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1.
On the basis of DFT calculations (B3LYP/6‐311+G**), the possibility to include solvent effects is considered in the investigation of the H2O‐exchange mechanism on [Be(H2O)4]2+ within the widely used cluster approach. The smallest system in the gas phase, [Be(H2O)4(H2O)]2+, shows the highest activation barrier of +15.6 kcal/mol, whereas the explicit addition of five H‐bonded H2O molecules in [{Be(H2O)4(H2O)}(H2O)5]2+ reduces the barrier to +13.5 kcal/mol. Single‐point calculations applying CPCM (B3LYP(CPCM:H2O)/6‐311+G**//B3LYP/6‐311+G**) on [Be(H2O)4(H2O)]2+ lower the barrier to +9.6 kcal/mol. Optimization of the precursor and transition state of [Be(H2O)4(H2O)]2+ within an implicit model (B3LYP(CPCM:H2O)/6‐311+G** or B3LYP(PCM:H2O)/6‐311+G**) reduces the activation energy further to +8.3 kcal/mol but does not lead to any local minimum for the precursor and is, therefore, unfavorable. 相似文献
2.
Density functional theory (DFT) calculations at ONIOM DFT B3LYP/ 6‐31G**‐MD/UFF level are employed to study molecular and dissociative water and ammonia adsorption on anatase TiO2 (001) surface represented by partially relaxed Ti20O35 ONIOM cluster. DFT calculations indicate that water molecule is dissociated on anatase TiO2 (001) surface by a nonactivated process with an exothermic relative energy difference of 58.12 kcal/mol. Dissociation of ammonia molecule on the same surface is energetically more favorable than molecular adsorption of ammonia (?37.17 kcal/mol vs. ?23.28 kcal/mol). The vibration frequency values also are computed for the optimized geometries of adsorbed water and ammonia molecules on anatase TiO2 (001) surface. The computed adsorption energy and vibration frequency values are comparable with the values reported in the literature. Finally, several thermodynamical properties (ΔH°, ΔS°, and ΔG°) are calculated for temperatures corresponding to the experimental studies. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
3.
Enthalpies of unsaturated oxygenated hydrocarbons and radicals corresponding to the loss of hydrogen atoms from the parent molecules are intermediates and decomposition products in the oxidation and combustion of aromatic and polyaromatic species. Enthalpies (ΔfH0298) are calculated for a set of 27 oxygenated and nonoxygenated, unsaturated hydrocarbons and 12 radicals at the G3MP2B3 level of theory and with the commonly used B3LYP/6‐311g(d,p) density functional theory (DFT) method. Standard enthalpies of formation (ΔfH0298) are determined from the calculated enthalpy of reaction (ΔH0rxn,298) using isodesmic work reactions with reference species that have accurately known ΔfH0298 values. The deviation between G3MP2B3 and B3LYP methods is under ±0.5 kcal mol?1 for 9 species, 18 other species differs by less than ±1 kcal mol?1 , and 11 species differ by about 1.5 kcal mol?1. Under them are 11 radicals derived from the above‐oxygenated hydrocarbons that show good agreement between G3MP2B3 and B3LYP methods. G3 calculations have been performed to further validate enthalpy values, where a discrepancy of more than 2.5 kcal mol?1 exists between the G3MP3B3 and density functional results. Surprisingly the G3 calculations support the density functional calculations in these several nonagreement cases. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 633–648, 2005 相似文献
4.
The dehydrogenation reaction of H2S by the 3∑- ground state of VS+: VS+ + H2S → VS2+ + H2 has been studied by using Density Functional Theory (DFT) at the B3LYP/DZVP level. It is found that the reaction proceeds along two possible pathways (A and B) yielding two isomer dehydrogenation products VS2+-1 (3B2) and VS2+-2 (3A1), respectively. For both pathways,the reaction has a two-step-reaction mechanism that involves the migration of two hydrogen atoms from S2 to V+, respectively. The migration of the second hydrogen via TS3 and that of the first via TS4 are the rate-determining steps for pathways A and B, respectively. The activation energy is 17.4 kcal/mol for pathway A and 22.8 kcal/mol for pathway B relative to the reactants. The calculated reaction heat of 9.9 kcal/mol indicates the endothermicity of pathway A and that of -11.9 kcal/mol suggests the exothermicity of pathway B. 相似文献
5.
Laser-ablated group V metal atoms (V, Nb, Ta) were co-deposited with water molecules in excess argon. The V atoms reacted with water to form the inserted HVOH molecule spontaneously. The Nb atoms reacted with water to form the NbOH2 complex and the inserted HNbOH molecule. Broad-band photolysis produced the H2VO and H2NbO molecules as well as the VO and NbO monoxides. For Ta + H2O reactions, neither TaOH2 nor HTaOH was observed, while the H2TaO molecule was produced on annealing, and the H2 elimination process was not observed on photolysis. The aforementioned species were identified via isotopic substitutions as well as density functional calculations. Qualitative analysis of the possible reaction paths leading to the observed products is proposed. The results have been compared with our earlier works concerning the Sc and group IV metal atoms with water reactions in order to observe existent trends for the early transition metal atoms. 相似文献
6.
7.
The water exchange reaction of [Be(H2O)2(1H‐imidazole‐4,5‐dicarboxylate)] and [Be(H2O)2(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]+ in water was studied by DFT calculations (RB3LYP/6‐311+G**) and identified as an associative interchange mechanism. The activation barriers for [Be(H2O)2(1H‐imidazole‐4,5‐dicarboxylate)] (16.6 kcal/mol) and [Be(H2O)2(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]+ (13.8 kcal/mol) are similar to the barrier for [Be(H2O)4)]2+ and independent of the overall charge. NICS calculations show no indication that the aromaticity of the imidazole ring is affected during the water exchange process. 相似文献
8.
The hydrogen, carbon dioxide, and carbon monoxide gas adsorption and storage capacity of lithium-decorated cyclopropane ring systems were examined with quantum chemical calculations at density functional theory, DFT M06-2X functional using 6-31G(d) and cc-pVDZ basis sets. To examine the reliability of M06-2X DFT functional, a few representative systems are also examined with complete basis set CBS-QB3 method and CCSD-aug-cc-pVTZ level of theory. The cyclopropane systems can bind to one Li+ ion; however, the corresponding the methylated systems can bind with two Li+ ions. The cyclopropane systems can adsorb six hydrogen molecules with an average binding energy of 3.8 kcal/mol. The binding free energy (ΔG) values suggest that the hydrogen adsorption process is feasible at 273.15 K. The calculation of desorption energies indicates the recyclable property of gas adsorbed complexes. The same number of CO2 and CO gas molecules can also be adsorbed with an average binding energy of −14.4 kcal/mol and −10.7 kcal/mol, respectively. The carbon dioxide showed ~3–4 kcal/mol better binding energy as compared to carbon monoxide and hence such designed systems can function as a potential candidate for the separation of these flue gas molecules. The nature of interactions in complexes was examined with atoms in molecules analysis revealed the electrostatic nature for the interaction of Li+ ion with cyclopropane rings. The chemical hardness and electrophilicity calculations showed that the gas adsorbed complexes are rigid and therefore robust as gas storage materials. 相似文献
9.
Rodrigo J Corrêa 《Tetrahedron letters》2003,44(39):7299-7302
Two adsorption complexes between pyrrole and alkaline T6 zeolite clusters were studied theoretically using DFT method. Results show that at B3LYP/6-311+G**//B3LYP/6-31G* the oxygen atoms in LiT6 are, in average, more charged than in CsT6. The cation-π complex is more stable than the complex possessing a hydrogen bond between T6 clusters and pyrrole. Correlations between alkaline cation hardness and ΔHadsorption (kcal/mol) showed a linear correlation for both complexes, indicating that the driving force for pyrrole adsorption is cation hardness. 相似文献
10.
Density functional theory (DFT) and Fourth‐order Möller–Plesset (MP4) perturbation theory calculations are performed to examine the possibility of hydrogen storage in V‐capped VC3H3 complex. Stability of bare and H2 molecules adsorbed V‐capped VC3H3 complex is verified using DFT and MP4 method. Thermo‐chemistry calculations are carried out to estimate the Gibbs free corrected averaged H2 adsorption energy which reveals whether H2 adsorption on V‐capped VC3H3 complex is energetically favorable, at different temperatures. We use different exchange and correlation functionals employed in DFT to see their effect on H2 adsorption energy. Molecular dynamic (MD) simulations are performed to confirm whether this complex adsorbs H2 molecules at a finite temperature. We elucidate the correlation between H2 adsorption energy obtained from density functional calculations and retaining number of H2 molecules on VC3H3 complex during MDs simulations at various temperatures. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011 相似文献
11.
V. Bertin A. Cruz G. Del Angel M. Castro E. Poulain 《International journal of quantum chemistry》2005,102(6):1092-1105
A comparative study of adsorption of H atoms and H2 molecules on Pd3Cu, Cu4, and Pd4 clusters has been performed through density functional calculations, using the hybrid B3LYP exchange‐correlation functional as implemented in the Gaussian98 program. For Pd atoms the relativistic small‐core effective core potential LANL and LANL2DZ basis set was used and for hydrogen a 6‐31G** basis set was used. The main emphasis is set in the reaction behavior of the different clusters with hydrogen atoms and molecules. We find that full geometry optimization does not appreciably change the metal cluster geometry either for certain reaction modes or the H and H2 capture parameters, but increases the number of reactive sites of the metal clusters. Also, we found that there is charge transfer competition between H and Cu atoms, which drastically diminishes H2 adsorption energy, related to the Pd cluster observed value. Edges and threefold sites are the principal hydrogen adsorption sites. Hydrogen has a great mobility over the metal clusters for different minima, especially when Cu is present; many initial pathways end in the same adsorption site. The observed hydrogen adsorption and binding energies are well reproduced by the calculations. Also, the adsorption mechanisms were determined. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
12.
V. K. Kochnev O. P. Charkin N. M. Klimenko 《Russian Journal of Inorganic Chemistry》2009,54(7):1114-1126
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. 相似文献
13.
V. A. Matsura N. S. Panina V. V. Potekhin V. B. Ukraintsev K. A. Khokhryakov V. V. Platonov O. M. Tatsenko A. I. Panin 《Russian Journal of General Chemistry》2004,74(7):975-979
The mechanism of the reaction of Pd
n
clusters with an H2 molecule was suggested on the basis of DFT B3LYP/HW calculations. The catalytic center in an elementary event of the process is one of the vertices of the Pd
n
cluster; spillover of hydrogen atoms along the cluster edges results in the formation of a stable Pd
n
H2 complex with a significant energy gain in the case of the singlet reaction channel. In such a mechanism, the cluster size should not significantly affect the reaction up to a certain moment; therefore, when simulating processes involving large clusters, we can restrict ourselves to relatively small sites of their surface. 相似文献
14.
de Lucas NC Correa RJ Albuquerque AC Firme CL Garden SJ Bertoti AR Netto-Ferreira JC 《The journal of physical chemistry. A》2007,111(6):1117-1122
Laser flash photolysis (LFP) studies, atoms in molecules (AIM) studies, and density functional theory (DFT) calculations have been performed in order to study the mechanism of the hydrogen abstraction by alpha-diketones in the presence of phenols. Laser irradiation of a degassed solution of 1,2-diketopyracene in acetonitrile resulted in the formation of a readily detectable transient with absorption at 610 nm, but with very low absorptivity. This transient decays with a lifetime of around 2 micros. The quenching rate constant for substituted phenols, kq, ranged from 1.10x10(8) L mol-1 s-1 (4-cyanophenol) to 3.87x10(9) L mol-1 s-1 (4-hydroxyphenol). The Hammett plot for the reaction of the triplet of 1,2-diketopyracene with phenols gave a reaction constant rho=-0.9. DFT calculations (UB3LYP/6-311++G**//UB3LYP/6-31G*) of the triplet complex ketone-phenol revealed that hydrogen transfer has predominantly occurred and that the reaction with alpha-diketones are generally 7 kcal/mol less endothermic than the respective reactions of the monoketones. These results together with the geometries obtained from the DFT calculations, natural bond order (NBO) analysis, and AIM results indicate that hydrogen abstraction for alpha-diketones is facilitated by the electrophilicity of the ketone, instead of neighboring group participation by the second carbonyl group. 相似文献
15.
An empirical correction to density functional theory (DFT) has been developed in this study. The approach, called correlation
corrected atomization–dispersion (CCAZD), involves short- and long-range terms. Short-range correction consists of bond (1,2-) and angle (1,3-) interactions, which remedies the deficiency of DFT in describing the proto-branching stabilization effects. Long-range correction
includes a Buckingham potential function aiming to account for the dispersion interactions. The empirical corrections of DFT
were parameterized to reproduce reported ΔH
f
values of the training set containing alkane, alcohol and ether molecules. The ΔH
f
of the training set molecules predicted by the CCAZD method combined with two different DFT methods, B3LYP and MPWB1K, with
a 6-31G* basis set agreed well with the experimental data. For 106 alkane, alcohol and ether compounds, the average absolute
deviations (AADs) in ΔH
f
were 0.45 and 0.51 kcal/mol for B3LYP- and MPWB1K-CCAZD, respectively. Calculations of isomerization energies, rotational
barriers and conformational energies further validated the CCAZD approach. The isomerization energies improved significantly
with the CCAZD treatment. The AADs for 22 energies of isomerization reactions were decreased from 3.55 and 2.44 to 0.55 and
0.82 kcal/mol for B3LYP and MPWB1K, respectively. This study also provided predictions of MM4, G3, CBS-QB3 and B2PLYP-D for
comparison. The final test of the CCAZD approach on the calculation of the cellobiose analog potential surface also showed
promising results. This study demonstrated that DFT calculations with CCAZD empirical corrections achieved very good agreement
with reported values for various chemical reactions with a small basis set as 6-31G*. 相似文献
16.
Heats of reaction and barrier heights have been computed for H + CH2CH2 → C2H5, H + CH2O → CH3O, and H + CH2O → CH2OH using unrestricted Hartree-Fock and Møller–Plesset perturbation theory up to fourth order (with and without spin annihilation), using single-reference configuration interaction, and using multiconfiguration self-consistent field methods with 3-21G, 6-31G(d), 6-31G(d,p), and 6-311G(d,p) basis sets. The barrier height in all three reactions appears to be relatively insensitive to the basis sets, but the heats of reaction are affected by p-type polarization functions on hydrogen. Computation of the harmonic vibrational frequencies and infrared intensities with two sets of polarization functions on heavy atoms [6-31G(2d)] improves the agreement with experiment. The experimental barrier height for H + C2H4 (2.04 ± 0.08 kcal/mol) is overestimated by 7?9 kcal/mol at the MP2, MP3, and MP4 levels. MCSCF and CISD calculations lower the barrier height by approximately 4 kcal/mol relative to the MP4 calculations but are still almost 4 kcal/mol too high compared to experiment. Annihilation of the largest spin contaminant lowers the MP4SDTQ computed barrier height by 8?9 kcal/mol. For the hydrogen addition to formaldehyde, the same trends are observed. The overestimation of the barrier height with Møller-Plesset perdicted barrier heights for H + C2H4 → C2H5, H + CH2O → CH3O, and H + CH2O → CH2OH at the MP4SDTQ /6-31G(d) after spin annihilation are respectively 1.8, 4.6, and 10.5 kcal/mol. 相似文献
17.
P.N. Skancke 《Chemical physics letters》1977,47(2):259-264
The interaction between the molecules ethylene and cis-N2H2 has been studied using a gaussian basis in a series of ab initio SCF calculations. The results obtained indicate that the synchronous hydrogen transfer reaction is a one-step reaction having an activation energy of around 60 kcal/mol. Our results do not lend support to the hypothesis that the rate of the overall reaction between C2H4 and N2H2 is controlled by the rate of isomerization of trans-diimide to the cis form. 相似文献
18.
Anagha Haridas Suvam Saha Shantabh Bedajna Prof. Dr. Sundargopal Ghosh 《欧洲无机化学杂志》2023,26(27):e202300312
Azametallacyclopropane-containing base stabilized borane complexes of group 5 transition metals have been synthesized and their structural aspects have been described. Treatment of Cp* based Ta and Nb chlorides, Cp*TaCl4 and Cp*NbCl4 with [LiBH4 ⋅ THF] followed by addition of ligands, such as 2-mercaptobenzothiazole, MBT, (C7H5NS2) and 2-mercaptobenzoxazole, MBO (C7H5NSO) led to the formation of complexes [Cp*M-[BHS(CH2ENC6H4)(C7H4NSE)] ( 1 : M=Ta, E=S; 2 ; M=Nb, E=S; 3 : M=Ta, E=O; 4 ; M=Nb, E=O, Cp*=pentamethyl-η5-cyclopentadienyl). By means of UV-vis absorption spectra, the electronic properties of these complexes associated with central metal atoms and heteroatoms (S or O) have been evaluated. In contrast, treatment of Cp*TaCl4 with 2-mercaptopyridine, MP, (C5H5NS) under the same reaction conditions yielded the agostic σ-borane Ta complex, [Cp*Ta(H3BNC5H4) (C5H4NS)(η2-S2)], 5 . Unlike 1 – 4 , where the metals interact with boron through bridging sulphur, 5 shows a notable σ-B−H bond interaction with Ta. All spectroscopic data of 1 – 5 along with the X-ray diffraction studies suggest complexes 2 , 4 , and 5 are base (amine) stabilized borane species. Computational studies based on Density Functional Theory (DFT) also supported this conclusion. 相似文献
19.
Oscar Mendoza 《Journal of organometallic chemistry》2005,690(6):1511-1522
The cocondensation reaction of lithium atoms and pure anisole leads to an ortho CH activation and the formation of lithium hydride. This simple two-component system allows the investigation of the reaction mechanism with included donor molecules. Therefore two anisole and one dilithium molecule, which was identified in an earlier spectroscopic study, were considered for the reaction pathway calculations.Firstly, two intermediates can be found along the reaction pathway, which show the reaction before and after the critical CH activation step. Secondly, a low-lying transition state can be identified, which allows the carbon hydrogen bond to be broken with an activation energy of less than 20 kcal/mol instead of more than 100 kcal/mol, if a free radical mechanism is employed. All calculations were performed at the B3LYP/6-31G** level of theory. 相似文献
20.
A detailed knowledge of the initial complexes is crucial for the better understanding of the reaction mechanisms between tetrachloro-p-benzoquinone (TCBQ) and hydrogen peroxide (H2O2). In the present study, the interaction modes and interaction mechanisms between TCBQ and H2O2 in the absence and presence of one, two, and three water molecules have been systematically investigated employing the B3LYP/6-311++G** level of theory in combination with the atoms in molecules theory and natural bond orbital (NBO) method. It was found that the introduction of water molecules can influence the original interaction modes between TCBQ and H2O2 through the formation of the intermolecular H-bonds. The interaction energies between TCBQ and H2O2 range from ?0.37 to ?2.75 kcal/mol for four stable complexes, which are smaller than that of the interaction between H2O2 and water molecule. Further energy decomposition analyses suggest that the coupling interactions between TCBQ and H2O2 are predominated by the electrostatic interactions regardless of the presence or absence of water molecules. In addition, the significant heat released from the interaction process in the presence of water molecules is expected to be favorable for the following reactions involving the production of the hydroxyl radical. 相似文献