Eduardo Victor Peris, University Jaume I, Castellón, Spain, and colleagues have developed a new type of MIM based on the coupling of two so-called metallotweezers, which consist of a rigid tether linking two flat "arms". The interlocked structure is unique as it is produced by the self-aggregation of two U-shaped structures. The two components of the mechanically interlocked molecule cannot separate because the bulky tert-butyl groups prevent disassembly through slippage. For an analogous tweezer lacking these groups, the dimeric structure is in equilibrium with the monomeric structure.

According to the definition proposed by 2016 chemistry Nobel laureate Fraser Stoddart, mechanically interlocked molecules consist of two or more separate components that can only be untangled by breaking covalent bonds. One large class are ‘wheel-and-axle’ rotaxanes, which consist of a dumbbell-shaped molecule is threaded through a large cyclic molecule.