Mo活化NH3的自旋禁阻反应机理

采用密度泛函理论的UB3LYP方法,计算研究了气相中Mo活化NH3的反应机理。为了理解由Mo活化NH3过程中自旋翻转行为,对自旋态分别为七、五、三和单等4个反应势能面进行了计算研究,其结果表明,Mo活化NH3的过程是通过各自旋态势能面交叉产生的典型的自旋禁阻反应,最低能量交叉点(MECPs)附近的系间窜越导致2步H转移和脱H2反应能垒降低。此外运用自然键(NBO)轨道理论分析了反应中较为重要的几个物种的成键特性。通过计算在最低能量交叉点(MECPs)附近不同自旋态之间的自旋-轨道耦合常数,再运用Landau-Zener跃迁几率公式估算了MECPs处系间窜越几率。所确定的最低能量反应路径为:7Mo+NH3→7IM1→7/5MECP1→5TS12→5IM2→5/3MECP2→3TS23→3IM3→3TS34→3IM4→3HMoN+H2。     

Theoretical investigations of spin-orbit coupling and intersystem crossing in reaction carbon dioxide activated by [Re(CO)2]+

In order to further explore the detailed reaction mechanism of carbon dioxide activated by [Re(CO)₂]⁺ complex, CCSD(T) methods was performed to determine related potential energy surface (PES). Crossing point is determined by using a partially optimized method. The result shows that larger spin-orbital coupling (155.37 cm⁻¹) and intersystem crossing probabilities in spin-forbidden region causes the electron to spin flip at the minimum energy crossing point and access to the lower singlet PES. Nonadiabatic rate constant k is estimated to be quite rapid, so transition state (¹TS1) is rate-controlled steps. In addition, the electronic structure of oxygen-atom transfer process is further analyzed by localized molecular orbital and Mayer bond order. The analysis finds that the form of main bonding orbital is the electron contribution from the p(O) in CO₂ to the empty d(Re) orbital.     

过渡金属重卡拜的合成、结构与反应性

过渡金属硅卡拜、锗卡拜、锡卡拜和铅卡拜是过渡金属分别与硅、锗、锡和铅之间形成三键的化合物。自从1996年首次发现钼锗卡拜以来,相继得到了一系列过渡金属锗卡拜、锡卡拜和铅卡拜化合物,而首例过渡金属硅卡拜则于2010年得以成功制备,标志着过渡金属与第14族元素之间形成三键的空白被全部填满。这些化合物的出现大大丰富和完善了过渡金属主族元素化学在成键、结构和反应方面的内容,引起化学界的重视。本文结合这方面最新的实验研究进展,系统全面总结了这些化合物的合成、结构和反应性,并对该领域的发展前景作了讨论。     

气相VO（∑＋）与CH3OH（1^A′）分子自旋禁阻反应C—H，O—H键活化机理的理论研究

采用密度泛函理论（DFT）B3LYP与cCsD方法研究了二重态和四重态势能面自旋禁阻反应VO（∑’）活化cH30H（1^A′）分子c—H,0—H键的微观机理．通过自旋一轨道耦合的计算讨论了势能面交叉点和可能的自旋翻转过程．在MEcP处,四重态和二重态问的旋轨耦合常数为131．14cm^-1．自旋多重度发生改变,从四重态系间穿越到二重态势能面形成中间体2^IM1,导致反应势能面的势垒明显降低．     

Spin-inversion mechanisms in the reactions of transition metal cations (Sc+, Ti+, V+, Cr+, Mn+, Fe+, Co+, Ni+, and Cu+) with OCS in the gas phase: A perspective from automated reaction path search calculations

The mechanisms including spin-inversion have been systematically studied for the M⁺ + OCS → MS⁺ + CO/MO⁺ + CS (M denotes a transition metal from Sc to Cu) ion-molecule reactions using the automated reaction path search method. We used the lowest mixed-spin potential energy surface obtained from the diagonalization of the spin-coupled Hamiltonian matrix, whose diagonal elements are taken to be the lowest two spin states. This scheme can effectively locate approximate minimum energy crossing points between the two potential energy surfaces with different spin multiplicities. The spin-orbit couplings at spin-inversion points have been calculated to understand the efficiencies of nonadiabatic transitions. The obtained reaction pathways and the calculated spin-orbit couplings are employed to interpret previous experimental studies.     

金属聚炔能带结构与化学键研究──Ⅰ．主链中金属对聚炔能带结构的影响

用紧束缚ＥＨＴ晶体轨道方法对含有过渡金属的聚炔化合物［─Ｃ≡Ｃ─Ｍ（ＰＨ_３）_２─Ｃ≡Ｃ─］_ｎ（Ｍ＝Ｐｄ，Ｐｔ，Ｎｉ）及［─Ｃ≡Ｃ─Ｍ─Ｃ≡Ｃ─］_ｎ（Ｍ＝Ｃｕ，Ａｇ，Ａｕ）进行了能带结构计算，发现在费米能级附近的导带或价带都是离域的ｄ－ｐπ键，这些能带对导电性起决定作用。根据重复单元碎片分子轨道和相互作用讨论了能带的组成与碎片分子轨道的相互关系。     

Gas Phase Ion Chemistry of Transition Metal Clusters: Production, Reactivity, and Catalysis

This review focuses on the use of mass spectrometry to examine the gas phase ion chemistry of metal clusters. Ways of forming gas phase clusters are briefly overviewed and then the gas phase chemistry of silver clusters is discussed to illustrate the concepts of magic numbers and how reactivity can be size dependent. The chemistry of other bare and ligated metal clusters is examined, including mixed metal dimer ions as models for microalloys. Metal clusters that catalyze gas phase chemical reactions such as the oxidation of CO and organic substrates are reviewed. Finally the interface between nanotechnology and mass spectrometry is also considered.     

气相中Co+催化CO与N2O反应机理的理论计算研究

采用密度泛函UB3LYP/6-311+G(2d)方法计算研究了Co+在基态和激发态下与N2O的反应机理,全参数优化了反应势能面上各驻点的几何构型,用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证,并用UB3LYP/6-311++G(3df,3pd)、单点垂直激发、Harvey等人的方法分别进行各驻点单点能校正,三重态和五重态反应势能面两个交叉点CP确定,最低能量交叉点(MECP)的优化及MECP处相应的自旋-轨道耦合常数(SOC)计算,计算结果表明,该反应为两步反应,较大的SOC值说明了在势能面上的翻转能够有效发生,且反应机理都为插入—消去反应,交叉点能够有效的降低反应的活化能,这在动力学和热力学上都是有利的。     

Statistical Adiabatic Channel Model Calculations of the Reaction of H Atoms and FO Radicals on Ab Initio Potential Energy Surfaces

The statistical adiabatic channel model has been used to calculate rate coefficients for the reaction between H atoms and FO radicals on potential energy surfaces based on density functional theory and ab initio calculations between 200 and 1000 K. The rate coefficient calculated at 300 K with the ab initio potential is in good agreement with a recently reported experimental value.     

Controlling the spin state of diphenylcarbene via halogen bonding: A theoretical study

Halogen bonding has recently become an effective tool to control the spin state of reactive carbenes. In this work, a series of the complexes of diphenylcarbene (DPC) that has a triplet ground state with several halogen bond donors RX were theoretically studied, and in particular, the influence of the formation of halogen bonding on the spin state of DPC was extensively explored. The spin flip depends on the difference of halogen bond energies between triplet and singlet, that is, when the difference is large enough a spin flip may occur. Furthermore, the variations of the geometries on complexation may induce the potential energy surfaces of different spin states to intersect, thus leading to intersystem crossing. Based on the energy analysis of the minimum energy crossing points (MECPs), the systems with a smaller MECP‐triplet energy barrier go through intersystem crossing more easily. Halogen bonds in the complexes, where a spin flip takes place, exhibit a partially covalent character, while other complexes show conventional behaviors of halogen bonding. According to charge decomposition analysis, the charge transfer from HOMO (DPC) to LUMO (RX) is identified as a prominent stabilizing interaction in the whole complexes.     

Minireview: A Caritical Review of the Transition Metal Ions Influence on Peroxyoxalate Chemiluminescence

ABSTRACT

A detailed study and evaluation of the presence of Cr(III), Zn(II) and Pb(II) and various parameters affecting the intensity of the chemiluminescent reaction of TCPO and 2-NPO with hydrogen peroxide in the presence of 3-aminofluoranthene, as the fluorophore, and imidazole (IMI) as catalyst, is presented. Depending on the unprotonated imidazole and fluorophore concentrations, these metal ions enhance the intensity of the fluorophore at pH's higher than 8.0. At pH = 7.0, in the presence of IMI/HIMI⁺ (IMI = 1×10^?2 mol.L^?1), tris(hydroxymethyl)aminomethane or HPO₄ ^2?/H₂PO₄ ^? buffers, no effect of these metal ions was observed. A critical comparison with the data reported in the literature is presented.     

Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between −3.11 and −3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd−O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.     

Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table

Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy.     

Accelerating the Construction of Neural Network Potential Energy Surfaces: A Fast Hybrid Training Algorithm

Machine learning approaches have been promising in constructing high-dimensional potential energy surfaces (PESs) for molecules and materials. Neural networks (NNs) are one of the most popular such tools because of its simplicity and efficiency. The training algorithm for NNs becomes essential to achieve a fast and accurate fit with numerous data. The Levenberg-Marquardt (LM) algorithm has been recognized as one of the fastest and robust algorithms to train medium sized NNs and widely applied in recent NN based high quality PESs. However, when the number of ab initio data becomes large, the efficiency of LM is limited, making the training time consuming. Extreme learning machine (ELM) is a recently proposed algorithm which determines the weights and biases of a single hidden layer NN by a linear solution and is thus extremely fast. It, however, does not produce sufficiently small fitting error because of its random nature. Taking advantages of both algorithms, we report a generalized hybrid algorithm in training multilayer NNs. Tests on H+H₂ and CH₄+Ni(111) systems demonstrate the much higher efficiency of this hybrid algorithm (ELM-LM) over the original LM. We expect that ELM-LM will find its widespread applications in building up high-dimensional NN based PESs.     

值得引入物理化学教材的重要内容:势能面交叉

势能面交叉既是内转换和系间窜越的实际通道,也是联系光化学和热化学的重要桥梁。势能面交叉引起的非绝热过程广泛存在于各种生物、化学和材料的体系当中。笔者建议将势能面交叉的相关内容引入物理化学课程的教材中,因为这不但会使教材内容更加丰富和成体系,而且有利于学生了解科技发展前沿,激发他们探索未知的兴趣。     

过渡金属硫化物催化剂催化加氢作用机理

负载型过渡金属(Co、Mo、Ni、W)硫化物催化剂广泛应用于石油炼制催化加氢过程。为了开发高性能的加氢催化剂,过渡金属硫化物催化剂催化活性相的结构与加氢脱硫性能的关系一直以来是催化研究的热点之一。本文从过渡金属硫化物催化剂的活性相结构和反应物在催化剂表面活性位上的吸附-催化反应机理两个方面阐述了过渡金属硫化物催化剂的催化作用研究进展,并对过渡金属硫化物催化剂催化机理研究存在的争议和未来的研究方向进行了分析。     

The History and the Current Revival of the Oxo Chemistry of Iron in its Highest Oxidation States: FeVI – FeVIII

The history of the oxo compounds of iron in its highest oxidation states is reviewed and modern activities in this long neglected area of inorganic chemistry are highlighted. The chemistry of ferrates(VI) is the most rapidly advancing branch owing to several potential applications in diverse fields such as environmental chemistry and energy storage. Convenient and high‐yield preparations of ferrates(VI) in high purity are presented, followed by a coverage of the analytical, spectroscopic, and structural characterization in the solid and in solution, with a focus on the stability of these compounds, which had long been under‐estimated. Particular attention has been paid to the fascinating mechanisms that have been proposed for the intriguing “self‐decay” of the [FeO₄]^2– dianion. Redox processes with inorganic and organic substrates are summarized including fresh and waste water treatment on the one hand and “super‐iron batteries” on the other. Recent advances in the experimental and computational approach to ferrates(VII) [FeO₄]^– and the elusive “iron tetroxide” [FeO₄] are described.     

Density Functional Theory Study on the Adsorption of CN on Transition Metal M（100） （M = Ni,Pd, Pt,Cu, Ag and Au） Surfaces

The adsorption of cyanide on the top site of a series of transition metal M（100） （M = Cu, Ag, Au, Ni, Pd, Pt） surfaces via carbon and nitrogen atoms respectively, with the CN axis perpendicular to the surface, has been studied by means of density functional theory and cluster model. Geometry, adsorption energy and vibrational frequencies have been determined, and the present calculations show that the adsorption of CN through C-end on metal surface is more favorable than that via N-end for the same surface. The vibrational frequencies of CN for C-down configuration on surface are blue-shifted with respect to the free CN, which is contrary to the change of vibrational frequencies when CN is adsorbed by N-down structure. Furthermore, the charge transfer from surface to CN causes the increase of surface work function.     

Exploring chemical reactivity of complex systems with path‐based coordinates: Role of the distance metric

Path‐based reaction coordinates constitute a valuable tool for free‐energy calculations in complex processes. When a reference path is defined by means of collective variables, a nonconstant distance metric that incorporates the nonorthonormality of these variables should be taken into account. In this work, we show that, accounting for the correct metric tensor, these kind of variables can provide iso‐hypersurfaces that coincide with the iso‐committor surfaces and that activation free energies equal the value that would be obtained if the committor function itself were used as reaction coordinate. The advantages of the incorporation of the variable metric tensor are illustrated with the analysis of the enzymatic reaction catalyzed by isochorismate‐pyruvate lyase. Hybrid QM/MM techniques are used to obtain the free energy profile and to analyze reactive trajectories initiated at the transition state. For this example, the committor histogram is peaked at 0.5 only when a variable metric tensor is incorporated in the definition of the path‐based coordinate. © 2014 Wiley Periodicals, Inc.