Multicomponent Metal–Organic Frameworks as Defect-Tolerant Materials

Abstract

Multicomponent metal–organic frameworks (MOFs) comprise multiple, structurally diverse linkers fixed into an ordered lattice by metal ions or clusters as secondary building units (SBUs). Here, we show how multicomponent MOFs are ideal platforms for engineering materials with high levels of vacancy defects. First, a new type of quaternary MOF that is built up from two neutral, linear ditopic linkers, a 3-fold-symmetric carboxylate ligand, and a dinuclear paddlewheel SBU was synthesized. This MOF, named MUF-32 (MUF = Massey University Framework), is constructed from dabco, 4,4′-bipyridyl (bipy), 4,4′,4″-nitrilotrisbenzoate (ntb), and zinc(II), and it adopts an ith-d topology. The zinc(II) ions and ntb ligand define an underlying [Zn2(ntb)4/3] sublattice (with pto topology) that is "load bearing" and maintains the structural integrity of the framework. On the other hand, the dabco and bipy ligands are "decorative", and high levels of vacancy defects can be introduced by their partial omission or removal. These defects can be generated by direct synthesis or by postsynthetic modification. The framework structure, crystallinity, and porosity are maintained even when vacancy levels of 80% are reached. Defect healing is possible by introducing free ligands in a solvent-assisted process to restore pristine MUF-32. Computational analysis reveals that the mechanical instability of the [Zn2(ntb)4/3] sublattice sets an upper limit on defect levels in this material.