A STUDY OF TEMPERATURE-DEPENDENT VALENCE BOND STRUCTURE OF TITANIUM

On the basis of energy and shape method for the determination of the valence bond （ VB ） structures of crystal, the valence bond structure of titanium is redetermined at room temperature and calculated in the whole temperature range of 0-1943K. The outer shell electronic distribution of Ti is ec^29907. （sc^0.4980 ＋ dc^2.4927） ef^1.0098 in crystal. The temperature dependences of the VB structures of hcp and bcc phases are the same. The VB structures of hcp and bcc phases monotonically increase or decrease with the increase in temperature, but show discontinuous changes at the phase-transformation temperature 1155K.

Coherence of the Even-Odd Rule with an Effective-Valence Isoelectronicity Rule for Chemical Structural Formulas: Application to Known and Unknown Single-Covalent-Bonded Compounds

Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunately not sufficient to ensure that a chemical structure is a valid chemical compound. In a previous article, a procedure has been described to draw 2D valid structural formulas: the even-odd rule. This rule has been applied first to single-bonded molecules then to single-charged single-bonded ions. It covers hypovalent, hypervalent or classic Lewis’ octet compounds. The funding principle of the even-odd rule is that each atom of the compound possesses an outer-shell filled only with pairs of electrons. The application of this rule guarantees validity of any single-covalent-bond chemical structure. In the present paper, this even-odd rule and its electron-pair criterion are checked for coherence with an effective-valence isoelectronic rule using numerous known compounds having single-covalent-bond connections. The test addresses Lewis’ octet ions or molecules as well as hypovalent and hypervalent compounds. The article concludes that the even-odd rule and the effective-valence isoelectronicity rule are coherent for known single-covalent-bond chemical compounds.

Valence bond structure of Ta-W alloys

The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal （CC） theory. This theory is based on cluster statistics of random alloys. By studying the correlativity between energy and volume of the CC in Ta- W alloys, the valence bond structure of CC is determined by the energy and shape method. Then, following additive law of CC, the valence bond structure of Ta-W alloys is calculated. It is found that the outer shell valence electronic distribution of Ta-W Mloys shows a continuous change in the whole composition range. The covalent electrons ec （dc, sc, and pc） increase, whereas near free electrons ef decrease with increasing W concentration. The bond length and single-bond radius decrease, whereas bond energy and bond valence increase with increasing W concentration. The mechanism of solid solution strengthening of Ta-W alloys is analyzed based on their valence bond structure.

The Influence of Bond Valence on Bond Covalency in RMn_2O_5 (R=La, Pr, Nd, Sin, Eu)

The relationship between bond valence and bond covalency in RMn2O5 (R = La, Pr, Nd.Sm, Eu) has been investigated by a semiempirical method. This method is the generalization of thedielectric description theory of Phillips. Van Vechten, Levine and Tanaka scheme. The resultsindicate that larger valences usually result in higher bond covalencies, in good agreement with thepoint that the excess charge in the bonding region is the origin of formation of bond covalency.Other factors, such as oxidation state of elements, only make a small contribution to bondcovalency.

Complementary method to locate atomic coordinates by combined searching method of structure-sensitive indexes based on bond valence method

Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index（GII） and bond strain index（BSI）, are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII ＆ BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions.

A New Group Theoretical Approach to the Nonorthogonal Problem in Valence Bond Theory

Introduction There has been a very significarnt resurgence of interest in ab initio valence bond calculations recently. This is because the VB calculation based on nonorthogonal basis can provide intuitive understanding about many very important phenomena in chemistry. However, practical calculation based on nonorthogonal basis is still a great challenge even to deal with a quite small system due to the well-known N! (or

Bond Valence Sum Analysis of Tl(Ⅰ) and Tl(Ⅲ) Complexes with O and N Donors

The influence of the lone pair of electrons in thallium complexes is analyzed using the bond valence sum method.Bond length data for metal-organic Tl complexes were obtained from the Cambridge Structural Database（CSD）,and problems with searching the CSD file for Tl complexes are discussed.The recommended R0 values for Tl（Ⅰ）-O of 2.162 ,Tl（Ⅲ）-O of 2.016 ,Tl（Ⅰ）-N of 2.286 ？,and for Tl（Ⅲ）-N of 2.014 used with b = 0.37 were derived from analyses of homoleptic Tl-O,Tl-N,and heteroleptic Tl-O and-N metal organic complexes.These R0 values can be used to assign correctly the oxidation state of Tl in complexes containing any combination of Tl-O or Tl-N bonds.Examples of questionable oxidation states for Tl complexes are given.The R0 value for Tl（Ⅲ）-Cl of 2.300 was also determined.

Bond-Valence Sum and Distortion of Coordination Polyhedra

By using the Lagrange's intermediate value theorem,it is derived mathematically that the structur-al distortion of a coordination polyhedron may lead to an increase in bond-valence sum of the cen-tral atom of ion .The applicabilities of the bond-valence model are discussed in the following two cases:the modeling of crystal structure ,and the indication of distortion degree of a coordination polyhedron.Also it is shown that a distorted polyhedron should be in favor of a longer average bond length or a smaller coordination number.

The mechanism of hydrogen abstraction by high valence transition metal oxo compounds

We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

Crystal Chemistry of Iron in Non-Metamict Chevkinite-(Ce): Valence State and Site Occupation Proportions

The ideal formula for chevkinite can be expressed as A4BC2D2Si4O22. It is important to determine the valence state and site occupation proportions for Fe among the B, C, and D octahedral sites as it may help to identify different species in the chevkinite group. Non-metamict chevkinite-（Ce） from Mianxi alkali feldspar-granite, Sichuan Province, China, was investigated using Moessbauer spectroscopy. The Fe^3＋/∑Fe ratio was 39.2%. A significant increase of Fe^3＋ occured during metamictization and annealing for chevkinite-group minerals. In metamict samples Fe tended to lower coordination, According to the correlation between bond length and isomer shift （IS）, the quadrupole doublets with IS = 1.10 and 0.94 mm·s^-1 can be assigned to Fe^2＋ in the B and C octahedral sites, respectively. Based on the correlation between octahedral distortion and quadrupole splitting （QS）, the quadrupole doublets with QS = 0.86 and 0.77 mm·s^-1 can be assigned to Fe^3＋ in the C and D sites, respectively. The simplified formula can be revised as： Ce4Fe^2＋ （Ti, Fe^2＋, Fe^3＋ ）2（Ti, Fe^3＋ ）2Si4（O,OH）22. It indicated that the non-metamict chevkinite-（Ce） belonged to Fe^2＋ end member of the chevkinite group because Fe^2＋ was the predominant component in the B site.

Study on Valence Band Offsets atStrained Heterojunctions

A method, which can predict the valence band offsets at strained layer heterojunctions under different strain situations only by calculating band structures and deformation parameters of the bulk materials, is suggested. The applicability of this method is verified by calculation of the valence band offsets at strained layer heterojuntions ,such as InP/InAs, InP/GaP, GaAs/InAs, GaP/GaAs and AlAs/InAs with various strain conditions.

Mo8^ⅤW2^ⅥO26（C5H5N）8·2H2O： A Novel Mixed-valence Heterometal Polyoxometalate

A new mixed-valence heterometal cluster Mo8VW2VIO26（C5H5N）8·2H2O has been synthesized under solvothermal conditions and characterized by X-ray single-crystal diffraction, IR, UV-vis and XPS spectroscopy. The title compound crystallizes in the triclinic system, space group P1 with a = 11.708（3）, b = 12.018（4）, c = 13.316（4） A, α = 112.184（4）, β = 97.844（4）, γ = 110.043（3）°, V = 1551.9（8） A3 and Z = 1 at 293（2） K. The final full-matrix least-squares refinement converged to R = 0.0414 for 4460 observed unique reflections with I 〉 2σ（I） and w R = 0.1290 for all data（5352） and S = 1.015. In addition, its thermal stability and fluorescent property have also been investigated.

不同V型辅助配体构筑的两个镉配位聚合物的合成、结构和荧光性质

在溶剂热条件下,合成了2个基于V型辅助配体(bipmo、bppmo)的镉配位聚合物{[Cd(bipmo)(NDC)]·1.75H_(2)O}_n (1)和{[Cd(bppmo)(NDC)(H_(2)O)]·H_(2)O}_(n) (2),其中H_(2)NDC=2,6-萘二羧酸,bipmo=双(4-(1H-咪唑-1-基)苯基)甲酮,bppmo=双(4-(吡啶-4-基)苯基)甲酮。利用单晶X射线衍射、键价和分析、红外光谱和元素分析对其结构进行了表征。研究发现,配合物1具有二重互穿的{6~3}拓扑结构。配合物2同样是3-连接的{6~3}拓扑,却存在三重穿插结构。分析表明,V型配体对最终结构的形成有很大影响。此外,对配合物1和2的发光性质也进行了详细研究。

价键原子指数用于酱香型习酒香气成分保留性质研究

酱香型习酒是一种风味极其独特的酱香型白酒,具有风味醇厚、幽雅细腻和回味悠长的香气,香气成分繁多而复杂.为探究酱香型白酒的主要挥发性物质的组成及香气风味成分的差异,研究建构酱香型习酒香气成分保留指数的定量结构-保留相关性模型,根据酱香型习酒香气成分分子中原子的空间与电性结构,基于拓扑理论,提出了一种新的结构参数-价键原子指数~mA.另计算了酱香型习酒香气成分的电拓扑状态指数(Em),优化筛选了指数中的~0A、E_(1)、E_(2)、E_(14),将4种结构参数作为神经网络三层结构的输入节点数,色谱保留指数作为三层结构的输出节点数,网络结构采用4-12-1方式.建立的预测香气成分保留指数模型的相关系数达到0.9965,计算得到的酱香型习酒香气成分保留指数RI预测值的平均相对误差为1.41%.结果表明,酱香型习酒挥发性香气成分的保留指数,与价键原子指数和电拓扑状态指数之间具有很好的非线性关系,非氢原子结构及—CH_(3)、>CH_(2)、—O—等基团,是影响酱香型习酒香气成分保留指数的主要因素.

高校化学化工课程教学改革探索——以“价键理论”及“分子轨道理论”教学为例

化工专业高等教育在我国工业发展中具有重要地位。本文以党的二十大精神为指导,明确了高校化学化工专业教学改革的重要意义及基本要求,分析了高校化工课程教学改革的现状与具体问题,探索了高校化工课程教学改革的目标与路径。以“价键理论”及“分子轨道理论”为例,提出高校化工课程教学改革应坚持以人为本以,问题为导向,明确了教育理念与核心能力、培养应用型人才、实现产学研一体化、丰富教学手段等探索。本文希望为高校化工课程教学改革提供了一些理论参考和实践借鉴。

不同化学价离子对羧基丁腈橡胶复合材料力学性能的影响

在羧基丁腈橡胶中分别加入金属氧化物氧化镁、氧化锌和氧化铝,系统研究了金属离子与羧基的相互作用,共混胶硫化特性,硫化胶动态力学性能,复合材料的形貌、拉伸性能及模量-温度关系。结果表明,金属氧化物与羧基丁腈橡胶形成离子键的难易程度与金属氧化物的碱性强弱有关;金属离子具有较高的电荷数、较小的半径和较强的电负性则有利于提高羧基丁腈橡胶复合材料在高温条件下的力学强度。

Chemical Bond Calculations of Crystal Growth of KDP and ADP

A novel method was proposed to calculate the crystal morphology (or growth habit) on the basis of chemical bond analysis. All constituent chemical bonds were distinguished as relevant and independent bonds according to their variations during the crystallization process. By employing the current method, the influence of specific growth conditions on the crystal morphology can be considered in the structure analysis process. The ideal morphologies of both KDP (KH2PO4) and ADP (NH4H2PO4) crystals were calculated and compared with our obtained crystallites at room temperature, which validates the present calculation method very well.

Strength of Intramolecular Hydrogen Bonds

The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used in practice.However,it has been argued that the seemingly enhanced intramolecular hydrogen bonding(IMHB)in unsaturated compounds may simply be a result of the constraints imposed by theσ-skeleton framework.Thus,it is crucial to estimate the strength of IMHBs.In this work,we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone.One approach is the block-localized wavefunction(BLW)method,which is a variant of the ab initio valence bond(VB)theory.Using this approach,it is possible to derive the geometries and energetics with resonance shut down.The other approach is Edmiston’s truncated localized molecular orbital(TLMO)technique,which monitors the energy changes by removing the delocalization tails from localized molecular orbitals.The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced byπ-resonance,and that this enhancement is not a result ofσconstraints.

Gravitational Chemical Bond with Real Magnetic Charges and True Antielectrons

The detection by the author of real magnetic charges, as well as true antielectrons in of atomic structures allowed him to establish that atomic shells, as well as shells of nucleons are electromagnetic, and not electronic. Namely electromagnetic shells are the sources of gravitational field which is the vortex electromagnetic field. The elementary source of gravitational field is the electromagnetic quasiparticle (S-Graviton) which consists of two coupled dipoles (the magnetic and electric) rotating in antiphase in the same atomic or nucleonic orbit. Electrons in atomic shells are rigidly embedded in the compositions of S-Gravitons and, as a rule, cannot individually participate, for example, in processes of interatomic chemical bonding. Depending on the vector conditions the gravitational fields can be both paragravitational (PGF) so and ferrogravitational (FGF). The overwhelming number of atomic shells and all shells nucleons emit PGF. Between the masses (bodies, atoms, nucleons, etc.) emitting of PGF is realized a force of gravitational “Dark energy” pressing masses to each other. It is the compression of masses by forces of the gravitational “Dark energy” that lies at basis Physics of chemical bond. Depending on implementation in atoms of the effects intra-atomic gravitational shielding/lensing (IAGS/L) discovered and investigated by the author, the gravitational interatomic bonding mechanisms are divided into two groups: non-covalent bonds (IAGS effect) and covalent bonds (IAGL effect). Within the framework of the gravitational bond mechanism of the latter group which is implemented with participation paragravitational orbitals, such chemical concept as valence acquires a real physical meaning. The replacing the erroneous electronic concept of chemical bonding by the gravitational concept implies replacing the notion “electronegativity” of element by the notion the “gravitational activity” while maintaining existing quantitative ability of atoms in molecules to attract atoms of other elements.

Bond-distorted Orbitals and Their Application to Benzene

The present paper covers a kind of localized orbitals, namely bond-distorted or-bitals in the valence bond calculation. Test calculation on benzene is reported. The results indicate that Dewar structures are important in the description of benzene.