MODELS OF SOLID-STATE INFLUENCES IN SYSTEMS WITH JAHN-TELLER DISTORTIONS*) R. Bo6a, M. Breza Department of lnorganic Chemistry, Slovak Technical University, 812 37 Bratislava, Czechoslovakia A system wlth the Jahn-Teller distortion, namely the complex CuC164-, has been investigated in various surroundings represented by [CuCI~- ... n Na+] a clusters. The degree of the tetra- gonal distortion has been calculated using the quantum-chemical CNDO method and compared with values produced by the point-charge model. INTRODUCTION Hexahalogen complexes of Cu(II) are known as systems exhibiting considerable tetragonal distortions from the ideal octahedral geometry [1, 2]. Although the Jahn- Teller mechanism of these distortions has been accepted in general, a more detailed understanding of particular factors operating in such distortions meets specific problems [3]. Theory of vibronic interactions is capable to predict an analytic form of the adiabatic potential surface (the total energy function of nuclear coordinates). Usually a "Mexican hat" type of potential (with an additional warping) results from the theoretical analysis of the Eg-eg or Eg-(a~ g+ eg) vibronic coupling [4-6]. Its para- meters, i.e. the elastic force constants and the vibronic coupling constants, may be determined by combining various experimental techniques [7]. However, such an interpretation of experimental data in terms of parameters of a Mexican hat type potential is complicated by the fact that experiments are done for solid state materials where a local symmetry of individual coordination polyhedra is often disturbed by their counterparts in the lattice. In other words, the adiabatic potential of an isolated complex, ET, is modified by a non-scalar lattice potential VL, SO that the real situation is more closely described by the potential of ET + VL. Its extremum points may have different characteristics when compared with the potential Er. Nevertheless, quantitative studies on solid-state effects in tetragonal distortions of coordination polyhedra are rather scarce [8, 9]. The present communication is focused on a comparison of equilibrium geometries calculated for hexacoordinated complexes with thoae where particular solid-state effects are taken into account. The CuC164- ion serves as a reference complex which is surrounded by several natrium cations. *) Presented at the International Symposium on Solid State Chemistry, October 28--31, 1986, Karlovy Vary, Czechoslovakia. 1230 Czech. J, Phys, B 38 (1988)