Charge-transfer transitions in CuCU 42− and CuBr 42− complexes: dependence on the metal-ligand distance

Abstract

Charge-transfer (CT) transitions in CuCl 4 2− and CuBr 4 2− are studied through SCF MS Xα calculations (using overlapping spheres and the Norman procedure) at different values of the metal-ligand distance, R. The calculated values of three CT transitions agree with experiment for CuCl 4 2− and explain the blue-shifts detected on going from (N-mpH) 2CuCL 4 to (creat) 2CuCl 4 as being due to the decrease of the average R value. The allowed CT bands ofCuBr 2−P 4 are predicted to undergo a red-shift of ≈ 7000 cm −1 with respect to those of CuCl 4 2− in agreement with the optical electronegativity scale. The present work predicts that the two 3e u → 3b lg and 2e u → 3b 1g, transitions are more sensitive to R than their energy separation, Δ (π, σ), in accordance with results on LiC:Cu 2+ and supports a value for the 3d charge in the 3b lg level of CuBr 4 2− of close to 50%.