Tetraimine macrocyclic transition metal complexes as building blocks for molecular devices

The synthetic strategy initiated by Busch and further developed in recent years resulted in an impressive variety of new azamacrocyclic ligand superstructures. In this contribution, we have reviewed papers containing general synthetic strategies, structural and electronic properties and results of electrochemical studies for a long series of neutral and charged macrocyclic tetraimine complexes of transition metals leading to a new type of homo- and heteronuclear[2]catenanes as examples of switchable molecular machines. The whole series consists of neutral and charged mono-, bis- and trismacrocycles and appropriate reference neutral molecules and many of their derivatives. The bismacrocyclic moieties are constructed from simpler tetraazamacrocyclic fragments. When two of them are linked through polymethylene chains, they form face-to-face biscyclidenes—rectangular box-like moieties. They can host some small guest molecules (water, π-electron-donating compounds) and are stabilized by hydrogen bonds with solvent molecules or a shell of neighboring counterions. Neutral thiol derivatives are used as recognition sites of monolayers self-assembled on electrode surfaces to be employed in devices based on donor–acceptor interactions.Our catenanes consist of bismacrocyclic transition metal complexes linked by aliphatic chains and interlocked with a substituted crown ether. We have proved that under external stimuli – electrochemical pulses – the heteronuclear catenane exhibits controlled intramolecular relocation of the crown ether between two positions. The relocation is possible due to π⋯π interactions between the aromatic fragments of the crown ether and the transition metal (Ni, Cu) coordinating macrocyclic rings.Our model tetraimine complexes of transition metals can also be used to solve the problem of controlling directional relative movement of molecular fragments present in complex supramolecules. On the way to this aim we have synthesized trismacrocyclic derivatives which are now appropriately modified to serve as components of complex catenanes.