Search

Abstract: Density functional theory calculations have been carried out to study the process of NO adsorption on neutral, anionic and cationic Ag8 clusters. Three cluster types have been considered in our study: D2d and Td structures are the most stable isomers in gas phase and C1 structure, which has the geometry of the most stable isomer adsorbed on rutile TiO2 (110) surface. Adsorption energies, N–O bond lengths and corresponding N–O vibration frequencies have been calculated for all structures. It has been shown that in the case of NO interaction with D2d structure the corresponding adsorption energies grow in the following order: E ads(cation)< E ads(neutral)< E ads(anion). The same regularity has been observed for NO interaction with silver tetramers in our previous study. For the Td structure the highest adsorption energy is also observed in case of anionic complex. However, for C1 structure other dependence has been observed: E ads(anion)< E ads(cation)< E ads(neutral). The adsorption of NO on neutral Ag8 cluster (C1 structure) is characterized by the largest N–O bond elongation which should be useful for NO fragmentation process. [ABSTRACT FROM AUTHOR]

Abstract: The formation enthalpies of tautomeric forms of 1,2,3-triazole, 4(5)-nitro-1,2,3-triazole and isomeric N-alkyl-4(5)-nitro-1,2,3-triazoles (alkyl=methyl, ethyl, isopropyl and tert-butyl) have been calculated with the density functional theory B3LYP method by means of designed isolobal, isodesmic and isomerisation reactions. The experimental ideal-gas formation enthalpy of 2-methyl-4-nitro-1,2,3-triazole has been determined based on the formation enthalpy in the crystalline state and the sublimation enthalpy. The experimental value of formation enthalpy (228.7±3.5kJmol−1) is in good agreement with the one obtained from reaction enthalpy calculations (233.5kJmol−1). The relative Gibbs energies for tautomeric forms of 1,2,3-triazole and 4(5)-nitro-1,2,3-triazole and isomeric N-alkyl-4(5)-nitro-1,2,3-triazoles in aqueous solution have also been calculated using the Conductor polarized continuum model (CPCM). The results of the calculations have been discussed concerning the relative stability of the titled compounds. [Copyright &y& Elsevier]

Abstract: The adsorption of Ag n (n =2,4,8) clusters on the partially reduced rutile (110) surface have been studied using DFT slab calculations. The geometry and electronic structure of silver clusters adsorbed near the oxygen vacancy as well as binding mechanism have been investigated. It has been found that the binding occurs through two types of interaction. Firstly, it is the interaction between cluster’s HOMO and surface eigenstates located on hollow-Ti atoms and, secondly, the overlap of MOs of the cluster with bridging oxygen atoms. The first type leads to charge transfer from the adsorbed cluster to the surface, therefore silver particles become positively charged upon adsorption. The second type leads to the deformation of adsorbed silver cluster, thereby increasing the overlap. The interaction between molecular orbitals of the cluster and orbitals of atoms lying at the vacancy is unlikely. It has been shown that the adsorption energy of Ag n clusters on stoichiometric surface are higher than those for reduced surface. Thus, the adsorption of silver clusters occurs preferably on stoichiometric surface far from oxygen vacancies. [Copyright &y& Elsevier]

Abstract: The CH acidity of all possible N-methyl substituted nitrotriazoles as well as of some 4-substituted 1,2,3-triazoles and N-alkyl-4-nitro-1,2,3-triazoles in the gas phase and in THF and DMSO solution has been calculated with the density functional theory B3LYP method. Electronic effects of substituents on the CH acidity of 4-substituted 1,2,3-triazoles have been examined using linear free energy relationship (LFER) methodology. In order to investigate the relation between the CH acidity of the heterocycles and their ability to undergo electrophilic substitution involving C–H bond cleavage, we have studied the reaction of isomeric N-alkyl-4-nitro-1,2,3-triazoles (alkyl=methyl, ethyl, isopropyl and tert-butyl) with HgBr2 in alkali solution. It was found that 1-isomers undergo mercuration readily, while mercuration of 2-substituted compounds do not occur under the same conditions, which is in agreement with the results of DFT calculations of the CH acidity of the compounds, showing that 2-isomers have considerably lower CH acidity than 1-isomers. [Copyright &y& Elsevier]

Abstract: Titanium dioxide with silver nanoparticles deposited on the surface is known to exhibit higher photocatalytic activity than the uncovered TiO2. A study of the electronic structure of such systems is necessary to understand this effect. A quantum chemical study of silver tetramers adsorption on stoichiometric rutile (110) surface has been carried out using periodic DFT calculations. A number of adsorption positions, which correspond to two basic adsorption sites on TiO2 (i.e. bridging oxygen rows and hollow sites) have been considered. The hollow sites turned out to be preferable for Ag4 adsorption. The population analysis has been performed to study mechanism of interaction between Ag4 and TiO2 surface. The binding has been shown to occur mainly through the interaction between cluster HOMO and rutile conduction band eigenstates. A significant overlap between Ag4 HOMO and titanium orbitals has been found in the case of hollow site adsorption, in contrast to adsorption over bridging oxygen rows, where there is only weak binding towards oxygen atoms. The adsorbed cluster has been found to have a significant positive charge, which is a result of a charge transfer into conduction band. [Copyright &y& Elsevier]

Abstract: The CH acidity in gas phase and in THF and DMSO solution of 12 N-alkyl substituted azoles have been calculated with the density functional theory B3LYP method. The computed pK a values of azoles in THF solution and positions of deprotonation agree with experimentally found. The calculation results enabled us to explain a great difference in reactivity of 2-alkyltetrazoles comparing with 1-alkyltetrazoles in processes involving C–H bond cleavage (mercuration, iodination, aminomethylation). For studied compounds and corresponding anions three geometric aromaticity indices were calculated and π-electron delocalization was studied by means of natural bond orbital analysis. The results obtained were used to explain positions of deprotonation of azoles’ molecules. [Copyright &y& Elsevier]

Abstract: Based on both total energy calculations and comparison of experimental and calculated characteristics of photoelectron spectra (PHES), the structural assignment of clusters and has been made using DFT model with recently developed S2LYP functional. The calculated characteristics of PHES for the assigned structures are in excellent agreement with the experimental ones. The electronic structure, geometry and energetic characteristics of low-lying isomers have also been studied. The calculated geometrical parameters of and clusters as well as the geometries of earlier established clusters have been compared with the geometrical characteristics of anionic sodium clusters. The structures of anionic silver and sodium clusters have been found to be very similar. The difference has been observed only for . Based on similarity of the geometries of silver and sodium clusters as well as on the comparison of calculated and experimental characteristics of PHES, the geometry of cluster has been assigned. [Copyright &y& Elsevier]