Geometrical configurations of Pu4 and the Jahn–Teller effect

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.     

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     

Dynamic nonlinear Jahn–Teller effect of the type E ⊗ ϵ

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 C_3v 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.     

Mitigation of Jahn–Teller distortion and Na+/vacancy ordering in a distorted manganese oxide cathode material by Li substitution

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-Na_0.67Li_0.05Mn_0.95O₂, 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-Na_0.67Li_0.05Mn_0.95O₂ 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-Na_0.67MnO₂ 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.     

The relevance of boranes and metallaboranes to the structures of p-block element nanoparticles

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.     

Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions

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 C_s and D_2h 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.     

Unexpected chirality transition and inversion mediated by dissolution–aggregation and the odd–even effect

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.     

Density functional theory of born couplings: Consequences for electron flow in Jahn–Teller molecules and superconductors

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.     

Activation of Si–H and B–H bonds by Lewis acidic transition metals and p-block elements: same,but different

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.     

The Structure of Mn(acac)3—Experimental Evidence of a Static Jahn–Teller Effect in the Gas Phase

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 (r_h1=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.     

Orbit–orbit interaction in the NO–Fe(II)Hemoproteins studied by the low-temperature magnetic circular dichroism: Dynamic Jahn–Teller effect detected by MCD

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.     

The electronic structure of tetrahedral III–V compounds: The ground state of boron nitride

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.     

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn – Teller Effect in Molecules

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.     

Skeletal structures of hexa-organo substituted triatomics R3XYZR3: A rationalisation using the second-order Jahn—Teller effect

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.