Rotors, Motors, and Machines Inside Metal-Organic Frameworks

Chemists have learned how to create molecules that mimic the rudimentary motions exhibited at the macroscopic level by some of the components of modern machinery. Almost all of these molecules are single-component examples that operate in solution, in isolation, and with incoherent motion. To create complexity and build more sophisticated systems comprising interacting mechanical components, methods must be found for organizing these molecules at much higher densities. One way to accomplish this is to incorporate them as building blocks inside solid-state crystalline materials known as metal-organic frameworks (MOFs). Herein, we review the handful of materials that have been able to accomplish this feat by transferring the motion of molecular rotors, motors, and machines into the solid state.