A thiadiazole-functionalized ZrIJIV)-based metalorganic framework as a highly fluorescent probe for the selective detection of picric acid † Mostakim SK and Shyam Biswas * A new, strongly luminescent ZrIJIV)-based metal-organic framework (MOF) material (1) having a UiO-68 (UiO = University of Oslo) framework topology and incorporating the π-conjugated, thiadiazolefunctionalized H 2 BTDB {H 2 BTDB = 4,4′-(benzoijc]ij1,2,5]thiadiazole-4,7-diyl)dibenzoic acid} ligand was synthesized under solvothermal conditions (150 °C, 24 h) using ZrCl 4 and the H 2 BTDB ligand in DMF (DMF = N,N-dimethylformamide). The phase-purity of as-synthesized 1 was ascertained by X-ray powder diffraction (XRPD) analysis, Fourier transform infrared (FT-IR) spectroscopy and elemental analysis. Based on the thermogravimetric analyses, 1 is thermally stable up to 400 °C. XRPD experiments verify that activated 1′ retains its crystallinity when exposed to water, acetic acid and 1 M HCl solutions. As revealed by the steady-state fluorescence titration experiments, the thermally activated form of the compound (1′) showed a selective sensing behaviour towards 2,4,6-trinitrophenol (TNP, commonly known as picric acid), even in the presence of other potentially competing nitroaromatic explosive compounds. The estimated detection limit of 1′ for sensing TNP in methanol suspension was found to be 1.63 × 10 −6 M. The highest fluorescence quenching ability of TNP can be attributed to both energy and electron transfer processes as well as electrostatic interactions between the hydroxyl group of TNP and the Lewis basic N-donor sites of the BTDB ligand. Endowed with its excellent detection efficiency, 1′ is a promising luminescent sensor material for the long-term, practical sensing of TNP.

A new Zr­(IV)-based UiO-67 metal–organic framework (1) was prepared with urea-functionalized biphenyl-4,4′-dicarboxylic acid (BPDC-urea) as the linker using conventional solvothermal technique and thoroughly characterized using X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric (TG), and N2 sorption analyses. The activated form of 1 (called 1′) exhibited excellent BET surface area in spite of having a large functional moiety (urea) in the linker side. The activated form of this material (1′) was successfully employed for the Friedel–Crafts alkylation of indole with β-nitrostyrene to achieve 97% yield in toluene at 70 °C for 24 h. Furthermore, the catalyst was used for four cycles, with no significant loss in its activity, and the reaction was heterogeneous in nature. The activity of 1′ was comparable to UiO-67-(NH2)2, whereas the activity was 2-fold higher compared to the parent UiO-67. Further, the activity of the BPDC-urea linker was nearly 2-fold higher than that of ZrCl4, suggesting the crucial role played by the urea moiety than the metal node. In addition, the catalyst (1′) exhibited a wide substrate scope, allowing the preparation of a series of compounds with moderate to high yields under the optimized reaction conditions. The roles of metal salt and linker in the catalysis have also been studied separately, and the mechanism for the catalysis has been clarified.

A Zr(IV)‐based UiO‐66 metal‐organic framework (MOF) (named 1) was synthesized by employing 1‐(aminomethyl)naphthalene‐2‐ol appended terephthalate linker and Zr(IV) salt via solvothermal method and subsequently characterized. Furthermore, the potential efficiency of activated (named 1′) form of as‐synthesized MOF was investigated as an organocatalyst for the ring‐opening of epoxide by methanol. The catalytic performance of 1 and 1′ was studied in the methanolysis of styrene oxide as a model substrate and the activity of 1′ was also examined with various alcohols. Under the optimized reaction conditions, the catalytic performance of 1′ reached 96 % conversion of styrene oxide to its corresponding product with 98 % regioselectivity. The reusability and stability of the catalyst were proved by recycling up to four runs in the methanolysis of styrene oxide. The Lewis acidity originating from metal nodes and hydrogen bond donating (HBD) sites in the linker is distributed homogeneously throughout the framework, thus playing crucial role in the activation of epoxide with easy accessibility.

A new boronic acid functionalized Zr(IV) metal−organic framework having the capability of sensing H 2 O 2 in live cells is reported. The Zr-MOF bears a UiO-66 structure and contains 2-boronobenzene-1,4-dicarboxylic acid (BDC-B(OH) 2 ) as a framework linker. The activated Zr-UiO-66-B(OH) 2 compound (called 1′) is highly selective for the fluorogenic detection of H 2 O 2 in HEPES buffer at pH 7.4, even in the presence of interfering ROS (ROS = reactive oxygen species) and other biologically relevant analytes. The fluorescent probe was found to display extraordinary sensitivity for H 2 O 2 (detection limit 0.015 μM) in HEPES buffer, which represents a lower value in comparison to those of the MOF probes documented so far for sensing H 2 O 2 using other analytical methods. Taking advantage of its high selectivity and sensitivity for H 2 O 2 in HEPES buffer, the probe was successfully employed for the imaging of intracellular H 2 O 2 . Imaging studies with MDAMB-231 cells revealed the emergence of bright blue fluorescence after loading with probe 1′ and subsequent treatment with H 2 O 2 solution.

A zirconium (Zr) metal–organic framework having a DUT-52 (DUT stands for Dresden University of Technology) structure with face-centered cubic topology and bearing the rigid 1-(2,2,2-trifluoroacetamido) naphthalene-3,7-dicarboxylic acid (H2NDC-NHCOCF3) ligand was prepared, and its solid structure was characterized with the help of the X-ray powder diffraction (XRPD) technique. Other characterization methods like thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy were applied to verify the phase purity of the compound. In order to get the solvent-free compound (1′), 1 was stirred with methanol for overnight and subsequently heated at 100 °C overnight under vacuum. As-synthesized (1) and activated (1′) compounds are thermally stable up to 300 °C. The Brunsuer Emmett-Teller (BET) surface area of 1′ was found to be 1105 m2 g–1. Fluorescence titration experiments showed that 1′ exhibits highly selective and sensitive fluorescence turn-on behavior toward cyanide (CN–) anion. The interference experiments suggested that other anions did not interfere in the detection of CN–. Moreover, a very short response time (2 min) was shown by probe 1′ for CN– detection. The detection limit was found to be 0.23 μM. 1′ can also be effectively used for CN– detection in real water samples. The mechanism for the selective detection of CN– was investigated systematically. Furthermore, the aerobic oxidation of cyclohexane was performed with 1′ under mild reaction conditions, observing higher activity than the analogous DUT-52 solid under identical conditions. These experiments clearly indicate the benefits of hydrophobic cavities of 1′ in achieving higher conversion of cyclohexane and cyclohexanol/cyclohexanone selectivity. Catalyst stability was proved by two consecutive reuses and comparing the structural integrity of 1′ before and after reuses by the XRPD study.