Molecular Borromean links based on metallocages

The Borromean link, which is characterized by structural integrity and aesthetic beauty, represents one of the most intriguing entanglements. However, the vast majority of Borromean links consist of three identical macrocycles, and there are very few examples of links constructed from dimeric cages. Here, facilitated by multiple aromatic stacking interactions between components, we demonstrate that two molecular cage-based Borromean links containing more than 1100 nonhydrogen atoms, especially 24 rhodium(III)/iridium(III) and six sodium(I) ions, can be constructed in high yield through the strategic selection of a tetrapyridyl ligand based on dibenzo-18-crown-6 and two binuclear building units, as demonstrated by X-ray crystallographic analysis, detailed nuclear magnetic resonance (NMR), electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), and elemental analysis.