Spin Inversion Processes Research Articles

Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations.

Spin-inversion mechanisms in O2 binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet-triplet, singlet-quintet, triplet-quintet, and quintet-septet spin-inversion processes. We found that the singlet-triplet spin-inversion points are located around the potential energy surface region at short Fe-O distances, whereas the singlet-quintet and quintet-septet spin-inversion points are located at longer Fe-O distances. This suggests that both narrow and broad crossing models play roles in O2 binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.

Computational Analysis of Two-State Reactivity in β-Hydride Elimination Mechanisms of Fe(II)– and Co(II)–Alkyl Complexes Supported by β-Diketiminate Ligand

β-Hydride elimination in Fe(II)– and Co(II)–alkyl complexes is known to occur through two different spin multiplicity states and is thus a good example of two-state reactivity. In this study, the automated reaction path search method combined with the mixed-spin effective Hamiltonian approach has been applied to understand the detailed reaction mechanisms including the characterization of the spin-inversion points between the high-spin and low-spin potential energy surfaces for the Fe(II)–C2H5 and Co(II)–C2H5 complexes supported by a β-diketiminate ligand. Density functional theory (DFT) with different exchange-correlation functionals has been used in the reaction path search calculations. We found that the β-hydride elimination process for these complexes consists of multiple steps including two spin-inversion points. We have also investigated the substituent effect in the β-diketiminate ligand to understand the steric and electronic effects on the spin-inversion process. The efficiency of the spin-inver...

Activation of acetonitrile by gas-phase uranium: bond structure analysis and spin–flip reaction mechanism

The reaction mechanism of uranium atom with acetonitrile molecule has been systematically studied on the quintet and triplet spin-state potential energy surfaces (PESs) at B3LYP level of density functional theory. Reaction site prediction and bonding evolution were analyzed using different methods. Crossing seams and possible spin inversion processes between different PESs are discussed by means of spin–orbit coupling (SOC) calculations. The results show that there are three crossing points in the reaction, which appear in the process of capturing hydrogen atom. Larger SOC constant (1545.80 cm−1) and intersystem crossing (ISC) probability ( = 0.72) between quintet and triplet indicate that the effective ISC would occur in the vicinity of the minimum energy crossing points.

Theoretical investigation on activation of ethene by the HNbN− anion in the gas phase

The two-state reaction mechanism of the C2H4 catalyzed by HNbN− on the singlet and triplet potential energy surfaces (PESs) is detailed studied by density functional theory (DFT) at the BMK/def2-TZVPD⋃TZVP level. A crossing point (CP) appears between the singlet and triplet PESs, and possible spin inversion processes is discussed by spin-orbit coupling (SOC) calculation. The result shows that the SOC is efficient. Where spin multiplicities of the reacting system is changed from the triplet state to the singlet PES near the crossing seam. In addition, the energetically most favorable pathway is discovered.

Theoretical Study on the Reaction Mechanism of Ti with CH3CN in the Gas Phase.

To gain a deeper understanding of the reaction mechanisms of Ti with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces (PESs) has been investigated at B3LYP level of density functional theory (DFT). Crossing points between the different PESs and possible spin inversion processes are discussed by spin-orbit coupling (SOC) calculation. In addition, the bonding properties of the species along the reaction were analyzed by electron localization function (ELF), atoms in molecules (AIM) and natural bond orbital (NBO). The results showed that acetonitrile activation by Ti is a typical spin-forbidden process; larger SOC (by 220.12 cm(-1)) and the possibility of crossing between triplet and singlet imply that intersystem crossing (ISC) would occur near the minimum energy crossing point (MECP) during the transfer of the hydrogen atom.

On the catalytic role of IrOn+(n = 0–2) in the oxygen transport activation of N2O by H2: A density functional study

A computational study of the oxygen-transfer reaction of N2O and H2 catalyzed by IrOn+(n=0–2) is completed, incorporates two possible reaction pathways along with quintet and triplet states. In this work, density functional theory method is used to determine all possible intermediates, transition states and products. The crossing points with the possible spin inversion processes are discussed using the intrinsic reaction coordinate approach. According to the calculated results of O-atom affinities, we predict that the 5/3IrOn+(n=0–2) has good O-transfer function from N2O to H2.

Spin-inversion and spin-selection in the reactions FeO(+) + H2 and Fe(+) + N2O.

The reactions of FeO(+) with H2 and of Fe(+) with N2O were studied with respect to the production and reactivity of electronically excited (4)Fe(+) cations. The reaction of electronic ground state (6)FeO(+) with H2 was found to predominantly produce electronically excited (4)Fe(+) as opposed to electronic ground state (6)Fe(+) corresponding to a spin-allowed reaction. (4)Fe(+) was observed to react with N2O with a rate constant of 2.3 (+0.3/-0.8) × 10(-11) cm(3) molecule(-1) s(-1), smaller than the ground state (6)Fe(+) rate constant of 3.2 (±0.5) × 10(-11) cm(3) molecule(-1) s(-1) (at room temperature). While the overall reaction of (6)FeO(+) with H2 within the Two-State-Reactivity concept is governed by efficient sextet-quartet spin-inversion in the initial reaction complex, the observation of predominant (4)Fe(+) production in the reaction is attributed to a much less efficient quartet-sextet back-inversion in the final reaction complex. Average spin-inversion probabilities are estimated by statistical modeling of spin-inversion processes and related to the properties of spin-orbit coupling along the reaction coordinate. The reaction of FeO(+) with H2 served as a source for (4)Fe(+), subsequently reacting with N2O. The measured rate constant has allowed for a more detailed understanding of the ground state (6)Fe(+) reaction with N2O, leading to a significantly improved statistical modeling of the previously measured temperature dependence of the reaction. In particular, evidence for the participation of electronically excited states of the reaction complex was found. Deexcitation of (4)Fe(+) by He was found to be slow, with a rate constant <3 × 10(-14) cm(3) molecule(-1) s(-1).

Theoretical investigation into the Co+ catalytic activity in the cycle reaction of N2O with C2H6 in the gas phase

The spin-forbidden mechanism of the reaction between N 2 O and C 2 H 6 catalyzed by Co + has been investigated using UB3LYP density functional theory. The Harvey method has been applied to optimize five minimum energy crossing points (MECP) on both triplet and quintet potential energy surfaces. Possible spin inversion processes are discussed by means of spin-orbit coupling calculations. According to the calculation of probability of electron hopping using the Landau-Zener formula, effective intersystem crossing may occur at each MECP. The energetic span model proposed by Kozuch has been applied to the catalytic cycles, and shows the turnover frequency reaches 3.35 × 10 –21 s –1 when Co + catalyzes the reaction to produce CH 3 CHO at 298K. The reaction of N 2 O and C 2 H 6 catalyzed by Co + is a typical two-state reaction. An energy span model has been applied to evaluate the catalytic performance of Co + .

Theoretical investigation for the cycle reaction of methane oxidation catalyzed by FeO&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt; in the gas phase

The mechanism of the spin-forbidden reaction of CH4 with O2 catalyzed by FeO+ (6Σ+, 4Π+) on both quartet and sextet potential energy surfaces has been investigated at the B3LYP level of theory. Six competitive reaction pathways for the catalytic reaction and Path 6 are likely in competition with other pathways from energetic viewpoint. There are 6 crossing points in Path 6 and the crossing points 1 and 3 are very important. The minimum energy crossing points (MECP) of corresponding crossing points are optimized. The potential energy surfaces and the possible spin inversion processes are discussed by means of spin-orbit coupling (SOC) and probability of intersystem crossing (ISC) calculations. The SOC of MECP1 is 947.58 cm-1, and MECP3 is 1372.51 cm-1. The probability of ISC are 0.535 and 0.590 respectively. In order to understand the competitive reaction mechanism involving H atom transfer, the activation strain model was adopted for a simple analysis of the competitive reaction. The energetic span ( δE ) model coined by Kozuch is applied in this cycle. X TOF (degree of TOF control) of all of transition state and intermediate are calculated, and the turnover frequency (TOF)-determining transition state (TDTS) and TOF-determining intermediate (TDI) are confirmed. In this catalytic reaction, the TOF is 5.6716×10-42 s-1.

Theoretical Study on the Two-State Reaction Mechanism for the Formation of a Pyridin-2-one Cobalt Complex from Cobaltacyclopentadiene and Isocyanate

The two-state reaction (TSR) mechanism of CpCo(C4H4) with isocyanate on the triplet and singlet potential energy surfaces has been investigated at the B3LYP level. The minimal energy crossing point (CPs) in the crossing seam between the potential energy surfaces are located using the method of Harvey et al., and possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. As a result, the two distinct reaction pathways for the formation of a pyridin-2-one cobalt complex have been found. For the first pathway, there are two key crossing points along the reaction pathway. The first crossing point, CP2, exists near 1B. The reacting system will change its spin multiplicity from the triplet state to the singlet state near this crossing region because the magnitude of the spin-multiplicity mixing (SOC1-e,1-center = 393.37 cm–1) increases in a small energy gap between high- and low-spin states will greatly enhance the probability of intersystem crossing. The single (P1ISC) and double (P2ISC) passes estimated at CP2 are approximately 0.28 and 0.48, respectively. The second crossing point, CP3, will again change its spin multiplicity from the singlet state to the triplet state in the Co–Cγ bond activation pathway, leading to a decrease in the barrier height of 1TS(CF) from 19.5 to 9.5 kcal/mol. Thus, the reaction system will access a lower energy pathway and then move on the triplet potential energy surface as the reaction proceeds. As for the second pathway, the formation of the initial transition is a very unfavorable process kinetically. However, from the beginning of 1H, TSR is a very favorable process kinetically and thermodynamically. After passing point CP5, the triplet potential energy surface can provide a low-cost reaction pathway toward the product complex.

Ab Initio Molecular Dynamics Study of the Reaction of U+ and U2+ with H2O in the Gas Phase: Direct Classical Trajectory Calculations

The gas phase reactions of U(+) and U(2+) with H2O were investigated using an ab initio molecular dynamics method. All of the information along the minimum energy path were calculated with density functional theory (DFT) and coupled cluster methods. For U(+) with H2O, the molecular dynamics simulations yield a branching ratio of 86% for the H2 elimination channel to 14% for the H atomic elimination channel in agreement with the quadruple ion trap mass spectrometry (QIT/MS) experimental ratio of 91% to 9%. In the case of U(2+) + H2O, there is a crossing of the potential energy surfaces (PES) after the first transition state. Crossing seams between the PES and possible spin inversion processes were studied by means of the intrinsic reaction coordinate (IRC) approach. For U(2+) with H2O, all trajectories are corresponds to H atom elimination channel, this is consistent with the Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experimental results. The chemical bonding evolution along the reaction pathways was discussed by using topological methodologies of the electron localization function (ELF).

On the gas-phase [formula omitted] (n = 1, 2) catalyzed reduction of N2O by H2: A density functional study

The mechanisms of the reactions between N2O and H2 in the gas phase catalyzed by PtOn+ (n=1, 2) have been investigated using UB3LYP and CCSD(T) levels of theory. The potential energy surfaces, crossing points and corresponding minimum energy crossing points have been explored. The involved possibility of spin inversion processes of 4/2MECPs are discussed by spin–orbit coupling (SOC) calculations, then the probability values of the quartet (P1ISC) and doublet (P2ISC) are estimated using the Landau–Zener-type model, respectively. The energetic span (δE) model coined by Kozuch was applied in this cycle to obtain some kinetic information. Furthermore, the TDTSs and TDIs were confirmed by the AUTOF program. The calculations showed that the δEs are 158.8 and 115.6kJmol−1, and the TOFs are 8.8×10−16 and 3.9×10−8s−1 for the title reaction catalyzed PtO+ and PtO2+ cations at 298K, respectively. To be compared with the PtO+, the PtO2+ has good catalytic function for the reaction of N2O+H2→N2+H2O in the gas phase at the standard temperature.

Theoretical investigation for the mediated activation of the C–CN in CH3CN by Zr atom in the gas phase

The insertion reaction of Zr (4d25s2) into the C–CN bond of CH3CN on the triplet and singlet potential energy surfaces (PESs) has been investigated at the density functional theory (DFT) using the hybrid exchange correlation functional B3LYP and B3PW91 level. The overall reaction is calculated to be exothermic by 54.59kcal/mol. After the nitrile pi-complex, two distinct reaction paths have been found; we have analyzed the crucial activation barriers of the elementary paths 1 and 2 using the activation strain model and the Curtin–Hammett principle (CHP). Crossing points (CPs) between the potential energy surfaces are located, the minimum energy crossing points (MECPs) are obtained using the algorithm in Harvey method and possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. These theoretical results can act as a guide to further theoretical and experimental researches.

Simple Mechanism for the Dimerization of Ethylene by Gas-Phase CrOH+

Dimerization of ethylene by gas-phase chromium hydroxide (CrOH+) has been experimentally observed. Recent theoretical work suggests the most likely mechanism associated with this process involves formation of a metallacycle intermediate and involves two spin-inversion processes. We propose a different mechanism that involves the formation of a chromium-aqua complex. While the energetics of this new mechanism are similar to previously proposed mechanisms, all intermediates and transition states remain on the same spin surface as both the reactants and products.

Theoretical investigations of spin–orbit coupling and kinetics in reaction NO2 with CO catalyzed by gas phase bare Ir+

The potential energy surface (PES) corresponding to the reaction NO2(2A1) with CO(1∑+) catalyzed by Ir+ has been investigated by using density functional theory (DFT). Minimum energy crossing points (MECPs) on the potential energy surfaces are located by using the methods of Harvey et al. The possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. As a result, the values of the SOC constants at 4/2MECP1 and 5/3MECP2 are 617 and 1187cm−1, respectively. The latter is found to be the energetically favored channel. The energetic span (δE) model coined by Kozuch was applied in this cycle to obtain some kinetic information. The turnover frequency (TOF) determining transition state (TDTS) and TOF determining intermediate (TDI) were confirmed, and the TOF was calculated by the AUTOF program at different temperatures.

Theoretical studies on the reaction of NO2 with CO catalyzed by bare Os+ cations and its kinetic information

The potential energy surface crossings for reaction between NO2(2A1) and CO(1∑+) catalyzed by Os+ have been investigated using the density functional theory (DFT). Minimum-energy crossing points (MECPs) between the potential energy surfaces and the possible spin inversion process are discussed by means of spin–orbit coupling (SOC) calculations. The latter is found to be the energetically favored channel. The energetic span (δE) model has been applied in this cycle to obtain some kinetic information. TDTS (TOF-determining transition state) and the TDI (TOF-determining intermediate) were confirmed, and TOF (E-representation) was calculated at different temperatures.

New insights into the two catalyst cycles of the Pt+-catalyzed oxidation of methane by oxygen: Spin–orbit coupling, spin-inversion probabilities, and kinetic information

Gas-phase Pt+-catalyzed oxidation of methane by oxygen includes two important and interested cycle reactions. They have been theoretically investigated using density functional theory (DFT) at B3LYP/6-311+G (3df, 3pd) level on their doublet and quartet potential energy surfaces (PESs). Three crossing points between the two potential energy surfaces are located. The possible spin inversion processes are estimated by means of spin–orbit coupling (SOC) calculations. The probability of electronic transition in the vicinity of the minimum energy crossing point (MECP) was treated with Landau–Zener-type theory. Finally, the minimum energy reaction paths were found. The energetic span (δE) model proposed by Kozuch has been applied to reveal the kinetic behavior of the two catalytic cycles. Some other theoretical analyses have been done using natural bonding orbital (NBO) and molecular orbital theory.

A two‐state reactivity rationale for the reaction of ta atom with acetonitrile in the gas phase

AbstractThe spin‐forbidden reaction mechanism of Ta (4F, 5d36s2) with CH3CN, on two different potential surfaces (PESs) has been investigated at the B3LYP, MP2, and CCSD level of theory. Crossing points between the PESs are located using different methods, and possible spin inversion processes are discussed by means of spin‐orbit coupling calculations. As a result, the reaction system will change its spin multiplicities near this crossing seam, leading to a significant decrease in the barrier of 2‐4TS3 from 24.17 to 5.36 kcal/mol, which makes the reaction access to a lower energy pathway and accelerate the reaction rate. © 2012 Wiley Periodicals, Inc.

A theoretician’s view of the Ce + mediated activation of the N [sbnd]H bond in ammonia

The insertion reaction of Ce +( 4H, 4f 15d 2) into the N H bond of ammonia on the doublet and quartet potential energy surfaces has been investigated at the density functional theory using the hybrid exchange correlation functional B3LYP level. Crossing points between the potential energy surfaces are located using different methods, and possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. As a result, there is a crossing point between the doublet and the quartet state surfaces. The reacting system will start in the quartet ground state, the change of the spin state probably occurring immediately after the formation of the electrostatic complex intermediate, leading to a significant decrease in the barrier height of 4TS12 from 17.3 to 2.5 kcal/mol, and then move on the doublet potential energy surface as the reaction proceeds. The minimum energy crossing point ( 2/4MECP) is located by using the methods of Harvey et al. On the basis of the calculated SOC value and potential energy surfaces, the estimated probability of ISC ( P ISC) at 2/4MECP is approximate 0.214. Additionally, the natural bond orbital (NBO) and natural resonance theory (NRT) analyses have been used to characterize the nature of the bonds for all of the minima and transition states along the optimal reaction paths. On the basis of the obtained results, it is possible to conclude that for the molecules considered the reaction is a spin-forbidden process, this is a typical two-state reactivity (TSR) reaction. These conclusions are consistent with the experimental observations.

Theoretical investigation on the reaction of N 2O and CO catalyzed by PtO +

The two-state reaction mechanism of PtO + with N 2O and CO on the quartet and doublet potential energy surfaces has been investigated at the B3LYP level. The computation results reveal that the reaction is an O-atom abstraction mechanism. Crossing points (CPs) between the potential energy surfaces (PESs) are located, and possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. The probability of hopping in the vicinity of the crossing has been calculated by the Landau–Zener-type model. The probability value shows the intersystem crossing occurs efficiently, which makes the reaction access to a lower energy pathway and accelerate the reaction rate.