Ring-size effects on the formation of dicopper(II) and dicopper(III) complexes with bimacrocycles, 13- and 14-membered tetraaza subunits

The double-ring macrocycle I, having 13-membered subunits, incorporates 2 CuII ions in aq. soln. in 3 pH-controlled steps, which involve progressive deprotonation of the coordinated amido groups of the ligand. The fully deprotonated neutral dicopper(II) complex undergoes a reversible oxidn. process to the dicopper(III) species according to 2 1-electron redox changes sepd. by 100 mV. This behavior is compared with that of the corresponding bimacrocyclic ligand having 14-membered subunits as well as with single-ring ref. systems. The 14-membered subunit forms the more stable complexes with CuII ion, whereas the 13-membered cavity favors the access to the trivalent state, with both single- and double-ring systems.