This review discusses recent advances in the use of molecular containers in complex chemical systems, focusing on three aspects: host–guest behaviour, structural transformations and reactivity modulation.

This review examines the growing variety of covalent reactions used to achieve the post-assembly modification of self-assembled metallosupramolecular complexes.

Post-assembly modification (PAM) is a powerful tool for the modular functionalization of self-assembled structures. We report a new family of tetrazine-edged Fe^II₄L₆ tetrahedral cages, prepared using different aniline subcomponents, which undergo rapid and efficient PAM by inverse electron-demand Diels–Alder (IEDDA) reactions. Remarkably, the electron-donating or -withdrawing ability of the para-substituent on the aniline moiety influences the IEDDA reactivity of the tetrazine ring 11 bonds away. This effect manifests as a linear free energy relationship, quantified using the Hammett equation, between σ_para and the rate of the IEDDA reaction. The rate of PAM can thus be adjusted by varying the aniline subcomponent.

Subcomponent self-assembly of two isomeric bis(3-aminophenyl)pyrenes, 2-formylpyridine and the metal ions FeII, CoII, and ZnII led to the formation of two previously unidentified structure types: a C2-symmetric MII4L6 assembly with meridionally coordinated metal centers, and a C3-symmetric self-included MII4L6 assembly with facially coordinated metal centers. In both structures the meta linkages within the ligands facilitate π-stacking between the pyrene panels of the ligands. A C2h-symmetric MII2L2 box was also obtained, which was observed to selectively bind electron-deficient aromatic guests between two parallel pyrene subunits. Similar donor–acceptor interactions drove the selective self-assembly of a singular MII4L4L′2 architecture incorporating both a pyrene-containing diamine and an electron-deficient NDI-based diamine. This heteroleptic architecture was shown to be thermodynamically favored over the corresponding homoleptic MII4L6 and MII4L′6 complexes, which were nonetheless stable in each others...