Beyond Platonic: How to Build Metal-Organic Polyhedra Capable of Binding Low-Symmetry, Information-Rich Molecular Cargoes

The field of metallosupramolecular chemistry has advanced rapidly in recent years. Much work in this area has focused on the formation of hollow self-assembled metal-organic architectures and exploration of the applications of their confined nanospaces. These discrete, soluble structures incorporate metal ions as ‘glue’ to link organic ligands together into polyhedra.Most of the architectures employed thus far have been highly symmetrical, as these have been the easiest to prepare. Such high-symmetry structures contain pseudospherical cavities, and so typically bind roughly spherical guests. Biomolecules and high-value synthetic compounds are rarely isotropic, highly-symmetrical species. To bind, sense, separate, and transform such substrates, new, lower-symmetry, metal-organic cages are needed. Herein we summarize recent approaches, which taken together form the first draft of a handbook for the design of higher-complexity, lower-symmetry, self-assembled metal-organic architectures.

Heterometal-Organic Cages as Photo-Fenton-like Catalysts

Metal-organic cages, a class of supramolecular containers constructed by the self-assembly of metal ions and organic ligands, show great promise as catalytic agents. In this work, we designed and synthesized a series of rhombic dodecahedral Ni-Cu heterometal imidazolate cages (Ni₈Cu₆L₂₄) that can act as highly active photo-Fenton-like catalysts. These cages possess a high ability to generate hydroxyl radicals (^•OH) under visible light in the presence of H₂O₂, which can rapidly degrade organic pollutants (e.g., rhodamine B, methylene blue, and methyl orange) into CO₂ and H₂O. Besides, they are robust catalysts, with high catalytic activity and reusability under conditions in high H₂O₂ concentration, providing potentially advanced materials for degrading persistent organic pollutants.

Self-assembly of a Mixed Valence Copper Triangular Prism and Transformation to Cage Triggered by an External Stimulus

A triangular prismatic metal-organic cage based on mixed valence copper ions has been designed and synthesized by using metallocycle panels and pillar ligands. The triangular prism will be quickly transformed to a 10-nuclear cage upon an external chemical stimulus, which features a bicapped square antiprism structure. This prismatic cage can act as a catalyst for oxidation of aromatic alcohols to their corresponding aromatic aldehydes with high yields at room temperature under O₂ atmosphere.

Self-assembly of mixed-valence and heterometallic metallocycles: efficient catalysts for the oxidation of alcohols to aldehydes in ambient air

Two mixed-valence Cu^II/Cu^I and two heterometallic Cu^II/Ag^I metallocycles have been synthesized by the assembly of designed metalloligands and Cu^I/Ag^I ions, respectively.

Cavity-based applications of metallo-supramolecular coordination cages (MSCCs)

This review describes cavity-based applications of cage-like SCCs such as molecular recognition and separation, stabilization of reactive species by encapsulation, as drug delivery systems and as molecular flasks.