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, SiF 6 @MOF-1, {[Cu(L) 2 (H 2 O) 2 ]·(SiF 6 )(H 2 O)} n , with exchangeable SiF 6 2- anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr 2 O 7 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 - , NO 3 - , HCO 3 - , SO 4 2- , SCN - , IO 3 - ) 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 2 O 7 2- shows strong orbital mixing and large driving forces for electron transfer than SiF 6 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.