Chemical Bonding in Solids

The most important of the current quantum-mechanical models of solids can be divided into one-electron (band) models and incomplete polyelectron theories. There are no complete polyelectron theories at present. However, the interatomic exchange forces become less important in lattices with high coordination numbers; a theory of metallic phases can therefore be developed, in principle, on the basis that the antisymmetrization is only local in atoms or groups of atoms.     

X-Ray Spectroscopic Investigation of Chemical Bonding in Solids

When an atom is incorporated into a molecule or a crystal, its X-ray spectrum undergoes characteristic changes, the study of which leads to important information on the nature of the chemical bonding and on the electronic structure in a substance. A number of examples are given to illustrate the possibilities of the X-ray spectroscopy of bonded atoms. Special attention is given to the displacement of the Kα lines, from which conclusions can be drawn regarding the charge on a bonded atom, as well as to the investigation of the emission bands resulting from valence electron transitions, which yields information on the energy band structure of the solid. X-ray spectroscopic studies on free molecules and theoretical work on the calculation of the molecular orbitals of simple molecules are finally reported.     

Application of Ligand Field Spectroscopy to Problems of Chemical Bonding in Solids

Selected examples (dⁿ systems) are presented to illustrate the interpretation of ligand field spectra (remission spectra) of solid inorganic compounds. In particular, this article demonstrates possible means for the investigation of weak cooperative interactions between transition metal coordination polyhedra and for the determination of the cation distribution in crystal lattices. The information value of the spectroscopic method to the chemist is critically discussed.     

Gamma Resonance Spectroscopy and Chemical Bonding

Gamma resonance spectroscopy makes it possible to observe directly hyperfine interactions in solids. In the field of chemistry the feature of greatest interest is the measurement of isomeric shifts of gamma lines because these shifts are proportional to the electron density at the nucleus and can thus give detailed information about the electronic structure of the chemical bond. After a brief introduction to gamma resonance spectroscopy, this paper deals with the fundamental problem of the interpretation of measured isomeric shifts in terms of electron densities and then gives representative examples of chemical information that can be obtained for transition elements from the shifts and the splitting of the gamma lines.     

Bonding Properties of Cyclopropane and Their Chemical Consequences

Among the cyclic compounds of carbon, cyclopropane and its derivatives are outstanding by virtue of their unusual structural, spectroscopic, and chemical properties. The cyclopropane ring more closely resembles the C?C double bond than the cyclobutane ring: it is a small ring with “double bond character”. Cyclopropyl and vinyl groups interact with neighbouring π-electron systems and p-electron centers; both cyclopropane derivatives and olefins form metal complexes, and add strong acids, halogens, and ozone; they both undergo catalytic hydrogenation and cycloadditions. While distinct differences in reactivity do exist–the double bond usually being more reactive than the three-membered ring–there are no fundamental differences in behavior.–Although cyclopropane derivatives have been known for more than 90 years, intensive studies have been limited to the past 25 years. The development of carbene chemistry has rendered cyclopropane derivatives far more readily accessible. In recent years, the synthetic potential of the small-ring function has been increasingly exploited. A considerable number of newly developed methods utilizing this approach clearly demonstrates that the reactivity of the cyclopropene ring, like that of the C?C double bond, qualify it as a “functional carbon group”. This development is in full swing; we may therefore justifiably devote considerable effort to the study of cyclopropane chemistry.     

Experimental Electron Densities and Chemical Bonding

Some recent results of charge density analysis by X-ray and neutron diffraction are discussed. Problems that have been studied in a number of laboratories include the nature of single, double, and triple bonds, lone-pair hybridization, bonding in some metals, alloys, and organometallic compounds, and the derivation of physical properties from X-ray diffraction densities. At the present stage of development of methods studies of series of related compounds are feasible and expected to find widespread application.     

固体表面填隙H的化学活性起源于泡利排斥效应

各类固体表面常对外来原子(离子)施加泡利排斥作用.它明显改变了表面填隙或者替位原子(离子)的物理性质.我们首先说明泡利排斥作用广泛存在于各类固体表面.并引进"泡利穴"的概念,用来定量计算固体表面低凹处填隙位置上的外来原子在泡利排斥作用下性质的改变.重点讨论了多相催化中最重要的过渡金属表面的"泡利穴".然后简短介绍我们已经发表的工作,即泡利穴中H原子薛定谔方程的解析.进一步,将填隙H的基态波函数和基态能与自由H原子做比较,显示其性质的改变.由此详细论证,填隙H化学活性增加的两个关键的物理原因是,填隙H电离能的明显降低及诱导电矩的存在.我们把这种激活方式简称为"固体表面填隙H的泡利激活",并讨论它对加氢反应的贡献.同时,对近年来催化研究中一个令人困惑的实验结果给出我们自己的解释.实验明确表明,对加氢反应起关键作用的是过渡金属"表面下的H原子",它们在加氢反应中非常活跃.而"表面H原子"没有参与加氢反应.我们论证,过渡族金属"表面下的H原子"正是被泡利激活的填隙H.限于讨论多相催化问题(固体表面填隙H原子的催化).但是"泡利激活"原则上可以推广到均相催化中.因为在均相催化中经常使用的催化剂通常也具有类似的泡利穴结构.我们只讨论泡利穴中填隙H的催化,但是原则上不难推广到其他元素,例如用类似方法探讨石墨烯表面填隙锂原子的泡利激活.近来的天文观测中发现,很多有机分子云团中(例如H_2O, CH_4, C_2H_2, C_2H_4…等云团),同时存在一些尺寸约0.001～10μm的尘埃物质(如C颗粒, SiO_2颗粒等等).两者的并存使我们猜测,或许这些尘埃物质(包括纳米颗粒)本身就是多相催化剂,其表面存在的"泡利穴"可能对分子的形成有重要贡献.     

Superconductivity and Chemical Bonding in Mercury

Band structure and Fermi surface calculations were performed for the metal mercury, for which superconductivity was discovered 87 years ago. The electronic properties of mercury were analyzed to find the origin of singlet electron pair formation and condensation which leads to superconductivity.     

Structure and Bonding in Cyclic Sulfur-Nitrogen Compounds

The coordination number of sulfur is used in this review as a classification principle; cyclic sulfur-nitrogen compounds in which the sulfur is di-, tri-, and tetracoordinated are discussed. Compounds with sulfur (and nitrogen) of coordination number 2 are electron-rich combinations of elements whose π-electrons are extensively delocalized. A correlation between the coordination number and the bond length can be observed in certain compounds containing tri- and tetracoordinated sulfur.     

The Bonding Nature of the Canonical Molecular Orbitals in Simple Diatomic Molecules

The bonding nature of the canonical molecular orbitals 2σg, 2σu and 3σg in the molecules N₂,O₂, F₂ and the related analogous molecular orbitals in the molecules P₂ and CO, is analysed using Weinhold's natural bond orbital set. When the canonical molecular orbitals can be well localized into natural bond orbitals, the covalent bond can be completely attributed to the bonding type natural bond orbitals. The decomposition of canonical molecular orbitals into the natural bond orbital basis then gives the weighted bond order as the component of the bonding portion in the canonical molecular orbital. The weighted bond order results match the photoelectron spectroscopy assignment quite satisfactorily.     

Approximating the Pauli Potential in Bound Coulomb Systems

It is shown that the Pauli potential in bound Coulomb systems can in good approximation be composed from the corresponding atomic fragments. This provides a simple and fast procedure how to generate the Pauli potential in bound systems, which is needed to perform an orbital‐free density functional calculation. The method is applicable to molecules and solids. © 2016 Wiley Periodicals, Inc.     

Zintl Phases: Transitions between Metallic and Ionic Bonding

Experimental studies on compounds of alkali and alkaline earth metals with semi- and metametals have considerably broadened the basis for a discussion of the transition from metallic to ionic bonding. Current interest is focused mainly upon the elucidation of the principles governing the structure of such compounds which are subject to a wide range of variation within this class of materials. A new definition of the term Zintl phase is proposed after consideration of available findings.     

Structure and Bonding in Cyclic Sulfur-Nitrogen Compounds—Molecular Orbital Considerations

The molecular structures of monocyclic sulfur-nitrogen ring systems, such as S₂N₂, S₃N, S₄N and S₅N, can be considered as examples of electron rich (4n + 2)π systems. The structures of S₄N₄, S₄N, P₄S₄, As₄S₄ and the bicyclic structures S₄N, S₄N as well as S₅N₆ can be rationalized on the basis of a planar tetrasulfur tetranitride with 12π electrons.     

Is the Pauli exclusive principle an independent quantum mechanical postulate?

Foundation of the Pauli exclusive principle is discussed. It is demonstrated that the indistinguishability principle is insensitive to the permutation symmetry of the wave function and cannot be used as a criterion for the verification of the Pauli exclusive principle. The heuristic arguments are given in favor that the existence in nature of only the nondegenerate permutation representations (symmetrical and antisymmetrical) is not occasional. As follows from our analysis of possible scenarios, the permission of degenerate permutation representations leads to contradictions with the concept of particle identity and their independence. Thus, the prohibition of degenerate permutation states by the Pauli exclusive principle follows from the general physical assumptions inside quantum theory, but the problem of spin–statistics connection is still open. It is pointed out that the Pauli exclusive principle and the Jahn–Teller effect have some similar features. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

The Physical Mechanism of the Chemical Bond

First the interplay of kinetic and potential energy via the uncertainty relation is described with the aid of a variational function for the ground state of the H atom. The H ion is used to illustrate the physical mechanism of the occurrence of the chemical bond. The formation of the chemical bond can be divided into three steps: 1. the quasi-classical (electrostatic) interaction of the unchanged electronic charges of the separate atoms; 2. the interference of the atomic orbitals, which (in the case of positive interference) leads to a displacement of charge into the bonding region and to a decrease in the kinetic energy; 3. deformation of the molecular orbitals to restore the correct balance of kinetic and potential energy. In simple models, it is often sufficient to consider just the second step. A two-electron bond is not fundamentally different from a one-electron bond. In larger molecules it is possible to distinguish between long-range and short-range interatomic contributions to the chemical bond. If the former are small, i. e. in molecules with non-polar bonds, a one-electron molecular orbital theory can be justified. Finally, the possibility of describing molecules by localized bonds is discussed.     

The Surface Chemical Bond

Adsorbed particles can be bound chemically to the surface of a solid (chemisorption). Modern variants of electron diffraction and electron spectroscopy now enable us to gain an insight into the nature of such surface chemical bonds, which play a key role in heterogenous catalysis and many other technically important phenomena such as adhesion, lubrication etc. Predominantly localized surface bonds can be compared to the covalent bonds in cluster compounds.     

Curie and Pauli Spins in Lithium Intercalated MCMB

The lithium-intercalated carbon was originally a laboratory treasure of physicists, but it has now become the key material for the rechargeable lithium battery, which has the highest specific energy among all known chemical power sources. Although numerous techniques have been invoked to study the structure-property relationship of lithium-intercalated carbons, the problem has not been fully solved so far. There are only a few papers reporting ESR (electron spin resonance) studies of lithium …     

Structure,Chemical Bonding and Properties of CoIn3, RhIn3, and IrIn3

CoIn₃, RhIn₃, and IrIn₃ were synthesized by reacting the elements in sealed tantalum tubes at 1170 K and subsequent annealing at 770 K. The structures of the three compounds (FeGa₃ type, space group P4₂/mnm) were refined from single crystal X-ray data: a = 682.82(6), c = 709.08(7) pm, wR2 = 0.0407, 397 F² values for CoIn₃, a = 698.28(8), c = 711.11(9) pm, wR2 = 0.0592, 418 F² values for RhIn₃, and a = 699.33(5), c = 719.08(5) pm, wR2 = 0.0625, 482 F² values for IrIn₃ with 16 parameters for each refinement. The structures may be considered as an intergrowth of tungsten-like building blocks of indium atoms and AlB₂-like slabs of compositions In&Co, In&Rh, and In&Ir, respectively. These are compared with the related intergrowth variants found for compounds with ordered U₃Si₂ and Zr₃Al₂ type structure. Semi-empirical band structure calculations for RhIn₃ reveal low density-of-states (DOS) at the Fermi level and negative Rh–Rh crystal orbital overlap populations (COOP) indicating antibonding Rh–Rh interactions. The bonding characteristics of CoIn₃, RuIn₃, and IrIn₃ are similar to RhIn₃. Magnetic susceptibility measurements of compact polycrystalline samples of CoIn₃, RhIn₃, and IrIn₃ indicate weak Pauli paramagnetism.