N. E. Kuz’menko

A theoretical study of the activation of methane by Gold(III) homoleptic complexes

The density functional theory method with the PBE functional, SBK pseudopotential, and extended basis sets was used to study the reaction between methane and gold(III) homoleptic complexes, namely, [AuX4]− (X = Cl, Br, I, H, CN, NH2, OH, CH3, and SH), [Au(X(CY)2X)2]− (X = S, Y = H; X = Y = O), Au2Cl6, [Au(X2(CY))2]+ (X = S, Y = NH2; X = O, Y = H), and [Au(acac)2]+, with the formation of electrophic substitution products. The activation of methane under mild conditions was found to be uncharacteristic of anionic and neutral complexes. According to calculations of cationic oxygen-containing complexes, the formation of methane complexes is possible in their reactions with methane. The energy barrier to this reaction noticeably decreases because of the activation of the C-H bond in this complex. The heat effects vary widely depending on the nature of the ligand. There is, however, no obvious correlation between their values and the activation energy of the reaction.

Quantum-chemical modeling of ethylene and acetylene adsorption on gold clusters

The interaction of ethylene and acetylene molecules with planar (2D) and nonplanar (3D) gold clusters Aun (n = 10, 12, 20) was studied by the density functional theory (DFT) method. The coordination of hydrocarbons at the vertices, edges, and fragments of the Au3 cluster was shown to form π, di-σ, and μ type complexes, respectively. The standard Gibbs energy and the C-C bond length of the hydrocarbon change during its adsorption in the series μ > di-σ > π complexes. The highest selectivity in adsorption of acetylene relative to that of ethylene was achieved on Au12 (3D) and Au20 (2D) clusters.

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C2H2, C2H4, C2H6) on the surface of a sorbent containing Ag0, Agδ+, and AgO sites. The dynamics of change in the structural characteristics of Agn (n ≤ 10) is analyzed and the adsorption of oxygen on Ag8 and Ag10 is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag8, Ag10, Ag10+, Ag10O, and Ag10O2 clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C2H2 increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Agδ+) but also to bind C2H2 and C2H4 directly to the sorbent’s surface.

Studying the adsorption and activation of benzene and chlorobenzene on Ni(12%)/Al2O3 by means of gas chromatography and quantum chemistry

In studying the surface and adsorption properties of Al2O3 and Ni(12%)/Al2O3 with respect to C6H6 and C6H5Cl, it is found that adsorbate-adsorbent interaction is stronger than adsorbate-adsorbate interaction. It is shown that the calculated isosteric heats of adsorption vary in a range of 61 to 45 kJ/mol depending on adsorption magnitude; for Ni(12%)/γ-Al2O3, as in the case of γ-Al2O3, the heat of adsorption of chlorobenzene is higher at low degrees of filling than that of benzene. According to density functional theory quantum-chemical calculations of the structures of complexes (NinC6H5Cl)z and (NinC6H6)z (n = 1, 4; z = −1, 0, +1), a nickel atom can penetrate into C6H5Cl along the C-Cl bond. It is concluded that a negative charge on nickel contributes to the efficient activation of the C-Cl bond and to an increase in the rate of desorption of benzene, a key step in the hydrodechlorination of chlorobenzene.

Activation of Oxygen on Palladium Nanocluster

A simulation of oxygen adsorption on a palladium nanocluster has been performed using density functional theory. It has been demonstrated that the formation of Pd8O2 complexes occurs according to the dissociation mechanism. The most probable centers of oxygen activation are atoms of metal with excess Pdδ− electron density. The possibility of identifying the oxygen coordination type on a Pd8 cluster using the IR spectra is discussed.

Efficacy of the Academic Competition (Olympiad) System of Admission to Higher Educational Institutions (in Chemistry)

The association between the academic competition (Olympiad) results and subsequent academic performance during the first two years at a higher educational institution was examined. The data for three cohorts (N = 738) of students of the Chemistry Department, Moscow State University, were analyzed, including the results of international and nationwide academic competitions in chemistry, university grade point averages, and Unified State Examination scores. It was shown that students admitted on the basis of academic competition results (winning or prize-winning) perform significantly better during the first two years at the university than those admitted on the basis of Unified State Examination scores. It was shown that the results of academic competitions of different levels are not equal in predicting subsequent academic performance for students.

Quantum-chemical simulation of the allyl isomerization of allylbenzene in the presence of gold atom

The isomerization of allylbenzene into trans- and cis-β-methylstyrene was simulated by the PBE density functional method for the allylbenzene-Auz (z = 0, +1) system. It was discovered that the activation energy falls and the rate constant of allylic isomerization of allylbenzene rises upon the transition from Au0 to Au+. The experimentally observed preferential formation of trans-isomer is verified by our calculations.

Quantum-chemical study of the effect of ligands on the structure and properties of gold clusters

The structures of [Au4(dpmp)2X2]2+clusters, where Х =–C≡CH,–СН3,–SCH3,–F,–Cl,–Br,–I, dpmp is bis((diphenylphosphino)methyl)(phenyl)phosphine, are calculated at the level of density functional theory with the PBE functional and a modified Dirac–Coulomb–Breit Hamiltonian in an all-electron basis set (Λ). Using the example of [Au4(dpmp)2(С≡CС6Н5)2]2+, the interatomic distances and bond angles calculated by means of PBE0/LANL2DZ, TPSS/LANL2DZ, TPSSh/LANL2DZ, and PBE/Λ are compared to X-ray crystallography data. It is shown that PBE/Λ yields the most accurate calculation of the geometrical parameters of this cluster. The ligand effect on the electronic stability of a cluster and the stability in reactions of decomposition into different fragments is studied, along with the capability of ligand exchange. Stability is predicted for [Au4(dpmp)2F2]2+ and [Au4(dpmp)2(SCH3)2]2+, while [Au4(dpmp)2I2]2+ cluster is unstable and its decomposes into two identical fragments is supposed.

Quantum chemical assessment of the ligand effect on the properties and structure of protected gold clusters

A procedure based on density functional theory is proposed for calculation of Au20(ХCH3)16 (Х = S, Se, Te) isomers. It is established that the most stable isomer for all X has a core‒shell structure: Au7@(AuXCH3)8(XCH3(AuXCH3)3)(XCH3AuXCH3)2. Optical and IR spectra, ionization potential, and electron affinity are calculated for the first time for all clusters. It is shown that a cluster protected by thiolate ligands has the greatest electronic and thermodynamic stability.

Adsorption of carbon oxide on tetrahedral bimetallic gold–copper clusters

The interaction between carbon oxide and [Au20–nCun]q clusters (n = 0, 1, 19, 20 and q = 0, ±1) is studied by means of DFT/PBE in the scalar relativistic approximation. To establish the composition and structure of an adsorption site, isomers of bimetallic Au19Cu and AuCu19 particles with different positions of the heteroatom at an apex, edge, and face of the tetrahedral framework are considered. The optimized structures are used as the basis to determine the electronic properties of clusters (average bond energy per atom, difference of energies between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), ionization potential, electron affinity energy). The calculated parameters shrink as the copper content in clusters grows. Among the uncharged models, the highest CO adsorption energy is typical of Au19Cu, the heteroatom of which lies at a cluster’s apex. The CO adsorption energy for cationic and anionic clusters grows in comparison to neutral clusters.