Copper(ii) and zinc(ii) complexation with N-ethylene hydroxycyclams and consequences on the macrocyclic backbone configuration

Abstract

We report a series of four cyclams and cross-bridged cyclams, N-functionalized by one hydroxyethyl arm, which may incorporate additional methyl(s) group(s). The Cu(II) and Zn(II) complexes of these ligands were synthesized and fully characterized. The investigation of the metal complexes in solid-state and in solution was carried via X-ray diffraction, NMR, EPR, absorption spectroscopy and DFT calculations. The influence of N-functionalization on their structural/stereochemical properties, electrochemical behavior and kinetic inertness was carefully studied and identified. N-Functionalization by a hydroxyethyl group did not influence importantly the stereochemical properties of the complexes. However, it stabilized the complexes kinetically and electrochemically. As for N-methylation, it induces significant distortion of the coordination geometry, decreasing the kinetic inertness of the complexes and stabilizing Cu⁺. Overall, this work expanded the family of cyclam and cross-bridged cyclam metal complexes and provides a detailed analysis of their structural features. The rather large body of data accumulated for this family of complexes provides opportunities to design systems with pre-determined properties for specific applications.