Organizing mechanically interlocked molecules to function inside metal-organic frameworks.

The idea that the workings of molecular switches, motors, and machines based on mechanically interlocked molecules can be transferred into the solid state by using them as the building blocks of metal-organic framework materials is addressed. This involves an in-depth review and analysis of the chemistry of coordination polymers and metal-organic frameworks in which the linkers are rotaxanes and catenanes. To date, two types of materials have been prepared: (1) coordination polymers in which the interlocked components are part of a complex architecture but do not display large amplitude molecular motion or function and (2) those that clearly demonstrate some type of supramolecular quality (molecular recognition) or relative motion between interlocked components (dynamics) reminiscent of their solution counterparts. The latter can be thought of as prototypes of solid-state molecular machines. The possibility of creating more sophisticated, solid-state materials that have the full characteristics of molecular switches, motors, and machines and the way forward for this chemistry is also discussed.