Electron density distribution in potassium bis -(carbonato)cuprate(II)

The electron density distribution in potassiumbis-(carbonato)cuprate(II) has been analyzed using x-ray diffraction data from an earlier structure determination. While the copper-ligand geometry is close to square planar the deformation density near the metal is strongly asymmetric. There are local maxima near the copper atom along the line of the Cu-K vectors. These resemble features found in corresponding regions in normal length metal-metal bonds. The observation is consistent with the long range nature of the Coulomb potential associated with the potassium ion.     

The intermolecular potential function of Smith–Thakkar type for C60

The intermolecular potential function of Smith–Thakkar type for C₆₀ has been proposed, and its expression is as follows

The unit of u(r) is J/mol, r is the distance between two C₆₀ molecules center and the unit is nm. Some properties of C₆₀ in the gas and crystal have been studied using the interaction potential of Smith–Thakkar type, such as stability of C₆₀ crystals, virial coefficient and lattice dynamics.     

Calculations of van der Waals interaction energies for Al, Cr, Fe, and Ir acetylacetonate crystals

Experimental data have been analyzed and interpreted for four volatile acetylacetonates of trivalent metals Al, Cr, Fe, and Ir. The crystal lattice energies were calculated by the atom-atom potential method. The lattice energies obtained by using the Buckingham potential are in better agreement with the sublimation heats of these metal complexes than those calculated from the Lennard-Jones potential. The experimental dependences of vapor pressure for the complexes are in satisfactory agreement with the values obtained from the calculated lattice energies and entropies of crystal-gas transitions.     

Vanadium Doped Sol-Gel TiO2 Coatings

A study of the experimental conditions required to obtain vanadium doped sol-gel TiO2 coatings is presented. Tetraethyl orthotitanate was employed as the TiO2 source and VCl3, VOSO4 · H2O and VOSO4 dissolved H2SO4 where employed as vanadium sources.Dip coating has been used to produce coatings on silicon wafers, spectral carbon electrodes and titanium electrodes. Both supported and unsupported films have been studied by UV-Vis spectra, IR spectroscopy and X-ray diffraction (XRD). The measurements have been made on samples as prepared and treated thermally at temperatures between 100°C and 300°C. The thermal treatment temperatures have been established from DTA/TGA measurements.The vanadium doped sol-gel TiO2 coatings have been tested as sensors for redox potential measurements in electrochemical processes. The influence of both the thickness of films and the nature of substrate has been investigated.     

Potential of zero total charge of platinum single crystals: A local approach to stepped surfaces vicinal to Pt(111)

The electrochemical behavior of platinum single-crystal electrodes is revisited, with special emphasis on the determination of the potential of zero charge. We show that the measure of the charge displaced during CO adsorption allows the determination of the potential of zero total charge (PZTC). The estimation of the potential of zero free charge (PZFC) is discussed, with different degrees of approximation. The application of this methodology to the study of the PZTC of platinum stepped surfaces vicinal to Pt(111) reveals a marked decrease of the PZTC due to the introduction of surface steps. This effect is interpreted as the result of the existence of markedly smaller surface potentials localized on step sites. The importance of considering local aspects of the interface is emphasized with the use of N₂O reduction as a sensitive probe to the local structure of the surface. It is proposed that the different local maxima observed in the absolute value of the reduction current correspond to the local values of PZTC. It is shown that there is, in general, good agreement between the overall PZTC, obtained from the CO displacement, and that calculated from the local values inferred from the N₂O reduction. Further insight is obtained with the application of the laser-induced temperature jump method. This technique is useful to calculate the potential of maximum entropy of the double-layer formation. The resulting value of this potential for Pt(111) is discussed in the light of the PZFC value obtained from different approaches. For stepped surfaces vicinal to Pt(111), two local maxima in the entropy of the double layer are observed that are close to the local PZTC values estimated from the N₂O reduction. This result suggests the existence of cooperative effects in the organization of the water dipoles close to the electrode surface. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1275–1292. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Transformations of 3,4-bisindolylmaleimides with differently bonded indole and maleimide moieties under the action of protic acids: A quantum chemical study

Intramolecular cyclization reactions of 3,4-bis(indol-3-yl)maleimides 1, 3-(indol-1-yl)-4-(indol-3-yl)maleimides 2, and 3,4-bis(indol-1-yl)maleimides 3 under the action of protic acids were studied in order to estimate the parameters of the interaction between protonated and unprotonated indole moieties. Geometric parameters, charge distributions, energy characteristics, and information concerning the frontier orbitals of bisindolylmaleimides 1–3 were obtained from density functional B3LYP/6-31G(d) quantum chemical calculations. Alternative pathways of protonation of bisindolylmaleimides with differently bonded indole and maleimide moieties were studied and pathways of cyclization of corresponding conjugated acids leading to polyannelated compounds were analyzed. All the key intermediates of the cyclization reactions correspond to stationary points on the potential energy surfaces (minima and transition states). Analysis of the potential energy surfaces revealed almost linear dependences of the activation energies of the cyclization reactions under study on the distances between the reaction centers, on the angle of approach of intramolecular electrophile, and on the energy gap (energy difference between frontier orbitals). The key role in the cyclization reactions is played by structural similarity between the starting indoleninium cations and the activated complexes of the reactions under study. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 754–760, May, 2006.     

Adiabatic Potential Energy Surface of the 1,2,3-Trifluorobenzene Cation-Radical

Ab initio study of the adiabatic potential energy surface (PES) for 1,2,3-trifluorobenzene cation-radical was carried out by the ROHF, UHF, MCSCF, MP2, and DFT (B3LYP) methods with the 6-31G* basis set. The PES in question is a pseudorotation surface at all calculation levels. The pseudorotation barrier height does not exceed 3.2 kcal/mol, suggesting a possibility for its manifestations in experimental EPR spectra.     

Crystal habit of fcc metal particles controlled by electrode potential in solution

The crystal habit of fcc metal particles formed on an amorphous carbon film electrode in solution at different electrode potentials is discussed. The fcc metal particles have different crystallographic habits depending on applied electrode potential; that is, icosahedral and/or decahedral particles are formed at lower potentials, and fcc single-crystalline or polycrystalline particles at higher potentials. It was found that decahedra and icosahedra of Cu-Au alloy particles are formed in the potential region of underpotential deposition (UPD) of Cu at which only fcc Au single-crystalline particles and Au polycrystalline particles appear. This is attributed to the charge transfer from the UPD Cu ions to the Au overlayer of Cu-Au alloy particles. The formation of decahedral and icosahedral Cu-Au alloy particles depends on the composition of the Cu-Au alloy. On the basis of these results it was deduced that the contraction of the surface lattice of the growing particles is responsible for the formation of icosahedral and decahedral particles. Received: 25 February 1997 / Accepted: 21 April 1997