Multicomponent Metal–Organic Frameworks as\nDefect-Tolerant Materials

Abstract

Multicomponent\nmetal–organic frameworks (MOFs) comprise\nmultiple, structurally diverse linkers fixed into an ordered lattice\nby metal ions or clusters as secondary building units (SBUs). Here,\nwe show how multicomponent MOFs are ideal platforms for engineering\nmaterials with high levels of vacancy defects. First, a new type of\nquaternary MOF that is built up from two neutral, linear ditopic linkers,\na 3-fold-symmetric carboxylate ligand, and a dinuclear paddlewheel\nSBU was synthesized. This MOF, named MUF-32 (MUF = Massey University\nFramework), is constructed from dabco, 4,4′-bipyridyl (bipy),\n4,4′,4″-nitrilotrisbenzoate (ntb), and zinc­(II), and\nit adopts an <b>ith-d</b> topology. The zinc­(II) ions and ntb\nligand define an underlying [Zn₂(ntb)_4/3] sublattice\n(with <b>pto</b> topology) that is “load bearing”\nand maintains the structural integrity of the framework. On the other\nhand, the dabco and bipy ligands are “decorative”, and\nhigh levels of vacancy defects can be introduced by their partial\nomission or removal. These defects can be generated by direct synthesis\nor by postsynthetic modification. The framework structure, crystallinity,\nand porosity are maintained even when vacancy levels of 80% are reached.\nDefect healing is possible by introducing free ligands in a solvent-assisted\nprocess to restore pristine MUF-32. Computational analysis reveals\nthat the mechanical instability of the [Zn₂(ntb)_4/3] sublattice sets an upper limit on defect levels in this material.