Cooperative Jahn-Teller Interactions Research Articles

Temperature Induced Spin Transition in Co(II) Complex

A microscopic theoretical approach for the description of spin transitions in mononuclear Co(II) compounds is suggested. Two types of interionic interactions are taken into account, namely, the electron-deformational interaction and the cooperative Jahn-Teller interaction arising from the coupling of the low-spin state of the Co(II) ion with the tetragonal vibrations of the nearest surrounding. The different role of these interactions in the spin transformation is demonstrated and discussed. A qualitative and quantitative explanation of the experimental data on the temperature dependence of the magnetic susceptibility for the [Co(pyterpy)2](PF6)2 compound is given

Interplay of Jahn-Teller Ordering and Spin Crossover in Co(II) Compounds

The spin crossover phenomena in Co(II) compounds are in the focus of the present paper. A microscopic theoretical approach for the description of spin transitions in mononuclear Co(II) compounds is suggested. Within the framework of this approach there are taken into account two types of interionic interactions that may be operative in the problem such as the electron-deformational interaction and the cooperative Jahn-Teller interaction arising from the coupling of the low-spin state of the Co(II) ion with the tetragonal vibrations of the nearest surrounding. The different role of these interactions in the spin transformation is demonstrated and discussed. On the basis of developed approach a qualitative and quantitative explanation of the experimental data on the temperature dependence of the magnetic susceptibility for the [Co(pyterpy)2](PF6)2, [Co(pyterpy)2](TCNQ)2⋅DMF⋅MeOH and [Co(pyterpy)2](TCNQ)2⋅MeCN⋅MeOH compounds is given.

The effect of cooperative Jahn–Teller interactions onC60− anions

Singly charged buckminsterfullerene anions,C60−, are subject to a strong intramolecular Jahn–Teller (JT) effect. When such ions interact with otherC60−ions in a solid through a cooperative JT effect, they will be subject to anadditional interaction. There are a number of different mechanisms thatcan cause this interaction. However, in the molecular field approximation,all can be modelled phenomenologically in terms of a symmetry-loweringinteraction written in terms of a linear combination of electronic operators for theh modes involved in the intramolecular JT effect. We will consider the combined effect of thisdistortion and the intramolecular JT effect. We will analyse the lowest adiabatic potentialenergy surface, and calculate the energies of the resultant vibronic states. The resultsare shown to have a complicated dependence on the particular combination ofh modes chosen, and the energies of the resultant vibronic states cannot easily be deducedfrom the form of the potential alone.

Theory of manganite superlattices

A theoretical model is proposed for the (0,0,1) superlattice manganite system ${({\text{LaMnO}}_{3})}_{n}{({\text{SrMnO}}_{3})}_{m}$. The model includes the electron-electron, electron-phonon, and cooperative Jahn-Teller interactions. It is solved using a version of the single-site dynamical mean-field approximation generalized to incorporate the cooperative Jahn-Teller effect. The phase diagram and conductivities are calculated. The behavior of the superlattice is found to be a good approximation to be an average over the density-dependent properties of individual layers, with the density of each layer fixed by electrostatics.

Strain in Jahn–Teller systems as a precursor to co-operative interactions

The effect of co-operative Jahn–Teller interactions on a Jahn–Teller system is modelled using a linear coupling Hamiltonian together with an applied strain. Two cases are treated: the relatively simple E ⊗ e system, and the more complicated p 2 ⊗ h system, which may be used to model C 60 2 - fullerene ions. In the E ⊗ e case, the Hamiltonian can be separated into a part that represents vibrations across a trough in the lowest adiabatic potential energy surface, and a part that represents rotations around the trough. The rotational part results in a wave function that can be conveniently expressed in terms of Mathieu functions, or alternatively as a Frobenius series. For the p 2 ⊗ h system, the Hamiltonian can again be separated into vibrational and rotational parts, and the rotational part can be solved in terms of Frobenius series. The energies of the solutions are presented graphically and interpreted by comparison with existing results in the literature that assume the strain is sufficiently strong to convert the rotation to a vibration.

CE correlations in a spin–orbital model for half-doped manganites

Using a finite-temperature diagonalization technique for a 8 × 8 site cluster, the charge-exchange phase was found to be stabilized together with charge order by the cooperative Jahn–Teller interaction between next-nearest Mn neighbors in the case of small antiferromagnetic interactions between t 2 g electrons.

Aqua Ions. 2. Structural manifestations of the Jahn-Teller effect in the beta-alums.

Variable-temperature single-crystal neutron diffraction structures of the alums CsM(III)(SO(4))(2).12D(2)O, where M(III) = Ti, V, Mn, and Ga, are reported. Structural differences are highlighted by the titanium and manganese alums, which undergo cubic (Pathremacr;) to orthorhombic (Pbca) phase transitions at approximately 13 and approximately 156 K, respectively. The structural instability exhibited by these salts is interpreted as arising from cooperative Jahn-Teller interactions, and these measurements characterize the structural changes that result from the coupling between the electronic and vibrational states. Although the symmetry changes associated with the phase transformations are analogous for the Ti and Mn alums, the low-temperature geometries of the tervalent hexaaqua cations are markedly different. Whereas the MnO(6) framework is subject to a pronounced tetragonal elongation, changes in the Ti-O bond lengths are very modest; but significant changes in the O-Ti-O bond angles and in the disposition of the coordinated water molecules are identified. The large differences in the transition temperatures and in the low-temperature stereochemistries of the [Ti(OD(2))(6)](3+) and [Mn(OD(2))(6)](3+) cations are related to the sensitivity of the energies of the t(2g) (O(h)) and e(g) (O(h)) orbitals to the various asymmetric vibrations of the hexaaqua complex.

Exchange interaction and Jahn—Teller correlations in novel tetranuclear supramolecular Cu(II) grid complexes: an ESR study

Novel tetranuclear Cu(II) complexes in which four Cu(II) ions are arranged in a square planar fashion by four bis(bipyridyl)pyrimidine ligands were investigated by X and Q band ESR in the temperature range 4.2-300 K. The ESR spectra of this grid-like structure were well simulated as rising from triplet species. Analysis of their intensities allowed the spectra to be assigned to the first excited triplet state, and revealed intramolecular antiferromagnetic coupling of the Cu(II) spins. The isotropic exchange interaction J was determined as −47 K and reducing to about −5 K on functionalizing the bridging pyrimidine ring at the 2-position by methyl or phenyl. For comparison an ESR investigation was also carried out on the mononuclear analogue Cu(II)—(terpyridine)2 complexes with substituted terpyridine ligands at the 5′ and 5″ position. Depending on the substitutent, the spectra exhibit a static or dynamic Jahn—Teller effect at room temperature. The temperature dependence of their g-values is examined by a modified Silver—Getz model which includes cooperative Jahn—Teller interactions. There is evidence that both an anisotropic spin exchange contribution to D = 0.0159 cm−1 and a coupled (static) Jahn—Teller effect are responsible for efficient coupling between the four Cu(II) ions in the grid complexes with non-substituted pyrimidine bridges.

Structural Characterization of YMexMn1−xO3 (Me=Cu, Ni, Co) Perovskites

The structural properties of the YMexMn1−xO3 (Me=Cu, Ni, Co) pseudobinary oxides have been studied by X-ray diffraction and electrical measurements. The powders were prepared by solid state reaction between the corresponding oxides. The incorporation in solid solution of small divalent cations, Cu2+, Ni2+, and Co2+, substituting for Mn in the hexagonal YMnO3 compound, leads to a phase transition in which a perovskite-type structure is formed. The amount of substituting cation necessary for such a transition depends on the cation nature and, to a small extent, on the ionic radius. The phase transition depends strongly on the progressive substitution of the Jahn–Teller Mn3+ cation and therefore of the cooperative Jahn–Teller interaction weakness. The steric influence plays a secondary role, as is shown by the very small variation of the tolerance factor, t, as a function of the cation content. The solid solutions with perovskite-type structure show semiconducting behavior. The conductivity mechanism is of a thermally activated small polaron hopping.

Crystal structure, ferromagnetostructural behavior and evidence of cooperative Jahn–Teller interactions of the complex [CuL]Cl·H 2O (L= N-glycyl-2(aminomethyl)benzimidazol), synthesized by a novel simple method of peptide bond formation.

[CuL]Cl·H 2O 1 (L= N-glycyl-2(aminomethyl)benzimidazol) compound crystallizes in the orthorhombic space group Pna2 1 with unit cell parameters a=7.140(5) A ̊ , b=17.621(5) A ̊ , c=9.941(5) A ̊ . Its structure shows that the copper(II) ion is tetra coordinated with a square planar geometry. The ligand acts as a tridentate and the chloride ion is the fourth ligand. Symmetry related units stack into helicoidal columns along the ā direction producing weakly bonded strips with dihedral angles of 2.6° between two consecutive molecular planes. UV/VIS spectrum of 1 shows one broad and weak band at 622 nm, characteristic of d–d transitions, indicative of low local Cu(II) symmetry. X band ESR spectra of 1 at 300 and 77 K are axial exchange narrow lines with g ∥=2.135 and g ⊥=2.028. However, the axial spectrum at 6.4 K shows an increment Δ g ∥=0.076(6) and Δ g ⊥=0.028(4) which suggests a cooperative Jahn–Teller interactions between complexes via the hydrogen-bonding network. Magnetic susceptibility data at 18–300 K and fitted to the modified Bleany–Bowers equation indicate a weak ferromagnetic coupling with 2J≅+17 cm −1, which is compatible with the helium temperature ESR results and with the helicoidal stacking into columns of the molecules along the a-axis with 78.9° Cu′–Cl′–Cu and 81.2° Cu′–N( 1)–Cu bonds angles. The synthesis is a novel, simple and efficient method: in aqueous conditions and heterogeneous phase with basic copper(II) carbonate, which carries out the formation of the stable peptide bond.

Theoretical Study of Pressure Effect on TDAE-C60

We have theoretically studied pressure effects on molecular ferromagnet C$_{60}$ complexes with tetrakis (dimethylamino) ethylene (TDAE), particularly the pressure-induced depression of the Curie temperature. The observed behavior is well simulated with our model based on a charge transfer induced intramolecular Jahn-Teller distortion and an intermolecular cooperative Jahn-Teller interaction. We emphasize that the theoretical simulation is carried out with reasonable parameters known for C$_{60}^-$ complexes. It is concluded that the enhancement of crystal field at C$_{60}$ site due to increasing pressure causes the depression of Curie temperature.

Electronic Factors Influencing the Local and Cooperative Jahn-Teller Interactions in Spinels with Copper(II) and Nickel(II)

Optical spectra and structural data of mixed crystals Cu x Zn 1- x Cr 2O 4, Ni x Zn 1- x Cr 2O 4, and Cu 1- x Ni x Cr 2O 4 are reported. The optical results are used as a probe characterizing the d -contributions to the Cu-O bonds. The cooperative Jahn-Teller forces are analyzed, extending the statistical model by Wojtowicz to the tetrahedral sublattice. Thermodynamical and optical data are used to estimate the corresponding cooperative strain energies. A microscopic bonding model is proposed which is based on the bonding properties of the oxygen ligands with respect to Cu 2+ due to the presence of the "contrapolarizing" Cr 3+ cations. This concept makes it possible to understand the enhancement of the local Jahn-Teller distortions with increasing cooperativeness.

ChemInform Abstract: The 5‐ and 6‐Coordinated Copper(2 +) Complexes with Terpyridine Ligands ‐ Cases v of Dynamic, Static and Cooperative Jahn‐Teller Interactions

Chemischer InformationsdienstVolume 17, Issue 38 Reviews ChemInform Abstract: The 5- and 6-Coordinated Copper(2 +) Complexes with Terpyridine Ligands - Cases v of Dynamic, Static and Cooperative Jahn-Teller Interactions D. REINEN, D. REINENSearch for more papers by this author D. REINEN, D. REINENSearch for more papers by this author First published: September 23, 1986 https://doi.org/10.1002/chin.198638360Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue38September 23, 1986 RelatedInformation

ESR studies of the state of Ti3+ and Ti2+ in Ti−Mg catalysts for olefin polymerization

ESR studies have revealed that in Ti−Mg catalysts after interaction with organoaluminium compounds, the Ti3+ ions formed are present mainly as TiCl3 associates. Isolated Ti3+ ions of various types are also detected. Part of titanium ions is in the divalent state and provides an ESR signal after oxidation by water to the trivalent state in the form of Ti3+ ordered by cooperative Jahn-Teller interaction.

Local and cooperative Jahn-Teller interactions of copper(2+) in host lattices with tetragonally compressed octahedra. Spectroscopic and structural investigation of the mixed crystals K(Rb)2Zn1-xCuxF4

Local and cooperative Jahn-Teller interactions of copper(2+) in host lattices with tetragonally compressed octahedra. Spectroscopic and structural investigation of the mixed crystals K(Rb)2Zn1-xCuxF4