Successive Ligand and Metal Oxidation: Redox Reactions Involving Binuclear CuI Complexes of Chelating Guanidine Ligands

New binuclear complexes of three-coordinate Cu-I have been synthesized with the ligand 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb). Subsequent oxidation of the ligand unit was achieved by reaction with Br-2 or I-2. Reaction with Br-2 leads to oxidation of both the ligand and the copper ions and formation of a bicationic dinuclear Cu-II complex. On the other hand, oxidation with I-2 leads only to oxidation of the ligand during the first step. A metastable coordination polymer of ladder-type structure results, in which the coordination number of the Cu-I ions increases to four. Electrical measurements show that this polymer is semiconductive with a band gap of around 1 eV. The electronic structure of the polymer was further studied by X-ray photoelectron spectroscopy (XPS), Raman and Vis/NIR spectroscopy It decomposes (with oxidation of the copper ions) in an exothermal reaction at temperatures around 230 degrees C. Oxidation of the copper ions and decomposition of the polymer can also be achieved by reaction of the polymer with phenanthroline.