Light Drives Colorful MOF Modification

The chemical nature of metal-organic framework (MOF) compounds can be modified after synthesis by removing protecting groups via photochemical reactions, report researchers at the University of California, San Diego (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201004736). Various types of these postsynthetic modification strategies have been used to introduce functional groups into MOFs, which are highly porous crystalline compounds being developed for gas storage and separation, catalysis, and other applications. Typically, these transformations are carried out by treating MOFs with chemical reagents or heat. UC San Diego’s Kristine K. Tanabe, Corinne A. Allen, and Seth M. Cohen took a different approach. The researchers prepared MOFs by reacting benzenetribenzoate units and zinc nitrate with dicarboxylic acid building blocks that were protected with nitrobenzyl groups. They then exposed the resulting crystals to ultraviolet light, which drove off the protecting groups and changed the crystals’ appearance from colorless to orange. In effect, the team induced a crystal-to-crystal transformation that left the lattice intact and exposed uncoordinated hydroxy groups, which is an uncommon chemical feature for this class of compounds and could be exploited in future applications.