Trz Ligands Research Articles

Application of first-row transition metal complexes bearing 1,2,3-triazolylidene ligands in catalysis and beyond.

Triazole-derived N-heterocyclic carbenes, triazolylidenes (trz) have become an interesting alternative to the ubiquitous Arduengo-type imidazole-derived carbenes, in part because they are stronger donors, and in other parts due to their versatile synthesis through different types of click reactions. While the use of trz ligands has initially focused on their coordination to precious metals for catalytic applications, the recent past has seen a growing interest in their impact on first-row transition metals. Coordination of trz ligands to such 3d metals is more challenging due to the orbital mismatch between the carbene and the 3d metal center, which also affects the stability of such complexes. Here we summarize the strategies that have been employed so far to overcome these challenges and to prepare first-row transition metal complexes containing at least one trz ligand. Both properties and reactivities of these trz complexes are comprehensively compiled, with a focus on photophysical properties and, in particular, on the application of these complexes in homogeneous catalysis. The diversity of catalytic transformations entailed with these trz 3d metal complexes as well as the record-high performance in some of the reactions underpins the benefits imparted by trz ligands.

Negative Thermal Expansion in the Noncarboxylate Based Metal–Organic Framework Cd(trz)Cl

Negative thermal expansion (NTE), as a counterintuitive phenomenon, has attracted considerable interest owing to its great scientific and technical value. Owing to the inherent structural flexibility, metal–organic frameworks (MOFs) have recently been recognized as an ideal platform for the study of NTE. However, the reported NTE MOFs are mainly restrained in the carboxylate based ones. Herein, we found that the noncarboxylate MOF Cd(trz)Cl (trz = 1,2,4-trizaole) can also exhibit intrinsic volumetric NTE, and a transition from NTE to PTE at high temperatures can be observed. The combined in situ synchrotron powder X-ray diffraction, Raman spectra measurements, and DFT calculations shed light on the fact that the NTE mainly originates from the synergistic effect of geometric flexibility and the enhanced out-of-plane rotation behavior of the trz ligand. This study not only demonstrates a new NTE material but also can help to extend the scope of NTE to the more diverse noncarboxylate based MOFs.

Carbohydrate-Functionalized Triazolylidene Iridium Complexes: Hydrogenation Catalysis in Water with Asymmetric Induction.

Two sets of carbohydrate‐NHC hybrid iridium complexes were synthesised in order to combine properties of carbohydrates and triazolylidene (trz) ligands in organometallic catalysis. One set features a direct trz linkage to the anomeric carbohydrate carbon, while the second set is comprised of an ethyl linker between the two functional units. Deprotection of the carbohydrate afforded hybrid complexes that efficiently catalyse the direct hydrogenation of ketones in water. The catalytic activity of the hybrid complexes was influenced by the pH of the aqueous medium and surpassed the activity of carbohydrate‐free or acetyl‐protected analogues (>90 % vs 13 % yield). While no enantiomeric induction was observed for the ethyl‐linked hybrids, a moderate enantiomeric excess (ee) was induced by the directly linked systems. Moreover, these carbohydrate‐trz hybrid complexes displayed mixed inhibitory activity towards a glycosidase from H. orenii that contain a glucose binding site.

Strongly Luminescent Pt(IV) Complexes with a Mesoionic N-Heterocyclic Carbene Ligand: Tuning Their Photophysical Properties.

The synthesis, electrochemistry, and photophysical properties of a series of bis-cyclometalated Pt(IV) complexes that combine the mesoionic aryl-NHC ligand 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene (trz) with either 1-phenylpyrazole or 2-arylpyridine (C∧N) are reported. The complexes (OC-6-54)-[PtCl2(C∧N)(trz)] bearing cyclometalating 2-arylpyridines present phosphorescent emissions in the blue to yellow color range, which essentially arise from 3LC(C∧N) states, and reach quantum yields of ca. 0.3 in fluid solutions and almost unity in poly(methyl methacrylate) (PMMA) matrices at 298 K, thus representing a class of strong emitters with tunable properties. A systematic comparison with the homologous C2-symmetrical species (OC-6-33)-[PtCl2(C∧N)2], which contains two equal 2-arylpyridine ligands, shows that the introduction of a trz ligand leads to significantly lower nonradiative decay rates and higher quantum efficiencies. Computational calculations substantiate the effect of the carbene ligand, which raises the energy of dσ* orbitals in these derivatives and results in the higher energies of nonemissive deactivating 3LMCT states. In contrast, the isomers (OC-6-42)-[PtCl2(C∧N)(trz)] are not luminescent because they present a 3LMCT state as the lowest triplet.

Synthesis and investigation of two new crystalline organic inorganic nano-hybrids based on Wells-Dawson vanadotungstates and 1H-1, 2, 4-triazole as electro- and photocatalysts

Two new Wells–Dawson polyoxometalate-based organic-inorganic hybrid materials, namely, {[O]2.75[trz]7[α2-P2W17VO62]•12H2O}2(1) and {[O]11.5[trz]7[α2-P2W14.4V3.6O62]}2(2) (trz=1-H-1,2,4-triazole) were synthesized under mildconditions, and characterized by FT-IR, 1H NMR and 31P NMR spectroscopy, powder X-ray diffraction, TGA, field emission SEM and cyclic voltammetry. These hybrids constructed from trz ligand and Wells–Dawson polyoxoanions, in which trzis connected to a mono-vanadium substituted [α2-P2W17VO62]7− in 1 and a hexa-vanadium substituted [P2W12V6O62]12−in 2 by hydrogen bonding interactions. The structures of 1 and 2 were determined by single-crystal X-ray diffraction. Electrocatalytical activities of compounds 1 and 2 in the form of modified carbon paste electrode (MCPE) towards the reduction of nitrite ion have been studied in different pH values at acidic buffer solutions. Compounds 1-MCPE and 2-MCPE exhibit good electrocatalytical activity for reduction of NO2−. Also, the photocatalytical properties of the compounds 1 and 2 for the degradation of methylene blue have been studied.

A Comparative Study of Molybdenum Carbonyl and Oxomolybdenum Derivatives Bearing 1,2,3-Triazole or 1,2,4-Triazoles in Catalytic Olefin Epoxidation.

The molybdenum(0)-carbonyl-triazole complexes [Mo(CO)3(L)3] [L = 1,2,3-triazole (1,2,3-trz) or 1,2,4-triazole (1,2,4-trz)] have been prepared and examined as precursors to molybdenum(VI) oxide catalysts for the epoxidation of cis-cyclooctene. Reaction of the carbonyl complexes with the oxidant tert-butyl hydroperoxide (TBHP) (either separately or in situ) gives oxomolybdenum(VI) hybrid materials that are proposed to possess one-dimensional polymeric structures in which adjacent oxo-bridged dioxomolybdenum(VI) moieties are further linked by bidentate bridging triazole (trz) ligands. A pronounced ligand influence on catalytic performance was found and the best result (quantitative epoxide yield within 1 h at 70 °C) was obtained with the 1,2,3-triazole oxomolybdenum(VI) hybrid. Both molybdenum oxide-triazole compounds displayed superior catalytic performance in comparison with the known hybrid materials [MoO3(trz)0.5], which have different structures based on organic-inorganic perovskite-like layers. With aqueous H2O2 as the oxidant instead of TBHP, all compounds were completely soluble and active. A pronounced ligand influence on catalytic performance was only found for the hybrids [MoO3(trz)0.5], and only the 1,2,4-trz compound displayed reaction-induced self-precipitation behavior. An insight into the type of solution species that may be involved in the catalytic processes with these compounds was obtained by separately treating [MoO3(1,2,4-trz)0.5] with excess H2O2, which led to the crystallization of the complex (NH4)1.8(H3O)0.2[Mo2O2(μ2-O)(O2)4(1,2,4-trz)]·H2O. The single-crystal X-ray investigation of this complex reveals an oxo-bridged dinuclear structure with oxodiperoxo groups being further linked by a single triazole bridge.

An unprecedented molybdenum oxide based helical MOF with peroxidase-like activity synthesized by surfactant-thermal method

Here, a new three-dimensional molybdate-based metal-organic framework (MOF), [Zn3(MoO4)2(trz)2(H2O)2] (1), (trz = 1,2,4-triazole) was successfully prepared by the surfactant-thermal method for the first time. Single crystal X-ray diffraction analysis reveals that the new compound possesses twofold meso-helical structure fabricated by Zn ions and trz ligand, and the inorganic MoO4-Zn nets insert into the helix arrays. In addition, Zn ions as their common junction stabilize the whole framework. As a kind of new peroxides mimic enzyme, the new compound can effectively catalyze the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, accompanied by a obvious color varvation of solution (1 min responsed time). Moreover, the result of colorimetric sensing of H2O2 is that the H2O2 detection limit is 0.25 μM, and the linear range is 1 to 80 μM.

ROMP synthesis of 1,2,3-triazolyl dendronized polymers with triethylene glycol branches as recyclable nanoreactors for Cu(I) “click” catalysis reaction in water

The design and construction of high-efficiency nanoreactor systems have attracted a great deal of attention for their potential applications in materials science, biomedicine and catalysis. Especially, understanding the relationship between the precise internal structure of nanoreactors and their catalytic performance is essential for catalyst design. Here we report two bulky G2 dendronized norbornene macromonomers 8 and 13 containing nine hydrophilic triethylene glycol (TEG) termini with three and nine, respectively, 1,2,3-triazole (trz) rings, and their controlled polymerizations via the ring-opening metathesis polymerization (ROMP) technique using Grubbs' third-generation olefin metathesis catalyst. The self-assemblies of the obtained dendronized polymers (DPs) 9 and 14 in water then yield novel micellar nanoreactors with different location distribution of the coordinative intradendritic trz ligands. The recyclable nanoreactors are used to support CuI ion generated by in situ reduction of CuSO4·5H2O via sodium ascorbate, and strongly activate the CuI-catalyzed azide alkyne cycloaddition (CuAAC) “click” reactions in water, leading to exceptional TONs up to 250 000 and TOFs up to 16 670 h−1. Remarkably, when the amount of CuI catalysts is less than 50 ppm, 9a-CuI exhibits considerably higher catalytic efficiency than 14a-CuI, which is attributed to the architectural difference of the two used DPs 9 and 14. This work highlights the role of the location of trz ligands in DPs nanoreactors on the catalytic efficiency of CuI catalyst, and the unique advantage of DP-type nanoreactors by less steric inhibition, compared to the congested dendrimers nanoreactors, and also rationalizes optimization in catalyst engineering.

Two mixed-addenda Nb/W polyoxometalate-based hybrid compounds containing multicopper units: synthesis, structures, and electrochemical and magnetic properties.

Two mixed-addenda Nb/W polyoxometalate (POM)-based hybrid compounds, [CuICu(μ3-OH)(H2O)6(trz)3]2(PW9Nb3O40)·13H2O (1) and [CuICu(μ3-OH)(H2O)4(Htrz)(trz)3]2(PW9Nb3O40)·13H2O (2), were synthesized under hydrothermal conditions. Single-crystal X-ray diffraction revealed that compound 1 contains planar triangular tricopper {Cu(μ3-OH)(trz)3} units, and these tricopper units link to each other to form a 1D anti-parallel chain. CuI ions connect the 1D chains by the coordination of trz ligands to form 2D layers in the ab plane. Compound 2 contains the same tricopper {Cu(μ3-OH)(trz)3} units as well as bicopper {Cu(Htrz)2} units. The tricopper units also form 1D chains and the bicopper units connect the 1D chains to form similar 2D layers and finally construct the 3D framework. In both compounds, each Nb/W mixed-addenda Keggin {PW9Nb3O40} unit links eight tricopper units to generate the final 3D structure. Magnetism studies indicate anti-ferromagnetic exchange interactions among the CuII ions within the tricopper units, with JCu-Cu values of -209.3 and -200.8 cm-1 in 1 and 2, respectively.

Steam-Assisted Synthesis of an Extra-Stable Polyoxometalate-Encapsulating Metal Azolate Framework: Applications in Reagent Purification and Proton Conduction.

Different from the conventional synthesis approaches, such as hydrothermal or solvothermal synthesis, a porous metal azolate framework encapsulating Keggin-type [SiW12 O40 ](4-) anions was prepared by an environmentally friendly, low-cost, and highly efficient steam-assisted conversion method for the first time. The nanosized polyoxometalates as a template were encapsulated by a zeotype 6(4) 4(8) cage constructed by 28 nuclear zinc atoms connected through 32 Trz ligands. The obtained composite exhibits excellent thermal and chemical stability; meanwhile, its special ability to selectively absorb water from alcohols makes it efficiently separate water from analytically pure ethanol, with the result that water content decreases from 0.23 to 0.05 wt %, which is superior to the standard of chromatographic grade ethanol (<0.1 wt %). Besides, alternating current (ac) impedance experiments also reveal that the hybrid is a kind of proton conductive material.

A Stable Polyoxometalate-Pillared Metal-Organic Framework for Proton-Conducting and Colorimetric Biosensing.

A stable metal-organic framework pillared by Keggin-type polyoxometalate, Cu6 (Trz)10 (H2O)4 [H2 SiW12 O40 ]⋅8 H2O (Trz=1,2,4-triazole) (1), has been prepared under hydrothermal condition. The 2D layer structure with a 22-member ring was formed by Cu(2+) ions, which are connected with each other via the Trz ligands on the ab plane. Thus, the 2D layers are further interconnected through Keggin polyoxoanions to generate a 3D porous network with a small 1D channel. Moreover, the presence of polyoxoanions make it exhibit selective adsorption of water and proton-conducting properties. Additionally it showed efficient intrinsic peroxidase-like activity, providing a simple and sensitive colorimetric assay to detect H2O2 .

A 3D Polyoxometalate‐Based Framework Constructed from Ag/trz Metal‐Organic Ribbons and P2W18 Polyoxoanions: Synthesis, Structure and Electrochemical Properties

AbstractA Wells‐Dawson Polyoxometalate‐based hybrid, Ag9(trz)3(Htrz)4 (H2O)(P2W18O62)·3H2O (1) (Htrz = 1,2,4‐1H‐triazole) was hydrothermally synthesized through using trz ligand and silver nitrate in the presence of [P2W18O62]6– polyoxoanion. In the 3D framework structure of compound 1, two kinds of wave‐like Ag/trz chains originated from trz ligands and silver cations are aggregated in a “2+1” mode by {Ag2/trz} linkages to result in a 1D Ag/trz metal‐organic ribbon, which is further extended into a 3D framework structure by [P2W18O62]6– polyoxoanions through Ag‐O covalent bonds. Additionally, the electrochemical properties of compound 1 have also been investigated.

Stabilization of AuNPs by monofunctional triazole linked to ferrocene, ferricenium, or coumarin and applications to synthesis, sensing, and catalysis.

Monofunctional triazoles linked to ferrocene, ferricenium, or coumarin (Cou), easily synthesized by copper-catalyzed azide alkyne (CuAAC) "click" reactions between the corresponding functional azides and (trimethylsilyl)acetylene followed by silyl group deprotection, provide a variety of convenient neutral ligands for the stabilization of functional gold nanoparticles (AuNPs) in polar organic solvents. These triazole (trz)-AuNPs are very useful toward a variety of applications to synthesis, sensing, and catalysis. Both ferrocenyl (Fc) and isostructural ferricenium linked triazoles give rise to AuNP stabilization, although by different synthetic routes. Indeed, the first direct synthesis and stabilization of AuNPs by ferricenium are obtained by the reduction of HAuCl4 upon reaction with a ferrocene derivative, AuNP stabilization resulting from a synergy between electrostatic and coordination effects. The ferricenium/ferrocene trz-AuNP redox couple is fully reversible, as shown by cyclic voltammograms that were recorded with both redox forms. These trz-AuNPs are stable for weeks in various polar solvents, but at the same time, the advantage of trz-AuNPs is the easy substitution of neutral trz ligands by thiols and other ligands, giving rise to applications. Indeed, this ligand substitution of trz at the AuNP surface yields a stable Fc-terminated nanogold-cored dendrimer upon reaction with a Fc-terminated thiol dendron, substitution of Cou-linked trz with cysteine, homocysteine, and glutathione provides remarkably efficient biothiol sensing, and a ferricenium-linked trz-AuNP catalyst is effective for NaBH4 reduction of 4-nitrophenol to 4-aminophenol. In this catalytic example, the additional electrostatic AuNP stabilization modulates the reaction rate and induction time.

"Click" synthesis of nona-PEG-branched triazole dendrimers and stabilization of gold nanoparticles that efficiently catalyze p-nitrophenol reduction.

Two new water-soluble 1,2,3-triazole-containing nona-PEG-branched dendrimers are obtained with nine intradendritic 1,2,3-triazoles (trz). Addition of HAuCl4 in water to these dendrimers quantitatively leads to the intradendritic formation of AuCl3(trz) moieties subsequent to complete Cl(-) substitution by trz on Au(III), whereas the analogous complexation reaction of AuCl3 with a linear PEG trz ligand forms only an equilibrium between trz-coordinated Au(III) and Au(III) that is not coordinated to trz. Reduction of the dendrimer-Au(III) complexes to Au(0) by NaBH4 then leads to stabilization of gold nanoparticles (AuNPs) in water. The sizes of the AuNPs stabilized by the dendritic macromolecules are further controlled between 1.8 and 12 nm upon selecting the stoichiometry of Au(III) addition per dendritic trz followed by NaBH4 reduction. With a 1:1 Au/trz stoichiometry, the AuNP size depends on the length of the PEG tether of the dendrimer; small dendrimer-encapsulated AuNPs are formed with PEG2000, whereas large AuNPs are formed with PEG550. With Au/trz stoichiometries larger than unity, Au(III) is reduced outside the macromolecule, resulting in the formation of large interdendritically stabilized AuNPs. The formation of very small and only mildly stabilized AuNPs by neutral hydrophilic triazole ligands offers an opportunity for very efficient p-nitrophenol reduction by NaBH4 in water at the AuNP surface.

Carbene Transfer from Triazolylidene Gold Complexes as a Potent Strategy for Inducing High Catalytic Activity

A series of gold(I) complexes [AuCl(trz)] were synthesized that contain 1,2,3-triazolylidene (trz) ligands with variable wingtip groups. In the presence of AgBF4, these complexes undergo ligand redistribution to yield cationic complexes [Au(trz)2]BF4 in high yields as a result of efficient carbene transfer. Identical reactivity patterns were detected for carbene gold complexes comprised of Arduengo-type IMes ligands (IMes = N,N'-dimesityl-imidazol-2-ylidene). Reaction of cationic complexes [Au(trz)2](+) with [AuCl(trz')] afforded the heteroleptic complex [Au(trz)(trz')](+) and [AuCl(trz)] (trz, trz' = triazolylidene ligands with different wingtip groups). Carbene transfer occurs spontaneously, yet is markeldy rate-enhanced in the presence of Ag(+). The facile carbene transfer was exploited as a catalyst activation process to form active gold species for the aldol condensation of isocyanides and aldehydes to form oxazolines. The catalytic activity is strongly dependent on the presence of Ag(+) ions to initiate catalyst activation. High turnovers (10(5)) and turnover frequencies (10(4) h(-1)) were accomplished. Structural analysis at early stages of the reaction support the critical role of triazolylidene dissociation to activate the precatalyst and dynamic light scattering revealed the presence of nanoparticles (±100 nm diameter) as potential catalytically active species. Furthermore, the triazolylidene scaffold had no impact on the diastereoselectivity of the oxazoline formation, and chiral triazolylidenes did not induce any asymmetry in the product. The facile dissociation of carbenes from [AuCl(carbene)] in the presence of Ag(+) ions suggests a less stable Au-Ccarbene interaction than often assumed, with potential implications for gold-catalyzed reactions that employ a silver salt as (putative) halide scavenger.

A (3,9)-connected cadmium 1,2,4-triazolate framework based on a trinuclear inorganic cluster

Hydrothermal reaction of 1,2,4-triazole with CdCl2 · 2.5H2O generated a 3-D metal-organic framework, {[Cd3Cl2(Trz)4] · H2O} n (1) (Trz = 1,2,4-triazole), which was characterized by elemental analysis, FT-IR, X-ray powder diffraction, X-ray single-crystal diffraction, TG/DTA, and photoluminescence measurements. Compound 1 crystallizes in the orthorhombic system, space group Pnma, a = 16.906(3) Å, b = 8.3151(17) Å, c = 13.080(3) Å, V = 1838.6(6) Å3, Z = 4. Cd(1) is coordinated by four nitrogen atoms and one chloride to form a distorted trigonal-bipyramidal geometry. Cd(2) is an octahedron defined by four triazole nitrogen atoms and two chlorides. Two Cd(2) and one Cd(1) are linked by μ 3-Cl(1) to give a [Cd3Cl] cluster, which is connected by μ 2-Cl(2) to generate a 1-D inorganic chain. The 1-D inorganic chains are extended by μ 3-Trz to form a 2-D hybrid layer in the b, c-plane, which is ultimately linked by residual triazole ligands to give a 3-D framework. The [Cd3Cl] clusters and the Trz ligands can be regarded as 9- and 3-connected nodes, which lead to an unusual (3,9)-connected net with Schläfli symbol of (423 · 613)(43). The solid 1 exhibits high thermal stability and shows strong blue fluorescence emission at 410 nm in the solid state at ambient temperature.

Synthesis, structure and characterizations of a novel 3D coordination polymer constructed from rare castellated inorganic chains

Self-assembly of CdCl 2 and 1,2,4-triazole under hydrothermal condition yields a novel three-dimensional coordination polymer, namely {[Cd 8 Cl 4 (Trz) 12 (H 2 O)]·2H 2 O} n ( 1 ) (Trz = 1,2,4-triazole). Single-crystal X-ray diffraction reveals that four of the five independent Cd centers are linked by two μ 2 -Cl and two μ 3 -Cl atoms to form novel heptanuclear [Cd 7 Cl 4 ] clusters, which are connected by the bridging water molecules to generate an unprecedented 1D castellated inorganic chain. Furthermore, the fifth unique Cd center and the castellated Cd–Cl–O chain are joint to each other via six different μ 3 -Trz ligands to give a 3D organic–inorganic hybrid framework of 1 . A novel 3D hybrid coordination polymer was obtained via the self-assembly of CdCl 2 and 1,2,4-triazole under hydrothermal condition, which is constructed from unprecedented 1D castellated Cd–Cl–O inorganic chains and μ 3 -triazole ligands. ► 1D castellated inorganic chain based on heptanuclear [Cd 7 Cl 4 ] clusters. ► 3D organic–inorganic hybrid framework with rod-packing topology. ► Strong blue photoluminescence attributed to LMCT.

Two zinc-triazole-biphenyldicarboxylate coordination polymers affording a 3D 4-connected 2-fold interpenetrating diamond net and a 2D 6-connected hxl net

Abstract Two new zinc-triazole-biphenyldicarboxylate frameworks based on secondary building units (SBUs), namely, Zn4(μ4-O)(trz)2(4,4′-bpdc)2 ( 1 ) and Zn2(trz)2(2,4′-bpdc) ( 2 ), [Htrz = 1,2,4-triazole, H2bpdc = biphenyldicarboxylate] have been synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction analyses, X-ray power diffraction, elemental analyses, infrared absorption spectra, and thermogravimetric analyses. Compound 1 is a 2-fold interpenetrating diamond topology constructed from [Zn4(μ4-O)(trz)2]4+ SBUs with tetrahedral [Zn4(μ4-O)] core and two trz ligands. Compound 2 is a 2D 6-connected hxl network based on [Zn2(trz)2]2+ SBUs. Additionally, these two compounds show emission properties at room temperature in the solid state.

Four Novel Three-Dimensional Pillared-Layer Metal-Organic Frameworks in the Zn/Triazolate/Carboxylate System: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties

Four novel zinc(II) metal-organic frameworks, {[Zn7(trz)6(1,3-bdc)4(H2O)2]·2H2O}n (1), {[Zn7(trz)6(hip)4(H2O)2]·8H2O}n (2), [Zn4(trz)4(Hnip)2(nip)]n (3), and [Zn5(trz)2(Hbtc)4(H2O)4]n (4) (Htrz = 1,2,4-triazole, 1,3-H2bdc = 1,3-benzenedicarboxylic acid, H2hip = 5-hydroxyisophthalic acid, H2nip = 5-nitroisophthalic acid, and H3btc = 1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized by reaction of Zn salt and Htrz with four different aromatic acids, respectively. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by X-ray powder diffraction, elemental analyses, IR spectra, and TG analyses. The structures of compounds 1 and 2 are isostructural and feature the 3D structure containing multidimensional intersecting ring channels formed by the interconnection of 2D layers {[Zn7(trz)6]8+}n with 1,3-bdc (1) or hip (2). Compound 3 consists of {[Zn4(trz)4]4+}n layers with (4, 82) topology arranged in the −ABAB− stacking sequence, which are connected by nip pillars to generate a novel 3D open framework. Compound 4 is also in a 3D structure containing 2D layer motifs, which are further linked by btc ligands to complete the structure. There are two different building units [Zn2(trz)2]2+ and [ZnO6] within the 2D layers of 4. All of the compounds 1−4 exhibit the 3D pillared-layer structures. In the 2D layer motifs of these four compounds, trz ligands connect Zn ions in different coordination modes, which reflect the tendency of the trz ligand to bridge multiple metal sites, and the aromatic carboxylate ligands in compounds 1−4 serve as the pillar between the 2D layers, creating the 3D open frameworks. Moreover, these four compounds exhibit emission properties at room temperature in the solid state.

Two Novel Triazole-Based Metal - Organic Frameworks Consolidated by a Flexible Dicarboxylate Co-ligand: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties

To explore the effects of a co-ligand on the construction of mixed-ligand metal–organic frameworks (MOFs), two new triazole-based complexes with a flexible dicarboxylate as a co-ligand, {[Zn4(trz)4(gt)2(H2O)2](H2O)2}n 1 and {[Cd2(trz)2(gt)(H2O)2](H2O)4}n 2 (Htrz = 1,2,4-triazole; H2gt = glutaric acid), were synthesized and their structures were fully characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray crystallography. Their thermal stability and luminescence emissions were further investigated to establish their structure–property relationship. Crystal structure determination showed that 1 is a neutral two-dimensional pillared-bilayer network consisting of 14-membered hydrophobic channels, whereas 2 is an infinite three-dimensional framework constructed from tetranuclear [Cd4(trz)4]4+ subunits. Interestingly, the overall structure of both MOFs can be solely supported by ZnII/CdII and trz anions, and were further consolidated by the introduction of a flexible gt co-ligand. In addition, the carboxylate groups in the co-ligand can also serve as a weak O–H···O hydrogen-bond acceptor to capture guest water molecules. The synchronous weight-loss behaviour of trz and gt anions presented by thermogravometric curves suggest their cooperative contributions to the thermal stability of the MOFs. In contrast, the fluorescence emissions of two complexes are significantly dominated by the core trz ligand, rather than the gt co-ligand and metal ions.