Tuning of the [Cu₃(μ-O)]^4+/5+ Redox Couple: Spectroscopic Evidence of Charge Delocalization in the Mixed-Valent [Cu₃(μ-O)]⁵⁺ Species

Trinuclear CuII-complexes of formula [CuII3(μ3-E)(μ-4-R-pz)3X3]±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 Cu37+-complex [Cu3(μ3-O)(μ-pz)3Cl3]− revealed an intervalence charge transfer band at 9550 cm−1 (ε = 2600 cm−1 M−1), whose analysis identifies this species as a delocalized, Robin−Day class-III system, with an electronic coupling factor, Hab, of 4775 cm−1.