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

Abstract

EPR of Cu(H2O) 2+6 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) 2+6 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) 2+6 complexes in “copper” crystals I and II is discussed in terms of cooperative JT effect. The main JT parameters of Cu(H2O) 2+6 complexes for the crystals under consideration are estimated.

Vibronic Effects in EPR Spectra of (NH4)2Cu(BeF4)2·6H20 Single Crystal

“…A characteristic feature of the EPR of Cu(II) ions in the Tutton salt crystals is that the g-faction and hyperfine splittings are temperature dependent for admixture Cu(II) ions, whereas for the Cu(H) salts the g-factors are practically temperature insensitive with exception of (NH4)2Cu(SO4)2 • 6H2O where such dependence was reported [6,7]. The g-faction exhibit a vibronic type behaviour (pseudoJahn-Teller effect) with an averaging tendency for the two larger g-faction (gz and gy ) on heating, whereas the gx value appearing along the shortest Cu-O(9) bond only weakly increases with temperature.…”

“…6H2O crystal [11] we have found a vibronic g-factor behaviour, which is however, much weaker as compared to that found in (NH4)2Cu(SO4)2 . 6H2O [7]. We will describe this behaviour in terms of the existing models and discuss their validity in condensed Cu(II) paramagnets.…”

“…In all Tutton salts of alkali metals the octahedra are elongated along the Cu-O(8) bond, according to the crystallographic notation [6], whereas in (NH4)2Cu(SO4)2 • 6H2O the octahedron elongation appears along the Cu-O(7) bond which can be due to the hydrogen bonds between NH+4 ions and coordinated water molecules. The Cu-O distances continuously increase on cooling demonstrating the complex fluxional behaviour and the values of the Cu-O bond lengths are determined by a balance between dynamical Jahn-Teller forces and lattice strains, although some contributions from a cooperative Jahn-Teller type interaction between Cu(II) complexes can be expected [7].…”

Restricted Validity of the Two-State Model Describing a Vibronic EPR g-Factors Averaging in Cs2Zn(SO4)2·6H2O Tutton Salt Crystals Doped with Cu2+Ions

“…This model has been successfully used for a description of Cu(H2O)P 2 + 6 vibronic complexes behaviour in K 2 Zn(SO4 ) 2 • 6H 2 O and after a generalization by Hitchman et al [2] it was found as a good approximation in some diamagnetic Tutton salt crystals doped with Cue+ ions [3]. However, a clear deviation from predictions of the model was found in ammonium Tutton salts [4], especially in (NH4 ) 2 Mg(SO4 ) 2 • 6H 2 0 [5].…”

“…The deformation of the hexaaqua octahedra in diamagnetic salts is rather small but becomes large, due to the strong Jahn-Teller effect in Cue+ doped salts. In Cs 2 Cu(SO4 ) 2 •6H2O the molecular structure of the Cu(H20) 6-complex is known [3] …”