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The present work has found seven stable geometrical configurations of Pu4 using the density functional method Becke3LYP with relativistic effective core potentials (RECP). Based on the Jahn–Teller effect, vibronic interaction and the resolution of group representations, the analysis of the relationships among these various geometrical configurations is in fair agreement with the calculated results. It is found that the spin–polarization effect is rather important for the plutonium clusters and, in general, actinide element molecules. 相似文献
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Pancracio Palting Jorge Ricardo Letelier Ying Nan Chiu 《International journal of quantum chemistry》2004,96(1):56-68
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 相似文献
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Jai Singh 《International journal of quantum chemistry》1981,19(5):859-871
By applying the projection operator method it is shown that the complicated Hamiltonian of a E ? ? JT system with nonlinear coupling coefficients can be written in terms of two Hamiltonians which are simple to handle and transform according to irreducible representations E, A1, and A2 of C3v point group. A variational approach is then used to calculate the ground state energy, using the Hamiltonian that transforms according to E, as an explicit function of the linear and nonlinear coupling parameters. The energies calculated in the strong coupling limit are finally compared with the corresponding previously calculated energies. 相似文献
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Yanchen Liu Chenchen Wang Shuo Zhao Lin Zhang Kai Zhang Fujun Li Jun Chen 《Chemical science》2021,12(3):1062
Layered manganese-based oxides are promising candidates as cathode materials for sodium-ion batteries (SIBs) due to their low cost and high specific capacity. However, the Jahn–Teller distortion from high-spin Mn3+ induces detrimental lattice strain and severe structural degradation during sodiation and desodiation. Herein, lithium is introduced to partially substitute manganese ions to form distorted P′2-Na0.67Li0.05Mn0.95O2, which leads to restrained anisotropic change of Mn–O bond lengths and reinforced bond strength in the [MnO6] octahedra by mitigation of Jahn–Teller distortion and contraction of MnO2 layers. This ensures the structural stability during charge and discharge of P′2-Na0.67Li0.05Mn0.95O2 and Na+/vacancy disordering for facile Na+ diffusion in the Na layers with a low activation energy barrier of ∼0.53 eV. It exhibits a high specific capacity of 192.2 mA h g−1, good cycling stability (90.3% capacity retention after 100 cycles) and superior rate capability (118.5 mA h g−1 at 1.0 A g−1), as well as smooth charge/discharge profiles. This strategy is effective to tune the crystal structure of layered oxide cathodes for SIBs with high performance.Li-Substitution in P′2-Na0.67MnO2 mitigates the anisotropic change of Mn–O bonds and Na/vacancy ordering, and hence significantly promotes its cycling stability and rate capability as a cathode material for sodium-ion batteries. 相似文献
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Thomas P. Fehlner 《Journal of organometallic chemistry》2009,694(11):1671-7827
Recent d-block element metallaborane chemistry, in which metal identity is varied with constant ancillary ligand, demonstrates how the rising energy of the d orbitals as one moves to earlier metals gives rise to non spherical cluster shapes that permit low formal cluster electron counts. In essence, the separation of frontier orbitals from “nonbonding” orbitals required by the isolobal analogy breaks down and the resulting mixing generates additional high-lying empty orbitals concurrently with shape change. A very similar mechanism explains recent p-block cluster chemistry albeit with variation in extent of external cluster ligation as the variable and separation of external lone pair orbitals from cluster bonding as the problem. Sensible, novel explanations of the shape/electron count relationships can be discovered for large group 13 clusters by recognizing the perturbation in cluster orbital energies when stabilization by ligand interactions is removed. These observations are pertinent to an understanding of large p-block clusters with internal atoms often referred to as nanoparticles. 相似文献
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Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions
Dr. Alexander S. Filatov Natalie J. Sumner Sarah N. Spisak Dr. Alexander V. Zabula Andrey Yu. Rogachev Prof. Marina A. Petrukhina 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15753-15760
Single‐crystal X‐ray diffraction studies of two polyaromatic radical anions crystallized as sodium salts, namely [Na(DME)3]+[C20H10?] ( 1 ) and [Na(DME)3]+[C24H12?] ( 2 ) are reported. This allowed the first structural evaluation of Jahn–Teller (JT) effects for monoreduced circulenes and a comparison between bowl‐shaped corannulene and planar coronene. The Cs and D2h symmetrical distortions are found to fit the experimental data for C20H10.? and C24H12.?, respectively. The continuous symmetry measure (CSM) analysis was carried out to provide a quantitative measure of the JT distortions in 1 and 2 . In addition, the X‐ray crystallographic results were fully supported by DFT calculations. 相似文献
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Yafei Ma Xiaoxiao Cheng Haotian Ma Zixiang He Zhengbiao Zhang Wei Zhang 《Chemical science》2022,13(45):13623
The evolution of hierarchical chirality at macromolecular and supramolecular levels in biological systems is ubiquitous; however, achieving precise control over transitions between them in polymer systems is still challenging. Here, we reported multiple chiroptical transitions and inversion phenomena in side-chain azobenzene (Azo) polymers, PAzo-l/d-m (m = 3, 6, 7, 8, 9, and 10, where m is the total number of atoms from the chiral stereocenter to the Azo unit), with different distances from the chiral stereocenter to the Azo unit. In the case of m = 3, an unexpected macromolecular-to-supramolecular chirality transition and inversion occurred in situ when the Azo-polymer underwent from a macromolecular-dissolved state to a supramolecular-aggregated state. To our surprise, an exciton-coupling induced multiple chiroptical inversion was observed upon the heating-assisted reassembly treatment, which was demonstrated to be driven by H- to J-aggregation transition. Furthermore, the odd–even effect was first established to regulate the supramolecular helical orientations (left- or right-handedness) in side-chain Azo-polymer assemblies.Unexpected chirality transition and inversion at molecular, macromolecular and supramolecular levels were realized by dissolution–aggregation and the odd–even effect, which is helpful for the design of advanced chirality-controllable materials. 相似文献
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N. Sukumar 《International journal of quantum chemistry》1995,56(5):423-432
The dynamics of Jahn–Teller systems has recently been discussed in terms of generalized electronic charge and current densities in nuclear-coordinate space. The introduction of the electronic phase as a function of both electronic and nuclear coordinates, in addition to the electronic density, was a crucial component of this formulation. Here, a densitybased treatment of Born couplings is derived from first-principles quantum mechanics beyond the Born–Oppenheimer approximation. Because of the degenerate electronic configuration of a Jahn–Teller molecule, there are an infinite number of ways in which the charge distribution can be oriented for the same energy, leading to a vanishing bond hardness for the molecule in the symmetric nuclear configuration. Further, the moving nuclear framework serves as the perturbation necessary to define the orientation of the charge density, leading to unhindered rotation of the charge cloud. This leads to the dynamical Jahn–Teller problem, namely, the coupling of electronic and nuclear motions through the Born coupling terms. Applications to superconductivity theory are discussed. © 1995 John Wiley & Sons, Inc. 相似文献
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In this Perspective we discuss the ability of transition metal complexes to activate and cleave the Si–H and B–H bonds of hydrosilanes and hydroboranes (tri- and tetra-coordinated) in an electrophilic manner, avoiding the need for the metal centre to undergo two-electron processes (oxidative addition/reductive elimination). A formal polarization of E–H bonds (E = Si, B) upon their coordination to the metal centre to form σ-EH complexes (with coordination modes η1 or η2) favors this type of bond activation that can lead to reactivities involving the formation of transient silylium and borenium/boronium cations similar to those proposed in silylation and borylation processes catalysed by boron and aluminium Lewis acids. We compare the reactivity of transition metal complexes and boron/aluminium Lewis acids through a series of catalytic reactions in which pieces of evidence suggest mechanisms involving electrophilic reaction pathways.In this Perspective we compare the ability of transition metals and p-block Lewis acids to activate electrophilically hydrosilanes and hydroboranes. The mechanistic similarities and dissimilarities in different catalytic transformations are analyzed. 相似文献
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《Angewandte Chemie (International ed. in English)》2017,56(49):15751-15754
The structure of free manganese(III) tris(acetylacetonate) [Mn(acac)3] was determined by mass‐spectrometrically controlled gas‐phase electron diffraction. The vapor of Mn(acac)3 at 125(5) °C is composed of a single conformer of Mn(acac)3 in C2 symmetry with the central structural motif of a tetragonal elongated MnO6 octahedron and 47(2) mol % of acetylacetone (Hacac) formed by partial thermal decomposition of Mn(acac)3. Three types of Mn−O separations have been refined (rh1=2.157(16), 1.946(5), and 1.932(5) Å. We have found no indication for a significant deviation of the ‐C−C−C−O−Mn−O‐ six‐membered rings from planarity, which is observed in the solid state. 相似文献
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A. P. Mineyev Yu. A. Sharonov N. A. Sharonova V. A. Figlovsky 《International journal of quantum chemistry》1979,16(4):883-889
This paper analyzes the low-temperature magnetic circular dichroism of NO–Fe(II)hemoproteins in detail. We include the Jahn–Teller effect in our consideration of the low-temperature MCD results. 相似文献
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The bond-orbital theory of III–V compounds, previously described by Coulson, Redei and Stocker, is used to calculate the effective atomic charges and the binding energy per bond in boron nitride. The theory is reformulated in a manner which is convenient for performing both ab initio and semiempirical calculations. Two different choices for the atomic-orbital exponents are considered and, in both cases, the results obtained from the ab initio method are at variance with the earlier calculations in predicting an electronic charge displacement from nitrogen to boron. The magnitude of the effective charges is found to vary according to the method of partitioning the overlap charge between the nitrogen and boron atoms. The use of orthogonalized Slater 2s functions is also examined. The semiempirical calculations are performed with an explicit inclusion of the Madelung energy from the outset. The ionicity in the bond is shown to be determined by the competition between the difference in orbital electronegativities and the difference in Madelung potential across the ends of the bond. Unfortunately, the semiempirical theory breaks down because the energy per bond passes through a maximum at the optimum value of the polarity parameter. The reasons for this behaviour are examined and discussed. 相似文献
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Upali A. Jayasooriya Roderick D. Cannon Christopher E. Anson Elisha Karu Ahmed K. Saad John P. Bourke Gordon J. Kearley Ross P. White 《Angewandte Chemie (International ed. in English)》1998,37(3):317-320
Intrinsic and extrinsic forces behind the distortion in metal atom clusters can be readily distinguished provided that the clusters are embedded in a suitable ligand environment and that the tunneling of the protons in the peripheral ligands is then analyzed by inelastic neutron scattering. For the [Cr3O(OOCCH3)6(H2O)3]Cl⋅6 H2O model system studied, the tunneling process is very sensitive to the local environment. Thus a tool is available to allow a better assessment of the cause of structural distortions. 相似文献
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C. Glidewell 《Journal of organometallic chemistry》1978,159(1):23-30
In compounds of type R3XYZR3 (R phenyl, methyl, benzyl; X, Z Al, Si, P, Ge, Sn; Y C, N, O, F) linearity of the XYZ skeleton is predicted by the second-order Jahn—Teller effect in those examples where the valence orbitals of X and Z are much less tightly bound than those of Y. When the X and Z orbitals are bound more tightly than those of Y, the XYZ skeleton is predicted to be non linear at Y. The effects of varying R, X and Z, and the contribution of π-interactions are discussed. 相似文献