Flexible Mono- and Bis-tetraazamacrocyclic Complexes of Copper and Nickel Stabilizing Different Oxidation States

The synthesis and structural properties of new mono- and bis-macrocyclic cyclidene complexes of copper(II) andnickel(II) are presented. The compounds with aliphatic ligands are flexible enough to stabilize metal centers in the three oxidation states +1, +2, and +3. All the electron-transfer processes in the 16-membered mono- and binuclear macrocyclic complexes of copper(II) and nickel(II) were fast and reversible. Two polymorphic forms of the 16-membered mononuclear complex of nickel(II) were isolated in the solid state and characterized. The 16-membered macrocyclic complexes show both U- and Z-shape conformations. The deviation of the macrocyclic ligand from planarity affects the electrochemical properties of the complexes and leads to stabilization of different oxidation states of the Cu and Ni metal centers. Substitution of the exocyclic nitrogen atoms with a second alkyl group increases the deviation from planarity and induces rotation of the functional groups at the meso position relative to the macrocyclic ring. In the bis-macrocyclic complexes, the electron-donating properties are improved and the formal potential of the metal(II)/metal(III) system is less positive with increasing linker length between the macrocyclic units. The acceptor properties of the metal(II) complexes are weaker, the formal potential of the metal(II)/metal(I) couple being shifted to more negative values.