Amine- and Imine-Functionalized Mn-Based MOF as an Unusual Turn-On and Turn-Off Sensor for d¹⁰ Heavy Metal Ions and an Efficient Adsorbent to Capture Iodine

Abstract

In this work, a Mn-based metal−organic framework (MOF) {[H-Phen] 2 [Mn 3 (FDA) 4 (H 2 O) 2 ]•2H 2 O} n (SM-1) has been synthesized solvothermaly using 2,5-furandicarboxylic acid (2,5-FDA) as a linker and 4,7-phenanthroline (4,7-Phen) as a coligand. SM-1 was characterized using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and crystallographic studies. Single-crystal X-ray data reveal that the SM-1 framework is constituted by trinuclear Mn secondary building units (SBUs) as a dianion ([Mn 3 (COO) 6 ] 2− ), 2,5-FDA, and free 4,7-phenanthrolinium cation [H-Phen] + rings containing uncoordinated amino and imino moieties, which provide extra stability to the framework and feasible recognition sites to interact with analytes. Overall, the MOF is anionic in nature, which is counterbalanced by two protonated phenanthrolinium cations, thus giving rise to +2 oxidation states for all three Mn ions. Topological analysis shows that SM-1 has a {4 4 .6 2 } point symbol having a 4-c uninodal net with sql topology. SM-1 is an excellent fluorescent sensor for d 10 heavy metal ions in an aqueous environment. SM-1 developed as a highly sensitive sensor exhibits a fluorescence "turn-on" response for Ag + and Cd 2+ ions and a fluorescence "turn-off" response in the case of Hg 2+ ion with much lower limit of detection (LOD) values. Moreover, SM-1 application is not limited to only sensing, but it can also serve as an adsorbent to capture hazardous substances. Owing to the presence of π-electron-rich moieties and uncoordinated nitrogen atoms in the SM-1 framework, it is also explored for efficient iodine uptake. SM-1 captures iodine reversibly in cyclohexane solution with high adsorption capacity within 36 h. Further, a plausible mechanism of sensing and iodine adsorption was also discussed briefly. As far as we know, this is the first example of a Mn-based anionic MOF functioning as a fluorescent chemosensor to simultaneously detect d 10 heavy metal ions in water and as an adsorbent to trap iodine. Thus, metal− organic chemistry has been employed to develop multifunctional MOF material for the sensing of hazardous metal ions and as an adsorbent for the removal of toxic iodine.

A bifunctionalised Pb-based MOF for iodine capture and dye removal

“…The presence of π-electron-rich walls of the py-Phen and bdc ligands and free –N donor atoms of py-phen in the SM-3 framework prompted us to examine the iodine adsorption performance of SM-3 in the solution phase. 64 At room temperature, 20 mg of fresh SM-3 crystals was added to a small glass vial containing a cyclohexane solution of iodine (300 mg L −1 ). With time it was noticed that the deep pink color of the iodine solution almost became colorless, suggesting that iodine adsorption takes place from the solution to the SM-3 network (Fig.…”

Exploiting a Multi-Responsive Oxadiazole Moiety in One Three-Dimensional Metal–Organic Framework for Remedies to Three Environmental Issues

“…This result for multimedia capture of iodine molecules is found to be among the highest reported ones and is comparable with those in the literature (Table S1). − …”

Syntheses, crystal structures and thermal decomposition studies of two novel Mn(ii)-MOFs with tetrazole-based carboxylic acids

“…The Mn–O distances are in the range of 2.153(5)–2.32(2) Å (Table 2), which are similar to those reported in the related Mn( ii )-MOFs. 3,11,19 The (L 1 ) 2− ligand in 1 shows only a kind of coordinated mode: each carboxylate adopts a μ 2 -bridging syn – anti bidentate fashion to connect two Mn( ii ) atoms [a tetradentate mode shown in Scheme 2], 27 while the tetrazolyl N atoms do not participate in coordination. The phenyl and two tetrazole rings in (L 1 ) 2− ligand are nearly coplanar because the phenyl ring make a dihedral angle of 4.18(2)° and 3.08(2)° with the N1-tetrazole and N5-tetrazole ring, respectively.…”

“…2d) with the Schläfli symbol (4 4 ·6 2 ). 3,27,28 These 2D layers are further stabilized by four kinds of intermolecular O–H⋯O, O–H⋯N, C–H⋯O and C–H⋯N hydrogen-bonding interactions (Table 3) to form a 3D supramolecular framework (Fig. 2e and f).…”

“…Consequently, the multi-functional MOFs with different dimensions (1D–3D) and interesting properties (luminescent sensing, dye adsorption, photocatalysis and proton conduction) may be constructed from the ligands and different metal ions. 3–10…”