Tetrahedral M II 4L6 (M = Fe, Zn) Cages Equipped with Walls Featuring Antiaromatic Pentalene Motifs.

Antiaromatic compounds are often difficult to work with due to their relative instability in comparison with aromatic analogues. As a consequence, their application in functional materials remains in its infancy. Here, we report the synthesis of porous M II 4L6 (M = Fe, Zn) coordination cages equipped with dibenzo-[a,e]-pentalene panels involving the antiaromatic motif of pentalene stabilized by benzannulation. Both cages encapsulate fullerene C60, with the more adaptable zinc-(II) cage also binding C70, undergoing pronounced structural reconfiguration upon C60 inclusion, and displaying broader affinity for polycyclic aromatic hydrocarbons. The cages selectively bind anthraquinone over its reduced form and interact with steroids such as testosterone and cholesterol. Remarkably, the chemical shifts of the guests are affected by the aromatic Clar sextets rather than the antiaromatic pentalene motif. These assemblies represent only the second reported example of a supramolecular cage with a cavity fully enclosed by antiaromatic walls and demonstrate that benzannulated antiaromatic motifs can be incorporated into cages without interrupting conventional host-guest behavior, while simultaneously allowing for a systematic tuning of magnetic shielding effects.