Strong Closed-Shell Interactions in Inorganic Chemistry.

The causes of the previously reported temperature dependence of the g values of the Cu(H2O)2+ 6 ions in Cu2 +doped Zn(H2O)6(GeF6) and the Tutton’s salts M2Zn(H2O)6(SO4)2, where M=K+, Rb+, NH+ 4, and Cs+, supplemented by new experimental measurements on the K+ salt, have been investigated. The ground state dynamics of the complexes have been modeled on the cubic E×e Jahn–Teller Hamiltonian perturbed by an orthorhombic lattice strain. For each compound, the vibronic energy levels and associated wave functions were calculated numerically, the overall g values at any temperature being given by a thermal average of the g values of the individual vibronic energy levels, because of rapid exchange between the levels. For the Tutton’s salts it was found that the low temperatureg values are strongly influenced by the tetragonal component of the lattice strain, with this corresponding to an axial compression of the ligand field. The temperature dependence of the gtensors, on the other hand, was found to depend largely on the orthorhombic component of the lattice strain. For the K+ and NH+ 4 salts, where structural data are available, the strain parameters derived using the model are in good agreement with the geometries reported for the Zn(H2O)2+ 6 host complexes. For Cu2 +doped Zn(H2O)6(GeF6) the model implies a lattice strain of tetragonal symmetry corresponding to a slight elongation of the axial metal–ligand bonds. The results are compared with those reported previously by Silver and Getz, and other workers, who used a simple model involving temperature dependent equilibria between energy levels corresponding to different orientations of the Cu(H2O)2+ 6 ions in the host lattices to interpret the temperature dependence of the gtensors.

https://espace.library.uq.edu.au/view/UQ:255898/UQ255898_OA.pdf

Interpretation of the temperature dependent g values of the Cu(H2O)2+6 ion in several host lattices using a dynamic vibronic coupling model

An inventory of the structural chemistry of thallium(I) shows many unexpected, almost random coordination numbers and coordination geometries that appear erratic and inconsistent. This nonstandard behavior is often ascribed to the specific lone-pair characteristics originating from relativistic effects. To provide data on a set of closely related compounds from which simple general rules of coordinative bonding at Tl(+) can be established, three thallium(I) anthranilates and three thallium(I) salicylates have been prepared from Tl(2)CO(3) and the corresponding 2-amino- and 2-hydroxy-benzoic acids and crystallized from aqueous solutions. All six compounds, the simple anthranilate (1) and salicylate (4) and the 3- and 4-methyl-substituted homologues (2, 3 and 5, 6) show different structures with large variations in the coordination motif. The coordination by oxygen in a geometry which covers less than a coordination hemisphere is the only common feature, complemented (only in 1) by a nitrogen coordination and by eta(6)-coordination of one (in 1, 2, 3, 6) or two phenyl rings (in 4). Tl-Tl contacts for which "thallophilic" bonding between closed shell metal atoms could be invoked, are generally very long (close to 4.0 A) or even well beyond the limit of standard van der Waals contacts. Hydrogen bonding is only obvious for the internal contacts of the amino- or hydroxy-benzoate ligands and does not contribute significantly to the assembly of the supramolecular structure which is dominated by oxygen bridges between thallium atoms. With the exception of 5, the formula units Tl[O(2)C(2-R)(3-R')(4-R'')C(6)H(2)] are generally aggregated into dimers of various configurations depending on the relative orientation of the edge-sharing four-membered rings, and these dimers are further linked into strings or columns establishing N-Tl or Tl-O contacts and arene coordination. The drastic changes induced in the structures upon only small variations such as methyl substitution in 3- or 4-position of the ligand suggest that thallium(I) coordination is generally restricted to one hemisphere of nearest neighbors, but is extremely flexible in this realm. The open hemisphere may be partially capped by arene coordination (which is weak at a distance of ca. 3.1 A to the centroid of the ring) or feature very weak thallophilic contacts.

Complexity of coordinative bonding in thallium(I) anthranilates and salicylates.

Effects of vibronic coupling on the EPR spectra of copper(II) doped K2ZnF4

The crystal structure of the deuterated Tutton salt (ND4)2[Cu(D2O)6](SO4)2 determined by X-ray diffraction at several temperatures between 100 and 321 K is reported. The intermediate and longest Cu−O bond lengths of the Jahn−Teller distorted octahedral Cu(D2O)62+ ion progressively converge as the temperature is raised above ∼200 K, and this is accompanied by a partial rotation of the ammonium and sulfate groups. The g-values derived from the EPR spectrum of the compound exhibit similar behavior, as do those of ∼1% Cu2+ doped into the isomorphous zinc(II) compound. The temperature dependence of the g-values of Cu2+-doped (ND4)2[Zn(D2O)6](SO4)2 may be interpreted satisfactorily by a model which assumes a Boltzmann thermal distribution between two energy states which differ solely in the orientation of the Cu(D2O)62+ ion in the lattice. However, such a model does not satisfactorily explain the behavior of pure (ND4)2[Cu(D2O)6](SO4)2, and it is suggested that this is due to cooperative interactions. A new mod...

Cooperative Jahn-Teller Interactions in dynamic copper(II) complexes. Temperature dependence of the crystal structure and EPR spectrum of deuterated ammonium copper(II) sulfate hexahydrate

EPR of Cu(H2O) pseudo Jahn-Teller (JT) centres in dia- and paramagnetic Tutton salt crystals A2M(SO4)2. 6H2O (I) with A = Rb, Cs, NH4 and M=Zn, Cu and K2M(ZrF6)2. 6H2O (II) crystals in the temperature range 300 to 4.2 K at frequencies 9.5 and 37 GHz is studied. The dynamic JT nature of Cu(H2O) centres in the whole class of Tutton salt crystals is established basing on the results of EPR study and X-ray data. The influence of the lowering of lattice symmetry on the configuration and properties of centres and crystals is analyzed. The character of the distortion of Cu(H2O) complexes in “copper” crystals I and II is discussed in terms of cooperative JT effect. The main JT parameters of Cu(H2O) complexes for the crystals under consideration are estimated.



[Russian Text Ignored].

The Lattice Structure Parameters and Configuration of Cu2+ Jahn-Teller Centres in Tutton Salt Crystals

The dynamics of the (NH4)2SbF5 crystal lattice showing the superionic phase transition is studied in a broad temperature interval by NMR and NQR methods, together with electrophysical and calorimetrical properties. The investigations establish the ionic state of the axial fluorine atom in relation to equatorial atoms in the [SbF5]2− complex. The successive phase transitions are revealed and the mechanism of phase transitions is elucidated. The phase transitions are caused by the reorientation movements of NH4 and [SbF5]2− groups. The paper also describes the influence of water solution inclusions in the crystal on the superionic phase transition.

Peculiarities of phase transitions and physical properties in (NH4)2SbF5

Results are presented of the investigation of the dielectric and acoustic properties of K3BiCl6 · · 2 KC1 · KH3F4 crystal which undergoes an improper ferroelectric phase transition at Tc = 130K. In the paraelectric phase the dielectric permittivity does not depend on temperature or frequency. In the ferroelectric phase relaxational dielectric dispersion of the Debye type occurs along the polar c-axis in the frequency range 105 to 1011 Hz. It is characterized by two relaxation times, τd = 1.3 × 10−9 s and τ 1.5 × 10−11 s. The dispersion in the interval 105 to 109 Hz is caused by the domain walls and produces the main contribution Δed = 40 to the static dielectric per-mittivity of multi-domain crystals and the changes in the ultrasound velocity and attenuation. The dielectric contribution of the ferroelectric dispersion in the frequency range 1 to 80 GHz is Δe = 10 and e∞ = 10.



Ergebnisse der Untersuchung der dynamischen dielektrischen und akustischen Eigenschaften des Kristalls K3BiCl6 · 2 KC1 · KH3F4, der bei Tc = 130 K einen unechten ferroelektrischen Phasen-ubergang aufweist, werden mitgeteilt. In der paraelektrischen Phase ist die Dielektrizitatskontante weder von der Temperatur noch von der Frequenz abhangig. In der ferroelektrischen Phase fallt die relaxationelle dielektrische Dispersion des Debye-Typs in der Richtung der polaren Achse in den Frequenzbereich 105 bis 1011 Hz, wobei die Dispersion durch zwei Relaxationszeiten. namlich τd = 1,3 × 10−9s und τf = 1,5 × 10−11 s, charakterisiert wird. Im Frequenzbereich 105 bis 109 Hz wird die Dispersion durch die Domanenwande bedingt und macht den Hauptanteil an der stati-schen Dielektrititatskonstante, an der Anomalie des Abklingens und an der Geschwindigkeits-veranderung des Ultraschalls aus. Die ferroelektrische Dispersion liegt jedoch im Frequenzbereieh von 1 bis 80 GHz, ihr dielektrischer Anteil ist Δe = 10 und e∞ = 10.

Relaxational Dynamics of the Improper Ferroelectric K3BiCl6 · 2 KC1 · KH3F4

Phase transition in ZnGeF6 · 6H2O

19F NMR spectra and relaxation times T,1, T2, T1e and electric conductivity in isostructural polycrystalline pentafluoroantimonates (III) M2SbF5 (M = Rb, K, Cs, Tl, NH4) are measured. It is found that the observed changes in the NMR spectra and relaxation times with temperature are determined by three types of motion: anisotropic and isotropic reorientations of [SbF5E]2− octahedra and diffusion motion of the fluorine ions. Parameters of these motions are found. All the compounds investigated show high conductivity at high temperature, amounting in the case of thallium and ammonium salts the values of σ = 101 to 100Ω−1 m−1 typical of superionic crystals. It is shown that the observed high conductivity is determined by fast diffusion motion of fluorine ions. On the basis of the data obtained a mechanism of fluorine ion diffusion is proposed. In (NH4)2SbF5 at 398 K a phase transition is found.



[Russian Text Ignored].

R. L. Davidovich

Papers

The Lattice Structure Parameters and Configuration of Cu2+ Jahn-Teller Centres in Tutton Salt Crystals

Peculiarities of phase transitions and physical properties in (NH4)2SbF5

Relaxational Dynamics of the Improper Ferroelectric K3BiCl6 · 2 KC1 · KH3F4

Phase transition in ZnGeF6 · 6H2O

NMR Study of Internal Motions in a New Family of Ionic Conductors M2SbF5