Sequence-Dependent Guest Release Triggered by Orthogonal Chemical Signals

Three
ZnII4L4 coordination cages,
assembled from trisiminopyridine ligands, exhibit differences in their
guest-binding selectivities and reactivity with tris­(2-aminoethyl)­amine
(tren), which enabled the design of a molecular network that responded
in distinct ways to different chemical signals. When two of these
cages were present in solution together, one of them was observed
to selectively encapsulate chloroform, and the other was observed
to selectively encapsulate cyclohexane. The two guests could be released
sequentially, in a specified order defined by the input of two separate
chemical signals: tren and perrhenate. Furthermore, the observed reactivity
of tren with the initial cage mixture provided control over the uptake
and release of perrhenate within the third cage formed in
situ. One of these tetrahedral cages has been identified
as a tight (Ka > 107 M–1) and selective host for perrhenate, an anion of great
physicochemical similarity to pertechnetate, both having uses in nuclear
medicine.