An Unlockable–Relockable Iron Cage by Subcomponent Self‐Assembly

In irons bound: Linear diamine and formylpyridine subcomponents form a tetrahedral cage with iron(II) in water (see scheme). This cage traps hydrophobic guests with high specificity within a rigid cavity, isolating them from the aqueous environment. The cage may be broken, releasing the guest, upon the addition of a triamine. It may also be unlocked by adding acid, allowing the guest to be reversibly released until base is added, relocking it within.