Carboxylic Acid Functionalized Clathrochelate Complexes:Large, Robust, and Easy-to-Access Metalloligands

Polycarboxylate ligands are among the most important building blocks for the synthesis of metal–organic frameworks (MOFs). The ability to access these ligands in an efficient way is of key importance for future applications of MOFs. Here, we demonstrate that mono- and dinuclear clathrochelate complexes are versatile scaffolds for the preparation of polytopic carboxylate ligands. The largely inert clathrochelate complexes have a trigonal-bipyramidal shape. The synthesis of functionalized clathrochelates with two, three, four, or five carboxylic acid groups in the ligand periphery can be achieved in a few steps from simple starting materials. Apart from being easily accessible, the metalloligands display interesting characteristics for applications in metallasupramolecular chemistry and materials science: they are rigid, large (up to 2.2 nm), and robust and they can show additional functions (e.g., fluorescence or extra charge) depending on the metal ion that is present in the clathrochelate core. The utili...