Improved Acid Resistance of a Metal-Organic Cage Enables Cargo Release and Exchange between Hosts.

Here we introduce the use of di(2-pyridyl)ketone in subcomponent self-assembly. When combined with a flexible triamine and zinc bis(trifluoromethylsulfon)imide, this ketone formed a new Zn 4 L 4 tetrahedron 1 bearing twelve uncoordinated pyridyl units around its metal-ion vertices. The acid stability of 1 was found to be greater than that of the analogous tetrahedron 2 built from 2-formylpyridine. Intriguingly, the peripheral presence of additional pyridine rings in 1 resulted in distinct guest binding behavior from that of 2 , affecting guest scope as well as binding affinities. The different stabilities and guest affinities of capsules 1 and 2 enabled the design of systems whereby different cargoes could be moved between cages using acid and base as chemical stimuli.