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.

Bifunctional MOFs in Heterogeneous Catalysis

“…2a). 143 The Claisen−Schmidt reaction is a classic base catalyzed aldol condensation reaction involving an aromatic aldehyde and a ketone forming conjugated β-hydroxy carbonyl compounds. The uncoordinated -NH group acts as the basic center and catalyzes the Claisen−Schmidt reaction (Figure 2b).…”

“…The formation of βenaminoesters is acid catalyzed, and the Cd 2+ center acts as the Lewis acidic center and catalyzes the reaction between ethyl acetoacetate and aniline (Figure 2c). 143 A two-dimensional (2D) MOF, [Cd(PBA)(DMF)]•DMF (Cd-PBA), (H 2 PBA = 5-(4-pyridin-3-yl-benzoylamino)-isophthalic acid), was found to be a catalyst for the base catalyzed (the N from the pyridine acts as the base center) Knoevenagel condensation reaction and the Lewis acid catalyzed (Cd centers) cyanosilylation of various aldehydes with trimethylsilyl cyanide. 158 There are many reports in the literature where only one of the functional groups (usually the Lewis basic functionality) was investigated toward catalytic studies.…”

“…The MOF [M 3 (C 10 H 4 O 7 N 1 ) 2 (8H 2 O)]·H 2 O (M = Cd, Mn), was explored toward the formation of the β-enaminoester (Lewis acid catalyzed), and the -NH moiety present in the ligand was exploited toward the Claisen–Schmidt reactions (Lewis base catalyzed) (Figure a) . The Claisen–Schmidt reaction is a classic base catalyzed aldol condensation reaction involving an aromatic aldehyde and a ketone forming conjugated β-hydroxy carbonyl compounds.…”

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs

“…The luminescence behaviour of MOF compounds has been exploited towards the detection of harmful substances in aqueous solutions. 36,67,[104][105][106] Although much of the study has been concentrated on the luminescence behaviour of the organic linkers of the MOFs, there has been increasing focus on utilising the lanthanide luminescence as the probe. [107][108][109][110][111] The good emission efficiency of the present Eu 3+ (2a,2b) and Tb 3+ (4a,4b) materials made exploring the use of these compounds towards fluorescence turn-off detection of some harmful pesticides and nitroaromatics in aqueous solution desirable.…”

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies

“…The versatility of the compounds has been established by their many interesting potential applications in the areas such as sorption, − separation, , luminescence, − catalysis, − proton conduction, − magnetism, , etc. The developments over the years allowed the focus of the research to shift toward preparing the compounds for tailor-made purposes such as high porosity and surface area, increased number of active catalytic centers, multiple chemical functionalities, etc. − To achieve these goals, one needs to make a careful choice of the metal node (ions), a linking ligand that hosts the multiple functionalities, and also a possible secondary ligand. There has been some progress in this direction as well. − …”