Stepwise incorporation of copper(II) into a double-ring octaaza macrocycle and consecutive oxidation to the trivalent state

The double-ring octaaza macrocycle bisdioxocyclam (I) was prepd. by the single-step aminolytic condensation of the appropriate tetraester and linear tetraamine in 1:2 molar ratio. The complexation of Cu(II) by I in aq. soln. was studied by potentiometry. Monometallic and dimetallic complex species form according to the ligand:metal ratio. In general, incorporation of Cu(II) ion into each tetraaza subunit promotes a simultaneous deprotonation of the 2 amido groups. The log k values of complexation equil. are compared with those for the ref. single-ring tetraaza macrocycle dioxocyclam. The [CuII2(bisdioxocyclamato(4-))] complex undergoes a reversible oxidn. to the dicopper(III) complex through 2 consecutive 1-electron steps, whose electrode potentials are sepd. by 110 mV.