Making interlocking structures is an intriguing and complex challenge. While we are getting to grips with generating systems composed of two identical components, such as catenanes, an outstanding challenge is making heterointerlocked systems (where the constituent structures are different). Now, Yong Cui, Yan Liu and co-workers from Shanghai Jiao Tong University have developed a route to both homo- and heterointerlocked metal–organic cages.

A metal templating method was used to form the interlocked cage structures. Cu(I) ions were chosen for this as they favour a tetrahedral geometry. These Cu ions gathered the ligands so that two bidentate phenanthroline groups were bound to each metal ion in a perpendicular arrangement (see red circles in the figure). Following the complexation of the Ni4tBu-sulfonylcalix[4]arene clusters (left chemical structures, represented as blue and grey circles in the figure) to link the ligands together at the vertices, the interlocked cage structures were formed.