A solvent-responsive coordination cage

The solvent-induced structural rearrangement of synthetic supramolecular structures typically requires a pronounced change in solvent polarity. We describe a ruthenium-based coordination cage, whose geometry and topology can be altered dramatically by using two closely related solvents: chloroform and dichloromethane. In chloroform, we observe an octanuclear prismatic cage, whereas a tetranuclear complex is formed in dichloromethane. The basis of this unusual solvent-sensitivity is the incorporation of metallacrown recognition units into a flexible, kinetically labile nanostructure.