Tuning of the [Cu3(μ-O)]4+/5+ redox couple:: Spectroscopic evidence charge delocalization in the mixed-valent [Cu3(μ-O)]5+ species

Trinuclear Cu-II-complexes of formula [Cu-3(II)(mu(3)-E)(mu-4-R-pz)(3)X-3](+/- n), E = O and OH; R = H, Cl, Br, CH(O) and NO2; X = Cl, NCS, CH3COO, and py, have been synthesized and characterized and the effect of substitution of terminal ligands, as well as 4-R-groups, in the one-electron oxidation process has been investigated by cyclic voltammetry. In situ UV-vis-NIR spectroelectrochemical characterization of the mixed valence Cu-3(7+)-complex [Cu-3(mu(3)-O)(mu-pz)(3)Cl-3](-) revealed an intervalence charge transfer band at 9550 cm(-1) (E = 2600 cm(-1) M-1), whose analysis identifies this species as a delocalized, Robin-Day class-III system, with an electronic coupling factor, H-ab, of 4775 cm(-1).