Multiple Functional Groups of Varying Ratios in Metal-Organic Frameworks

TLDR

Complex arrangements of multiple functional groups in MOF pores can produce properties beyond simple additive effects. The authors synthesized 18 multivariate MOF‑5 structures by mixing 1,4‑benzenedicarboxylate with eight functionalized derivatives, yielding ordered zinc‑oxide backbones but disordered functional‑group distributions. These mixed‑linker MOFs can incorporate many functionalities, and one variant, MTV‑MOF‑5‑EHI, achieves up to 400 % higher CO₂/CO selectivity than the best single‑linker analogues.

Abstract

We show that metal-organic frameworks (MOFs) can incorporate a large number of different functionalities on linking groups in a way that mixes the linker, rather than forming separate domains. We made complex MOFs from 1,4-benzenedicarboxylate (denoted by "A" in this work) and its derivatives -NH2, -Br, -(Cl)2, -NO2, -(CH3)2, -C4H4, -(OC3H5)2, and -(OC7H7)2 (denoted by "B" to "I," respectively) to synthesize 18 multivariate (MTV) MOF-5 type structures that contain up to eight distinct functionalities in one phase. The backbone (zinc oxide and phenylene units) of these structures is ordered, but the distribution of functional groups is disordered. The complex arrangements of several functional groups within the pores can lead to properties that are not simply linear sums of those of the pure components. For example, a member of this series, MTV-MOF-5-EHI, exhibits up to 400% better selectivity for carbon dioxide over carbon monoxide compared with its best same-link counterparts.