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.

Two [N⋅⋅⋅I ⋅⋅⋅N] halogen-bonded dimeric capsules using tetrakis(3-pyridyl)ethylene cavitands with different lower rim alkyl chains are synthesized and analyzed in solution and the gas phase. These first examples of symmetrical dimeric capsules making use of the iodonium ion (I ) as the main connecting module are characterized by H NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), electrospray ionization mass spectrometry (ESI-MS), and ion mobility-mass spectrometry (TW-IMS) experiments. The synthesis and effective halogen-bonded dimerization proceeds through analogous dimeric capsules with [N⋅⋅⋅Ag ⋅⋅⋅N] binding motifs as the intermediates as evidenced by the X-ray structures of (CH Cl ) @[3 a ⋅Ag ⋅(H O) ⋅OTs ] and (CH Cl ) @[3 a ⋅Ag ⋅(H O) ⋅OTs ], two structurally different capsules.

Lineare Diamin‐ und Formylpyridin‐Einheiten bilden mit Eisen(II) einen tetraedrischen Käfig (siehe Schema), der hydrophobe Gastspezies hoch spezifisch in seinem Hohlraum aufnimmt und von der wässrigen Umgebung abschirmt. Beim Öffnen des Käfigs durch Zusatz eines Triamins wird die eingeschlossene Spezies freigesetzt. Alternativ zerfällt der Käfig bei Zugabe von Säure, doch dieser Prozess kann durch Base rückgängig gemacht werden, sodass die Gastspezies reversibel freigesetzt und eingeschlossen wird.

Subtle differences in metal-ligand bond lengths between a series of [M(4)L(6)](4-) tetrahedral cages, where M = Fe(II), Co(II), or Ni(II), were observed to result in substantial differences in affinity for hydrophobic guests in water. Changing the metal ion from iron(II) to cobalt(II) or nickel(II) increases the size of the interior cavity of the cage and allows encapsulation of larger guest molecules. NMR spectroscopy was used to study the recognition properties of the iron(II) and cobalt(II) cages towards small hydrophobic guests in water, and single-crystal X-ray diffraction was used to study the solid-state complexes of the iron(II) and nickel(II) cages.

Cyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal–organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[5]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane–protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host–guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.