Uniform distribution of post-synthetic linker exchange in metal–organic frameworks revealed by Rutherford backscattering spectrometry

Abstract

Rutherford backscattering spectrometry (RBS) has been used for the first time to study post-synthetic linker exchange (PSE) in metal–organic frameworks. RBS is a non-invasive method to quantify the amount of introduced linker, as well as providing a means for depth profiling in order to identify the preferred localization of the introduced linker. The exchange of benzenedicarboxylate (bdc) by similarly sized 2-iodobenzenedicarboxylate (I-bdc) proceeds considerably slower than migration of I-dbc through the UiO-66 crystal. Consequently, the I-bdc is found evenly distributed throughout the UiO-66 samples, even at very short PSE exposure times.

A new approach to enhancing the CO2 capture performance of defective UiO-66 via post-synthetic defect exchange

“…PSE ( Figure 2a) involves replacement of a dicarboxylic linker (BDC in this work, see Figure 1) by another dicarboxylate having the same size and bearing a functional group (PyDC or ABDC in this work, see Figure 1). The resulting mixed-linker MOF displays homogeneous distribution of functionalized linkers throughout its structure, 30 unless crystallite size is not in the 10-100 µm range, where formation of core-shell structures could be observed. 31 If the new linker does not bear bulky and heavy functional groups (as is the case of this work), no drastic changes in the porosity of the framework are expected, which allows isolation of the effect of chemical modification on the physical-chemical properties of the framework.…”

Post‐Synthetic Ligand Exchange in Zirconium‐Based Metal–Organic Frameworks: Beware of The Defects!

“…PSE has since been demonstrated to be as imple,y et powerful, tool to introduce functionalities in the crystal structure of highly stable Zr-MOFs that are not accessible via direct synthesis. [4] Recent reports have shed some light onto microstructural aspects,e videncing that either homogeneous solid solutions [5] or core-shell architectures [6] can be formed upon PSE, mainly depending on crystal size.The possible role of defects during PSE has not yet been the object of thorough investigation, even though it is now well established that Zr-MOFs can contain alarge number of defects. [7] Defects reduce the connectivity of the [Zr 6 O 4 (OH) 4 ] 12+ clusters by substitution of bridging dicarboxylate linkers with terminal groups, usually monocarboxylates derived from crystallisation modulators used during the synthesis.…”

Mixed-Ligand Metal–Organic Frameworks and Heteroleptic Coordination Cages as Multifunctional Scaffolds—A Comparison

“…In contrast to this, Ott and Primetzhofer used Rutherford backscattering spectrometry to investigate the exchange of BDC-I (I = iodine) within UiO-66. 21 They found a homogeneous distribution over the whole crystal even after very short PSE times, indicating fast diffusion of the ligand and comparably slow exchange. The difference in the two observations is attributed to steric and electronic effects of iodine on the ligand exchange.…”