research papers
The maximum wavelength λd - d of the transition between d orbitals of tetrachlorocuprates depends on the deformation D of the CuCl42- tetrahedron in these crystals. On the basis of their experimental absorption spectra, the relation between λd - d and D is given for many tetrachlorocuprates so that the symmetry of the CuCl42- ion can be predicted in some other crystals on the basis of the position of the d-d transition.