AB-INITIO CALCULATIONS OF THE ELECTRON-TRANSFER MATRIX ELEMENT IN CU-I-CU-II MIXED-VALENCE COMPOUNDS

A theoretical analysis of the electron-transfer matrix element, V-ab, for some cluster models intended to mimic the properties of the [NEt4] [Cu2Cl4] mixed-valence compound prepared by Willet et al.(1) is report ed. On the basis of ab initio unrestricted Hartree-Fock calculations, both V-ab and the potential energy profiles versus an idealized electr on-transfer reaction coordinate have been calculated for different sce narios. Our best estimate for V-ab is found to be 971 cm(-1) in agreem ent with experimental related work. The physical factors governing the amplitude of the electronic coupling as well as the shape of the ener gy profiles have been analyzed. It is shown that in order to account f or a correct type II behavior within the Robin-Day classification, the polarization effects induced on the cluster by the environment have t o be included. The dependence of V-ab on the nature of the ligands bri dging the Cu-I-Cu-II centers is discussed. Our results for a family of compounds of formula [(Cl2CuX2CuCl2)-X-I-Cl-II](3-) (X = Cl-, OH-, SH -) show that both V-ab and the energy profiles are largely dependent o n the nature of X.