An ESCA investigation of some copper complexes

A series of copper complexes have been investigated by ESCA. All complexes were salts of the tetraphenylphosphonium ion. The binding energies of all the atoms in the complexes were determined. From the binding energies of the ligand atoms we estimated the effective charges on these atoms. For this purpose we used linear relations of the formE_b = kq + E_bO which had been established previously within our scheme of C 1s (phenyl) as internal standard. From the data thus obtained, the effective charge on the copper atom was estimated. A linear relation between binding energy and the effective charge on the copper atom was found, i.e.,E_b(Cu) = 1.52q_Cu + 932.2ESCA spectra were recorded for the complexes bis(1,3-diphenyl-1,3-propanediono) copper (II) and bis(3-phenyl-2,4-pentanediono) copper (II). By a combination of the XPS binding energies and IR intensities of the ν_CH vibrations of the phenyl groups in the complexes with empirical relations between these entities and the effective charges of the atoms and groups, a fairly complete mapping of the charge distributions of these complexes has been achieved.     

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.     

The influence of adsorbed molecules on Na-sites in NaY zeolite investigated by triple-quantum MAS NMR spectroscopy

The effect of hydration and benzene adsorption on resonance and the quadrupolar interaction in NaY zeolites is studied by triple-quantum MAS NMR spectroscopy. In the case of a C₆D₆/NaY system, the results show that with an increase in benzene loading, there is an up-field trend in isotropic chemical shift (δ_CS) and a decreasing second order quadrupolar effect (χ_s) for the site II sodium ions. It was found that adsorbed benzene molecules have a slight effect on the environment of sodium ions on site I. All the sodium sites in NaY are influenced upon hydration. The up-field shift of the sodium δ_CS reflects the effect of coordination of oxygen atoms on sodium cations due to hydration. The magnitude of χ_s for hydrated sodium sites increases and then falls off with water loading. The increase in χ_s is due to the initial hydration among SI-, SI′- and SII-sodium ions, while the decrease is the result of approaching the final stage of saturated hydration.     

Isomerism in dihalogenometal porphyrins and phthalocyanines: a theoretical study of dihalogenotitanium complexes

Trans- and cis-isomers of dihalogenotitanium porphyrins and phthalocyanines, TiX₂P and TiX₂Pc (X = F, Cl, Br, I; P = porphyrin, Pc = phthalocyanine), which provide a good example of isomerism in dihalogenometal porphyrin and phthalocyanine complexes, have been studied by density functional theory calculations using the B3LYP hybrid method and triple-ζ valence basis sets. All eight complexes have two isomers, trans-isomer of D _4h symmetry and cis-isomer of C _2v symmetry with halogen atoms located in the same plane with two meso-atoms. In the case of difluorotitanium phthalocyanine the cis-isomer is preferable in the gas phase, while in all porphyrin complexes and remaining three phthalocyanine complexes the trans-isomers have lower energies than cis-isomers. Electrostatic repulsion between the halogen atoms and central nitrogen atoms of the macroheterocycle seems to play the major role in determining the preference of the trans- or cis-isomer.     

Autoionization cross section of lithium atoms excited by electron impact

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn ₁ l ₁ n ₂ l ₂ detected at the “magic” observation angle of 54.7°. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 × 10⁻¹⁸ cm² in the energy interval of 56.4–60 eV and a subsequent monotonic drop to a value of 10⁻¹⁸ cm² at 600 eV. We have discovered a “thin” cross section structure that reflects the presence of strong resonances of Li⁻ ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s2)2S, (1s2s2p)⁴ P, 1s(2s2p ³ P)² P), and 1s(2s2p ¹ P)² P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4%. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.     

Studies on energy band structure of NbC and NbN using DFT

Energy band structure of NbC and NbN are calculated using generalized gradient approximation (GGA) within density functional theory (DFT) including five high symmetry points W, L, Γ, X and K. The lowest band corresponds to 2s band of non metal (C and N) atoms and the next lowest band is formed by 2p nonmetal. The decomposing points of t _2g states (Γ ₂₅), e _g states (Γ ₁₂) and C or N 2p states (Γ ₁₅) show interesting behavior different from earlier reports.     

Determination of landau fermi-liquid parameters in si-MOSFET systems

We analyze experimental data in order to evaluate Landau Fermi-liquid parameters. By using row data of recent Shubnikov-de Haas measurements, we derive, as a function of the electron density n _s, results for the compressibility mass of the charged two-dimensional electron gas. The compressibility mass is nearly equal to the transport mass even in the density region where the transport mass has the tendency to diverge. We conclude that Landau Fermi-liquid parameter F ₀^s (n _s) is nearly independent of electron density and close to zero. This result is derived for silicon (100) and silicon (111) surfaces. We also obtain the dependence of F ₁^s (n _s), determining the transport mass, and of F ₀^a (n _s), determining the spin susceptibility. The text was submitted by the authors in English.     

Mn3<Emphasis Type="Italic">s</Emphasis> X-ray photoelectron spectra of polynuclear trimethylacetate complexes of manganese

The Mn3s X-ray photoelectron spectra of manganese at oms in mono-, bi-, tri-, and hexanuclear trimethylacetate Mn complexes and Mn^IICl₂, Mn^IIIOOH, Mn^IVO₂. ionic compounds were measured. The 3s spectra of the manganese atoms in Mn^II, Mn^III, and Mn^IV valent states were calculated within the isolatedion approximation. The relationship between the characteristics of the Mn3s spectra and the magnetic moments of the manganese ions in the complexes is discussed.     

Investigation of the π–π stacking interactions without direct electrostatic effects of substituents: the aromatic∥aromatic and aromatic∥anti-aromatic complexes

Stability of the π–π stacking interactions in the ben∥substituted-ben and ben∥substituted-COT complexes was studied using the computational quantum chemistry methods (where ben and COT are benzene and cyclooctatetraene, ∥ denotes π–π stacking interaction, substituted-ben and substituted-COT are benzene and cyclooctatetraene which substituted with four ethynyl-X groups, respectively, and X = OH, CH₃, H, F, CF₃, CN and NO₂). In these complexes electron-withdrawing substituents lead to larger binding energies and electron-donating ones lead to weaker interactions compared to X = H. There are meaningful correlations between the Hammett constants and binding energies. The atoms in molecules (AIM) analysis shows that formation of these complexes is accompanied by increase in the electron charge densities at the ring critical points of the substituted-ben and substituted-COT rings which leads to increase/decrease of the π–π stacking interactions in the ben∥substituted-ben/ben∥substituted-COT complexes. The charge transfer occurs from benzene to substituted-ben in the ben∥substituted-ben complexes and from substituted-COT to benzene (with the exception of X = CN) in the ben∥substituted-COT ones. Nuclear magnetic resonance calculations demonstrate that interactions of the more aromatic substituted-ben/less anti-aromatic substituted-COT rings with benzene in the ben∥substituted-ben/ben∥substituted-COT complexes can be helpful to enhance strength of the π–π stacking interactions. Thus, regardless of ring size, the π–π stacking interaction is an aromatic–aromatic interaction and π electron cloud properties of interacting rings affect on the strength of this interaction.     

Impact broadening and shift rates for the 6p2 3PJ′ → 7s 3P J o transitions of lead induced by collisions with argon and helium

The collisional broadening and shift rate coefficients of the 283.39 nm (6p ^{2 3}P₀ → 7s ³P₁ ^o ), 364.06 nm (6p ^{2 3}P₁ → 7s ³P₁ ^o ), 368.45 nm (6p ^{2 3}P₁ → 7s ³P₀ ^o ) and 405.90 nm (6p ^{2 3}P₂ → 7s ³P₁ ^o ) Pb lines by He and Ar have been measured by fitting the experimental absorption line shapes to theoretical Voigt profiles. The absorption measurements were performed in a resistively heated, Pb loaded oven with an integrated dc noble gas discharge to produce also Pb atoms in the 6p ^{2 3}P¹ and 6p ^{2 3}P² metastable states. The diffusion of the metastable atoms out of the discharge zone into the neutral noble-gas atmosphere enabled the line-shape and shift measurement of the lines involving the metastable states without the influence of the discharge plasma.     

Optical absorption studies of copper phthalocyanine thin films

The optical absorption of thermally evaporated copper phthalocyanine (CuPc) was studied in the UV-VIS-NIR region. The absorption spectra recorded in the UV-VIS region show two well-defined absorption bands of the phthalocyanine molecules, namely, the Soret (B) and the Q-band . The Q-band shows its characteristic splitting (Davydov splitting) of the main absorption peak in the metal phthalocyanine correlates with the relative tendencies of the metal to out-of-plane bonding. Some of the important spectral characteristics such as the molar extinction coefficient (ε_molar), the oscillator strength (f), the electric dipole strength (q²) and absorption half-bandwidth (Δλ) of the principle optical transitions were evaluated. The analysis of the spectral behavior of the absorption coefficient α in the absorption region revealed two indirect allowed transitions with corresponding energies 2.95±0.03 and 1.55±0.02 eV.The spectra of the infrared absorption allow characterization of vibration modes for the powder, as-deposited material and thin films of CuPc annealed at 423 K for two hours. Discussion of the obtained results and their comparison with the previous published data are also given.     

Surface potential images of polycrystalline organic semiconductors obtained by Kelvin probe force microscopy

P-type copper phthalocyanine (CuPc) and n-type hexadecafluorophthalocyanina-tocopper (F₁₆CuPc) polycrystalline films were investigated by Kelvin probe force microscopy (KPFM). Topographic and corresponding surface potential images are obtained simultaneously. Surface potential images are related with the local work function of crystalline facets and potential barriers at the grain boundaries (GBs) in organic semiconductors. Based on the spatial distribution of surface potential at GBs, donor- and acceptor-like trapping states in the grain boundaries (GBs) of p-CuPc and n-F₁₆CuPc films are confirmed respectively. In view of spatial energy spectrum in micro-scale provided by KPFM, it is going to be a powerful tool to characterize the local electronic properties of organic semiconductors.     

Melting heat of a nanoparticle

Expressions for the melting point (T _m ), freezing temperature (T _N < T _m ), entropy change per atom (Δs), latent heat (Δh = T _m Δs), and volume change (Δv) for the solid-liquid phase transition are derived from a model of a nanocrystal in the form of a parallelepiped with a variable shape of the surface. These quantities are studied as a function of the number of atoms (N) and the shape of the nanoparticle. Calculations carried out for copper nanoparticles show good agreement with the results of computational experiments. It is shown that functions Δs, Δh, and Δv vanish in a certain range of cluster dimension N ₀ and a hysteresis between the melting point and freezing temperature disappears, T _N (N ₀) = T _m (N ₀). In such a cluster, the phases become physically identical. For nanocopper, this dimension falls into the range N ₀ = 49–309 and grows when the shape of the nanoparticle deviates from the energetically most favorable one.     

Determination of landau fermi-liquid parameters in si-MOSFET systems

We analyze experimental data in order to evaluate Landau Fermi-liquid parameters. By using row data of recent Shubnikov-de Haas measurements, we derive, as a function of the electron density n _s, results for the compressibility mass of the charged two-dimensional electron gas. The compressibility mass is nearly equal to the transport mass even in the density region where the transport mass has the tendency to diverge. We conclude that Landau Fermi-liquid parameter F ₀^s (n _s) is nearly independent of electron density and close to zero. This result is derived for silicon (100) and silicon (111) surfaces. We also obtain the dependence of F ₁^s (n _s), determining the transport mass, and of F ₀^a (n _s), determining the spin susceptibility.     

Peculiarities of crystal structures and magnetic properties of Cu(II) and Ni(II) mixed-ligand complexes on the 1,3-dithiole-2-thione-4,5-dithiolate basis

Mixed-ligand Cu(II) and Ni(II) complexes, [Cu(dmit)(bpy)]₂ (I), [Ni(dmit)(phen)₂] (II) and [Ni(dmit)(phen)₂]·CH₂Cl₂ (III) (dmit=1.3-dithiole-2-thione-4.5-dithiolate, phen=1.10-phenantroline, bpy=2.2′-bipyridine) have been prepared by ligand exchange between phen or bpy and (Bu₄N)₂[M(dmit)₂] (M=Ni, Cu) and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray analysis and by investigation of magnetic and resonance properties. In complex I, the monomeric units form dimers in a head-to-tail arrangement by weak coordination bonds between copper and dithiolate sulfur atoms and π–π interactions between dmit and bpy from neighboring monomers. Dimers in I are further extended into chains by weak Cu–S(thione) contacts. In crystal packing of complex II and III, there exists a weak π–π interaction between two parallel phen molecules of the adjacent complexes. As a consequence, the magnetic and resonance characteristics of copper complex may be described in approximation of exchange-coupled pairs of Cu²⁺ ions with ion spin S=1/2. The nickel complexes are described by isotropic exchange model for single-site spin S=1.     

Features of the bremsstrahlung accompanying collisions with a hydrogen atom in an excited state

The features of the bremsstrahlung appearing during a collision of a fast charged particle with a hydrogen atom (or hydrogenic ion) in an excited state are investigated. It is shown that the emission spectrum of photons with energies greater than the ionization potential of a given excited state (except the 2s state) displays narrow lines, which are caused by de-excitation of the atom in an intermediate state. It is demonstrated that the scattering of a charged particle on an excited hydrogen atom produces a feature which is not observed in the case of scattering on a ground-state hydrogen atom. Expressions are obtained for the generalized dynamic polarizability of the hydrogen atom and hydrogenic ions in the 1s, 2s, and 3s states. A method is developed for deriving expressions for the generalized dynamic polarizabilities of other excited states through the use of the Coulomb Green’s function and representation of the electronic wave function in terms of the differentiation of the generating functions of Laguerre polynomials. The bremsstrahlung cross sections for electrons and positrons colliding with hydrogen atoms in the 1s, 2s, and 3s states are calculated. Zh. Tekh. Fiz. 69, 7–13 (October 1999)     

Effect of Deuteration on Quasiline Electronic‐Vibrational Spectra of Phthalocyanine

Quasiline electronicvibrational spectra of fluorescence and absorption (excitation of fluorescence in selective recording) of the molecules of phthalocyanine deuterated around the periphery of benzene rings (H₂Phcd ₁₆) and the center of the macrocycle (D₂Phc) are obtained. The vibrational frequencies of the ground state are almost insensitive to this deuteration (except for vibrations with the participation of angular deformations). In excitation spectra, changes in deuteration are more pronounced due to the effects of nonadiabatic vibronic interaction of the vibrational sublevels of the S ₁ state and of the purely electronic level S ₂.     

Some comments on the electronic properties of the surface space charge layer of copper phthalocyanine thin films

A simple analysis, using a theory of the surface space charge layer of semiconductors, of the published values of the work function φ and surface ionization energy Φ_s of copper phthalocyanine (CuPc) thin films was performed. Using a well known position of the Fermi level E_F within the band gap E_g the values of its absolute band bending eV_s and surface electron affinity X_s were determined. A small negative value of the absolute band bending eV_s = −0.17 ∓ 0.15 eV has been interpreted by the existence of the filled electronic surface states localized in the band gap below the Fermi level E_F. Such states were predicted theoretically for thin films and the crystalline surface of CuPc, and attributed to surface lattice defects of a high concentration.     

Electrical properties of hybrid phthalocyanines thin films using gold and lead electrodes

The electrical properties of mixed copper phthalocyanine (CuPc) and nickel phthalocyanine (NiPc) thin films devices with gold and lead electrodes have been investigated. The two phthalocyanines were co-evaporated and deposited on to a pre-cleaned glass substrate by thermal evaporation technique at room temperature. By the co-sublimation technique an integrated phthalocyanine sample was prepared. At low voltages the film showed an ohmic conduction whereas at higher voltage levels the conduction mechanisms were dominated by space charged limited conduction (SCLC). The value of mobility of holes were calculated as μ= 3.1×10^-8 m² V^-1 s^-1 which is lower for the mixed phthalocyanines whereas the trap concentrations N_t(e) = 8.06 ×10²⁵ m^-3 have increased in the SCLC region. Further the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident.     

Electronic band structures of the alkali metals and of the noble metals and their α-phase alloys

In the monovalent metals the electronic band structure is strongly affected by the size of the band gap E _s-E _p at the Brillouin zone faces, a large gap implying a large distortion of the Fermi surface. Here E _s and E _p are the energies of the purely s-like and p-like states on the zone faces. We have made crude estimates of E _s-E _p for the alkali and noble metals, in terms of the s-p excitation energy Δ_sp of the free atoms. These suggest a single model which correlates most of the experimental information about the band structures of these metals. In particular the Fermi surface of lithium appears to make considerable contact with the zone faces. In the α-phase alloys of the noble metals, the solute always has a larger value of Δ_sp than the solvent, which raises the energy E _p relative to E _s. The Fermi surface becomes more nearly spherical in copper alloys than in copper, since E _p<E _s, whereas it distorts further in the gold alloys (E _p>E _s). This accounts for many Knight shift, electronic specific heat, magnetic susceptibility and other data on these alloys. Furthermore it provides the extension of Jones' explanation of the Hume-Rothery rule demanded by the non-spherical Fermi surface in pure copper and gold.