K-absorption spectral investigations on some dimeric copper(II) carboxylate complexes

The X-ray K-absorption edge position and the extended fine structure of copper in some copper(II) carboxylate complexes involving metal-metal exchange interaction have been investigated using a 40 cm bentcrystal spectrograph. It has been found that the edge position in these complexes shifts towards the higher energy side as the pK_a value of the corresponding acids increases. Sharp and narrow main peaks have been observed in all these complexes except the monomeric complex, copper(II) trichloroacetate. Estimates of metal-ligand average bond distances have also been made.     

X-ray absorption investigations of copper resinate blackening in a XV century Italian painting

Investigations of the darkening phenomenon of copper resinate observed in a XV century easel painting were carried out by X-ray absorption spectroscopy (XAS) at the GILDA beamline of the European synchrotron radiation facility (ESRF, Grenoble, France). X-ray absorption near edge structure and extended X-ray absorption fine structure (EXAFS) measurements were collected at the Cu K-edge on an original painting sample, as well as on fresh pigment standards and on painting models. The study was aimed at providing structural information of the oxidation states and the local chemical environment (neighbouring atoms and bond distances) of copper in the unaltered and blackened pigments in order to elucidate the discoloration mechanism. Complementary information on optical and molecular properties of copper resinate were obtained by UV-vis and Fourier transform infrared spectroscopies. EXAFS analysis evidenced that the local chemical environment of Cu in copper resinate can be described using neutral copper acetate as a model. It consists, essentially, of bimetal Cu²⁺ carboxylate complexes with a distorted octahedral coordination. Such a structure is retained in the blackened pigment, although some differences were observed. It has been found that the alteration takes place without change of the valence state of Cu(II) ions, while the formation of the copper oxides CuO and Cu₂O responsible for the embrownment is excluded. On the basis of the XAS results we deduced that discoloration of copper resinate may be related to local modification of the copper coordination structure as evidenced by the observation of an increase of the Cu–Cu and Cu–C distances in the EXAFS spectra. PACS  78.70.Dm; 61.10.Ht     

X‐ray K absorption spectral studies of copper (II) hydroxamic acid mixed ligand complexes

X‐ray absorption spectra at the K‐edge of copper have been studied in copper mixed ligand complexes having hydroxamic acid as one of the ligands. The X‐ray absorption spectra have been recorded at BL‐8 Dispersive Extended X‐ray Absorption Fine Structure (EXAFS) beamline at the 2.5‐GeV INDUS‐2 Synchrotron Source, RRCAT, Indore, India. The data obtained has been processed using EXAFS data analysis program Athena. The energies of the K absorption edge, chemical shifts, edge‐widths and shifts of the principal absorption maximum in the complexes have been determined and discussed. The chemical shift data have been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase‐uncorrected bond length and has also been determined by Lytle, Sayers and Stern's (LSS) graphical method. The results obtained from LSS and the Fourier transformation methods are comparable with each other. The first shell bond length has also been estimated by Lytle's and Levy's methods from the EXAFS data. Copyright © 2014 John Wiley & Sons, Ltd.     

Charge transfer-transitions and X-ray photoelectron spectroscopy of copper(II) complexes

Satellite structure in the X-ray photoelectron (Cu 2p) spectra of some squareplanar cupric complexes has been compared to electron paramagnetic resonance and electronic spectra results on the electronic structure of these complexes. It is shown that these satellites can be assigned to various ligand → metal 3d or ligand → ligand* transitions within the monopole selection rules of the sudden approximation.     

Finite difference method calculations of X-ray absorption fine structure for copper

The finite difference method is extended to calculate X-ray absorption fine structure (XAFS) for solid state copper. These extensions include the incorporation of a Monte Carlo frozen phonon technique to simulate the effect of thermal vibrations under a correlated Debye–Waller model, and the inclusion of broadening effects from inelastic processes. Spectra are obtained over an energy range in excess of 300 eV above the K absorption edge—more than twice the greatest energy range previously reported for a solid state calculation using this method. We find this method is highly sensitive to values of the photoelectron inelastic mean free path, allowing us to probe the accuracy of current models of this parameter, particularly at low energies. We therefore find that experimental data for the photoelectron inelastic mean free path can be obtained by this method. Our results compare favourably with high precision measurements of the X-ray mass attenuation coefficient for copper, reaching agreement to within 3%, and improving previous results using the finite difference method by an order of magnitude.     

X-ray spectral and Mossbauer investigations of structure defects and the degree of inversion of manganese-zinc ferrites

X-ray and Mossbauer spectroscopy is used to investigate the effect of vacuum cooling on the valence of cations of manganese and iron, nonstoichiometry and the degree of inversion of manganese-zinc ferrites. The dependence of the valency of the cations of manganese and iron, the degree of inversion, and the degree of nonstoichiometry on the partial pressure of oxygen produced in the cooling stage is established. An interrelationship is found between the defects and the degree of inversion of manganese-zinc ferrites.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 15–18, March, 1982.     

Pressure- and photo-induced phase transition in mixed-valence gold complexes

The pressure- and photo-induced phase transition in mixed-valence gold complexes of Cs₂Au₂X₆ (X = Cl, Br, and I) has been investigated by means of the Raman scattering. The Raman-active Au-X stretching modes were deactivated by the pressure, which indicates a pressure-induced phase transition from the mixed-valence (MV) state to the single-valence (SV) state. The electronic phase diagrams of Cs₂Au₂X₆ (X = Cl and Br) as a function of pressure and temperature have been derived. A photoinduced phase transition from the MV state to the SV state has been found for Cs₂Au₂Br₆. The observed time behavior accompanying this phase transition is successfully interpreted by the Avrami model, indicating the three-dimensional character of the MV cluster growth.     

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl₂].H₂O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl₂].H₂O (4), where salen^2? = N,N′‐ethylenebis (salicylidenaminato); salophen^2? = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C₁₆H₁₂N₂O₂Cl₂)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Intermediate range order in concentrated aqueous solutions of copper nitrate. X-ray diffraction and Raman investigations

Concentrated aqueous solutions of copper nitrate of different concentrations (0.66 mol dm⁻³ up to 4.84 mol dm⁻³) have been investigated by X-ray diffraction at room temperature. In these solutions a maximum of intensity (prepeak) is observed at low values of Q (approx. 0.6 to 1 Å⁻¹) suggesting the existence of an intermediate range order in their structure, in agreement with previous investigations on different electrolytes. In order to get information on the solvation shell of the copper cation, Raman spectroscopy experiments have been performed for the more concentrated solution. Polarization observations, isotopic substitution of the solvent and the comparison with a Raman spectrum of a concentrated aqueous solution of aluminum nitrate were performed in order to improve the interpretation of the obtained results with these convergent observations.     

X-ray photoelectron investigation of charge distribution in copper(II) phthalocyanine complexes

The charged states of atoms in unsubstituted copper(II) phthalocyanine (CuPcH₁₆) and hexade-cafluorinated copper(II) phthalocyanine (CuPcF₁₆) complexes and in thin films of them deposited on silicon substrates by vacuum thermal evaporation are investigated by X-ray photoelectron spectroscopy (XPS). The C(1s), N(1s), Cu(2p) core level energies and the charged states of atoms in the studied complexes are calculated using the DFT method. The performed experimental study and theoretical calculations show that the introduction of electron acceptor substituents into benzene rings mostly affects the atoms of benzene rings and insignificantly affects the charge state of nitrogen atoms in the pyrrole ring.     

Structural investigations of DNA-polycation complexes

The internal structure of DNA-polycation complexes is investigated by synchrotron small-angle X-ray scattering (SAXS). Hexagonal packing of DNA is observed for DNA complexed with poly-L-lysine (PL), poly-L-arginine (PA), spermine (Sp), and linear and branched polyethyleneimine (lPEI and bPEI, respectively). Variations in the internal spacings and degree of long-range ordering are dependent on both polycation type and concentration of added salt. With increasing concentration of monovalent salt, a discontinuous phase transition is observed from compact to loose bundles and finally to an isotropic network phase. This salt-induced melting transition was found to be universal for all polyplexes studied and is in quantitative agreement with a simple free energy model based solely on electrostatic and entropic contributions. Using the osmotic stress method, bulk modulus (K) is measured for PL-DNA and PA-DNA polyplexes at various salt concentrations. With increasing osmotic force, we show that the salt-induced melting transition is shifted and compression in the loose bundle regime is in qualitative agreement with our model.     

Quantum chemical and NMR investigations on structure of surface complexes

The semiempirical quantum chemical CNDO/2 method is used to calculate models of specific interaction between benzene, toluene, and butene molecules, respectively, and ions or hydroxyls representing active sites of adsorption on zeolitic surfaces. From energy minima of full potential curves the stabilization energies of the surface complexes have been obtained. On the basis of proposed complexes theoretical carbon-13 NMR chemical shifts of adsorbed molecules are calculated. The theoretical results are in rather good agreement with the experimental ones, confirming the conception of surface complexes. Moreover, experimental paramagnetic shifts of surface complexes containing Co²⁺ ions are tried to interprete in a quite similar way.     

Mechanism of mass spectral fragmentation of dinuclear copper(ii) complexes with heterocyclic dithiocarbamates and octaazamacrocyclic ligand

The mass spectral fragmentation of five dinuclear Cu(II) complexes of the general formula [Cu₂(Rdtc)tpmc] (ClO₄)₃, where tpmc and Rdtc refer to N, N, N, N-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc), or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, has been investigated. The results were shown to be of mechanistic significance, clarifying the major products of their fragmentation. A possible mechanism entails a multi-step decomposition process that can be separated into individual steps depending on their molecular structures. Every step is determined to some extent by the nature of the intermediates.__________Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 38–42, January–February, 2005.     

Generalization of a method of X-ray fluorescent spectral analysis with allowance for the absorption characteristics of specimens

It is shown that the Losev formula is fulfilled for any spectral distribution of the primary radiation. The proposed analytical procedure was tested with the presence in the specimen of elements with absorption edges between the analytical line and the absorption edge of the element being determined.     

PT L3 near edge structure of halogen-bridged mixed-valence pt complexes and pd-pt mixed-metal complexes

X-ray absorption near edge structure (XANES) of halogen-bridged mixed-valence Pt complexes and halogen-bridged Pd-Pt mixed-metal complexes have been measured using synchrotron radiation with a high energy resolution. In Pd-Pt mixed metal complexes, we demonstrate that the degree of the valence is estimated from the intensity of the white line at the Pt L₃ edge. In the mixed-valence complexes, the electron system is proved to be the Peierls insulator with a charge density wave of renormalized d electrons of Pt, where the total valence of Pt^IV- and Pt¹¹ is conserved without excess electrons from ligands or anions.     

Combined X-ray absorption and X-ray diffraction under high pressure

ABSTRACT

X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are two complementary structural techniques. Their combination improves the understanding of the effect of pressure on materials as illustrated by examples taken from studies on different types of materials (semiconductors, molecular solid, ferroelectric perovskite and gas mixture). The introduction of nanopolycrystalline diamonds anvils has extended XAS to high-energy edges with the possibility to use energy-scanning XAS beamlines where XRD can be performed in addition to XAS experiments.     

X-ray photoemission and X-ray absorption studies of Hf-silicate dielectric layers

Photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) measurements have been performed on HfSi_xO_y and HfSi_xO_yN_z dielectric layers, which are potential candidates as high-k transistor gate dielectrics. The hafnium silicate layers, 3-4 nm thick, were formed by codepositing HfO₂ and SiO₂ (50%:50%) by MOCVD at 485 °C on a silicon substrate following an IMEC clean. Annealing the HfSi_xO_y layer in a nitrogen atmosphere at 1000 °C resulted in an increase in the Si⁴⁺ chemical shift from 3.5 to 3.9 eV with respect to the Si⁰ peak. Annealing the hafnium silicate layer in a NH₃ atmosphere at 800 °C resulted in the incorporation of 10% nitrogen and the decrease in the chemical shift between the Si⁴⁺ and the Si⁰ to 3.3 eV. The results suggest that the inclusion of nitrogen in the silicate layer restricts the tendency of the HfO₂ and the SiO₂ to segregate into separate phases during the annealing step. Synchrotron radiation valence band photoemission studies determined that the valence band offsets were of the order of 3 eV. X-ray absorption measurements show that the band gap of these layers is 4.6 eV and that the magnitude of the conduction band offset is as little as 0.5 eV.