UDC 539.19We present results of ab initio and DFT calculations of the structure and IR vibrational spectra of the monomer and dimers of N,N-dimethylformamide (DMF). The calculations were carried out in the B3LYP/cc-pVDZ approximation with subsequent force-field scaling. The calculated characteristics of the vibrational spectra of DMF show satisfactory agreement with experimental values, allowing them to be used in spectral and structural analysis.Introduction. Dimethylformamide (DMF) is one of the simplest amides and has several interesting properties. DMF does not contain an NH group, which is responsible for the nature of the intermolecular structure formed by this compound in the condensed state. The methyl and aldehyde groups act as proton donors in forming dimeric and polymeric structures of DMF. Therefore, in contrast with the closest analogs of DMF, formamide (FA) and methylformamide (MFA), the molecular clusters of DMF that are formed in the liquid phase have comparatively weak binding energies and vibrational spectra that are unperturbed by the effect of strong H-bonds. Thus, DMF is a convenient subject for studying the structural and spectral characteristics of molecular systems that are important from biological and technical viewpoints. Furthermore, liquid DMF is an important aprotic dipolar solvent. DMF often fulfills the role of an organic ligand in complexes with ions and compounds of various metals owing to the presence in it of the carbonyl.The molecular structure and vibrational spectra of DMF were studied several times both experimentally [1-9] and theoretically [7,8,[10][11][12]. However, the question of whether the molecular skeleton is planar or non-planar has not yet been answered. Also, the low symmetry of the molecule is responsible for significant interactions between vibrational modes. This causes definite difficulties in assigning vibrational bands and lines. Therefore, vibrational spectra of monomeric and dimeric forms of DMF have also not been conclusively interpreted.Herein results of quantum-chemical calculations of the structure and energy and spectral characteristics of DMF monomer and dimers are presented. Experimental IR absorption spectra are interpreted. Vibrational spectra of DMF are modeled in the gas and liquid phases.Experimental. IR absorption spectra of DMF were recorded in the range 400-4000 cm -1 on a Bruker Vertex 70 spectrophotometer. The first sample was prepared as a solution of DMF in CCl 4 (0.05 M). The second sample was pure DMF. IR spectra of the samples were recoded in a KBr cuvette (0.05 mm).Calculations. Structural and spectral characteristics of DMF monomer and dimers were calculated using the applied quantum-chemical program GAMESS [13,14]. The results were visualized using the MacMolPlt program [15]. The standard basis sets cc-pVDZ and cc-pVTZ [16], DFT methods, and the hybrid functional B3LYP [17][18][19] were utilized to optimize the equilibrium structure and calculate the force field and harmonic vibrational eigenfrequencies and intensities in IR spec...

UDC 539.19 Structural models are designed and spectral characteristics are computed based on DFT calculations for a complex of uranium tetrachloride with two molecules of dimethylsulfoxide (UCl 4 ⋅2DMSO). The calculations were carried out using a B3LYP hybrid functional in the LANL2DZ effective core potential approximation for the uranium atom and a cc-pVDZ all-electron basis set for all other atoms. Two structural variants were found for the complex. In the first of them, which is more stable, DMSO molecules are coordinated to the central uranium atom through oxygen atoms whereas in the second one, whose energy is 225 kJ/mol higher, the coordination proceeds through sulfur atoms. The obtained spectral characteristics are analyzed and compared with experimental data. Spectral features that are characteristic of the complexation process are identified. The adequacy of the proposed models and the agreement between calculation and experiment are demonstrated.Introduction. Dimethylsulfoxide (DMSO) occupies a special place among polar organic solvents containing C=O, S=O, or P=O electron-donating groups and; consequently, tending to form coordination complexes. In contrast with dimethylformamide (DMF), hexamethylphosphoramide (HMPA), and other compounds, DMSO can coordinate to the central metal atom in certain instances not only through the O atom but also through the S atom [1][2][3][4][5]. The latter type of coordination is accompanied by a short-wavelength shift of the S=O stretching vibrational frequency whereas coordination of the former type shifts the frequency to longer wavelength. Thus, the spectral position of this vibrational frequency can act as a highly reliable signature of the complex structure.Herein structural variants of the complex of UCl 4 with two DMSO molecules are discussed based on quantum-chemical calculations of the electronic structure and an analysis of previously obtained IR spectra [6,7]. Such complexes provide an example of polymerization involving organic and inorganic ligands and, in particular, can serve as a model for uranium complexation. Their spectral and structural characteristics can be used for the preparation of uranium oxides that are used in nuclear energy.Experimental and Calculations. IR absorption spectra of pure DMSO and UCl 4 ⋅2DMSO pressed into KBr pellets [6], suspended in a mineral-oil mull [7] for the middle IR region, or pressed into a polymeric matrix [6] for the long-wavelength region were recorded on a Vertex 70 spectrophotometer (Bruker) in the ranges 400-4000 cm

539.19Structural models were built and spectral characteristics were calculated based on ab initio calculations for the monomer and dimers of dioxouranium monochoride UO 2 Cl. The calculations were carried out in the effective core potential LANL2DZ approximation for the uranium atom and all-electron basis sets using DFT methods for oxygen and chlorine atoms (B3LYP/cc-pVDZ). The monomer UO 2 Cl was found to possess an equilibrium planar (close to T-shaped) configuration with C 2v symmetry. The obtained spectral characteristics were analyzed and compared with experimental data. The adequacy of the proposed models and the qualitative agreement between calculation and experiment were demonstrated.Keywords: ab initio calculations, effective core potential, IR spectrum, dioxouranium monochloride.Introduction. The actinide elements react with oxygen to form many stoichiometric and non-stoichiometric compounds. In this respect, the uranium-oxygen system is unparalleled in complexity. Uranium behaves as a multivalent element in compounds with oxygen and forms stoichiometric and non-stoichiometric phases, some of which are unstable at room temperature [1][2][3].Despite the variety of uranium oxides, only three are commonly mentioned in the literature: UO 2 , U 3 O 8 , and UO 3 . These have high practical significance because they are the most important intermediates for producing uranium metal and its fluorides among such compounds as ammonium uranyl nitrate dihydrate, uranium peroxide, and ammonium uranyl tricarbonate. One of the most important applications of UO 2 is in fuel rods of many types of modern nuclear reactors. UO 2 , being a ceramic fuel for nuclear reactors, is highly resistant to corrosion, radiation, and heat. This makes it possible to attain significantly higher temperatures in reactors than if metallic uranium were used [4,5]. The principal method for synthesizing UO 2 is calcination of uranium salts with subsequent reduction [4]. The drawbacks of this method are the many steps and duration in addition to the use of high temperatures (up to 2000 K) and explosive oxygen. Another convenient method for synthesizing UO 2 is direct reduction of uranyl nitrate hexahydrate in a saturated alcohol solution in an autoclave at 473-453 K for 0.5-1.0 h. The proposed methods for synthesizing UO 2 could simplify the process and decrease significantly its temperature and time.One of the reaction products of UO 2 , for example, with halogens, is dioxouranium monochloride UO 2 Cl, which has definite practical value [3,4] and is a water-insoluble dark-brown compound. The DTA curve of UO 2 Cl (Fig. 3, curve 1 in [6]) shows one endotherm at 665

Electronic absorption spectra of nanoclusters of uranium tetrachloride are obtained experimentally and analyzed over a wide spectral range, from the visible to the IR. The structure of the long wavelength electronic absorption spectra is discussed in terms of the structure and electron-donor number of the attached ligand. Molecules of dimethyl sulfoxide (DMSO), hexamethyl phosphotriamide (HMPT), and water were used as ligands. The effect of the symmetry of the surroundings of the U 4+ ion on the structure of the electronic spectrum is examined.

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