A Water‐Stable Cationic SIFSIX MOF for Luminescent Probing of Cr 2 O 7 2− via Single‐Crystal to Single‐Crystal Transformation

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 (H₂ O)₂ ]·(SiF₆ )(H₂ O)}_n , with exchangeable SiF₆ ^2- anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr₂ O₇ ^2- 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 ^- , SO₄ ^2- , 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, Cr₂ O₇ ^2- shows strong orbital mixing and large driving forces for electron transfer than SiF₆ ^2- , 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.