Lanthanide-2,3,5,6-Tetrabromoterephthalic Acid Metal–Organic Frameworks: Evolution of Halogen···Halogen Interactions across the Lanthanide Series and Their Potential as Selective Bifunctional Sensors for the Detection of Fe³⁺, Cu²⁺, and Nitroaromatics

Abstract

Two series of lanthanide metal–organic frameworks (MOFs) formulated as {Ln2(TBrTA)3­(H2O)8­·2H2O} n [Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9)] series 1, {[Ln3(TBrTA)6]­[Ln­(H2O)8]­·6H2O} n [Ln = Ho (10), Er (11), Tm (12), Yb (13), Lu (14)] series 2, respectively, were synthesized via slow evaporation with tetrabromoterephthalic acid (H2TBrTA) and structurally characterized by X-ray crystallography, infrared spectroscopy, and thermal analysis. Lanthanide contraction effects result in a change in the structure from a two-dimensional (2D) MOF with sql topology for La–Dy (series 1) to a three-dimensional (3D) MOF with pcu network topology for Ho–Lu (series 2). Supramolecular interactions also evolve from Br···Br, Br···O, π–π, and hydrogen bonding interactions in series 1 to Br···Br and hydrogen bonding interactions in series 2. The nature of Br···Br interactions transition from a combination of type I, type II, and quasi-type I/type II in series 1 to only type II in series 2. Furthermore, as the size of the Ln­(III) ion decreases, the strength of the type II Br···Br interactions increases. The anionic frameworks in series 2 are charge balanced by [Ln­(H2O)8]3+ cations in the pores that are encapsulated by an unprecedented three-dimensional (3D) “Star of David” dodecamer water cluster. Photophysical studies demonstrate that TBrTA is an efficient sensitizer of Eu3+(5D0) and Tb3+(5D4) luminescence as excitation into ligand bands leads to bright red and green emission, respectively, the spectral profiles of which display only metal centered emission bands. Emission from compound 6 is significantly quenched in the presence of Fe3+ (87%) and Cu2+ (75%) ions mainly due to competitive absorption of excitation energy, which leads to an inner-filter effect. In addition, the emission of 6 is more than 85% quenched by nitroaromatic compounds (NACs) such as 4-nitrophenol, dinitrophenol, and trinitrophenol (picric acid) with competitive absorption, photoinduced electron transfer, and electrostatic processes the main mechanisms of quenching. This study is the first to show that X···X interactions in extended structures such as MOFs can be tuned with the lanthanide contraction and also reveals that Ln-TBrTA MOFs can be used as bifunctional sensors for the detection of Fe3+ and Cu2+ as well as explosive nitroaromatics.

A Highly Stable Luminescent Eu‐MOF Exhibiting Efficient Response to Nitrofuran Antibiotics through the Inner Filter Effect and Photoinduced Electron Transfer

“…The decay lifetime of 1 at 613 nm is 497.55 µs and quantum yield at 393 nm is 14.59 %. Under the same experimental conditions, free H 3 BTCTB only exhibits a broad emission band centered at 449 nm upon excitation at 343 nm, which is resulting from the intraligand π – π * or n –π * electron transitions , . Blue fluorescence of H 3 BTCTB ligand can also be visualized by the naked eye under UV light irradiation (Figure inset).…”

Di-functional luminescent sensors based on Y3+ doped Eu3+ and Tb3+ coordination polymers: fast response and visible detection of Cr3+, Fe3+ ions in aqueous solutions and acetone

“…As one of the most promising classes of porous materials, coordination polymers (CPs) or metal-organic frameworks (MOFs), constructed from organic ligands and metal ions or clusters via self-assembly, have been considered as the most promising means for chemical and biological sensors for metal ions, [3][4][5][6][7] organic solutions, [8][9][10] nitro aromatics [11][12][13][14] and so on, because it is simple, sensitive, selective and responsive. [15][16][17][18][19] Luminescent CPs or MOFs could be divided into two main types.…”

Coordination Polymers Based on a Biphenyl Tetraphosphonate Linker: Synthesis Control and Photoluminescence

“…Among the assorted reasons why there are so many reports in the area of MOFs and PCPs, and why they remain an attractive topic of research, one can point out their tunable chemical structure and/or their multifunctional properties [2]. The ability to design a network with specific pore sizes and shapes is one of the main features why these materials are good candidates for multiple applications in different research areas like gas storage and separation [3,4], catalysis [5,6], sensing [7][8][9][10][11], and drug delivery [12,13], among others [14][15][16][17][18][19][20][21].…”

“…[39] However, this approach did not significantly reduce the number of nodes ultimately leading instead to a mixture of different node approaches, hence in this manuscript we decided to maintain the classical approach. For this case, the notations {4 3 }, {4 9 •6}, {4 6 } correspond to the three H 8−x btp x− residues and {4 13 •6 2 }, {4 5 •6 3 •8 2 }, {4 6 •8 8 •10} corresponds to the metal centers. [where Ln 3+ = Ce 3+ (2Ce), Pr 3+ (2Pr), and Nd 3+ (2Nd)] was elucidated for the La 3+ -based material.…”

“…Using the same topological strategy previously described for 1 (again, the hydrogen bonds were not included in the calculation), this new MOF structure is a new hexanodal 5,6,6,7,7,8-connected network with total point symbol {3•4 12 8 •6 2 } notations correspond to the metal centers and H 8−x btp x− residues, respectively. We note that in this framework La1 and La3 exhibit the same point and extended symbol being, thus, equivalent hence the six-connectivity nature of the network.…”