Theoretical study of isomerism of acetylene compounds with aluminum clusters doped with 3d transition metals

Structural characteristics, vibrational frequencies, and energies of ten isomers of acetylene compounds with the centered aluminum cluster Al₁₃ and its analogues Al₁₂M doped with 3d transition metal atoms (M = Ti-Ni) in the states of different multiplicity have been calculated by the density functional theory method. In addition to “coordinated” intermediates in which the C₂H₂ molecule is coordinated through its C-C bond to the M vertex, an M-Al edge, or a trigonal face of the [MAl₂] cluster, “fragment” isomers have been considered in which the acetylene molecule is broken into fragments (C₂H + H, CH + CH, H + CH + C, and 2P + 2H) differently inserted into the aluminum cage and enlarging it to Al₁₂MC₂. For most compounds, low-lying isomers have structures 1–4 (the C₂H₂ molecule is coordinated to an Al₂M face), 1–5 (two CH fragments are added to adjacent Al₂M faces), and 1–8 (with a five-coordinate C* atom). Structure 1–1, in which the C₂H₂ molecule is coordinated through the C-C bond to the M dopant is unstable against transformation into 1–4 with a low barrier. An isomer with unusual structure 1–9 has been localized in which two five-coordinate C* atoms built into the aluminum cage are located in adjacent quasi-planar tetragonal [MAl₃] faces and are bonded to the central aluminum atom (Al_c) through the fifth bonds. The substitution of electronegative substituents X= F and Cl for H atoms in isomers 1–8 and 1–9 makes the latter more basic and clearly more favorable. The five-coordinate C* atoms in them are able to add acceptor ligands of the BH₃ and AlH₃ type and to increase the coordination number of the carbon atom to six with a considerable decrease in energy. The trends in the change in structural characteristics and relative energies of isomers with a change in M dopants along the 3d series, electronegativity of X substituents, and electronic state multiplicity have been analyzed.     

Theoretical Study of Isomers of Doped Clusters M<Subscript>2</Subscript>Al<Subscript>42</Subscript> with Light Element Dopants M inside and on the Surface of the Aluminum Cage

Structures, energies, and spectroscopic characteristics of the isomers of the family of doubly doped М₂Al₄₂ clusters with dopants M from the first two periods and H, Cu, and Zn atoms located in different positions at the surface and in the inner cavity of the aluminum cage have been calculated by the density functional theory method. The effect of the dopant nature on the relative energies of isomers and on the energies of their dissociation along the channels М₂Al₄₂ → 2М + Al₄₂ and М₂Al₄₂ + 2Al → 2М+ Al₄₄. The results are compared with the results of previous DFT calculations of endohedral (M@Al₁₂) and exohedral (Al@)MAl₁₁) isomers of the simpler doped clusters MAl₁₂ with the same dopants M. The influence of the aluminum cage size on the relative energy stability of the surface and and internal sopant positions is considered.     

Theoretical modeling of dissociative addition of an H<Subscript>2</Subscript> molecule to doped aluminum clusters FeAl<Subscript>12</Subscript> and CoAl<Subscript>12</Subscript>

The potential energy surfaces (PES) of the reactions FeAl₁₂ + Н₂ → FeН₂Al₁₂ (1) and CoAl₁₂ + Н₂ → CoН₂Al₁₂ (2) of dissociative addition of an H₂ molecule to Fe- and Co-doped aluminum clusters have been calculated by the density functional theory method. Local minima on the PES in the vicinity of low-lying isomers, intermediates, and transition states have been found, and their structural and spectroscopic characteristics and energies have been calculated. The energies of the successive stages of the catalytic cycle have been evaluated, and the channels corresponding to the minimum energy path of the reactions have been studied. Differences between the structural characteristics and energies of key structures in reactions (1) and (2) have been considered. The results are compared with previous calculations of the PES of hydrogenation reactions performed for related clusters doped with nickel and titanium atoms.     

Theoretical study of isomerism of compounds of N2 and N2H2 molecules with aluminum clusters Al13 and Al12Ti

Segments of the potential energy surfaces corresponding to successive elementary stages of multistep fragmentation of nitrogen and diimine molecules upon their reaction with the aluminum cluster Al₁₃ and its doped analogue Al₁₂Ti have been calculated by the density functional theory method. The minimum energy pathways of these reactions have been calculated for the stages of physisorption, chemisorption, and N₂ and N₂H₂ fragmentation with different ways of insertion of fragments into the Al₁₃ and Al₁₂Ti cages. Relative energies, structural characteristics, and vibrational frequencies of coordinated and fragment isomers have been calculated, the barriers separating these isomers have been evaluated, and molecular diagrams of the reactions have been constructed. The effect of doping on the relative energies of intermediates and activation barriers has been considered. A conclusion has been drawn that doping with titanium should facilitate the reactions of molecular nitrogen with aluminum clusters. Unusual isomers with a five- and six-coordinate nitrogen atom N* have been localized. The results are compared with the data of analogous previous calculations of the PES of isomers corresponding to stepwise fragmentation of an acetylene molecule in related Al₁₃C₂H₂ and Al₁₂TiC₂H₂ derivatives.     

Energetic Insight into the Formation of Solids from Aluminum Polyoxocations

The ε‐Keggin [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ ion (AlAl₁₂⁷⁺) is a metastable precursor in the formation of aluminum oxyhydroxide solids. It also serves as a useful model for the chemistry of aluminous mineral surfaces. Herein we calculate the enthalpies of formation for this aqueous ion and its heterometal‐substituted forms, GaAl₁₂⁷⁺ and GeAl₁₂⁸⁺, using solution calorimetry. Rather than measuring the enthalpies of the MAl₁₂^7/8+ ions directly from solution hydrolysis, we measured the metathesis reaction of the crystallized forms with barium chloride creating an aqueous aluminum solution monospecific in MAl₁₂^7/8+. Then, the contributions to the heat of formation from the crystallized forms were subtracted using referenced states. When comparing the aqueous AlAl₁₂⁷⁺ ion to solid aluminum (oxy)‐hydroxide phases, we found that this ion lies closer in energy to solid phases than to aqueous aluminum monomers, thus explaining its role as a precursor to amorphous aluminum hydroxide phases.     

Theoretical study of elementary reactions of dissociative addition of an H<Subscript>2</Subscript> molecule to doped aluminide clusters MAl<Subscript>12</Subscript> (M = Cr,Mo, and W)

The potential energy surfaces of elementary reactions of dissociative addition of one and two H₂ molecules to Cr-, Mo-, or W-doped aluminide clusters MAl12 in the states of different multiplicity have been calculated by the density functional theory method. The results are compared with the previous calculations of analogous reactions involving the singlet and triplet TiAl₁₂ cluster. The effect of the dopant nature and electronic state multiplicity on the energies and activation barriers of hydrogenation reactions is considered.     

Theoretical study of the isomerism of stepwise-hydrogenated b-doped aluminum clusters BAl12H− 2n (n = 1-6) with the [B@Al12]t- framework

The structure, energy, vibrational, and magnetic characteristics of stepwise-hydrogenated borondoped aluminum clusters B@A₁₂H _2n ^t- (n = 1–6) have been calculated by ab initio density functional theory B3LYP method with the basis sets 6-31G* and 6-311+G*. The results are compared with those of analogous calculations of the related series Al@A₁₂H _2n ^t- . The substitution of boron for the endohedral aluminum atom sharply changes the structure of isomers, their arrangement on the energy scale, and their stability toward the elimination of H₂ molecules. Differences in the behavior of these properties on varying n in the Al@A₁₂H _2n ^t- and B@A₁₂H _2n ^t- families are traced, and the effect of the dopant on these properties is examined.     

A two‐step reaction scheme leading to singlet carbene species that can be detected under matrix conditions for the reaction of Zr(3F) with either CH3F or CH3CN

The results obtained from CASSCF‐MRMP2 calculations are used to rationalize the singlet complexes detected under matrix‐isolation conditions for the reactions of laser‐ablated Zr(³F) atoms with the CH₃F and CH₃CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(³F) + CH₃F evolves to the radical products ZrF· + ·CH₃. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(¹D) + CH₃F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic‐matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low‐multiplicity channel produces the inserted structures H₃C? Zr? F and H₂C?ZrHF experimentally detected. For the Zr(³F) + CH₃CN reaction, a similar two‐step reaction scheme involving the radical fragments ZrNC· + ·CH₃ explains the presence of the singlet complexes H₃C? Zr? NC and H₂C?Zr(H)NC revealed in the IR‐matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc.     

Evolution of (GaAl) n Clusters and Chemisorptions of H2 on (GaAl) n Clusters

The growth behavior of (GaAl) _n (n = 1–12) and the chemisorptions of hydrogen on the ground state geometries have been studied with the three-parameter hybrid generalized gradient approximation due to Becke-Lee–Yang–Parr (B3LYP). The dissociation energy, the second-order energy differences, and the HOMO–LUMO gaps indicate that the magic numbers of the calculated (GaAl) _n clusters are n = 4 and 6. To my knowledge, this is the first time that a systematic study of chemisorptions of hydrogen on gallium aluminum clusters. The onefold top site of aluminum atom is identified to be the most favorable chemisorptions site for one hydrogen chemisorptions on most (GaAl) _n clusters. In general, dissociative chemisorptions of a hydrogen molecule on a top site of aluminum atom is found common for all sizes clusters considered here except for (GaAl) _n (n = 1–3) clusters. The stability of the (GaAl) _n H _m complexes shows that both large second-order difference and large fragmentation energies for (GaAl)₁₀H₂ and (GaAl)₁₁H₂ make these species behaving like magic clusters.     

Studies of the spin-Hamiltonian parameters and the Jahn–Teller distortions for tetragonal Cu(H2O)62+ clusters in trigonal A2Mg3(NO3)12·24H2O (A = La,Bi) crystals

The anisotropic and isotropic spin-Hamiltonian parameters (g factors and hyperfine structure constants) of tetragonal Cu(H₂O)₆²⁺ clusters due, respectively, to the static and dynamic Jahn–Teller effects for Cu²⁺ in trigonal A₂Mg₃(NO₃)₁₂·24H₂O (A = La, Bi) crystals are calculated from the high-order perturbation formulas based on the cluster approach. In the approach, the admixture between the d orbitals of 3dⁿ ion and the p orbitals of ligand ion via covalence effect is considered. All of the calculated results are in agreement with the experimental values. The tetragonal elongations (characterized by ΔR = R_// ? R_⊥) of Cu(H₂O)₆²⁺ cluster due to the Jahn–Teller effect in A₂Mg₃(NO₃)₁₂·24H₂O crystals are acquired from the calculations. The results are discussed.     

A global potential energy surface and time‐dependent quantum wave packet calculation of Au + H2 reaction

A global potential energy surface (PES) corresponding to the ground state of AuH₂ system has been constructed based on 22 853 ab initio energies calculated by the multireference configuration interaction method with a Davidson correction. The neural network method is used to fit the PES, and the root mean square error is only 1.87 meV. The topographical features of the novel global PES are compared with previous PES which is constructed by Zanchet et al. (Zanchet PES). The global minimum energy reaction paths on the two PESs both have a well and a barrier. Relative to the Au + H₂ reactants, the energy of well is 0.316 eV on the new PES, which is 0.421 eV deeper than Zanchet PES. The calculation of Au(²S) + H₂(X¹Σ_g⁺) → AuH(X¹Σ⁺) + H(²S) dynamical reaction is carried out on new PES, by the time‐dependent quantum wave packet method (TDWP) with second order split operator. The reaction probabilities, integral cross‐sections (ICSs) and differential cross‐sections are obtained from the dynamics calculation. The threshold in the reaction is about 1.46 eV, which is 0.07 eV smaller than Zanchet PES due to the different endothermic energies on the two PESs. At low collision energy (<2.3 eV), the total ICS is larger than the result obtained on Zanchet PES, which can be attributed to the difference of the wells and endothermic energies.     

The DFT study on mechanisms for NCO with C2H5 reaction

A detailed investigation has been performed at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311+G(d,p) level for the reaction of NCO with C₂H₅ by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable on the singlet PES than on the triplet PES. On the singlet PES, the initial addition processes are barrierless and release lots of energy. The dominant channel occurs via the fragmentations of the initial adduct C₂H₅NCO and C₂H₅OCN to form C₂H₄ + HNCO and HOCN, respectively. With higher barrier heights, other products such as CH₄ + HNC + CO, CH₃CHNH + CO, CH₃CH + HNCO, and CH₃CN + H₂ + CO are less competitive. On the triplet PES, the entrance reactions surpass significant barriers; therefore, it could be negligible at the normal atmospheric condition. However, the most feasible channel on the triplet PES is the direct hydrogen abstraction channel to form CH₂CH₂ + HNCO. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of the mechanism for C-H bond activation in spin-forbidden reaction between Ti<Superscript>+</Superscript> and C<Subscript>2</Subscript>H<Subscript>4</Subscript>

The mechanism of the spin-forbidden reaction Ti⁺(⁴F, 3d²4s¹) + C₂H₄→TiC₂H₂ ⁺ (²A₂) + H₂ on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing points between the potential energy surfaces and the possible spin inversion process are discussed by means of spin-orbit coupling (SOC) calculations. The strength of the SOC between the low-lying quartet state and the doublet state is 59.3 cm⁻¹ in the intermediate complex IM1-⁴B₂. Thus, the changes of its spin multiplicity may occur from the quartet to the doublet surface to form IM1-²A₁, leading to a sig-nificant decrease in the barrier height on the quartet PES. After the insertion intermediate IM2, two distinct reaction paths on the doublet PES have been found, i.e., a stepwise path and a concerted path. The latter is found to be the lowest energy path on the doublet PES to exothermic TiC₂H₂ ⁺(²A₂) + H₂ products, with the active barrier of 4.52 kcal/mol. In other words, this reaction proceeds in the following way: Ti⁺+C₂H₄→⁴IC→IM1-⁴B₂→^4,2ISC→IM1-²A₁→[²TS_ins]→IM2→[²TS_MCTS]→IM5→TiC₂H₂ ⁺(²A₂)+H₂. Supported by ‘Qinglan’ Talent Engineering Funds by Tianshui Normal University.     

Quantum chemical study of butane isomerization on clusters of aluminum and cobalt chlorides. Mixed complexes

Activated complexes and routes of the model catalytic process, viz., butane isomerization by the aluminum and cobalt chloride complexes, were calculated by the DFT/PBE/TZ2p quantum chemical method. Alkanes are activated via the alkyl mechanism to form binuclear bimetallic alkyl clusters, where the Co atoms are linked by the metal-metal bonds. The revealed binuclear complexes can transform into bimetallic alkyl clusters with similar energy in which the transition metal atoms are linked by bridges of the Cl atoms. The full model of the catalytic cycle was developed for the maximum multiplicity (7), and particular key regions related to the cleavage and formation of the C-C bonds were calculated with a lowered multiplicity (5 and 3). The sequence of mutual rearrangements of the polynuclear complexes provides the possibility of C-C bond cleavage in alkanes and formation of the metal-carbon bonds. The calculated energy barriers of particular stages of the cyclic catalytic process of butane isomerization are not higher than 29 kcal mol^?1 for multiplicity 7 and by ～10 kcal mol^?1 lower for a lower multiplicity.     

Preparation and structural characterization of [(η5-C5H5)2Zr(SC6H5)]2O. A qualitative description of the bonding in oxo-bridged dicyclopentadienyl-transition metal dimers

The hydrolysis of (η⁵-C₅H₅)₂Zr(SC₆H₅)₂ was shown previously by IR spectroscopy to produce an oxo-bridged complex. The molecular structure of this material has been determined by X-ray diffraction methods and consists of two (η²-C₅H₅)₂Zr(SC₆H₅) units linked by an oxo bridge. The ZrOZr bond is nonlinear at 165.8(2)° with a Zr?Zr interatomic separation of 3.902(1)Å. The two independent SZrO bond angles of 98.7(1) and 103.3(1)° are consistent with a d° electronic structure for each zirconium atom. The relatively short ZrO distances of 1.968(3) and 1.964(3) Å support the presence of partial double-bond character arising from the donation of electron density from filled p_π-orbitals on the oxygen atom to unfilled d-orbitals on the electron deficient d⁰ metal atoms. This bonding feature requires based upon orbital symmetry arguments that the (ML)₂O molecular core in [(η⁵-C₅H₅)₂ML]₂O complexes must be nonplanar with a dihedral angle between the two LMO planes less than 90°. For [(η⁵-C₅H₅)₂Zr(SC₆H₅)]₂O, dihedral angle of 61.7° was observed. The compound crystallizes in an orthorhombic space group, Pbca, with refined lattices parameters a 16.458(4), b 20.281(5), and c 17.016(4) Å. Full-matrix least-squares refinement of 2613 diffractometry data I > σ(I) led to a final discrepancy index R(F₀²) = 0.044.     

Theoretical study of the activation barriers of elementary reactions of hydrogenation of aluminide clusters X@Al<Subscript>12</Subscript> and X@Al<Stack><Subscript>12</Subscript><Superscript>−</Superscript></Stack> with dopants X = Al,Si, and Ge

The transition states and activation barriers h of elementary reactions of addition of the H₂ molecule to aluminide clusters Al₁₃, Al ₁₃ ^? , Al₁₃H ₂ ^? , Al₁₃H ₄ ^? , Si@Al₁₂, Ge@Al₁₂, and LiAl₁₃ were calculated within the B3LYP approximation of the density functional theory using 6–31G* and 6–311+G* basis sets. The barriers h for all diamagnetic clusters were found to be high (～30–40 kcal/mol). The outer-sphere cation Li⁺ decreases while the endohedral electronegative dopants Si and Ge increase the barrier by a few kcal/mol. The hydrogenation barrier of the neural paramagnetic cluster Al₁₃, which has free valence, decreases to ～20 kcal/mol. The addition of a hydrogen atom or a Cl₂ molecule to both paramagnetic and diamagnetic aluminum clusters occurs without a barrier. The first stage of the reaction (addition of H₂ to an Al-Al edge) is in all cases the critical stage of aluminide hydrogenation. The barrier h of this reaction is several times higher than the barriers to migration of hydrogen atoms over the metal cage. The migration of H atoms occurs simultaneously with considerable distortions of the Al₁₃ cage even to the extent that it changes its structural motif. The addition of the H₂ molecule to the Al@TiAl₁₁ cluster containing the peripheral titanium atom occurs with a small barrier, whereas the barrier to elimination of H₂ from the dihydride Al@TiAl₁₁H₂ is reduced to ～15 kcal/mol. Based on the calculations, the conclusion was drawn that the elementary reactions of hydrogenation and dehydrogenation for Ti-doped aluminide clusters should occur considerably faster and under milder conditions than for homonuclear aluminides.     

Ionization-recombination equilibrium in cold cluster plasma under conditions of retardation by high energy barrier

The kinetics of charge separation in a cold plasma was studied with the degradation reaction in molecular clusters HCl(H₂O) _n + m(H₂O) ? H₃O⁺(H₂O) _{n + m ?1}Cl^?, taken as an example, which precedes chlorine adsorption on the ice surface in the stratosphere. The formation of a vast population of H⁺, Cl^? ion pairs stabilized in water clusters ensures the intense binding of chlorine in ice microcrystals that occur in stratospheric clouds. The accumulation of chlorine in the stratosphere is recognized as the main cause of the destruction of the protective ozone layer. The ion buildup effect is a result of the balance between opposite ionization and recombination processes in the presence of a high energy barrier that retards ion recombination in water clusters. A kinetic equation for the process was obtained and its solution was analyzed. The parameters of the barrier were calculated by computer simulation.     

Reaction mechanism of the preferential oxidation of the CO reaction in an H<Subscript>2</Subscript> stream over Cu–Ni bimetallic catalysts: A computational study

The preferential oxidation (PROX, CO + H₂ + O₂ → CO₂ + H₂O) of the CO reaction in an H₂ stream is the simplest and most cost-effective method to remove CO gas to less than 10 ppm in reformed fuel gas. We study the mechanism of PROX of the CO reaction in the H₂ stream catalyzed by Cu _n Ni (n = 3-12) clusters using a density functional theory (DFT) calculation to investigate bimetallic effects on the catalytic activation. Our results indicate that the Cu₁₂Ni cluster is the most efficient catalyst for H₂ dissociation and the Cu₆Ni cluster is the most efficient catalyst for CO-PROX in excess hydrogen among Cu _n Ni (n = 3-12) clusters. To gain insight into the adsorption and dissociation of the H₂ molecule effect in the catalytic activity over the Cu₁₂Ni cluster and the potential energy surfaces about PROX of CO oxidation on the Cu₆Ni cluster, the nature of the interaction between the adsorbate and substrate is analyzed by detailed electron local densities of states (LDOS) as well as molecular structures.     

Massenspektrometrische Messung der Stabilität der gasförmigen Komplexe MAl2Cl8 (M  Be,Fe, Zn,Cd, Pt) Der Zusammenhang der Stabilität der Gaskomplexe MAl2Cl8 mit den Koordinationszahlen im festen Dichlorid

Mass Spectrometric Measurements of the Stability of the Gaseous Complexes MAl₂Cl₈ (M ? Be, Fe, Zn, Cd, Pt). Connection between the Stability of the Complexes MAl₂Cl₈ and the Coordination of M and Cl in the Solid Dichloride The equilibria MCl_2,s + Al₂Cl_6,g ? MAl₂Cl_8,g mit (M ? Fe, Zn, Cd, Pt) have been measured by mass spectrometry (effusion from double cells). The corresponding equilibrium with BeCl₂ has been calculated from older measurements. All the ΔH° and ΔS° data of this type of reaction have been collected from the literature. A clear connection exists between the thermodynamic data and the coordination of M and Cl in the solid dichlorides.     

Synthesis of d2 η-cycloheptatrienyl-η-cycloheptadienyl-zirconium and -hafnium using the metal vapours

Cocondensation of cycloheptatriene with zirconium or hafnium vapours gives, after vacuum pyrolysis of the reaction mixture the diamagnetic d² compounds [m(η-C₇H₇)(η-C₇H₉)].