Fused aza-heterocyclic ligands: expanding the MOF chemist's toolbox

• Published in: CrystEngComm 2022-12, Vol.24 (47), p.8197-827
• Main Authors: Wood, Oskar G, Hawes, Chris S
• Format: Article
• Language: English
• Subjects: Adenine; Bonding strength; Heterocyclic compounds; Hypoxanthine; Imidazole; Ligands; Metal-organic frameworks; Purines; Pyrazole; Transition metals; Triazoles
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/d2ce01475k

Azolate-containing ligands have played an important role in the development of water-stable metalorganic frameworks (MOFs) and related materials due to their particularly strong bonding with earth-abundant first row transition metal ions. Fused ring analogues of pyrazole, imidazole and triazole offer untapped potential to expand the scope of these systems as compact, robust anionic bridging ligands with much greater control over bridging geometries, pendant functionalities and electronic properties. The current design approaches in these systems have been directed by two separate methodologies. In one direction, the simple azoles imidazole, pyrazole and 1,2,4-triazole have been built up by adding fused ring functionality to increase complexity and allow new linker geometries. Meanwhile, in the search for biologically-compatible MOFs, purines such as adenine and hypoxanthine have been explored as linkers and their backbone functionalities optimised to prioritise stability and bridging geometry, leading independently to MOF linkers with similar key features. This highlight article surveys the convergence of these two approaches which both point to the benefits of fused 56 ring systems for their electronic and structural properties, and considers the key features that the ideal compact and stable heterocyclic linkers in functional metalorganic frameworks might contain. Fused azolate ligands are hydrolytically-stable linkers for metalorganic frameworks. Their unique geometries and capacity for functionalisation have opened new pathways at the convergence of simple N-heterocycles and biologically relevant purines.