Intrinsic and Lattice-Induced Distortion of the Tetrachlorocuprate Ion

Abstract

In an effort to determine how much of the distortion of the tetrahedral complex, CuCl₄²⁻, may be ascribed to the Jahn—Teller effect, we have studied the changes in the optical and EPR spectra which occur when this ion is embedded in several different lattices. Although the corresponding lattice constants of the isostructural crystals Cs₂CuCl₄ and Cs₂ZnCl₄ differ by only about 3%, gross differences exist between the g tensors of CuCl₄²⁻ suspended in these lattices. These findings are corroborated by a comparison of the optical spectra of the two complexes. The effects are discussed in terms of an LCAO—MO analysis of the primarily 3d(Cu) wavefunctions of the complex, and it is shown that the changes in ionic properties are connected principally with a change in the amount of ligand character in the e, primarily 3d orbitals. The analysis points towards the conclusion that the low symmetry (point group C_s) of the ion is an intrinsic property and that the dominant mechanism of the tetragonal component of the distortion of the ionic symmetry from T_d is the Jahn—Teller effect.