Design and Construction of a Luminescent and Highly Stable 3D Metal–Organic Framework with a [Zn₄(μ₃-OH)₂]⁶⁺Core

Abstract

A highly stable and luminescent 3D metal–organic framework (MOF), {[Zn4(μ3-OH)2(BTC)2(BBI4PY)2]·10H2O} n (Zn-MOF), with a rare [Zn4(μ3-OH)2]6+ core has been synthesized using a new rigid and functionalized pillar linker, 2,6-bis­(pyridin-4-yl)-1,7-dihydrobenzo­[1,2-d:4,5-d′]­diimidazole (BBI4PY) in combination with Zn­(OAc)2·2H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) under solvothermal conditions. Unlike other MOFs with the [Zn4(μ3-OH)2]6+ core, Zn-MOF was synthesized without using an external base, as the intrinsic basicity of BBI4PY served the purpose. Furthermore, it retains crystallinity and phase purity up to 350 °C on the basis of TGA and in situ variable temperature PXRD, correlating with its solid-state structure. Using the dehydrated Zn-MOF, water sorption studies show uptake of 220 cm3 g–1 (corresponds to 10 water molecules). A large hysteresis in desorption isotherm signifies strong interactions between adsorbed water and Lewis basic sites present in the framework. The reversible nature of water sorption was further manifested by TGA and PXRD studies. As an example of its application, the highly fluorescent and electron-rich nature of Zn-MOF has been utilized for the selective sensing of Fe3+ and 2,4,6-trinitrophenol (TNP) in water with detection limits of 3.7 and 1.8 ppm, respectively. The mechanistic details for the turn-off quenching have been elucidated with the help of Stern–Volmer plots, spectral overlap, lifetime studies, and density functional theory calculations. This mechanistic evidence reveals that a combination of strong hydrogen bonding with resonance energy transfer and photoinduced electron transfer (PET) processes is synchronously responsible for the quenching of the fluorescence intensity of Zn-MOF.

Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso‐Hydroxylation of Arylboronic Acids

“…Notably, these K sv and LOD values of 1 and 2 are comparable/quite better than some of the previously reported CPs/MOFs used for the detection of NACs. [54][55][56][57] A comparative list comprising a number of Zn-and Cd-based CPs/MOFs which have been utilised for the detection of various NACs are provided with the Table S5 of the Supporting Information. electron-rich moieties and coordinated DMF molecule and Cl atom along with the uncoordinated amidic functionality which is renowned for hydrogen-bonding interactions.…”

A Comprehensive Overview on Advanced Sensing Applications of Functional Metal Organic Frameworks (MOFs)

“…electron-deficient moieties like Fe 3 + and TNP in water (Figure 5). [55] Zhang et al developed MOF fused test strips for the recognition of hazardous organic molecules in wastewater. They fabricated some Tb-HIP strips by recycling the filter paper, which is used to filter the lanthanide MOF powder, [Tb-(HIP)(H 2 O) 5 ] ⋅ (H 2 O) ⋅ (HIP) 1/2 (HIP = 5-hydroxyisophthalate) and then encapsulated with polymethyl methacrylate (PMMA) polymer net.…”

“…The electron‐rich nature and exceptional fluorescence of Zn‐MOF have been further used for the specific detection of electron‐deficient moieties like Fe 3+ and TNP in water (Figure 5). [55] …”

“…(a) Comparison of quenching/enhancement percentages of fluorescence intensity by the addition of an aqueous solution of metal ions (500 μL, 1 mM). (b) Change in the emission spectrum of Zn-MOF upon the incremental addition of a Fe 3 + solution (1 mM) in water (λ ex = 390 nm).Reproduced with permission from Ref [55]…”

Luminescent, Helical and Highly Stable Zn(II) and Cd(II) Coordination Polymers: Structural Diversity and Selective Sensing of 4‐Nitroaniline in Water

“…Luminescent CPs (LCPs) and MOFs (LMOFs) are designed for sensing on the basis of their structural diversity, tailorable pore size and tuneable chemical and physical properties. For the development of LCPs and LMOFs, the introduction of either π‐electron rich aromatic moieties with some recognition site into the frameworks or metal ions (Zn 2+ , Cd 2+ or Ln 3+ ) or the combination of both can be used to detect the emission signal during sensing [2d,4–15] …”