Postsynthetic Ligand and Cation Exchange in Robust Metal–Organic Frameworks

Abstract

Postsynthetic ligand and metal ion exchange (PSE) processes are shown to readily occur in several "inert" metal-organic frameworks (MOFs), including zeolitic imidazolate frameworks (ZIFs). Ligand exchange can occur between solid samples, as was demonstrated under relatively mild conditions with two robust, topologically distinct MOFs, MIL-53(Al) and MIL-68(In). Interestingly, ligand PSE is not observed with MIL-101(Cr), which is attributed to the kinetic inertness of the Cr(III) ion. In addition to ligand exchange, metal ion (cation) PSE was also studied between intact MOF microcrystalline particles. Metal ion transfer between MIL-53(Al) and MIL-53(Fe) was readily observed. These PSE reactions were monitored and the products characterized by a number of techniques, including aerosol time-of-flight mass spectrometry, which permits single-particle compositional analysis. To show the potential synthetic utility of this approach, the PSE process was used to prepare the first Ti(IV) analogue of the robust UiO-66(Zr) framework. Finally, experiments to rule out mechanisms other than PSE (i.e., aggregation, dissolution/recrystallization) were performed. The results demonstrate that PSE, of either ligands or cations, is common even with highly robust MOFs such as UiO-66(Zr), MILs, and ZIFs. Furthermore, it is shown that PSE is useful in preparing novel materials that cannot be obtained via other synthetic methods.

Physical aging in glassy mixed matrix membranes; tuning particle interaction for mechanically robust nanocomposite films

“…52 Ti exchanged UiO-66 based composites were strikingly different from each of the other polymer additive combinations studied; exhibiting the best properties in PIM-1, but among the worst for PTMSP and Matrimid composites (Figure 2). Structurally, Ti 5 UiO-66 is isomorphous to UiO-66; however post-synthetic exchange (PSE) 54 has been shown to increase polymer interaction, partially separate charge, increase surface area and further expose Ti (Table S3, ESI). [56][57][58] We propose that Ti 5 UiO-66's exposed Ti IV forms a chelation complex with PIM-1's terminal catechol groups (Figure 4).…”

Investigation of zeolitic imidazolate frameworks using 13 C and 15 N solid-state NMR spectroscopy

“…For example, ZIF-68 (GME topology), which is synthesised with 2-nitroimidazolate and benzimidazolate (in a 1:1 ratio), has both hydrophilic and hydrophobic pores [11]. There are a few examples of ZIFs that have been prepared with more than one metal centre [12][13][14], which can result in a material that possesses different metal coordination environments, with a unique chemistry that can be exploited for various applications, such as catalysis.…”

Photochemical Hydrogen Production with Metal–Organic Frameworks

“…While post-synthetic modification methods have been explored for many different MOFs, including the aforementioned water-stable frameworks, post-synthetic ligand exchange is a rather new but powerful concept. Examples have been shown even for highly stable MOFs such as UiO-66, MIL-53 and ZIF-8 [37][38][39].…”