Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions.

Abstract

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M3(C10H4O7N1)2(8H2O)]·H2O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg2+ ions in an aqueous medium with good selectivity. The interactions between Hg2+ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg2+ ions and in the range mandated by the WHO. The interactions between Hg2+ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.