Flexibility engenders induced-fit guest binding within metastable conformers of an octahedral coordination cage

Encapsulation of guest molecules within coordination cages depends on the compatibility of their respective sizes and shapes. Recently, a flexible octahedral coordination cage has been reported such that the size and shape of its internal cavity can adapt upon guest encapsulation. This feature enables the cage to conform optimally to the geometry of its guest. Here we report that rotations within the flexible ligand of this cage lead to the formation of metastable cage conformers. The conformational differences between the ligands for these conformers are translated onto marked differences in the geometry of their internal cavities, and we therefore have observed different guest binding properties associated with each conformer. Furthermore, transformation between these states can be triggered upon induced-fit guest binding.