Comparison of the Complexation of Open‐Chain and Cyclic N 2 S 2 Ligands with Cu + and Cu 2+

The complexation properties of the open‐chain N 2 S 2 ligands 1–4 are described and compared to those of analogous N 2 S 2 macrocycles 5–7 . With Cu 2+ , the open‐chain ligands give complexes with the stoichiometry CuL 2+ and CuLOH + , the stabilities and absorption spectra of which have been determined. The ligand field exerted by these ligands is relatively constant and independent of the length of the chain. With Cu + , the species CuLH   2 3+ , CuLH 2+ , and CuL + were identified and their stabilities measured. The redox potentials calculated from the equilibrium constants and measured by cyclic voltammetry agree and lie between 250 and 280 mV against SHE . The comparison between open‐chain and cyclic ligands shows that ( 1 ) a macrocyclic effect is found for Cu 2+ but not for Cu + , ( 2 ) the ligand‐field strength is very different for the two types of ligands, and ( 3 ) the redox potentials span a larger interval for the macrocyclic than for the open‐chain complexes.