The synthesis and structural properties of tetraazamacrocyclic ligands and their neutral and protonated 14-, 15-and 16-membered complexes of Cu II and Ni II are described. Molecules of the free 14-membered ligands have a nonplanar, step-like structure of the central molecular fragments. Conformational changes are introduced upon protonation, with the protons pointing above and below the macrocycle plane. This prevents the formation of intramolecular N-H···N hydrogen bonds. On insertion of the transition metal ions a planar structure of the macrocycle is obtained, which has consequences for the electrochemical behaviour of the complexes. The deviations from planarity increase with increas-

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