Effect of pressure on the Cl-→Cu2+ charge transfer in A2CuCl4 layer perovskites (A = CnH2n+1NH3, n = 2,3) and (3-Chloroanilinium)8[CuCl6]Cl4: structural correlations

The dependence of the Cl^-→Cu²⁺ charge transfer (CT) band at 26 000 cm^-1 with the local structure of the Jahn-Teller elongated CuCl4-6 unit is investigated. For this purpose we report hydrostatic pressure experiments performed on the title compounds. The results indicate that the first CT band experiences a pressure-shift of - 1000 and + 1200 cm^-1 in the 0-80 kbar range for each compound, respectively. This different shift in behaviour is explained by the distinct anisotropic compression of CuCl4-6 related to the crystal dimensionality.