A study of the electronic structure of the hexafluorobenzene and pentafluorobenzene molecules by ultrasoft X-ray emission spectroscopy

The electronic structure of the hexafluorobenzene and pentafluorobenzene molecules was studied by ultrasoft X-ray emission spectroscopy. The FK _α and CK _α spectra of these compounds in the gas phase were obtained. The results of quantum-chemical calculations performed at the RHF/STO-6G//6-31G level were used to construct the theoretical spectra. The highest occupied molecular orbitals were found to consist largely of the 2p _π carbon atomic orbitals. The contribution of fluorine orbitals was small. π-Type interactions mainly involved deeper valence orbitals.     

X-ray emission spectroscopy and the electronic structure of heterocyclic compounds

The electronic structure of the pyridine molecule has been investigated by x-ray emission spectroscopy. The NK _y and CK _y emission spectra have been measured. Ab initio and MNDO calculations have been carried out and individual bands in the spectra have been identified subsequently. The calculations produce spectral contours which approximate those of the experimental spectra.For Communication 3 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1484–1487, November, 1993.     

X-ray emission spectroscopy and theoretical study of the electronic structure of hexamethyldisiloxane and octamethylcyclotetrasiloxane

Electronic structure of hexamethyldisiloxane and octamethylcyclotetrasiloxane has been studied by means of X-ray emission spectroscopy and quantum-chemical simulation at the density functional theory level. From the analysis of the fine structure of X-ray emission SiKβ₁-spectra and simulated densities of electronic states, the special features of chemical interactions of Si, O, and C atoms in these molecules are determined.     

X-ray and quantum chemical study of the electronic structure of glycine and its metal complexes

OK_α spectra of glycine and some transition metal complexes with glycine ligands were obtained. The electronic structure of the glycine zwitterion is calculated by a quantum chemical method, and a theoretical X-ray spectrum of the glycine molecule is constructed. The nature of the metal-ligand bond in the compounds is discussed on the basis of experimental spectra and theoretical calculations. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Moscow State Academy of Light Industry, Novosibirsk Branch. Moscow State Academy of Light Industry. Novosibirsk State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 112–116, July–August, 1994. Translated by L. Smolina     

A study of the electronic structure of octavinylsilsesquioxane and dendron with chromium based compounds by X-ray photoelectron spectroscopy and quantum chemical modeling in the DFT approximation

The electronic structure and some features of octavinylsilsesquioxane interaction with sulfene chloride chromium acetylacetonate complex were studied by means of XPS and DFT. According to XPS, spectrum lines have close positions for all the studied compounds, half-width for dendrons not exceeding 2 eV. For octavinylsilsesquioxane, the broader lines appear due to the action of substrate atoms. Chemical composition of a dendron was determined by analyzing the concentrations of atoms in different chemical states and a residual content of chlorine atoms. Chemical bonding between the complex and octavinylsilsesquioxane is provided by the covalent interaction of carbon and sulfur atoms.     

A quantum chemical study of the electronic structure of substituted germocanes

The PRIRODA (riDFT method, BLYP functional, hf.bas basis set) and Gaussian 98 (HF method, 6-311G(d,p) basis set) programs are used to calculate the spatial and electronic structures of a number of molecules of substituted germocanes with a general formula of R,Rs’Ge(XCH₂CH₂)₂Y (where X = C, O, S, and Y = N, O, S). With the use of the AIM method the topological characteristics of Ge—Y donation bonds are calculated in these molecules. An analysis of the obtained data shows that up to the values of Ge—Y interatomic distances of ~2.7 Å these bonds can be considered as the intermediate type bonds. At Ge—Y distances of ~3.0 Å these bonds become ionic, therefore the Coulomb interaction between oppositely charged Ge and Y atoms mainly contributes to Ge—Y bonding.     

X-ray emission spectroscopy and electronic structure of heterocyclic compounds 3. Pyrrole

The electronic structure of the pyrrole molecule has been investigated by X-ray emission spectroscopy. The NK and CK spectra have been recorded. The theoretical spectra were prepared on the basis of non-empirical calculations. The structure of the HOMO was investigated similarly. The particularly high resolution in the CK spectrum permitted the identification of the X-ray transitions from the upper orbitals to the atomic orbitals of carbon atoms in different positions relative to the nitrogen atom.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1333–1338, October, 1993.In conclusion the authors express their great thanks to Professor D. S. Urch (Queen Mary College, London) for donation of the ONM crystal and to N. A. Osmakov (Institute for the Physics of Semiconductors, Siberian Branch, Russian Academy of Sciences, Novosibirsk) for help in carrying out the calculations.     

Study of electronic structure of certain phenazasilines by quantum chemistry and UV spectroscopy methods

A spectroscopic and quantum-chemical investigation of heterocyclic derivatives of 9,10-dihydroanthracene, viz., phenazasilines EtN(C₆H₄)₂SiMe₂ (I), MeN(C₆H₄)₂SiMe₂ (II), and EtN(C₆H₄)₂SiHME (III), was carried out. The experimental absorption spectra were theoretically interpreted by calculating the electronic structure of the molecules by the CNDO/S3 method, whose system of semiempirical parameters was supplemented by the silicon parameters. The nonplanar structure of the phenazasiline heterocyclic ring and the presence of two butterfly type conformations in the molecule of III was taken into account. The calculated bond lengths and oscillator forces of the electronic transitions agree well with the UV spectroscopy data and the photoelectronic spectrum of the molecule of II. The polarization spectra of phenazasilines I–III were predicted.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 229–232, March–April, 1985.     

Conformational properties and electronic structure of tetrahydrotetrazines studied by photoelectron spectroscopy and quantum chemical calculations

The photoelectron (PE) spectra of tetrahydro-1,2,3,4-tetrazines 1 and 2 and tetrahydro-1,2,4,5-tetrazines 3–5 have been recorded and their conformations have been investigated by ab initio SCF calculations. While v-tetrazine2 is planar, tetrazines 1 and 3–5 each possess two low-energy conformations, according to ab initio HF and Becke3LYP methods. Attempts to assign ionization potentials to molecular orbitals obtained by semiempirical PM3 calculations indicate that this method is not suited for the compounds studied. Best results were obtained when the ab initio hybrid method Becke3LYP of the density functional theory was employed. Two conformers of 1 and 3–5 are present in the gas phase and their PE spectra are superimposed one upon the other. For v-tetrazine1, ionizations arising from half-chair and unsymmetrical boat conformers have similar energies and cannot be separated in the PE spectrum. For s-tetrazine3, on the other hand, the spectrum clearly shows different ionizations of both half-chairs, 3ee and 3ae.     

X-ray emission spectroscopy and electronic structure of heterocyclic compounds. 1. Furan

The electronic structure of the furan molecule was investigated by x-ray spectroscopy. A quantum-chemical calculation (ab initio) was undertaken, and the results were compared with the experimental data. The interpretation of the x-ray spectra of the molecule, the carbon atoms of which have a different energy position for the 1s levels, is discussed in detail. The electronic transitions from the MO to these core levels are clearly recorded in the carbon x-ray spectrum. It was shown experimentally that the HOMO is an orbital in which the electron density is localized at the carbon atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1635, December, 1991.     

Characterization of hexavalent chromium interaction with Sargassum by X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry calculation

Hexavalent chromium represents higher toxicity in aqueous solutions. It can be removed by such low-cost biosorbents as Sargassum sp. In this study, X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry (QC) calculation were used to study the interactions between hexavalent chromium and Sargassum sp. during the biosorption. It was found that most of the adsorbed Cr(VI) ions were reduced to Cr(III) after the biosorption. The electrons for the reduction of Cr(VI) were possibly supplied from the Sargassum biomass, some organic compounds of which were oxidized. Cr(III) ions were coordinated with the oxygen atoms from either carboxyl or hydroxyl functional groups to form an octahedral structural metal complex. The coordination numbers of the formed Cr complex were 4-6, and bond length of Cr-O was 1.98?. QC calculation proved the possible formation of the Cr(III) metal complex, and revealed that carboxyl from biomass could be strongly bound with Cr(III). A three-step removal mechanism of Cr(VI) by Sargassum was proposed.     

The electronic structure of iron carbonyl complexes as probed by X-ray emission spectroscopy and quantum-chemical calculations

The electronic structure of the polynuclear iron carbonyl complexes [Et₂N][Fe₄N(CO)₁₂], [Et₄N]₂[Fe₅C(CO)₁₄], and [Et₄N]₂[Fe₆C(CO)₁₆] has been studied by X-ray emission spectroscopy and quantum-chemical calculations. The fine structure of the FeKβ₅ X-ray emission spectra characterizes the distribution of iron valence p electrons over the molecular orbitals of the compounds. Comparison of the fine structure of the FeKβ₅ X-ray emission spectra with the densities of states of all atoms in the molecules has made it possible to determine in detail the character and specific features of chemical bonding in the complexes.     

X-ray spectral and quantum chemical analyses of the electronic structure of poly(monofluorocarbon)

The electronic structure of poly(monofluorocarbon) has been studied by X-ray spectral and quantum chemical methods. Calculations were performed in terms of the MNDO method, with the fluorographite layer modeled by clusters of different sizes. The high-resolution CK_a and FK_a spectra have been obtained; the calculated spectra are consistent with the experimental ones. It has been shown that carbon and fluorine are bonded mainly through the σ bonds. The p orbitals of fluorine atoms that are perpendicular to the C-F bond are not involved in the chemical bond, while the transitions from the molecular orbitals consisting of these p orbitals are responsible for the main maximum in the FK_a spectrum. Deceased. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 630–635, July–August, 1995. Translated by I. Izvekova     

Structural and spectroscopic study of the excited electronic states of silver dihalides by quantum chemical methods

The structural and electronic properties of the excited electronic states of AgX(2) (X = F, Cl, Br, and I), have been calculated, taking electron correlation and spin-orbit coupling into account and employing improved relativistic-effective-core potentials for silver and the halogen atoms. The relative ordering of the excited states of these molecules has been discussed via molecular-orbital arguments. The spin-orbit splittings of three degenerate electronic states ((2)Pi(g), (2)Pi(u), and (2)Delta(g)) have been calculated and the spin-orbit induced inter-state (Sigma - Pi) coupling has been discussed. The composition of the spin-orbit eigenstates is analyzed in terms of scalar-relativistic electronic states. Finally, a theoretical prediction of the photodetachment bands of the title molecules has been accomplished.     

A study of ruthenium electrodes by cyclic voltammetry and X-ray emission spectroscopy

Hydrogen and oxygen adsorption properties of ruthenium surfaces are characterized and shown to be analogous to those of other noble metals. Ruthenium dissolves on potential cycles, the rate of dissolution on cycles to 1.54 V being much greater than for Pd, Rh, Ir, Pt and Au. Treatment in hot chromic acid or potential cycling to 1.3 V or above results in significant changes in the voltammogram. X-ray emission spectroscopy has demonstrated that these changes are associated with the formation and growth of an oxygen-containing layer on the ruthenium surface. Electron micrographic analysis of the surface layer included in replicas revealed that the layer is essentially amorphous. Correlations between the thickness of the layer from replica shadowing experiments and X-ray emission measurements indicated that the composition of the layer at 0.03 V was predominantly RuO with a considerable degree of non-stoichiometry. The charge on the voltammogram when oxide is present is interpreted in terms of oxidation of hydrated RuO to hydrated RuO₂ by a mechanism involving the addition and removal of protons, with corresponding changes in the valence state of the metal atom. Comparisons are made with the properties of thermally-produced RuO₂.     

X-ray spectral and quantum chemical study of the electronic structure of thiacalix[4]-arenes and their acyclic analogs

An X-ray photoelectron and X-ray emission study of the charge state of thiacalix[4]arenes is performed with a comparison with the data of quantum chemical calculations. Relaxation corrections between the Kohn-Sham orbital energies calculated by the DFT method and experimental parameters of the X-ray emission and photoelectron spectra of the studied compounds are estimated. It is shown that the formation of a cyclic aromatic system in thiacalixarenes results in a decrease in the energy of orbitals involving p-π interactions of the bridging sulfur atoms and aromatic moieties, which determines the features of the X-ray emission spectra of the studied compounds.     

(Amidomethyl)dimethylsilanol hydrohalides: Synthesis, NMR and IR studies. Characteristic features of the electronic structure from high-resolution X-ray study and quantum chemical calculation

(C,O)-chelate silanol hydrohalides RC(O)NHCH₂SiMe₂OH · HHal (2a,b and 5b), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH₂SiMe₂Cl (6a,b) and disiloxanes [RC(O)NHCH₂SiMe₂]₂O (8a,b) (R = Me (a), Ph (b); Hal = Cl (2), Br (5)), were obtained by several routes. The original scheme of hydrolysis of the above chlorides was discussed in detail. X-ray analysis has shown that the silanol hydrohalogenides PhC(O)NHCH₂SiMe₂OH · HX (2b and 5b) in the crystal exist in the form of cation-anion pairs [PhC(O)NHCH₂SiMe₂(OH₂)]⁺ · X⁻ (14b · Cl⁻ and 14b · Br⁻) assembled by H-bonds in a 3D framework. The Si atom in the cation has a trigonal bipyramidal configuration with the oxygen atom of the carbonyl group and protonated hydroxyl exo-substituent in axial positions. The endocyclic Si-O bonds are equal with an average of 1.905 Å while the exocyclic Si-O bonds are 1.979 and 2.009 Å, for Hal = Cl and Br, respectively.Quantum chemical calculations have shown that the cation [PhC(O)NHCH₂SiMe₂(OH₂)]⁺ (14b) is stable only in the crystal. Based on a high-resolution X-ray study and a quantum chemical calculation, it was found that the chemical bonding pattern in the OSiO axial fragment of the cation 14b corresponds to a three-centred four electron interaction. The cation 14b should be considered as a silylium cation stabilized by coordinated H₂O molecules rather than a silyloxonium ion.     

Structural defects and the electronic structure of zirconium hydrides: x-ray emission spectra and quantum chemical calculations

X-ray emission spectroscopy and the Green function LMTO band method was used to study the effect of structural defects in the hydrogen sublattice on the electronic structure and chemical bonding in ZrH₂.Institute of Metal Physics, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 70–74, November–December, 1989.     

Ultrasoft X-ray emission and the electronic structure of the acetaldehyde molecule

The electronic structure of the acetaldehyde molecule was studied by the ultrasoft X-ray emission method with the use of quantum-chemical calculations. The OK _?? and CK _?? spectra of the compound in the gas phase were obtained. Quantum-chemical calculations were performed at the RHF/6-311++G** level. The calculation results were used to construct theoretical X-ray spectra. The experimental spectra are interpreted.