The effect of the alkaline environment on the oxidation of glucose into gluconic acid (gluconate ion) without the participation of a catalyst was studied by the density functional theory. It has been shown that the solvation environment destabilizes the intermediates of the reaction and, first of all, the glucose diolate R-CHO(OH)& oline;, the formation of which becomes unlikely. As a consequence, under real catalytic conditions, glucose diolate should be formed on the surface of the catalyst. Destabilization of intermediates, as well as an increase in the energy difference between the triplet and singlet states of the R-CHO(OH)& oline;... O2 complex in the solution enhances the activation barrier in an alkaline environment to 140 kJ/mol (101 kJ/mol in the gas phase). Of the two main factors, glucose diolate instability and high activation barrier, the first of them plays a decisive role in preventing the reaction from taking place in solution.

Natural bond orbitals (NBO) method was used to study electronic structure of the Ni(II) complexes with pincer and alkynyl ligands [C6H3-1,3-(OPPh2)(2)]Ni-C equivalent to C-(4-C6H3N2S) (1) and its protonated form [[C6H3-1,3-(OPPh2)(2)]Ni=C=CH-(4-C6H3N2S)](+) (2). The Complex 2 is formed as a result of proton attaching to & Scy;(beta) carbon of the -& Scy;equivalent to & Scy;- bond of alkynyl ligand. The electron donation from ligands to Ni2+ is dominate process in the complex 1. In the complex 2, electron transfer is described by three processes: ligands - metal donation, Ni2+ to vinylidene ligand back donation and interligand interaction.

The authors summarize results from calculations using the density functional theory for atoms and small silver clusters on surfaces of nanostructured cerium(IV) oxide, along with the adsorption and transformations of O2 and CO molecules on these systems. Stoichiometric Ce21O42, which has {100} and {111} nanofacets with adsorption centers containing four and three oxygen atoms, is used to model surfaces of cerium oxide. It is shown the O4-center is a center of the selective adsorption of metal atoms. A silver atom on an O3‑center is less stable but it shows a greater ability to activate an O2 molecule. Results from calculations on the {100} and {111} faces of Ce21O42 nanoparticles are compared to data for infinite CeO2(100) and CeO2(111) surfaces. The efficiency of Ag/Ce21O42 atomic complexes is shown in the oxidation of carbon monoxide.

Methanol dehydrogenation on Pt nanoparticles was studied as a model reaction with the focus on size and structure effects employing the density functional theory approach. The effect of cluster morphology is manifested by the higher adsorption energy of COHx intermediates on vertexes and edges of model nanoparticles compared to closely packed terraces. Moreover, due to the size effect, the adsorption sites of Pt79 nanoparticles (1.2 nm in diameter) exhibit considerably higher adsorption activity than the same sites of Pt201 (1.7 nm). Thus, particles with a size of about 1 nm are shown to be more active due to the superposition of two effects: (i) a higher surface fraction of low-coordinated adsorption sites and (ii) higher activity of these sites compared to particles with a size of about 2 nm.

Density functional theory and the extended charge decomposition analysis (ECDA), the natural population analysis (NPA) as well as the quantum theory of atoms in molecules (QTAIM) were used to gain insight into the nature of metal-metal and metal-ligand interactions in binuclear manganese-platinum vinylidene complexes with phosphine ligands at the Pt atom: Cp(CO)(2)MnPt(mu-C=CHPh)(P-P) (1 P-P=(PPh3)(2), 2 P-P=dppm). The complexes 1 and 2 can be represented as pi-complexes of the Pt-phosphine moiety (M) with the metalla-allene ligand Cp(CO)(2)Mn=C=CHPh (L). The substitution of PPh3 groups at the Pt atom by dppm ligand leads to a growth of the L <- M back-interaction as the result of approaching the CO group at the Mn atom to the Pt atom induced by the decrease in steric disincentives caused by phosphine ligands. Topological analysis of the charge density points to the indirect metal - metal bonding mediated by a couple of the 2e-2c metal -carbon interactions and the semi-bridging coordinated carbonyl group. (C) 2022 Elsevier B.V. All rights reserved.

Various COx species formed upon the adsorption and oxidation of CO on palladium and silver single atoms supported on a model ceria nanoparticle (NP) have been studied using density functional calculations. For both metals M, the ceria-supported MCOx moieties are found to be stabilised in the order MCO < MCO2 < MCO3, similar to the trend for COx species adsorbed on M-free ceria NP. Nevertheless, the characteristics of the palladium and silver intermediates are different. Very weak CO adsorption and the small exothermicity of the CO to CO2 transformation are found for O4Pd site of the Pd/Ce21O42 model featuring a square-planar coordination of the Pd2+ cation. The removal of one O atom and formation of the O3Pd site resulted in a notable strengthening of CO adsorption and increased the exothermicity of the CO to CO2 reaction. For the analogous ceria models with atomic Ag instead of atomic Pd, these two energies became twice as small in magnitude and basically independent of the presence of an O vacancy near the Ag atom. CO2-species are strongly bound in palladium carboxylate complexes, whereas the CO2 molecule easily desorbs from oxide-supported AgCO2 moieties. Opposite to metal-free ceria particle, the formation of neither PdCO3 nor AgCO3 carbonate intermediates before CO2 desorption is predicted. Overall, CO oxidation is concluded to be more favourable at Ag centres atomically dispersed on ceria nanostructures than at the corresponding Pd centres. Calculated vibrational fingerprints of surface COx moieties allow us to distinguish between CO adsorption on bare ceria NP (blue frequency shifts) and ceria-supported metal atoms (red frequency shifts). However, discrimination between the CO2 and CO32− species anchored to M-containing and bare ceria particles based solely on vibrational spectroscopy seems problematic. This computational modelling study provides guidance for the knowledge-driven design of more efficient ceria-based single-atom catalysts for the environmentally important CO oxidation reaction.

A series of trinuclear μ3-vinylidene ReFePt clusters were synthesized by the application of two approaches: (i) reactions of the binuclear RePt μ-vinylidene complexes with Fe2(CO)9; (ii) ligand substitution or exchange reactions at the Pt atom in the synthesized ReFePt clusters. The molecular structures of CpReFePt(μ3-CCHPh)(CO)5[P(OEt)3]L [L = CO; P(OEt)3] were determined by an X-ray diffraction study. The obtained compounds were studied by IR and 1H, 13C and 31P NMR spectroscopy. The spectroscopic study revealed that the clusters CpReFePt(μ3-CCHPh)(CO)5[P(OEt)3]L [L = CO; P(OEt)3] and CpReFePt(μ3-CCHPh)(CO)6[P(OPri)3] undergo isomerization upon dissolution, resulting in three isomers with different positions of the μ3-vinylidene ligand over the ReFePt core. The redox properties of the clusters were studied by electrochemical methods. The relatively stable cation-radicals obtained by chemical oxidation of CpReFePt(μ3-CCHPh)(CO)6[P(OPri)3] and CpReFePt(μ3-CCHPh)(CO)5[P(OEt)3]2 with ferrocenium tetrafluoroborate were characterized by EPR spectroscopy.

We studied the hydration and the first hydrolysis reaction of U(IV) and Np(IV) ions in an aqueous environment, applying a relativistic density functional method together with a recently proposed variant of a continuum solvation model where the solute cavities are constructed with effective atomic radii, based on charge-dependent scaling factors. In this way, one obtains improved solvation energies of charged species. We demonstrate that solute cavities, constructed with scaled atomic radii as described, permit one to calculate hydrolysis constants of acceptable accuracy. As a consequence, one is also able to estimate free hydration energies of U(IV) and Np(IV) in adequate agreement with empirical data. According to the model calculations, U(IV) is coordinated by eight to nine water molecules, while the preferred coordination number of Np(IV) is 8. For the highly charged ions under study, the modified solvation model simultaneously yields improved geometries, hydration energies, and hydrolysis constants.

Metal–metal and metal–ligand bonding in vinylidene ReFePt complex was studied by density functional method and topological analysis of electron density. Topological analysis did not found direct bonding between the metal atoms pointing to indirect metal–metal interaction mediated via the bridging vinylidene ligand. At the same time, the delocalization index δ(Fe,Pt) reveals the strong Fe–Pt interaction that allows for supposing a chemical bonding between these atoms

A series of reactions of Cp(CO)2Mn[double bond, length as m-dash]C[double bond, length as m-dash]CHPh with different gold(i) complexes of [Au-C[triple bond, length as m-dash]C-R]n (R = 4-C5H4N, C6H5) and (tht)AuCl yielded one novel trinuclear MnAuMn cluster. The structure of this cluster can be rationalized as being formed of a vinylidene Mn-Au binuclear and Mn-acetylide fragments, and the binding between those is achieved mainly through the sharing of the electron pair of the single Mn-C σ-bond of an acetylide unit with the gold center.

The density functional method was used to study vibrational frequenciesof the surface species involved in the reaction of the methanol dehydration via pathway CH₃OH→CH₃O→CH₂O→CHO→СОon a ideal Pt(111) surface and surface of nanoparticle Pt79. Connection of spectral features with stability and coordination of the adsorbed molecules was discussed. The determined vibrational features enable identification of themain reaction intermediates

The initial release of cations upon oxidation of metal sulfides commonly produces a metal-deficient surface and undersurface layers, which should greatly affect the properties of materials but are still poorly understood. We employed density functional theory + U simulation of chalcopyrite (012) and (110) surfaces with up to a half of surface iron removed together with X-ray photoelectron spectroscopy (XPS) of fast-frozen chalcopyrite oxidized in aqueous solutions. It was calculated that the centers comprising tri- or pentasulfide anions or tri- and disulfide complexes have the negative formation energy of 1.2-1.5 eV per one extracted Fe atom, while defects with disulfide anions are disadvantageous. The surfaces are typically "metallic" with comparable densities of S sp and Cu 3d states at the Fermi level. Upon performing cryo-XPS studies, it was found that sulfide surfaces depleted in iron but not in copper, and polysulfide anions S-n(2-) with n ( )>= 5 arose. As oxidation progresses, a deficit of Cu occurs, and S-S chains grow. Upon warming up to room temperature, polysulfide species partially volatilize, so S-s(2-) and S(3)(2- )anions appear to prevail, while the minor contribution of disulfide remains unchanged. The high stability of "polysulfide" centers is considered responsible for retarded oxidation and leaching ("passivation") of chalcopyrite; metallic DOS is important for the physical properties of the surfaces.

The effect of the nature of paramagnetic adsorption centers of the dehydroxylated silica surface - nonbridging oxygens (NBO) or silicon atoms with dangling bond (E') - on the oxidation of adsorbed subnanometer-sized silver clusters Ag-n (n = 3, 4, 7) has been clarified by density functional theory using embedded cluster models. The interaction with NBO centers results in the formation of positively charged Ag moieties, while at E' centers metal species remain rather neutral. At both surface defects, the electronic and structural properties of Ag species resemble the features of free Ag-n(+) clusters. As a result, O-2 molecular adsorption on the supported Ag clusters follows the trends established for cationic species. O-2 is weakly adsorbed in a terminal mode on the Ag trimers and heptamers and is strongly bound to the Ag tetramers in a bridge mode. The stability of O-2 molecular and dissociative adsorbed forms at the supported Ag-3 and Ag-7 species is similar, whereas on Ag-4 cluster O-2 dissociation is preferred. The heights of the O-2 dissociation barriers are determined by the initial activation of molecularly adsorbed O-2 and the deformation of supported metal clusters along the reaction pathway. The high activation energies make O-2 dissociation unlikely and manifest that small Ag clusters trapped by silica paramagnetic defects highly resistant to the oxidation.

Silver single atoms and small clusters supported on a model Ce21O42 nanoparticle have been studied computationally at a DFT+U level. It was found that silver atoms, trimers and tetramers are oxidized upon interaction with the {100} and {111} nanofacets of the ceria particle. The most stable surface complexes are formed via interaction of the silver species with two-coordinated O-2c atoms of the {100} nanofacet. The binding energies of the silver atom, trimer, and tetramer are calculated to be similar to 2.2, similar to 2.9 and 3.1 eV, respectively. Binding of these silver species located on the {111} facet is less severe, by 1.0 eV for the single atom and by 0.4-1.1 eV for Ag-3 and Ag-4 clusters. Stability of the lowest-energy supported silver species on the two types of ceria nanofacets decreases in the order of Ag/Co21O42{100} > Ag-4/Ce21O42{100} > Ag-3/Ce21O42{100} > Ag-3/Ce21O42{111} > Ag-4/Ce21O42{111} > Ag/Ce21O42{111}, pointing out on the supremacy of the denucleation trend.

The review is dedicated to the elaboration and application of hybrid quantum mechani-cal/molecular mechanical methods for heterogeneous catalytic systems, including single atoms and clusters of transition metals immobilized on covalent oxide supports. The following issues are considered: (1) elaboration of the hybrid covEPE method for modeling of covalent sys-tems of the zeolite and silicate types, (2) computations of the properties of atoms and small titanium, rhodium, iridium, and gold clusters localized in cavities or embedded in the zeolite framework, and (3) computations of small silver and tantalum clusters anchored at the dehydr-oxylated and hydroxylated silica surfaces. The calculations were performed by the density functional theory (DFT) with the Becke—Perdew (BP) exchange-correlation potential.

The structure and the first step of hydrolysis of hydrated Pu(IV) ion in aqueous medium were studied using relativistic density functional theory and the polarizable continuum model (PCM). According to calculations, the Pu(IV) ion was mainly coordinated with eight water molecules. The calculated distance Pu-O of 238-241 pm was in good agreement with the experimental value ((239 +/- 2) pm). It was demonstrated that for the correct replication of constants log K-1(0) of the first hydrolysis step, it was important to use scaling multipliers adequate to the charge of the hydrated complex when constructing the density that included the solvated complex in PCM model. The calculated values of log K-1(0) of -1.1...-0.2 were close to the experimentally defined range (-0.6-0.6). The correct replication of hydrolysis constants allowed considering the calculated range of the hydratation free energies of the Pu(IV) ion of 6070-6157 kJ/mol as a reasonable prediction of experimental values.