Dependence of the Cl- → Cu2+ charge transfer with hydrostatic pressure in the pure and Cu-doped A2MCl4 (M = Mn, Cd, Cu) layer perovskite.: Structural correlations

This work investigates the dependence of the Cl- --> Cu2+ Charge Transfer (CT) bands with the local structure around Cu2+ in the Jahn-Teller CuCl64- complexes formed in layer chloroperovskites with the K2NiF4-type structure. We present experimental results on the variation of the first CT band of CuCl64- with hydrostatic pressure in the 0-80 kbar range. The study has been carried out in CuCl64- formed either as impurity in Cu2+-doped crystals or in pure A(2)CuCl(4) compounds in order to establish structural correlations. A noteworthy feature is the redshift undergone by the first CT band at about 26 000 cm(-1) upon pressure in all the investigated systems. This redshift is interpreted in terms of anisotropic distortions of the octahedral elongated CuCl64- complex. MS-X alpha and Extended Huckel calculations of the electronic structure around the D-4h equilibrium geometry allow us to establish correlations between the energy shift and the structural distortions of the complex.