An Unusual Dimeric Structure of a Cu(I) Bis(thiosemicarbazone) Complex:  Implications for the Mechanism of Hypoxic Selectivity of the Cu(II) Derivatives

The electrochemical reduction of Cu(II) bis(thiosemicarbazone) complexes [Cu(II)(btsc)] is accompanied by protonation to give an unstable Cu(I) intermediate [Cu(btscH₂)]⁺. The nature of this intermediate was probed by reaction of bis(thiosemicarbazone) ligands with a Cu(I) precursor which gave a novel helical dimeric dicationic complex. The dependence of these reactions on the ligand backbone substituents is discussed together with their possible relevance to the use of Cu(II) bis(thiosemicarbazone) ligands as hypoxic selective imaging and therapeutic agents.