氯代苯阳离子的密度泛函理论研究

采用B3LYP方法及6-311G(d,p)和6-311+G(d,p)基组,对12种氯代苯阳离子进行了理论研究,优化其电子基态的结构,计算了对应分子的垂直电离势(VIP)和绝热电离势(AIP).依据Jahn-Teller理论,确定了1,3,5-C6H3Cl3+和C6Cl6+离子分别具有C2v(2B1)和D2h(2B2g)结构(对应分子分别为D3h和D6h结构).其余10个离子的构型的对称点群与对应分子相同,但构型参数值有明显差别.用B3LYP方法计算的各氯代苯分子的垂直电离势和绝热电离势与实验值符合得很好.     

巯基偶氮苯单分子电子传输的取代基效应

用密度泛函理论B3LYP/6-31G**计算巯基偶氮苯分子及分子离子的空间构型和电子结构, 研究取代基对巯基偶氮苯单分子电子传输的影响. 结果表明, 拉电子基(—COOH、—NO2)的引入, 可以提高巯基偶氮苯单分子电子传输体系的稳定性, 使体系LUMO的离域性增高、S原子反应活性增强、HOMO-LUMO能隙显著减小, 进而降低电子传输能垒, 有利于分子电子传输. 相同取代基的分子离子比分子具有更小的HOMO-LUMO能隙, S—Au键更易形成, 金属-分子-金属结构的电子传输性更强.     

氟代苯阳离子的理论研究

用B3LYP方法及6-311G(d,p)和6-311 G(d,p)基组,对十二种氟代苯阳离子做了理论研究,优化了它们的电子基态的结构,计算了对应分子的垂直电离势(VIP)和绝热电离势(AIP)．依据Jahn．Teller理论,计算确定了1,3,5-C6H3F^ 3和C6F^ 6离子分别具有C2v(2↑B)和D2h(2↑B2g)结构(对应分子分别为D3h和D6h结构)．其余十个离子的构型的对称点群与对应分子相同,但构型参数值有明显差别．自然布居分析计算表明这些离子的正电荷主要分布在与F原子相连的C原子和各H原子上．B3LYP／6-311 G(d,p)级别上计算的各氟代苯分子的VIP和AIP值和实验值符合得很好．     

CS2+离子 C2Σg+←B2Σu+跃迁的Franck-Condon因子计算以及与光解离谱的比较

将线性三原子分子离子CS2+的对称伸缩振动简化为SC和S之间的简谐振动, 用谐振子的势能曲线和波函数对CS2+分子离子 C2Σg+和 B2Σu+电子态(对称伸缩)振动能级间跃迁的Franck-Condon因子进行了计算, 得到的结果与 C2Σg+←B2Σu+跃迁的光解离谱实验强度进行了比较, 对前人给出的分子数据(转动常数、分子平衡核间距)进行了验证和分析, 讨论了经由 C2Σg+←B2Σu+电子态振动能级间跃迁的光解离机理.     

CS+2离子(～C)2∑+g←(～B)2∑+u跃迁的Franck-Condon因子计算以及与光解离谱的比较

将线性三原子分子离子CS+2的对称伸缩振动简化为SC和S之间的简谐振动,用谐振子的势能曲线和波函数对CS+2分子离子(～C)2∑+g和(～B)2∑+u电子态(对称伸缩)振动能级间跃迁的Franck-Condon因子进行了计算,得到的结果与(～C)2∑+g←(～B)2∑+u跃迁的光解离谱实验强度进行了比较,对前人给出的分子数据(转动常数、分子平衡核间距)进行了验证和分析,讨论了经由(～C)2∑+g←(～B)2∑+g电子态振动能级间跃迁的光解离机理.     

BF分子X1∑+,A1∏和B1∑+电子态的势能函数

使用SAC/SAC-CI和D95++,6-311++g,6-311++g**及D95(d)基组,分别对BF分子的基态X1∑+、第一简并激发态A1∏和第二激发态B1∑+的平衡结构和谐振频率进行优化计算.对所有计算结果进行比较,得出6-311++g**基组为最优基组.运用6-311++g**基组和SAC方法对基态X1∑+,SAC-CI方法对激发态A1∏和B1∑+进行单点能扫描计算,并用正规方程组拟合Murrell-Sorbie函数,得到相应电子态的势能函数解析式,由得到的势能函数计算了与X1∑+,A1∏和B1∑+态相对应的光谱常数,结果与实验数据较为一致.     

环丙烯基自由基H-F力的abinitio研究

环丙烯基自由基是我们熟知的最小环状化合物。人们用不同的理论方法对它进行了预测。一般认为平面构型(D_(3h)对称性)要经受Jahn-Teller畸变以消除π轨道的简并性,畸变过程如图1所示。我们研究了此类三元环自由基引起的键的“弯曲效应”,以便对这类“张力”分子的成键特性及Jahn-Teller畸变、芳香性等给出某些理论信息,探讨其理论计算结果所能阐明的问题。     

密度泛函理论研究2种新型染料分子的分子内电荷转移现象

采用量子化学方法研究了2种新型有机染料分子P1和P4,几何优化和基态性质计算采用B3LYP密度泛函,基组为6-311G(d).由于P1和P4分子中分别存在2个对称的吸电子基团,所以2个染料分子的电子结构存在明显的特点:2个紧邻简并最低空轨道(LowestUnoccupied Molecular Orbital,LUMO)轨道.P1和P4最高占据轨道(Highest Occupied Mo-lecular Orbital,HOMO)到LUMO轨道的跃迁能级差分别为2.79和3.26eV.同时,采用含时密度泛函方法(Time-Dependent Density Functional Theory,TDDFT)研究了2个染料分子的激发态性质.通过电荷差异密度理论方法(Charge Different Density,CDD)直观的展示了分子内电荷转移的现象.对于P1,电荷转移的方向是从苯甲酸基团到2个二氰乙烯基噻吩苯基团;对于P4,电荷是由2个二氰乙烯基联苯基团基团向苯甲酸基转移.     

Sin/Si-n(n=2-6)的结构和电子亲合能的密度泛函理论研究

选用四种不同的密度泛函理论方法(B3LYP,BLYP,BP86,B3P86),在全电子的双ζ加极化加弥散函数基组(DZP++)下,研究Sin/Si-n (n=2 -6 )体系的结构和电子亲合能.预测Si2 /Si-2 ,Si3 /Si-3 ,Si4 /Si-4 ,Si5 /Si-5 和Si6 /Si-6 的基态结构分别为C∞h(3Σ-g ) /C∞h(2Σ+g ),D3h(3A′2 ) /C2υ(2A1 ),D2h(1Ag) /D2h(2B2g),D3h(1A′1 ) /D3h(2A″2 )和C2υ(1A1 ) /D4h(2A2u).在电子亲合能方面,B3LYP方法预测的电子亲合能是最可靠的.预测Si2,Si3,Si4,Si5和Si6的电子亲合能分别为 2. 05, 2. 34, 2. 16, 2. 48和 2. 13eV.     

硼环平面八配位及九配位的铝和镓

用硼环Bn平面配位金属中心M,两者必须在几何和电子结构上良好匹配.对Al和Ga而言,B8环半径略小,完全平面的D8hAl@B8^-（1）和D8hGa@B8^-（3）均为具有一个虚频的过渡态;金属中心沿体系八重轴轻微向上移动（0.3-0.5）所形成的C8vAl@B8^-（2）和C8vGa@B8^-（4）才是体系的稳定几何构型.轻微畸变的C8v阴离子具有准平面结构,与D8h平面结构在能量上非常接近.广泛的结构搜索表明,B9环与Al和Ga中心良好匹配,D9hAl@B9（5）与D9hGa@B9（6）均为直径约4.45的完美轮状中性分子,它们在得到的所有异构体中能量最低.在D9h5和6中,Al和Ga平面九配位中心携带的净原子电荷分别为＋1.3｜e｜和＋1.5｜e｜,其Wiberg总键级为2.5和2.8;而周边相邻B-B原子间的WBIB-B键级接近1.5,具有明显的双键特征.D9hAl@B9中中心原子的电子组态（Al3s^0.423px^0.343py^0.343pz^0.34）表明,Al在配合物中主要失去3s2价电子,其sp2杂化轨道和3pz原子轨道部分参与了体系的离域σ键和离域π键.结果表明,D9hAl@B9有三个离域的π轨道（简并的HOMO和HOMO-2）和三个离域的σ轨道（简并的HOMO-1和HOMO-4）,分别符合4n＋2休克尔芳香性规则,因而具有σ＋π双重芳香性.M@B8-和M@B9（M=Al,Ga）体系的核独立化学位移（NICS（1））均为较大的负值（介于-17~-26ppm）,进一步确定了体系的芳香性本质. C8vAl@B8^-和C8vGa@B8^-阴离子的计算单电子剥离能分别为ADE=3.41,3.23eV和VDE=3.52,3.32eV,而D9hAl@B9和D9hGa@B9中性分子的计算第一电离势分别为IP=8.51,8.34eV.这些结果为在光电子能谱实验中表征这些分子提供了依据.     

An investigation of the electron density of a Jahn–Teller‐distorted CrII cation: the crystal structure and charge density of hexakis(acetonitrile‐κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate

In the crystal structure of the title homoleptic Cr^II complex, [Cr(CH₃CN)₆](C₂₄H₂₀B)₂·CH₃CN, the [Cr(CH₃CN)₆]²⁺ cation is a high‐spin d⁴ complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the Cr^II cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the Cr^II cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the Cr^II cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex.     

Distortions of π‐Coordinated Arenes with Anionic Character

A qualitative analysis of the distortions that operate on the π system of bridging arenes with anionic character is presented and substantiated by computational studies at the density functional B3LYP and CASSCF levels. The observed effects of bonding to two metal atoms and of the negative charge are an expansion of the arene ring due to the partial occupation of π* orbitals, an elongation or compression distortion accompanied by a loss of the equivalence of carbon‐carbon bonds due to a Jahn–Teller distortion of the arene dianions, and a ring puckering due to a second‐order Jahn–Teller distortion that may appear independently of the existence of the first‐order effect. The workings of the orbital mixing produced by these distortions have been revealed in a straightforward way by a pseudosymmetry analysis of the HOMOs of the distorted conformations. The systems studied include Li^I and Y^III adducts of benzene, as well as trimethylsilyl‐substituted derivatives in the former case. An analysis of the structural data of a variety of purported di‐ and tetraanionic arene ligands coordinated to transition metals in several bridging modes has reproduced the main geometrical trends found in the computational study for the benzene and trimethylsilyl‐substituted benzene dianions, allowing a classification of the variety of structural motifs found in the literature.     

Magnetic criteria of aromaticity in a benzene cation and anion: how does the Jahn–Teller effect influence the aromaticity?

The aromatic/antiaromatic behavior of the Jahn–Teller (JT) active benzene cation and anion has been investigated using Density Functional Theory (DFT) calculations of Nuclear Independent Chemical Shifts (NICS) and magnetic susceptibility. NICS parameters have been scanned along the Intrinsic Distortion Path (IDP) for the benzene cation showing antiaromaticity which decreases with increasing deviation from D_6h to D_2h symmetry. Changes in NICS values along the IDP from D_6h to C_2v in the benzene anion revealed non-aromatic character.     

Jahn—Teller effects in substituted benzene cations. IV. Intermode interactions and intensity anomalies in sym-trifluorobenzene ions

A theoretical treatment of coupling between Jahn—Teller modes is given which includes both linear and quadratic Jahn—Teller coupling. Effects of two and three mode interactions on the B?²A″₂ → X?²E″ transition of the sym-trifluorobenzene ions are studied, within the linear coupling approximation, for modes 6, 7, 8 and 9. Quadratic coupling effects are considered in a companion paper (part V). The results show that discrepancies previously noted between observed relative band intensities and those calculated on the basis of single Jahn—Teller modes cannot be accounted for by multimode interactions or by Fermi resonance effects operating in conjunction with Jahn—Teller effects. Jahn—Teller combination bands are shown to have several components, the most intense of which are assigned. Particular attention is paid to various possible assignments of the 8^0,0_{1,$\text{1}\text{2}$} and 6^0,0_{3,$\text{1}\text{2}$} vibronic transitions in the light of the multimode interaction analyses.     

Jahn–Teller Effects in Molecular Cations Studied by Photoelectron Spectroscopy and Group Theory

The traditional “ball‐and‐stick” concept of molecular structure fails when the motion of the electrons is coupled to that of the nuclei. Such a situation arises in the Jahn–Teller (JT) effect which is very common in open‐shell molecular systems, such as radicals or ions. The JT effect is well known to chemists as a mechanism that causes the distortion of an otherwise symmetric system. Its implications on the dynamics of molecules still represent unsolved problems in many cases. Herein we review recent progress in understanding the dynamic structure of molecular cations that have a high permutational symmetry by using rotationally resolved photoelectron spectroscopy and group theory. Specifically, we show how the pseudo‐Jahn–Teller effect in the cyclopentadienyl cation causes electronic localization and nuclear delocalization. The fundamental physical mechanisms underlying the vaguely defined concept of “antiaromaticity” are thereby elucidated. Our investigation of the methane cation represents the first experimental characterization of the JT effect in a threefold degenerate electronic state. A special kind of isomerism resulting from the JT effect has been discovered and is predicted to exist in all JT systems in which the minima on the potential‐energy surface are separated by substantial barriers.     

A multi-configuration LCAO–MO study for complex unsaturated molecules. II. Application to the benzene cation

The method of the MC –LCAO –MO approach, described in the preceding paper, is further applied to the benzene cation. Through the iteration process the π-electron energies and the molecular shapes are computed for the ground and two lowest excited states of the cation in both D_6h and D_2h geometries. A remarkable fact obtained is that a comparatively small variation of the geometrical structure (c. 0.010 – 0.013 Å bond length difference) brings about a considerable change of the energy value (c. 0.85 – 1.25 eV). The π-electronic excitation energies obtained from the iteration process are compared with the transition energies calculated from the usual method in which the structures of the excited states are assumed to be the same as the corresponding ground state structures. The difference in the excitation energy between the cation and the anion, and the CI effect on the excited states, are discussed. It is found that the doubly excited configurations play an important role in CI , which is somewhat different from that of the singly excited configurations. The stabilization energy due to the Jahn–Teller distortion is estimated for the ground state of the cation.     

Excited states and photochemistry of saturated molecules. ab initio calculations on methane

STO 4G calculations are carried out on methane in both tetrahedral and Jahn—Teller distorted C_2v and C_3v symmetries. Large increases in CH bond lengths are predicted in all states, and the ^IB₁ state in C_2v symmetry is predicted to dissociate to ^IB₁ methylene and ¹A₁ H₂ width no energy barrier. THe results are compared with earlier INDO calculations, and the latter are found to qualitatively consistent with the ab initio results.     

A new aqua­hydroxido­copper(II) oxo­vanadium(IV) vanadate,Cu(H2O)(OH)VO(VO4)

Single crystals of the title compound have been prepared hydro­thermally. Vanadate tetrahedra and distorted oxovanadium octahedra form layers, linked by two independent Cu atoms located on inversion centres. Each Cu atom is surrounded by six O atoms, forming an octahedron distorted by Jahn–Teller elongation. One of the two independent interlayer spaces bridged by the Cu atoms is significantly more compact than the other.     

Geminal approach to vibronic models of superconductivity in crystals. I. The Jahn–Teller effect

Electronic geminals constructed as linear combinations of binary products of site functions are used to formulate a vibronic model of superconductivity in crystals that is based upon the approximation of independent correlated electron pairs obtained variationally from an electron‐pair Hamiltonian and the Jahn–Teller effect. The cyclic symmetry of the system is taken into account and the geminals are sorted into doubly degenerate pairs. The Herzberg–Teller expansion of the pair Hamiltonian in terms of vibrational modes leads directly to the Jahn–Teller effect. A contact transformation of the vibronic Hamiltonian containing only linear terms lowers the energy of the system by a second‐order term associated with the Jahn–Teller stabilization energy. A possible model for superconductivity in solids is proposed on the basis of the Jahn–Teller effect. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Resonance raman scattering in the region of a forbidden non-degenarate electronic state by a doubly degenerate vibration

It is shown that the resonance Raman scattering from a forbidden non-degenerate electronic state by a doubly degenerate mode depends strongly on Jahn—Teller interactions within an allowed doubly degenerate electronic state that lends its intensity to the scattering forbidden state.