Correlation of Zero Field Splittings and Site Distortions III. MnBr₄ ^2- and Crystal Structure Refinements for Rb₃ZnBr₅ and Cs₂ZnBr₄

Abstract

C o r r e la tio n o f Z e ro F ield S p littin g s a n d S ite D is to r tio n s III . M n B r42~ a n d C r y s ta l S tr u c tu r e R e fin e m e n ts f o r R b 3Z n B r 5 a n d C s g Z n BM. Heming and G. Lehmann Institut für Physikalische Chemie, Westfälische Wilhems-Universität, Münster and G. Henkel and B. Krebs Institut für Anorganische Chemie, Westfälische Wilhelms-Universität, Münster Z. Naturforsch. 36a, 286-293 (1981); received January 31, 1980 EPR data for Mn2+ in Cs2ZnBr4, Rb3ZnBr5, Cs3CdBr5 and [(CH3)4Nl2ZnBr4 single crystals were determined and the crystal structures of Rb3ZnBrs and Cs2ZnBr4 were refined. Superposition analysis of the fine structure data for the latter two compounds resulted in an intrinsic zero field splitting parameter 62 for MnBr42_ of + 0.44 cm-1 suggesting a sizeable positive contribution of covalency. Cs3CdBrs was prepared in single crystals for the first time. It crystallizes in a primitive tetragonal space group. From the fine structure parameter 62° and the above value of 62 an elongation of the CdBr42~ tetrahedra along the c-axis with a bond angle of 105.7° was deter mined. This result is in agreement with the anisotropy of the 55Mn hyperfine splitting constant with A\\ = -68.6 and A±= -70.6 • 10~4 cm~i. IntroductionThe zero field splittings of S-state ions are -at least for their largest part -determined by the distortions of their first coordination spheres. Growing though not yet generally accepted evidence for this statement stems from quantitative correla tions of sign and size of the second order axial split ting parameter 62° with deviations of bond angles [1] and bond lengths [2] from cubic symmetry, from evaluation of uniaxial strain data for Mn2+ and Fe3+ in MgO and CaO [3] and from various applications [4][5][6] of the superposition model of Newman [7]. With a very large body of available EPR data such correlations are in most cases limit ed by the accuracy of the necessary crystal struc ture data (if complete parameter sets are at all available). For Fe3+ the sign of 62° is also still un known in many cases. Almost completely unknown is the dependence of the intrinsic zero field splitting parameter b2 [7] on the type of ligand, since the available data are restricted to a few ligands only.As part of a systematic study, EPR data for MnBr42~ in single crystals of four compounds were evaluated. The results for two of these were subReprint requests to Dr. G. Lehmann, Institut für Physi kalische Chemie, Westf. Wilhelms-Universität, Schloss platz 4, D-4400 Münster.jected to a superposition analysis using the results of simultaneous crystal structure refinements for these compounds. The resulting value of b2 allowed for the determination of the distortion angle of the CdBr42_ groups with Ü2d site symmetry in the third compound from the EPR results for Mn2+ in this compound alone. ExperimentalSingle crystals of manganese-doped Cs2ZnBr4, RbßZnBrs and [(CH3)4N]2ZnBr4 were grown by slow evaporation of acidified aqueous solutions of the components at 333 K. In all th...

Superposition Model Analysis of the Spin Hamiltonian Parameters of Two Gd3+ Doped Thorium Dichalcogenides

“…The high sensitivity of our treatment to the distortions is confirmed by the distortion diagrams, introduced in Ref. [18], from which we obtain the values of Tab. 6, to be compared with the experimental values given in Tabs.…”

The Refined Structure of ThS2 and the Implications on the Superposition Model Analysis of ThS2: Gd3+ Spin Hamiltonian Parameters

“…Alternatively, the methods of distortion diagrams introduced in [8] showed that the experimental data could not be fitted with the assumption (2) for the parameters, when the Gd3+ ion was displaced.…”

“…Second degree parameters (units of 10~4cm_1) and direction of the crystal field principal axis for selected values of the Gd3+ in plane displacements. They are deduced from the distortion diagrams [8], using the two exponents power law with the parameters (2). Table 5.…”

Correlation of Zero Field Splittings and Site Distortions V. Mn2+ in Cs2Zn3S4

“…For the meaning of the numbers on the ordinate see Figure 2. Since this is a rotation from v to x, the experimental curve in this case is given by -(b 2 + cos 2 <p • bt)/lb 2 where <p is the angle to the b (the magnetic y) axis. responsible.…”

“…The orientations of the a-and b-axes in the plane of the layers were determined by X-ray precession photographs. EPR measurements were performed on a commercial Q-band spectrometer at room temperature, details of the experimental procedure and the evaluation of numerical data were previously reported [2], [10]. Since the crystals are sensitive against humidity and air, they were handled in a glove box under dry nitrogen and were completely covered with the glue UHU-hart (UHU-Vertrieb GmbH, D-7580 Bühl) during the measurements.…”