New Zr-MOFs composed of hetero-linkers with an fcu topology via post-synthetic ligand insertions

Abstract

The synthesis of metal-organic frameworks (MOFs) composed of hetero-linkers is important for tuning framework properties. Despite tremendous endeavor, it is still challenging to synthesize Zr-MOFs with hetero-linkers of different lengths. Recently, preparations of Zr-MOFs of 12-connectivity that contain hetero-linkers were reported via sequential insertions of additional linkers into an 8-c Zr-MOF, PCN-700. Since the Zr clusters, [Zr6O4(OH)4(COO)12] SBUs, in PCN-700 are alternating in two different orientations, the 12-c MOF obtained is not of an fcu topology. Here we report the preparation of a series of new Zr-MOFs with an fcu topology via post-synthetic ligand insertions using hetero-linkers of different lengths. A solvothermal reaction of ZrOCl2 and 2,6-naphthalene dicarboxylic acid (H2NDC) with coplanar conformation of the carboxylate residues produced a new flexible Zr-based MOF, [Zr6O4(OH)4(NDC)4(H2O)8](monoacid)4 (ZRN), with an 8-c bcu topology. A series of new Zr-MOFs with an fcu topology can be obtained via simple soaking method. When ZRN crystals were put into a solution of functionalized 1,4-benzene dicarboxylic acid (H2XBDC), even though the shortest distance between the closest neighboring Zr-SBUs with potential linkage sites in ZRN is longer than the length of XBDC derivative but the XBDC linkers are inserted into the remaining potential linkage sites to form a new framework with a 12-c fcu topology. Single crystal structure analyses confirmed the different binding modes of the inserted linkers between [Zr6O4(OH)4(COO)12] SBUs depending on the functional groups of the inserted hetero-linkers