Competition between hydrogen bond and σ-hole interaction in SCS-HArF and SeCSe-HArF complexes

A computational study of the complexes formed between HArF and XCX (X?=?O, S, and Se) has been performed at the MP2/aug-cc-pVTZ level. Two types of complexes were found. One is formed through a hydrogen bond with XCX as the electron donor and the other is formed through the σ-hole interaction with XCX as the electron acceptor. The OCO-FArH complex is more stable than the OCO-HArF complex, whereas the XCX-HArF (X?=?S and Se) complex is more stable than the XCX-FArH complex. The distant H-Ar bond is shortened and exhibits a blue shift, but the associated one displays a red shift in SCS-HArF and SeCSe-HArF complexes. When compared with XCX-HF complex, the structure of the complex suffers a great effect from the inserted noble gas atom. The natural bond orbital (NBO) and atoms in molecules (AIM) have been performed for a better understanding of the interactions.     

A–X⋯σ Interactions—Halogen Bonds with σ-Electrons as the Lewis Base Centre

CCSD(T)/aug-cc-pVTZ//ωB97XD/aug-cc-pVTZ calculations were performed for halogen-bonded complexes. Here, the molecular hydrogen, cyclopropane, cyclobutane and cyclopentane act as Lewis base units that interact through the electrons of the H–H or C–C σ-bond. The FCCH, ClCCH, BrCCH and ICCH species, as well as the F₂, Cl₂, Br₂ and I₂ molecular halogens, act as Lewis acid units in these complexes, interacting through the σ-hole localised at the halogen centre. The Quantum Theory of Atoms in Molecules (QTAIM), the Natural Bond Orbital (NBO) and the Energy Decomposition Analysis (EDA) approaches were applied to analyse these aforementioned complexes. These complexes may be classified as linked by A–X···σ halogen bonds, where A = C, X (halogen). However, distinct properties of these halogen bonds are observed that depend partly on the kind of electron donor: dihydrogen, cyclopropane, or another cycloalkane. Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A–X···σ halogen bonds.     

H2XP…SHY复合物中磷键与硫键的理论研究

用从头算量子化学方法MP2 与CCSD(T)研究了H₂XP和SHY (X, Y=H, F, Cl, Br)分子的P与S之间形成的磷键X―P…S与硫键Y―S…P的本质与规律以及取代基X与Y对成键的影响. 计算结果表明, 硫键比磷键强, 连接在Lewis 酸上的取代基的电负性增大导致形成的磷键或硫键增强, 键能增大, 对单体的结构和性质的影响也增大; 而连接在Lewis 碱上的取代基效应则相反. 硫键键能为8.37-23.45 kJ·mol^-1, 最强的硫键结构是Y 电负性最大而X 电负性最小的HFS…PH₃, CCSD(T)计算的键能是16.04 kJ·mol^-1; 磷键键能为7.54-14.65 kJ·mol^-1, 最强的磷键结构是X 电负性最大而Y 电负性最小的H₂FP…SH₂, CCSD(T)计算的键能是12.52 kJ·mol^-1. 对磷键与硫键能量贡献较大的是交换与静电作用. 分子间超共轭lp(S)-σ^*(PX)与lp(P)-σ^*(SY)对磷键与硫键的形成起着重要作用, 它导致单体的极化, 其中硫键的极化效应较大, 从而有一定的共价特征.     

Carbene–aerogen bonds: an ab initio study

Through the use of ab initio calculations, the possibility of formation of σ-hole interaction between ZO₃ (Z = Ar, Kr and Xe) and carbene species is investigated. Since singlet carbenes show a negative electrostatic potential on their divalent carbon atom, they can favourably interact with the positive electrostatic potential generated by the σ-hole of Z atom of ZO₃. The characteristic of this interaction, termed as ‘carbene–aerogen’ bond, is analysed in terms of geometric, interaction energies and electronic features. The energy decomposition analysis indicates that for all complexes analysed here, the electrostatic energy is more negative than the polarisation or dispersion energy term. According to the electron density analysis, some partial covalent character can be ascribed to Xe???C interactions. In addition, the carbene–aerogen bond exhibits cooperative effects with the H???O hydrogen-bonding interaction in ternary complexes where both interactions coexist. For a given carbene, the amount of these cooperative effects increases with the size of the Z atom. The results obtained in this work may be helpful for the extension and future application of σ-hole intermolecular interactions as well as coordination chemistry.     

Single- and double-pion production in nucleon collisions on the nucleon and on nuclei—the ABC effect and its origin in a dibaryonic resonance

The ABC effect-an intriguing low-mass enhancement in the ππ invariant mass spectrum-is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or ³He reveal this effect to be a σ-channel phenomenon associated with the formation of a ΔΔ system in the intermediate state and combined with a resonance-like behavior in the total cross-section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in pn and NNππ systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of NΔ resonances is reexamined.     

形式矩阵环上的σ-双导子和σ-交换映射

令K=(RNMS)是一个具有零迹理想的形式矩阵环,σ是K的一个满足σ(E11)=E11,σ(E22)=E22的自同构.本文确定了K的σ-双导子和σ-交换映射的一般形式,证明了在一定条件下K的每个σ-双导子都可以表示成一个外σ-双导子与一个内 σ-双导子的和.此外,本文给出了K的任意σ-双导子(σ-交换映射)是内 σ-双...     

Stereoselective Processes Based on σ-Hole Interactions

The σ-hole interaction represents a noncovalent interaction between atoms with σ-hole(s) on their surface (such as halogens and chalcogens) and negative sites. Over the last decade, significant developments have emerged in applications where the σ-hole interaction was demonstrated to play a key role in the control over chirality. The aim of this review is to give a comprehensive overview of the current advancements in the use of σ-hole interactions in stereoselective processes, such as formation of chiral supramolecular assemblies, separation of enantiomers, enantioselective complexation and asymmetric catalysis.     

Structural characterization of the Ta-rich part of the Ta-Al system

The Ta-rich part of the Ta-Al system has been investigated. On the one hand, the accommodation of the non-stoichiometry in the σ phase has been studied by Rietveld refinement of X-ray powder data obtained from different samples on both sides of the ideal composition (Ta₂Al, P4₂/mnm, tP30). On the other hand, the structure of the β phase has been determined ab initio from powder synchrotron data (analyzed composition Ta_50.7Al_49.3, refined composition Ta_52.6(5)Al_47.4(5) (Ta_45.2(4)Al_40.8(4)), stoichiometric composition Ta₄₈Al₃₈, mP86, P2₁/c, a=9.8707(1) Å, b=9.8766(1) Å, c=16.3539(2), β=116.478(1), R_B=2.6%). This phase is shown to be closely related to the group of the topologically close packed phases. In addition, phase relations have been accurately determined in the Ta-rich end of the system.     

距离空间上测度正则性的推广

本文给出了单调类与σ代数关系的充要条件,进一步得出距离空间的开集全体产生的最小单调类与产生的σ代数相等.利用这关系,证明了距离空间上的σ-有限测度也是正则测度.推广了距离空间上有限测度的正则性.