Is it possible to use charge transfer bands to measure impurity-ligand distances?: Experimental and theoretical results on Cu2+ doped (C2H5NH3)2CdCl4

The present work is focused on the effects produced by hydrostatic pressure on Cu2+ (<100ppm) doped (C2H5NH3)(2)CdCl4 single crystal. The energy E-u(pi) of the e(u)(pi) --> b(1)g(similar tox(2) - y(2)) charge-transfer transition of (C2H5NH3)(2)CdCl4: Cu2+ undergoes a red shift of 1400 cm(-1) on passing from ambient pressure to 40 kbar. To understand this fact theoretical calculations of the CuCl64- complex using four different methods have been carried out. Based on these calculations, it is concluded that the experimental red shift undergone by E-u(pi) can only be reasonably explained through a decrease of similar to25 pm in R-ax and an increase of similar to7 pm in R-eq leading to a decrement of the CuCl64- volume. Variations of any metal-halide distances down to 0.1 pm can be well detected through the shifts of the charge-transfer band energy upon pressure.