Metal–organic frameworks generated from oligomeric ligands with functionalized tethers

Abstract

Metal–organic frameworks (MOFs) can be prepared from oligomeric organic ligands to prepare materials referred to as oligoMOFs. Studies of oligoMOFs are relatively limited, with most existing reports focused on fundamental structure–property relationships. In this report, functional groups, such as terminal alkynes and pyridine groups, are installed on the tether between 1,4-benzene dicarboxylic acid (H₂bdc) groups of the dimer ligands. It was found that the position of the pyridine donor atom had pronounced effects on the synthesis and structure of Zn(II)-based isoreticular MOFs (IRMOF-1 analog, oligoIRMOF). Importantly, simple H₂bdc ligands with pendant pyridine groups (i.e., not part of an dimeric ligand), were unable to produce crystalline phases or produced new MOF phases, showing the importance of the oligomeric ligand in directing structure. Dimeric ligands with two H₂bdc groups and a terminal alkyne produced a crystalline and porous oligoIRMOF that enables postsynthetic modification (PSM) via ‘click’ chemistry to introduce other functional groups into the pores of the material. This oligoIRMOF could be cross-linked using reagents containing multiple azide functional sites. Taken together, these studies are among the first examples of oligoMOFs with functionalized tethers and demonstrate the versatility, utility, and unique opportunities for new chemistry provided by oligoMOFs.