A Water-Stable Cationic SIFSIX MOF for Luminescent Probing of Cr O 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, SiF @MOF-1, {[Cu(L) (H O) ]·(SiF )(H O)} , with exchangeable SiF anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr O 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 , NO , HCO , SO , SCN , IO ) revealed no such transformations to take place, as per line with quenching studies. Density functional theory calculations revealed that despite a lesser binding affinity, Cr O shows strong orbital mixing and large driving forces for electron transfer than SiF , 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.