Single-Crystal\nto Single-Crystal Mechanical Contraction\nof Metal–Organic Frameworks through Stereoselective Postsynthetic\nBromination

Abstract

The\nproperties of metal–organic frameworks (MOFs) can be\ntuned by postsynthetic modification (PSM) to introduce specific functionalities\nafter their synthesis. Typically, PSM is carried out on pendant functional\ngroups or through metal/ligand exchange, preserving the structure\nof the MOF. We report herein the bromination of integral alkyne units\nin a pair of Zr⁴⁺ and Hf⁴⁺ MOFs, which proceeds\nstereoselectively in a single-crystal to single-crystal manner. The\nchemical and mechanical changes in the MOFs are extensively characterized,\nincluding the crystal structures of the postsynthetically brominated\nmaterials, which show a mechanical contraction of up to 3.7% in volume.\nThe combination of stability and chemical reactivity in these MOFs\nleads to the possibility of tuning mechanical properties by chemical\ntransformation while also opening up new routes to internal pore functionalization.