Towards universal substituent constants: Parameterizing bond critical point properties with electronegativity descriptors

The properties of substituents have long been quantified by their effect elsewhere in a molecule. Ideally, intrinsic properties detailing the true properties of a substituent would be used. These properties are ideally transferable between molecules, to be robust and applied in different situations. Through a study on the bond critical point (BCP) properties of 117 substituents and 17 substrates we find that BCP properties from the quantum theory of atoms in molecules are not transferable between different bonded atoms. However, a substituent's changing electronegativity between substrates help quantify the observed variation. The relationship between changing electronegativities and critical point properties enables development of a relationship to predict critical point properties between a substituent and a new substrate, using only the electronegativity of a substituent attached to hydrogen, and the critical point property between the substituent and H.     

Correlation of bond metallicity measures to electronegativity for binary oxides

We have investigated alkali, alkaline‐earth, and rutile binary oxides within density functional theory (DFT) and Bader's atoms‐in‐molecules theory, focusing on properties of bond and ring critical points, and their relations to band gap and Pauling electronegativity. We find linear relations of kinetic energy density, electron density, and the gap divided by kinetic energy density at the bond critical points to the difference of Pauling electronegativities of the cation and oxygen anion. At the ring critical points of rutile compounds, we also find that some bond metallicity measures are linearly related to the difference of electronegativities. This study extends our knowledge about the relations between bond critical points, band gap, and electronegativity, but also shows for the first time a quantitative relation between quantities at the ring critical points and global properties of the compounds.     

DFT/TD-DFT study on halogen doping and solvent contributions to the structural and optoelectronic properties of poly[3,6-carbazole] and poly[indolo(3,2-b)-carbazole]

The polycarbazoles have been proved to be a good organic semiconductor. These are investigated by quantum chemical studies using B3LYP density functional theory (DFT), and the studies have given a detailed understanding on the impact of carbazole units and an introduction to the electron donating on the optoelectronic properties. The electron withdrawing groups of halogen atoms (chlorine, bromine and iodine) have been substituted into the side chain of the poly[3,6-carbazoles] (PCs) and poly[indolo(3,2-b)-carbazoles] (PICs) and analysed. The band was assigned in the gas phase at 354.8 and 365.1 nm for PCs and PICs which are in good agreement with experimental values of 350 and 390 nm. The calculated results show that the selected three halogen derivatives exhibit a strong blue shift in the toluene solvent medium, with high electronic transition. It is found that PCs, PICs and their derivatives have a narrow band derived in the conduction band, and it is composed of 3p, 4p and 5p states; thus, the energy gap of PCs and PICs increased between the highest occupied molecular orbital and lowest unoccupied molecular orbital energy level by the addition of electron acceptor group atoms. The doped PC and PIC electronegativities are well plotted by an electrostatic potential map, and the plot reveals that chlorine-doped PCs and PICs have less electronegativity and bromine-doped polymer has high electronegativity than that of the chlorine-doped polymers. The results obtained from these studies will expose the affairs between the molecular geometry and electronic and optical properties of the investigated polymers.     

Electronegativities of elements in covalent crystals

A new electronegativity table of elements in covalent crystals with different bonding electrons and the most common coordination numbers is suggested on the basis of covalent potentials of atoms in crystals. For a given element, the electronegativity increases with increasing number of bonding electrons and decreases with increasing coordination number. Particularly, the ionicity of a covalent bond in different environments can be well-reflected by current electronegativity values; that is, the ionicity of chemical bonds increases as the coordination number of the bonded atoms increases. We show that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalent crystals, which will be very useful for studying various chemical and physical properties of covalent materials.     

电负性均衡

电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。     

Electronic properties of oxides: Chemical and theoretical approaches

An original analysis of the electronic and chemical properties of oxides is proposed based on the electronegativity χ and the chemical hardness η. This model which has been applied to various oxide based metals, degenerate semiconductors and optical properties of transition metal oxides allows explaining their electronic behaviors: Strong electronegativity and weak chemical hardness characterize oxides of transition elements with high oxidation state. Strong electronegativity and strong chemical hardness feature insulators with a large optical gap. Weak electronegativity and moderate chemical hardness describe alkali and alkaline earth oxides and weak electronegativity and strong chemical hardness are for ionic oxides with a relatively large optical gap. For a few illustrative case studies, ab intio electronic band structure calculations within the density functional theory framework are used.     

The influence of promoters and poisons on carbon monoxide adsorption on Rh(100): a DFT study.

Density functional theory calculations were performed to determine the pairwise lateral interaction energies between carbon monoxide and coadsorbed elements from the first three rows of the periodic table on a Rh(100) surface. The atoms were placed in a c(2x2) arrangement of fourfold hollow sites and the carbon monoxide probe molecule in a p(2x2) arrangement, so that each CO molecule had four atoms as nearest neighbours. The alkali atoms show an attractive interaction with CO while the other atoms show a repulsive interaction. For second-row elements the maximum repulsion is at nitrogen and for third-row elements at sulphur. Attempts to correlate the interaction energies with properties of the system, such as electronegativity, distances, or change in work function, failed, which implies that each combination of adsorbates needs to be calculated separately.     

Bond critical points in the electronic structures of the main group diatomic hydrides of lithium through bromine

The bond critical points and associated electronic properties of the diatomic hydrides of the twenty-one main group elements from lithium to bromine have been calculated with large basis sets. As part of a systematic study of the polarity of chemical bonds, the position of the bond critical point, the charge density at the bond critical point, the Laplacian of the charge density at the bond critical point, and the molecular dipole moment of each molecule have been calculated. Particular attention has been paid to the effect of bond length elongation and contraction on the electronic properties. Variation of the bond length reveals that with atoms of low electronegativity, the bond critical point of AH tends to follow atom A, whereas with atoms of high electronegativity, the bond critical point tends to follow the hydrogen atom as the bond lengthens. Furthermore, it is shown that some properties of the diatomic hydrides vary monotonically within each row of the periodic table, while others effect a classification according to the character of the bond.     

端接配体原子的电负性对磁耦合作用的影响

应用微扰理论，分析了端接配体原子的电负性对体系磁耦合作用的影响。研究 表明，随着端接配体原子电负性的增大，磁中心间的耦合作用减弱。应用密度泛函 理论和对称性破损方法对双核铜（II）模型体系进行了计算，计算结果验证了上述 结论。     

Molecular electronegativity in density functional theory (II) --Direct calculation of group electronegativity and the atomic charges in a group

On the basis of a more precise expression of the atomic effective electronegativity deduced from the density functional theory and electronegativity equalization principle, a new scheme for calculating the group electronegativity and the atomic charges in a group is proposed and programed, and various parameters of electronegativity and hardness are given for some common atoms. Through calculation, analysis and comparison of more than one hundred groups, it is shown that the results from this scheme are reasonable and may be extended.     

基于密度泛函理论分析团簇ConMoS(n=1~5)电子性质、光学性质及磁性

为了从理论层面深入探究团簇 Co_nMoS(n=1~5)的电子性质、光学性质及磁性,弄清其内在关联,依据拓扑学原理和密度泛函理论,在B3LYP/def2-TZVP量子化学水平和多个自旋多重度下对该团簇进行结构优化并分析。结果表明：团簇ConMoS共有21种稳定构型;通过对NPA(自然布居分析,natural population analysis)电荷、静电势、亲电指数、电离势、光学电负性和折射率等分析得出,金属原子有高概率失去电子,非金属原子相对更容易得到电子,团簇Co₅MoS中的构型5a在最稳定构型中有高的得失电子能力、反应活性和折射率,Co和Mo原子易发生亲核反应,S原子易发生亲电反应;对该团簇自旋布居数、原子磁矩、轨道磁矩和态密度分析发现,该团簇磁性主要由Co原子的d轨道提供,且团簇Co₃MoS表现出了比其它尺寸团簇更为稳定和优异的磁性。最终得出团簇Co₃MoS在磁性方面有较好的表现且构型5a在活性和光学领域有一定的潜力。     

Electronegativity and hardness in the chemical approximation

The chemical electronegativity of an atom (Mulliken definition) has been identified with the average value of χ, the electronegativity function given by the rigorous density functional theory. An appropriate definition of hardness is developed, and a scale of hardness for bonded atoms is proposed. The electrodynamical atom model is demonstrated to produce a simple relation between atomic hardness and size. Electronegativity has been calculated for bonded atoms in a variety of molecules and crystals, covalent and ionic, without any specific approximation for the energy function E(q). Expressions for the electronegativity of a molecule have been derived and critically discussed.     

基于密度泛函理论分析团簇ConMoS(n=1~5)电子性质、光学性质及磁性

为了从理论层面深入探究团簇Co_nMoS （n=1~5）的电子性质、光学性质及磁性,弄清其内在关联,依据拓扑学原理和密度泛函理论,在B3LYP/def2-TZVP量子化学水平和多个自旋多重度下对该团簇进行结构优化并分析。结果表明：团簇Co_nMoS共有21种稳定构型;通过对NPA （自然布居分析,natural population analysis）电荷、静电势、亲电指数、电离势、光学电负性和折射率等分析得出,金属原子有高概率失去电子,非金属原子相对更容易得到电子,团簇Co₅MoS中的构型5a在最稳定构型中有高的得失电子能力、反应活性和折射率,Co和Mo原子易发生亲核反应,S原子易发生亲电反应;对该团簇自旋布居数、原子磁矩、轨道磁矩和态密度分析发现,该团簇磁性主要由Co原子的d轨道提供,且团簇Co₃MoS表现出了比其它尺寸团簇更为稳定和优异的磁性。最终得出团簇Co₃MoS在磁性方面有较好的表现且构型5a在活性和光学领域有一定的潜力。     

A valence bond study of three-center four-electron pi bonding: electronegativity vs electroneutrality

Three-center four-electron (3c4e) pi bonding systems analogous to that of the ozone molecule have been studied using modern valence bond theory. Molecules studied herein consist of combinations of first row atoms C, N, and O with the addition of H atoms where appropriate in order to preserve the 3c4e pi system. Breathing orbital valence bond (BOVB) calculations were preformed at the B3LYP/6-31G**-optimized geometries in order to determine structural weights, pi charge distributions, resonance energies, and pi bond energies. It is found that the most weighted VB structure depends on atomic electronegativity and charge distribution, with electronegativity as the dominant factor. By nature, these systems are delocalized, and therefore, resonance energy is the main contributor to pi bond energies. Molecules with a single dominant VB structure have low resonance energies and therefore low pi bond energies.     

Regulation of Excited-State Intramolecular Proton Transfer Process and Photophysical Properties for Benzoxazole Isothiocyanate Fluorescent Dyes by Changing Atomic Electronegativity

Excited-state intramolecular proton transfer (ESIPT) is favored by researchers because of its unique optical properties. However, there are relatively few systematic studies on the effects of changing the electronegativity of atoms on the ESIPT process and photophysical properties. Therefore, we selected a series of benzoxazole isothiocyanate fluorescent dyes (2-HOB, 2-HSB, and 2-HSeB) by theoretical methods, and systematically studied the ESIPT process and photophysical properties by changing the electronegativity of chalcogen atoms. The calculated bond angle, bond length, energy gap, and infrared spectrum analysis show that the order of the strength of intramolecular hydrogen bonding of the three molecules is 2-HOB < 2-HSB < 2-HSeB. Correspondingly, the magnitude of the energy barrier of the potential energy curve is 2-HOB > 2-HSB > 2-HSeB. In addition, the calculated electronic spectrum shows that as the atomic electronegativity decreases, the emission spectrum has a redshift. Therefore, this work will offer certain theoretical guidance for the synthesis and application of new dyes based on ESIPT properties.     

One‐, two‐, and three‐electron bonding: An “in vitro” theoretical study using noninteger nuclear charges evidences the crucial role of electronegativity in the strength of symmetrical bonds

Fictitious hydrogen atoms H*_A of variable nuclear charge 0.5 ≤ Z_A ≤ 2 (and thus of variable electronegativity) are used to study the intrinsic dependency of chemical bonding on electronegativity. Dissociation energy and equilibrium distance are reported for symmetrical 1‐, 2‐ and 3‐electron H*_AH*_A systems and 2‐electron dissymmetrical H*_A‐H ones. Dealing with symmetrical systems, the strongest two‐electron bonds are found for Z_A ≈ 1.2. Oneelectron and three‐electron strongest bonds occur respectively with low (ca. 0.7) and high (ca. 1.7) Z_A values and can become stronger than the corresponding 2‐electron system. Comparison with data on real systems leads to conclude that electronegativity is a prevailing atomic property in the control of the dissociation energy of symmetrical 1‐, 2‐ and 3‐electron bonds. A simplified mathematical model at Hartree‐Fock or Heitler‐London level with a minimal basis set reproduces these trends semi‐quantitatively and provides the overall shape of the dissociation curves. Finally some points are qualitatively discussed from MO analysis, which emphasize the dependence of the bonding/antibonding properties on the nucleus charge Z_A and their occupancy number. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

N, P, and As ylides and aza- and arsa-Wittig reactions from topological analyses of electron density

The nature of bonding between N, P, and As constituent atoms in ylide systems with the R(3)XYR' formula (X = N, P, As; Y = N, P, As; R = F, H; R' = H, CH(3)) has been characterized by ab initio (MP2/6-311++G**) and density functional theory (B3LYP/6-311++G**) calculations. Its electronic structure has been analyzed through electron density with the quantum theory of atoms in molecules and the electron localization function (ELF). The characteristics of the central bond are inspected with the calculated rotational barriers. The results show that N has a behavior different from that of the remaining pnicogen atoms (P, As), where the bond is much stronger. Fluorine substituents strengthen the X-Y bond, reduce the bond distance, and increase the electron density in the central bond so that the substituent pulls charge from the bond in the pnicogen X atom. For the N-pnicogen ylides, the results showed different bonding characters between F and X atoms; depending on the position of the F atom, the difference of the bond character is sensed by the basin synaptic order, as it is deduced from the analysis of the ELF basins. The energy profiles of the rotational barriers have been calculated at the MP2/6-311++G** level, indicating that the electronegativity of the substituents is a relevant factor that has consequences in the characteristics of the X-Y bond.     

Synthesis of Chlorine‐Substituted Graphdiyne and Applications for Lithium‐Ion Storage

Chlorine‐substituted graphdiyne (Cl‐GDY) is prepared through a Glaser–Hay coupling reaction on the copper foil. Cl‐GDY is endowed with a unique π‐conjugated carbon skeleton with expanded pore size in two dimensions, having graphdiyne‐like sp‐ and sp²‐ hybridized carbon atoms. As a result, the transfer tunnels for lithium (Li) ions in the perpendicular direction of the molecular plane are enlarged. Moreover, benefiting from the bottom‐to‐up fabrication procedure of graphdiyne and the strong chemical tailorability of the alkinyl‐contained monomer, the amount of substitutional chlorine atoms with appropriate electronegativity and atom size is high and evenly distributed on the as‐prepared carbon framework, which will synergistically stabilize the Li intercalated in the Cl‐GDY framework, and thus generate more Li storage sites. Profiting from the above unique structure, Cl‐GDY shows remarkable electrochemical properties in lithium ion half‐cells.