Supramolecular systems: Metallo-molecular machines and stimuli responsive metallo-macrocycles and cages

Well-controlled and regulated molecular switches and machines are essential for life and are exploited in all biological systems. Inspired by this, synthetic chemists have been attempting to develop comparable non-biological switches and machines. Over the past 20 years efforts to generate mechanically interlocked (catenanes and rotaxanes), non-interlocked and macrocyclic/cage based metal-containing switching systems has increased enormously. Architectures that generate large scale molecular motion or the translocation of molecular cargo have been developed. Similarly, systems that can bind and release guest molecules or turn off and on molecular catalysis have also been realized. This article will outline some important historical examples in the area then present a range of interesting advances that have been made in the past 5 years.