two or three fluorine atoms.