A Water‐Stable Cationic SIFSIX MOF for Luminescent Probing of Cr₂O₇²⁻ via Single‐Crystal to Single‐Crystal Transformation

Abstract

The sensing and monitoring of toxic oxo‐anion contaminants in water are of significant importance to biological and environmental systems. A rare hydro‐stable SIFSIX metal−organic framework, SiF₆@MOF‐1, {[Cu(L)₂(H₂O)₂]·(SiF₆)(H₂O)}_n, with exchangeable SiF₆²⁻ anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr₂O₇²⁻ oxo‐anion in an aqueous medium having high sensitivity, selectivity, and recyclability through fluorescence quenching phenomena. More importantly, the recognition and ion exchange mechanism is unveiled through the rarely explored single‐crystal‐to‐single crystal (SC‐SC) fashion with well‐resolved structures. A thorough SC‐SC study with interfering anions (Cl⁻, F⁻, I⁻, NO₃⁻, HCO₃⁻, SO₄²⁻, SCN⁻, IO₃⁻) revealed no such transformations to take place, as per line with quenching studies. Density functional theory calculations revealed that despite a lesser binding affinity, Cr₂O₇²⁻ shows strong orbital mixing and large driving forces for electron transfer than SiF₆²⁻, and thus enlightens the fluorescence quenching mechanism. This work inaugurates the usage of a SIFSIX MOF toward sensing application domain under aqueous medium where hydrolytic stability is a prime concern for their plausible implementation as sensor materials.