Ahetraet-The dynamic Jahn-Teller distortion in single crystals of Cu" doped magnesium Tutton's salt, MgK2(S0&.6Hz0, was studied by EPR spectroscopy. The directions of the g tensor axes were found to coincide with those of A at room temperature as well as at 113 K and were correlated with the Mg-0 directions in the lattice. Two spatially distinct sites of copper were detected in the crystal. The g and A values were also calculated from the polycrystalline samples at various temperatures. A &,zground state has been assigned for Cu", as in the isomorphous zinc Tutton's salt. The Silver and Getz model was applied to understand the dynamics of Jahn-Teller (JT) activity. The system was found to undergo dynamic JT distortion at all temperatures. At low temperatures, the [CU(H~O),]~' ion has three possible degenerate vibronic states corresponding to three possible directions for the long axis of the octahedron. The energy separations between the three inequivalent JT valleys were estimated as 6,. 2 = 90 and 61.J= 370 cm-'. The lattice strain parameter V, and the JT stabilization energy EJT were also estimated as 19,140 and 1030 cm-' respectively. From the EIT value, the JT distortion present in the system was classified as a case of "strong" coupling. WE HAVE studied the EPR spectra of Cu I* doped single crystals to understand Jahn-Teller distortion and its ground state in low symmetry environments [l-6]. When the crystal symmetry is octahedral, the Cu" ion, with d9 electronic configuration, has the ground state arrangement of six electrons in the low lying tzg orbital and the other three electrons in the doubly degenerate eg orbital [7-lo]. The orbital degeneracy is lifted either by a lowering in symmetry arising due to charge compensating vacancies, crystalline fields etc., or by Jahn-Teller distortion [ 111. The ground state will be d+,,2 or d,2 depending upon whether the tetragonal distortion is an axial elongation or compression, respectively. In most of the cases, the symmetry is low enough to lift the orbital degeneracy without the necessity of invoking Jahn-Teller distortion. In the majority of Cu" systems studied so far, the ion was found to have a 4 ~2 ground state corresponding to the axial elongation. The d,zground state has been observed only in a few cases, like Cu" in Hoffmann-type benzene and aniline clathrates [5], K,CuF, [12], CU(NH~)~C~~ [I3], Cu(NH3)2Br2 [131, WdW2WM2
P41, W-U2WNH3)2(Cr04)2 141, etc. me axial compression arises, in all these cases, due to two of the octahedrally disposed ligands coming closer to the copper due to crystal packing. We have proved [5] in our laboratory that when the external forces imposed by the crystalline structure are removed, the octahedrally compressed copper complex will revert back to tetragonal elongation. This was seen in our EPR studies on Cu" doped Hoffmann-type benzene and aniline clathrates, where a change in the ground state from 42to dXLy2 was observed in going from clathrated to declathrated complex. The low symmetry crystal fields have very interesting consequences on the electronic structure of Cu", the important one being mixed dx2-y2 and d z2 ground states [ 151. Examples of mixed ground states are Cu" in ZnF, [16], &catena p-sulphato-aquo-tris(imidazol)cadmium(II)
[17], Zn(nap), (4-MePy)2, Zn(hfa)2(2,2'-bipy) and Zn(hfa)2(Py)2 [18]. Such mixed ground states lead to orthorhombicity of g tensors and low magnitudes of hyperiine coupling. In fact, the hyperfine coupling values observed in our laboratory for Cu" in single crystals of dinitrotris(antipyrine) zinc(I1) [6] were the lowest ever reported in the literature. In this paper, we report the single crystal and powder EPR studies of Cu" in magnesium Tutton's salt, MgK2(S04)2-6H20 (abbreviated as MPSH), in the temperature range of 360 to 77 K. The results were interpreted considering a 4+2ground state