Toxic oxo-anion capture by metal-organic frameworks (MOFs): insights via single-crystal-to-single-crystal transformations.

The contamination of water bodies and soil with toxic oxo-anions poses significant environmental and health risks. Conventional water treatment technologies often fall short in addressing the selective and efficient removal of these contaminants due to challenges related to their solubility, mobility, and persistence in natural systems. In this regard, metal-organic frameworks (MOFs) have emerged as one of the most promising classes of materials for oxo-anion removal. Despite numerous advances in the sensing capabilities of MOFs, the identification of intermediate steps, as well as the precise location and exact binding interactions of the entrapped oxo-anions, is still in its infancy and requires in-depth structural analysis of SC-SC transformations during the ion-exchange processes. In this review, we aim to summarize recent progress in MOF sensors for which SC-XRD structural insights into the entrapped oxo-anions are available and discuss these findings in detail to enhance molecular-level understanding of the ion-exchange process in MOF chemistry. Most importantly, we present a 'critical analysis' section considering several critical aspects that are often overlooked during development and made future recommendations in the 'future prospects' section.