氧化钼表面不同氧位对氢吸附性能的从头计算研究

 用从头计算Hartree－Fock方法研究了MoO3（010）和（100）晶面上几种结构不等价氧的成键特征和电子结构,并考察了H＋在不同氧位上的吸附性能以及吸附后形成的OH从表面脱附的性质．结果表明,在氧化钼晶体中,钼氧原子间的成键具有离子性和共价性相结合的特性,且几种不等价氧与钼之间的成键性质各不相同：端氧或不对称桥氧与钼的成键具有较强的共价性,而对称桥氧具有较强的离子性;H＋在MoO3（010）和（100）晶面上几种不等价氧位都能形成稳定的吸附,而在端氧位的吸附最稳定;H＋吸附形成的OH都与表面有较强的作用,端氧位的OH最难脱附,而桥氧位的OH在表面的活动性较大,故桥氧位很可能是丙烯选择氧化过程中脱氢反应的活性中心．     

Ab Initio Molecular Dynamics with Explicit Solvent Reveals a Two‐Step Pathway in the Frustrated Lewis Pair Reaction

The role solvent plays in reactions involving frustrated Lewis pairs (FLPs)—for example, the stoichiometric mixture of a bulky Lewis acid and a bulky Lewis base—still remains largely unexplored at the molecular level. For a reaction of the phosphorus/boron FLP and dissolved CO₂ gas, first principles (Born–Oppenheimer) molecular dynamics with explicit solvent reveals a hitherto unknown two‐step reaction pathway—one that complements the concerted (one‐step) mechanism known from the minimum‐energy‐path calculations. The rationalization of the discovered reaction pathway—that is, the stepwise formation of P?C and O?B bonds—is that the environment (typical organic solvents) stabilizes an intermediate which results from nucleophilic attack of the phosphorus Lewis base on CO₂. This finding is significant because presently the concerted reaction‐path paradigm predominates in the rationalization of FLP reactivity. Herein we point out how to attain experimental proof of our results.     

Polar-Covalent Bonding Beyond the Zintl Picture in Intermetallic Rare-Earth Germanides

A comparative chemical bonding analysis for the germanides La₂MGe₆ (M=Li, Mg, Al, Zn, Cu, Ag, Pd) and Y₂PdGe₆ is presented, together with the crystal structure determination for M=Li, Mg, Cu, Ag. The studied compounds adopt the two closely related structure types oS72-Ce₂(Ga_0.1Ge_0.9)₇ and mS36-La₂AlGe₆, containing zigzag chains and corrugated layers of Ge atoms bridged by M species, with La/Y atoms located in the biggest cavities. Chemical bonding was studied by means of the quantum chemical position-space techniques QTAIM (quantum theory of atoms in molecules), ELI-D (electron localizability indicator), and their basin intersections. The new penultimate shell correction (PSC0) method was introduced to adapt the ELI-D valence electron count to that expected from the periodic table of the elements. It plays a decisive role to balance the Ge−La polar-covalent interactions against the Ge−M ones. In spite of covalently bonded Ge partial structures formally obeying the Zintl electron count for M=Mg²⁺, Zn²⁺, all the compounds reveal noticeable deviations from the conceptual 8−N picture due to significant polar-covalent interactions of Ge with La and M ≠ Li, Mg atoms. For M=Li, Mg a formulation as a germanolanthanate M[La₂Ge₆] is appropriate. Moreover, the relative Laplacian of ELI-D was discovered to reveal a chemically useful fine structure of the ELI-D distribution being related to polyatomic bonding features. With the aid of this new tool, a consistent picture of La/Y−M interactions for the title compounds was extracted.     

Adatom Defect Induced Spin Polarization of Asymmetric Structures

The spin polarization of carbon nanomaterials is crucial to design spintronic devices. In this paper, the first-principles is used to study the electronic properties of two defect asymmetric structures, Cap-(9, 0)-Def [6, 6] and Cap-(9, 0)-Def [5, 6]. We found that the ground state of Cap-(9, 0)-Def [6, 6] is sextet and the ground state of Cap-(9, 0)-Def [5, 6] is quartet, and the former has a lower energy. In addition, compared with Cap-(9, 0) CNTs, the C adatom on C₃₀ causes spin polarization phenomenon and Cap-(9, 0)-Def [6, 6] has more spin electrons than Cap-(9, 0)-Def [5, 6] structure. Moreover, different adsorb defects reveal different electron accumulation. This finding shows that spin polarization of the asymmetric structure can be adjusted by introducing adatom defects.     

Electronic structure and chemical bond in carbides crystallizing in the Fe-W-C system

The electronic energy structure of MC, M₆C, and M₁₂C carbide systems and iron martensite in the absence of spin polarization was studied by the local coherent potential method using the cluster version of the MT approximation in terms of multiple scattering theory. The local partial density of the electronic states of atoms in crystals was calculated and their electronic structures were compared. The peculiarities of chemical bonding in crystals are discussed.     

Methylene Bridging Effect on the Structures,Lewis Acidities and Optical Properties of Semi-planar Triarylboranes

Three synthetic methods towards semi-planar triarylboranes with two aryl rings connected by a methylene bridge have been developed. The fine-tuning of their stereoelectronic properties and Lewis acidities was achieved by introducing fluorine, methyl, methoxy, n-butyl and phenyl groups either at their exocyclic or bridged aryl rings. X-ray diffraction analysis and quantum-chemical calculations provided quantitative information on the structural distortion experienced by the near planar hydro-boraanthracene skeleton during the association with Lewis bases such as NH₃ and F⁻. Though the methylene bridge between the ortho-positions of two aryl rings of triarylboranes decreased the Gibbs free energies of complexation with small Lewis bases by less than 5 kJ mol⁻¹ relative to the classical Lewis acid BAr₃, the steric shielding of the CH₂ bridge is sufficient to avoid the formation of Lewis adducts with larger Lewis bases such as triarylphosphines. A newly synthesized spirocyclic amino-borane with a long intramolecular B−N bond that could be dissociated under thermal process, UV-irradiation, or acidic conditions might be a potential candidate in Lewis pairs catalysis.     

Revitalizing Spin Natural Orbital Analysis: Electronic Structures of Mixed-Valence Compounds,Singlet Biradicals,and Antiferromagnetically Coupled Systems

Chemical systems with open-shell electronic structure have been gaining attention these days. Their potential applications in first-row transition metal catalysis, molecular wires, photovoltaics and other potential applications have urged the adoption of a simple analysis tool to better understand their open-shell electronic structures, especially the role played by the unpaired electrons. Despite its lack of popularity, spin natural orbital (SNO) analysis is a tool we found to well-suit this purpose. We have therefore re-examined how the SNO could help us analyze some interesting open-shell systems, including mixed-valence compounds, singlet biradicals, and antiferromagnetically coupled systems. We found that some interesting patterns emerge from SNO analysis, especially those associated with exchange interaction. © 2019 Wiley Periodicals, Inc.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

Experimental and Ab Initio Equilibrium Structures of cis-Thionylimide,HNSO: Estimation of the Laurie Correction

The equilibrium structure of cis-thionylimide, HNSO has been determined using high-level ab initio calculations and various experimental procedures. The Laurie correction to the N-H bond length is discussed and it is shown that it can be estimated by ab initio methods. The results are found to be in good agreement and the best equilibrium structure is (in Å for the bond lengths): r(N–H) = 1.020(1), r(N–S) = 1.510(2), r(S–O) = 1.448(1), (HNS) = 115.94(39)°, and (NSO) = 120.44(10)°.     

A Quantum-chemical Analysis on the Lewis Acidity of Diarylhalonium Ions

Cyclic diaryliodonium compounds like iodolium derivatives have increasingly found use as noncovalent Lewis acids in the last years. They are more stable toward nucleophilic substitution than acyclic systems and are markedly more Lewis acidic. Herein, this higher Lewis acidity is analyzed and explained via quantum-chemical calculations and energy decomposition analyses. Its key origin is the change in energy levels and hybridization of iodine's orbitals, leading to both more favorable electrostatic interaction and better charge transfer. Both of the latter seem to contribute in similar fashion, while hydrogen bonding as well as steric repulsion with the phenyl rings play at best a minor role. In comparison to iodolium, bromolium and chlorolium are less Lewis acidic the lighter the halogen, which is predominantly based on less favorable charge-transfer interactions.     

Homocatenation of Aluminum: Alkane‐like Structures of Li2Al2H6 and Li3Al3H8

A new class of aluminum homocatenated compounds (Li_nAl_nH_2n+2) is proposed based on quantum chemical calculations. In these compounds, Al abstracts an electron from Li, becoming valence isoelectronic with C, Si, and Ge, thus mimicking respective structural features of Group 14 hydrides. Using the Coalescence Kick search program coupled with density functional theory calculations, we investigated the potential energy surfaces of Li₂Al₂H₆ and Li₃Al₃H₆. Then single‐point‐energy coupled‐cluster calculations were performed for the lowest energy structures found. Indeed, the global minima established for Li₂Al₂H₆ and Li₃Al₃H₆ contain the Al₂H₆^2? and Al₃H₆^3? kernels, which are isostructural with ethane (C₂H₆), disilane (Si₂H₆), digermane (Ge₂H₆) and propane (C₃H₈), trisilane (Si₃H₈), trigermane (Ge₃H₈) molecules, respectively. Structural, energetic, and electronic characteristics of the Li₂Al₂H₆ and Li₃Al₃H₈ compounds are presented and the viability of their synthesis is discussed.     

The Electronic Structures and Chemical Bonding of Some Dinuclear and Trinuclear Low－valence Molybdenum Complexes Containing Thiolate Bridges

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Synergistic Effects of Lewis Bases and Substituents on the Electronic Structure and Reactivity of Boryl Radicals

Boryl radicals have the potential for the development of new molecular entities and for application in new radical reactions. However, the effects of the substituents and coordinating Lewis bases on the reactivity of boryl radicals are not fully understood. By using first‐principles methods, we investigated the spin‐density distribution and reactivity of a series of boryl radicals with various substituents and Lewis bases. The substituents, along with the Lewis bases, only affect the radical reactivity when an unpaired electron is in the boron p_z orbital, that is, for three‐coordinate radicals. We found evidence of synergistic effects between the substituents and the Lewis bases that can substantially broaden the tunability of the reactivity of the boryl radicals. Among Lewis bases, pyridine and imidazol‐2‐ylidene show a similar capacity for stabilization by delocalizing the spin density. Electron‐donating substituents, such as nitrogen, more efficiently stabilize boryl radicals than oxygen and carbon atoms. The reactivity of a boryl radical is always boron based, irrespective of the spin density on boron.     

Electronic structures and chemical bonding in 4d transition metal monohalides

Bond distances, vibrational frequencies, dipole moments, dissociation energies, electron affinities, and ionization potentials of MX (XM = Y-Cd, X = F, Cl, Br, I) molecules in neutral, positively, and negatively charged ions were studied by density functional method, B3LYP. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides ionic component, covalent bonds are formed between the 4d transition metal s, d orbitals, and the p orbital of halogen. For both neutral and charged molecules, the fluorides have the shortest bond distance, iodides the longest. Although the opposite situation is observed for vibrational frequency, that is, fluorides have the largest value, iodides the smallest. For neutral and anionic species, the dissociation energy tends to decrease with the increasing atomic number from Y to Cd, suggesting the decreasing or weakening of the bond strength. For cationic species, the trend is observed from Y to Ag.     

Ab Initio Theoretical Investigation on the Geometrical and Electronic Structures of AlAun-/0 (n = 2-4) Clusters

A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of AlAu n 0/-(n=2-4) clusters has been performed in this work. AlAu n-anions prove to possess ground states of the V-shaped C2v AlAu2 - , umbrella-shaped C3v AlAu3- , and perfect tetrahedral T d AlAu4- , while their neutrals favor the V-shaped C2v AlAu2 , perfect planar triangular D3h AlAu3 , and severely distorted C s AlAu4 , respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C s AlAu4 . Molecular orbitals (MOs) analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in Al-Au bonds, which is smaller than the BAu n0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of Al-Au bonds between 100-400 cm -1 have been calculated to facilitate future experimental characterization of these clusters.     

Reply to the Comment on “Realization of Lewis Basic Sodium Anion in the NaBH3− Cluster”

We reply to the comment by S. Pan and G. Frenking who challenged our interpretation of the Na^?:→BH₃ dative bond in the recently synthesized NaBH₃^? cluster. Our conclusion remains the same as that in our original paper ( https://doi.org/10.1002/anie.201907089 and https://doi.org/10.1002/ange.201907089 ). This conclusion is additionally supported by the energetic pathways and NBO charges calculated at UCCSD and CASMP2(4,4) levels of theory. We also discussed the suitability of the Laplacian of electron density (QTAIM) and Adaptive Natural Density Partitioning (AdNDP) method for bond type assignment. It seems that AdNDP yields more sensible results. This discussion reveals that the complex realm of bonding is full of semantic inconsistencies, and we invite experimentalists and theoreticians to elaborate this topic and find solutions incorporating different views on the dative bond.