Ran Fang

An efficient sensor for Zn2+ and Cu2+ based on different binding modes

An efficient sensor for Zn(2+) and Cu(2+) was designed based on different binding modes. The sensor displays ratiometric signals for Zn(2+), due to the Zn(2+)-triggered amide tautomerization; while dual-mode selective behaviors for Cu(2+) result from the deprotonation of the amide tautomer.

2D lanthanide MOFs driven by a rigid 3,5-bis(3-carboxy-phenyl)pyridine building block: solvothermal syntheses, structural features, and photoluminescence and sensing properties

A new series of five lanthanide(III) metal–organic frameworks with a general formula of [Ln3(bcpb)4(μ-HCOO)(μ-H2O)(H2O)2(DEF)]n (1–5) was generated by solvothermal reactions from Ln(NO3)3·6H2O {Ln = Eu (1), Tb (2), Gd (3), Dy (4), and Sm (5)} and 3,5-bis(3-carboxyphenyl)pyridine (H2bcpb) in an aqueous N,N-diethylformamide (DEF) medium. The obtained products were characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis (TGA), and powder and single crystal X-ray diffraction. The latter reveals that all compounds (1–5) are isostructural and feature very intricate 2D metal–organic frameworks. These were topologically analyzed, revealing a very complex hexanodal underlying net that can be simplified further to a binodal 3,5-connected layer with the 3,5L52 topology. Solid-state photoluminescence properties of 1–5 were studied in detail. Compound 1 exhibits a strong red luminescence upon excitation at 338 nm and its lifetime is 532 μs. Compound 2 shows an intense green luminescence upon excitation at 336 and its lifetime is 981 μs. The triplet state (3ππ*) of bcpb2− studied by using the Gd(III) derivative 3 demonstrated that the ligand effectively populates Tb(III) emission (Φ = 70.96%), whereas the corresponding Eu(III) derivative 1 shows a weak luminescence efficiency (Φ = 15.81%) as the triplet state of bcpb2− has a poor match with the 5D0 energy level of Eu(III). A notable feature of 1 is its remarkable sensing ability for Cu2+ ions and 2,4,6-trinitrophenol (TNP). Besides, a series of heterobimetallic Tb-based MOFs, [Tb3(1−x)Eu3x(bcpb)4(μ-HCOO)(μ-H2O)(H2O)2(DEF)]n {x = 0.001, 0.002, 0.003, 0.01, 0.02, 0.03, 0.04, 0.10, 0.15, 0.20} (compounds 2a–2j, respectively), was prepared. The luminescence studies reveal that the simultaneous presence of the characteristic sharp emission bands of Eu3+ and Tb3+ allows the tuning of the photoluminescence colors of such materials by adjusting the doping concentration of the Eu3+ ions.

Structural diversity in new coordination polymers modulated by semirigid ether-linked pyridine-phthalate building block and ancillary ligands: syntheses, structures, and luminescence properties

Seven new 2D or 3D coordination polymers based on the flexible and semirigid pyridine-phthalate building block H2pbda (3-(pyridin-3-yloxy)benzene-1,2-dicarboxylic acid), namely 3D [Cd(pbda)]n (1), 3D [Cd3(OH)2(pbda)2]n (2), 3D [Cd(pbda)(4,4′-bpy)]n (3), 3D {[Co(pbda)(4,4′-bpy)]·2H2O}n (4), 2D {[Zn(pbda)(1,4-bib)]·H2O}n (5), 2D {[Cd(pbda)(1,4-bib)]·H2O}n (6), and 3D {[Co(pbda)(4,4′-bibp)]·2H2O}n (7), were prepared by hydrothermal reactions in the presence (optional) of an ancillary ligand selected from 4,4′-bpy (4,4′-bipyridine), 1,4-bib (1,4-bis(imidazol)butane), or 4,4′-bibp (bis(benzimidazol)propane). Compounds 1–7 were fully characterized and their crystal structures were classified from the topological viewpoint, resulting in the following topological networks: gis in 1, crb in 2, ins in 3 and 7, fsc-3,4-C2/c in 4, and sql in 5 and 6. The results revealed that the crystal architectures and the coordination modes of pbda building blocks are influenced by various factors, including the nature of metal cations, the solution pH, the temperature, and the presence of N-donor ancillary ligands. In addition, TGA data show that almost all compounds are thermally stable up to 300 °C. Zn(II) and Cd(II) derivatives are also strong luminescent emitters.

Two Schiff-base fluorescent sensors for selective sensing of aluminum (III): Experimental and computational studies.

Two Schiff-base fluorescent sensors have been synthesized, which both can act as fluorescent probes for Al(3+), upon addition of Al(3+), they exhibit a large fluorescence enhancement which might be attributed to the formation of 1:1 ligand-Al complexes which inhibit photoinduced electron transfer (PET) progress, and that the proposed binding modes of the sensors and Al(3+) are identified by theoretical calculations.

Hybrid materials based on novel 2D lanthanide coordination polymers covalently bonded to amine-modified SBA-15 and MCM-41: assembly, characterization, structural features, thermal and luminescence properties

Three novel 2D coordination polymers [Tb2(μ4-L)2(μ-HL)(μ-HCOO)(DEF)]n (Tb-L), [Eu(μ4-L)(L)(H2O)2]n (Eu-L), and [Nd(μ4-L)(L)(H2O)2]n (Nd-L) were assembled from the corresponding lanthanide(iii) nitrates and 5 methoxy-(4-benzaldehyde)-1,3-benzenedicarboxylic acid (H2L) as a main multifunctional building block bearing carboxylate and aldehyde functional groups, using H2O/DEF {DEF = N,N-diethylformamide} as a reaction medium. The obtained coordination polymers were isolated as stable microcrystalline solids and fully characterized by elemental analysis, FT-IR spectroscopy, TGA, BET, PXRD, and single-crystal X-ray diffraction methods. Their structures feature intricate 2D metal-organic networks, which were topologically classified as underlying layers with the 4,6L26 (for Tb-L) or sql (for Eu-L and Nd-L) topologies. Besides, a novel series of mesoporous hybrid materials wherein the Tb-L, Eu-L, or Nd-L coordination polymers are covalently grafted into the amine-functionalized SBA-15-NH2 or MCM-41-NH2 matrices (via the formation of Schiff-base groups) was also synthesized and fully characterized. These hybrid materials show high thermal and photoluminescence stability, as well as remarkable chemical resistance to boiling water, and acidic or alkaline medium. Luminescent properties of the parent coordination polymers and derived hybrid materials are investigated in detail, showing that the latter combine the luminescent characteristics (intense green or red emissions and excellent stability) of lanthanide coordination polymers and structural features of ordered mesoporous silica molecular sieves. Moreover, light emitting devices were assembled, by coating the hybrid materials onto the surface of UV-LED bulbs, and showed excellent light emitting properties.

Computational study on the NHC-catalyzed synthesis of 2,3-disubstituted indoles: mechanism, key intermediate and the role of the catalyst

In this work, the possible reaction mechanisms and the role of N-heterocyclic carbene (NHC) catalysts in the umpolung reaction of imines to generate 2-substituted indole-3-acetic acid derivatives were investigated by density functional theory (DFT). Two different NHCs (named A-NHC and B-NHC) were studied as model catalysts. Calculations revealed that the whole reaction includes four steps: (1) the formation of a key aza-Breslow intermediate, (2) an intramolecular 1,4-addition, (3) a second 1,2-proton transfer, and (4) the desorption of the NHC to give 2-substituted indole-3-acetic acid derivatives. Furthermore, the nucleophilic attack of the NHC on the imine carbon or β-carbon of the α,β-unsaturated ester is the rate-limiting step that determines which intermediate is formed (the aza-Breslow or deoxy-Breslow intermediate). Analysis of the global reaction index indicates that NHCs play a vital role in the polarity reversal of an imine carbon atom or a β-carbon from the α,β-unsaturated ester. This strengthens the nucleophilicity of an imine carbon or a β-carbon from the α,β-unsaturated ester as a Lewis base. In addition, B-NHC has a slightly higher nucleophilicity value, which makes the reactivity of B-NHC slightly better than that of A-NHC. The theoretical results obtained not only rationalize the experimental observations well but also provide important insight into the mechanistic details of the reaction.

Multifunctional Ln–MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone

A new series of five three-dimensional Ln(III) metal-organic frameworks (MOFs) formulated as [Ln4(μ6-L)2(μ-HCOO)(μ3-OH)3(μ3-O)(DMF)2(H2O)4] n {Ln3+ = Tb3+ (1), Eu3+ (2), Gd3+ (3), Dy3+ (4), and Er3+ (5)} was successfully obtained via a solvothermal reaction between the corresponding lanthanide(III) nitrates and 2-(6-carboxypyridin-3-yl)terephthalic acid (H3L). All of the obtained compounds were fully characterized, and their structures were established by single-crystal X-ray diffraction. All products are isostructural and possess porous 3D networks of the fluorite topological type, which are driven by the cubane-like [Ln4(μ3-OH)3(μ3-O)(μ-HCOO)]6+ blocks and μ6-L3- spacers. Luminescent and sensing properties of 1-5 were investigated in detail, revealing a unique capability of Tb-MOF (1) for sensing acetone and metal(III) cations (Fe3+ or Ce3+) with high efficiency and selectivity. Apart from a facile recyclability after sensing experiments, the obtained Tb-MOF material features a remarkable stability in a diversity of environments such as common solvents, aqueous solutions of metal ions, and solutions with a broad pH range from 4 to 11. In addition, compound 1 represents a very rare example of the versatile Ln-MOF probe capable of sensing Ce3+ or Fe3+ cations or acetone molecules.

Computational study on GaCl3-mediated reactions of donor–acceptor cyclopropanes with aromatic aldehydes: mechanism and role of GaCl3 and aldehydes

By means of density functional theory (DFT), the mechanism and role of GaCl3 and aldehydes for the GaCl3-mediated reaction of donor–acceptor (D–A) cyclopropanes and arylaldehydes have been reported in this work. DFT calculations reveal that the title reaction proceeds through three main steps: (1) the isomerization of 2-arylcyclopropane-1,1-dicarboxylates r1 to generate the ethylidenemalonate gallium complex 1a or 2-styrylmalonates 1b. (2) Subsequently, reaction between 1a (or 1b) and aromatic aldehydes would induce the formation of substituted indenes (Stage I). (3) Finally, reaction between the formed substituted indenes and aromatic aldehydes would give the polycyclic lactones (Stage II). According to our calculation, aldehydes not only participate in the reaction as a reactant, they can also promote the reaction as a co-catalyst for their proton-shuttle feature. For this reason, some excess of aldehyde is essential for implementing the process. The excess GaCl3 will hydrolyze with the water formed in Stage I, which ensures that the reaction of Stage II is carried out under acidic conditions. Furthermore, the usual [3 + 2] cycloaddition of DACs with aromatic aldehydes has also been studied. The theoretical results not only well rationalize the experimental observations but provide insights into the details of the reaction.

Computational Exploration of Counterion Effects in Gold(I)-Catalyzed Cycloisomerization of ortho-(Alkynyl)styrenes

A detailed theoretical analysis of the mechanism and chemoselectivity for gold(I)-catalyzed reaction of o-(alkynyl)styrene containing an isopropyl and a methyl at the terminal position of the alkene has been reported in this work. Two different counterions (SbF6– and OTs–) were studied as model catalysts. According to our calculation, for SbF6–, the reaction pathway is more prone to direct 1,2-H shifts (isopropyl H) than the elimination and ring expansion pathway. However, an elimination pathway affords the indenyl derivative by forming p-toluenesulfonic acid (HOTs), which may be the main pathway in the presence of OTs–. The chemoselectivity for the title reaction is mainly determined by the electronic effect of the counterion and the substituent rather than the steric effect. In other words, less basic SbF6– mainly provides the charge separation effect rather than assisted proton elimination. However, the more basic OTs– mainly assist proton elimination through the formation of HOTs. In addition to the good agreement with the experimental data, the density functional theory results also provide a significant contribution to the understanding of the reaction mechanism.