Isoreticular Contraction of Metal-Organic Frameworks Induced by Cleavage of Covalent Bonds

Isoreticular chemistry, in which the organic or inorganicmoietiesof reticular materials can be replaced without destroying their underlyingnets, is a key concept for synthesizing new porous molecular materialsand for tuning or functionalization of their pores. Here, we reportthat the rational cleavage of covalent bonds in a metal-organicframework (MOF) can trigger their isoreticular contraction, withoutthe need for any additional organic linkers. We began by synthesizingtwo novel MOFs based on the MIL-142 family, (In)BCN-20B and (Sc)BCN-20C,which include cleavable as well as noncleavable organic linkers. Next,we selectively and quantitatively broke their cleavable linkers, demonstratingthat various dynamic chemical and structural processes occur withinthese structures to drive the formation of isoreticular contractedMOFs. Thus, the contraction involves breaking of a covalent bond,subsequent breaking of a coordination bond, and finally, formationof a new coordination bond supported by structural behavior. Remarkably,given that the single-crystal character of the parent MOF is retainedthroughout the entire transformation, we were able to monitor thecontraction by single-crystal X-ray diffraction.