Guest Encapsulation Alters the Thermodynamic Landscape of a Coordination Cage

The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, rigid capsules with small windows can efficiently protect their contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a “Janus” nature of a Pd6L4 coordination cage previously reported to tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a capsule-shaped host (C) in a quantitative yield. Extracting the guest affords the empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way towards controlling functional properties of coordination cages “on demand”

Guest encapsulation alters the thermodynamic landscape of a coordination host

The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, a rigid cage with small windows can efficiently protect its contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a “Janus” nature of a Pd6L4 coordination host previously reported to exist exclusively as a tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a cage-shaped host (C) in quantitative yield. Extracting the guest affords empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way toward controlling functional properties of coordination hosts “on demand”