The synthesis and structural properties of tetraazamacrocyclic ligands and their neutral and protonated 14-, 15- and 16-membered complexes of CuII and NiII 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 increasing macrocycle size. As a consequence the donor properties are weaker, the redox potential is shifted towards more positive values and the contribution of chemical reactions can be observed. The formation of host–guest complexes between the strongest metal-containing donors and transition-metal-containing bismacrocyclic acceptors of suitable size is proved in solution and the gas phase by voltammetric and ESI MS methods. The transition metal building blocks described in this contribution can be applied in the synthesis of new redox-active rotaxane and catenane systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)