Mixed-ligand Strategy Research Articles

Auxiliary Ligand-Dependent Adaptive Regulation of Uranyl Coordination in Mixed-Ligand Uranyl Compounds of Flexible Biphenyltetracarboxylic Acid.

The mixed-ligand strategy is one of the important methods for preparing new materials and regulating the properties of materials. In this work, by introducing different auxiliary ligands (ALs), we have obtained a series of mixed-ligand uranyl complexes (1-6) from a flexible biphenyltetracarboxylic acid (H4bptc) with an adjustable orthogonal conformation and studied the influence of different organic base molecules on the coordination and assembly of H4bptc with a uranyl cation. It is found that the coordinated ALs, including 4,4'-bipyridine-1,1'-dioxide and 1,10-phenanthroline, partially occupy the coordination sites of the uranyl center and directly affect the molecular conformations and uranyl coordination of flexible bptc linkers. On the other hand, noncoordinated ALs such as protonated 4,4'-bipyridine ([H2(4,4'-bpy)]2+) or dimethylammonium, which work as counterions in the form of encapsulated guests or hydrogen-bonded templates, also have a nonnegligible impact on the conformation and coordination of bptc linkers. Most interestingly, the AL-mediated evolution of uranyl coordination by the bptc linker and coordination geometry of the uranyl center is clearly observed, which suggests the adaptability of flexible bptc linkers to take suitable molecular configurations and uranyl coordination modes so as to adapt to the external regulator agents and varying environment. The physicochemical characterization of these uranyl compounds, especially photoluminescence, is addressed and discussed, and the results reveal that compound 5 has the potential to serve as a multifunctional radiation detection material for UV light and X-ray radiation.

Mixed-Ligand Strategy for the Construction of Photochromic Metal–Organic Frameworks Driven by Electron-Transfer Between Nonphotoactive Units

Metal–organic frameworks (MOFs), as an emerging hybrid material, have been well explored in numerous areas such as adsorption, separation, catalysis, magnetism, photoluminescence, etc. Recently, th...

Near-infrared (NIR-II) luminescence for the detection of cyclotetramethylene tetranitramine based on stable Nd-MOF

Near-infrared-emissive materials as novel materials have drawn much attention for their unique properties of deep tissue penetration, high spatial resolution and low light damage to biological tissues. Lanthanide MOFs (Ln-MOFs) with high stability and near-infrared emission located in the near-infrared-II window (1000–1700 ​nm) is urgently needed to be developed in recent years. To tackle this challenge, a near-infrared-emissive lanthanide-based metal-organic frameworks (Nd-MOF-Y) [Nd(L-F4)1.5(L-N) (H2O)]n [L-F4 ​= ​2,3,5,6-Tetrafluoroterephthlonic acid, L-N ​= ​1.10-phenanthroline] based on mixed ligands strategy has been successfully prepared. The stability measurements show that Nd-MOF-Y possesses high water stability, chemical stability (pH ​= ​3–11), thermal stability (below 80 ​°C) and mechanical stability (vacuum environment). Luminescence performance studies exhibit the near-infrared-II emission characteristics and Nd-MOF-Y can detect cyclotetramethylene tetranitramine in the near-infrared range with high sensitivity, selectivity, cyclicality and low detection limit. Taking advantages of the stability and NIR-II emission, Nd-MOF-Y can be suitable for the biomedical applications in future.

Three Co/Ni(II)-MOFs with dinuclear metal units constructed by biphenyl-3,3′,5,5′-tetracarboxylic acid and N-donor ligands: Synthesis, structures, and magnetic properties

Three new dinuclear complexes {[Co2(bpta)(2,2′-bipy)(H2O)]·2CH3CN·3H2O}n (M ​= ​Co (1), Ni (2)), and {[Co(H2bpta)(4,4′-bipy)]·H2O}n (3) have been obtained through a mixed-ligands strategy. They were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. Structural analysis reveals that different dinuclear SBUs are formed by carboxylate groups of H4bpta ligands binding with metal ions in 1−3. The H4bpta ligands act as μ7-κ2:κ2:κ1:κ2 and μ3-κ2:κ0:κ1:κ0 coordination modes, respectively. For 1 and 2, the hexa-coordinated Co/Ni(II) ions are connected to form [M2(OCO)2(μ2-O)] SBUs by syn−syn-OCO− and μ2–oxo carboxylate bridges. The structures show (4,4)-connected 3D net with {42.84}-pts topology by bpta4− ligands linking [M2(OCO)2(μ2-O)] SBUs. Complex 3 possesses penta-coordinate geometry and displays a (2,6)-connected 2D layer formed by H2bpta2− and 4,4′-bipy ligands linking dinuclear [Co2(OCO)2] SBUs. The studies of the magnetic properties of 1−3 in the temperature range 1.8–300 ​K reveal that weak antiferromagnetic interaction exists in the triple and double bridging SBUs of the complexes 1 (J ​= ​−11.32 (6) cm−1) and 3 (J ​= ​−0.84(4) cm−1). Complex 2 exhibits ferromagnetic exchange (J ​= ​1.02(7) cm−1) in dinuclear [Ni2(OCO)2(μ2-O)] units.

A new 3D Cd(II) coordination polymer constructed by mixed-ligand strategy: synthesis, crystal structure and properties

A new 3D Cd(II) coordination polymer, {[Cd2(btc)(HL)(H2O)]·3H2O} n (1) (H2L= 3-(1H-pyrazol-4-yl)-5-(pyridin-2-yl)-1, 2, 4-triazole; H3btc = 1,3,5-benzenetricarboxylic acid), has been synthesized by hydrothermal reaction of Cd(NO3)2·4H2O, H2L and H3btc. It has been structurally characterized by element analysis, IR. X-ray single-crystal analysis was carried out for 1, which crystallizes in the monoclinic system, space group P21/n. The single X-ray diffraction reveals that compound 1 exhibits 3D framework structure. The luminescence properties of H2L and compound 1 were investigated at room temperature in the solid state. Furthermore, the thermal decomposition behavior of the compound is characterized by thermogravimetric analyses.

A New Mixed-Ligand Ni(II) Complex: Crystal Structure, Protective and Anti-Inflammatory Activities of its Nanoparticles on Acute Viral Myocarditis by Reducing the Release of Inflammatory Cytokines TNF-α and IL-1β

By means of the mixed-ligand strategy, a new Ni(II)-bearing coordination complex [Ni(pda)(bimb)(H2O)](H2O)1.5(1, bimb = 6,6′-bis(1H-benzo[d]imidazol-2-yl)-2,2′-bipyridine, H2pda = 4,4′-(pyridine-2,6-diyl)dibenzoic acid) is successfully obtained by the reaction of Ni(NO3)2·6H2O, bimb, and H2pda under hydrothermal reaction conditions. Furthermore, the nanoparticles of 1 (nano-1) with a size distribution of around 160 nm can be produced via a grinding method. In the section of biological research, we describe the anti-inflammatory activity of nano-1 on the acute viral myocarditis model. In the CVB3-induced acute viral myocarditis model, the treatment effect of nano-1 is evaluated by determining the mice survival rate and the CVB3 titer. The anti-inflammatory activity of nano-1 is determined by the ELISA assay of TNF-α and IL-1β levels in plasma.

A multifunctional pseudo-polyrotaxane coordination polymer based on the trinuclear cluster [Co3(COO−)4(OH−)2]: Synthesis, structure and properties

A trinuclear cobalt-based multifunctional coordination polymer with a dual loop pseudo-rotaxane motif, namely [Co3(DPFE‧H+)2(sdba2−)4(OH−)2](DPFE‧2H+)(CH3CN) (1), has been synthesized by a mixed ligand strategy under hydrothermal conditions (DPFE = 2,7-di(pyridin-4-yl)-9H-fluorene, H2sdba = 4,4′-sulfonyldibenzoic acid). Compound 1 has 1D + zero-dimensional (0D) → 1D armed pseudo-polyrotaxane character, in which the 1D dual ring chain [Co3(COO−)4(OH−)2(sdba2−)4 is threaded by doubly protonated free DPFE ligands. The trinuclear cobalt cluster and π-electron rich system involving the ligands jointly endow compound 1 with magnetism, photocatalytic and electrochemical properties. Magnetic property measurements of 1 indicate that there exists weak antiferromagnetic coupling in the trinuclear [Co3(COO−)4(OH−)2] unit, the experiments of photocatalytic degradation of dyes demonstrated that 1 has good catalytic activity for the degradation of methylene blue (MB) and the electrochemical results show that compound 1 exhibits a specific capacitance of 52.25 F g−1 at a current density of 1 A g−1 and retains 93.75% specific capacitance after 960 cycles.

Two cadmium(II) coordination polymers as multi-functional luminescent sensors for the detection of Cr(VI) anions, dichloronitroaniline pesticide, and nitrofuran antibiotic in aqueous media.

Two ternary cadmium(II) coordination polymers, with the formulas being {[Cd(tptc)0.5(bpz)(H2O)]·0.5H2O}n (CP 1), and [Cd(tptc)0.5(bpy)]n (CP 2), were designed through mixed ligands strategy. Benefiting from the excellent chemical stability and luminescent property, two Cd(II) CPs possessing efficient multi-functional fluorescent responses toward Cr(VI) anions, 2,6-dichloro-4-nitroaniline pesticide, and nitrofuran antibiotic in aqueous media with high sensitivity, selectivity, and excellent recyclable behaviors with the detection limits (LODs) are 235ppb for CrO42- anion, 343ppb for Cr2O72- anion, 112ppb for DCN pesticide, 62ppb for NFT antibiotic for CP 1, and 173ppb for CrO42- anion, 270ppb for Cr2O72- anion, 638ppb for DCN pesticide, 184ppb for NFT antibiotic for CP 2, respectively. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photoinduced electron transfer (PET).

Three coordination complexes based on mixed ligand strategy: Coordination diversities and nitrobenzene detections

Three new coordination complexes (HNU-40, 41 and 42) were synthesized by using mixed ligand strategy, which exhibit coordinated diversities and distinct dimensions. The structure of HNU-40 is the closed loop with the sized of 7.4 Å × 7.9 Å. HNU-41 displays a zig-zag one-dimensional chain structure, and the coordination mode of Zn2+ ions in the adjacent two chains is different. While, HNU-42 features a two-dimensional interpenetrating structure which are based on the hexagonal net. Three complexes behaved effective detection of nitrobenzene with good selectivity, anti-interference and circulation. In addition, the mechanism of fluorescence quenching is also discussed.

A luminescent pillar-layer Zn(II) metal–organic framework for the ultrasensitive detection of nitroaniline

A pillar-layer Zn (II) MOF (1), demonstrating a two-fold interpenetrating pcu topological net, has been facilely assembled from the mixed-ligand strategy. The result of tolerance towards organic solvents indicates MOF 1 shows an exceptional chemostability. The luminescence measurement reveals that MOF 1 is a promising luminescent chemosensor in the ultrasensitive detection of nitroaniline with low detection limits. Besides, the possible luminescent quenching mechanism of MOF 1 toward nitroaniline was investigated by the UV–Vis spectral overlap experiment.

Two new coordination polymers driven by polycarboxylate and N-donor spacers: Photocatalytic performance and theoretical analysis

Two new coordination polymers (CPs) namely, [Cd2(btc)(bmi)2·4H2ODMF] (1) and [Zn2(L)(bmi)·5H2O] (2) have been synthesized utilizing mixed ligand strategy by reacting Cd(II) salt with benzene-tetracarboxylic acid (H4btc) and 1,5-bis(2-methylimidazol-1-yl)pentane (bmi) and Zn(II) salt with 5-[bis(4-carboxybenzyl)-amino]isophthalic acid (H4L) and 1,5-bis(2-methylimidazol-1-yl)pentane (bmi). The single crystal X-ray diffraction indicated that 1 has 2D network with (4,4) topology based on [Cd2(COO)4] secondary building units (SBUs), while 2 displays an undulating 2D (4, 4)-network by μ4-(L)4− ligands, which can be further interlinked into 3D supramolecular layer through hydrogen bonding interactions. Both of them have been tested as possible photocatalysts for the photodegradation of a model organic dye methyl violet (MV). The photocatalytic studies indicate that 1 and 2 show potential photocatalyts for degradation of MV. Furthermore, the possible photocatalytic mechanisms have been explained on the basis of density of states plots.

Three Cd(II)-based luminescent metal-organic frameworks constructed from the mixed-ligand strategy for highly selective detection of nitrobenzene

Three new Cd(II) luminescent metal-organic frameworks (LMOFs), namely {[Cd(bib) (bdc)]·DMF·H2O}n (1), {[Cd(bib)(ndc)(H2O)]·DMF}n (2) and {[Cd2(bib)2(bpdc)2]·1.5H2O} (3) (bib ​= ​1,3-bis(1-imidazolyl)benzene, H2bdc ​= ​1,4-benzenedicarboxylic acid, H2ndc ​= ​1,4-naphthalenedicarboxylic acid, H2bpdc ​= ​biphenyl-4,4′-dicarboxylic acid and DMF ​= ​N,N-dimethylformamide), have been synthesized by combining the V-shaped bib ligand and different dicarboxylate ligands under solvothermal conditions. Complex 1 displays a 4-fold interpenetrated 3D framework with sra topology. Complex 2 presents a 2D (4,4) layer structure derived from bib and ndc2− mixed spacers. Complex 3 is a 2-fold interpenetrated array based on 2D (4,4) wave-like coordinated layers. The structural diversity among these complexes can be realized by the abduction of linear dicarboxylate ligands. The results demonstrate that the length of dicarboxylate ligands makes an impact on the structural diversity. Moreover, the complexes 1–3 can be well dispersed in different solvents, which exhibit highly selective and sensitive detection for nitrobenzene (NB) over other solvents by means of fluorescence quenching effect. The work illuminates fine-tuning of structure and in turn sensing properties towards LMOFs based on the reasonable selection of organic ligands.

Boronic acid-decorated metal-organic frameworks modified via a mixed-ligand strategy for the selective enrichment of cis-diol containing nucleosides

Functional metal–organic frameworks (MOFs) constructed via a pre-installation strategy of introducing mixed organic ligands have attracted considerable interest in various fields. In the present study, boronic acid decorated magnetic Zr-MOFs were successfully synthesized by introducing 3-carboxyphenylboronic acid ligands as fragments. The prepared material was used as an adsorbent for the enrichment of cis-diol-containing nucleosides. The adsorbent has excellent performance with regard to the enrichment and separation of the nucleosides. This may be attributed to its abundant boronic acid functional groups, and the convenience of magnetic separation it provides. The obtained material was chemically stable over a large pH range. The degree of linearity of the nucleosides was excellent (0.02–10 μg mL−1), and the detection and quantification limits were low (0.006–0.016 μg mL−1 and 0.02–0.05 μg mL−1, respectively). Furthermore, it was possible to attain adsorption equilibrium within 10 min. The high efficiency of this method makes it suitable for the successful extraction of nucleosides from human urine samples, with satisfactory recoveries of 88–146%, and 1.7–9.4% precision. We believe that the fabricated functional magnetic MOFs have great potential for the analysis of other cis-diol-containing target, and the pre-installation strategy could be adapted for the wider application of MOFs.

Synthesis and magnetic properties of two Mn-based coordination polymers constructed by a mixed-ligand strategy

Two Mn(ii) CPs have been synthesized by mixed-ligand strategy and measured for their magnetic properties. Moreover, analysis of the magnetic structure–effect relationship indicates that 1 and 2 have different Mn chains of magnetic interactions.

Luminescent coordination polymers constructed using a mixed-ligand strategy for highly selective luminescence sensing of nitrobenzene, Fe3+ and Cr2O72− ions and photodegradation of rhodamine B

Using a mixed ligand strategy, ten new LCPs were constructed. They all display highly sensitive and selective luminescence sensing for NB, Cr2O72−and Fe3+ ions. Moreover, 3–10 also exhibit high photocatalytic activities toward the degradation of RhB.

Rational synthesis of an ultra-stable Zn(ii) coordination polymer based on a new tripodal pyrazole ligand for the highly sensitive and selective detection of Fe3+ and Cr2O72- in aqueous media.

A mixed-ligand strategy has been used to construct stable luminescent coordination polymers (CPs). An ultra-stable Zn(ii) coordination polymer, [Zn(H3tpb)(Hbtc)]n (1) was hydrothermally synthesized by employing a new tripodal pyrazole ligand H3tpb and a classical carboxylic ligand H3btc (H3tpb = 1,3,5-tris(pyrazolyl)benzene, H3btc = 1,3,5-benzenetricarboxylic acid). Complex 1 exhibits a 2D sql network. Importantly, 1 not only possesses excellent thermal stability but also shows superior chemical stability in terms of water resistance, acid/base aqueous solutions tolerance (pH = 2-12), and organic solvents resistance. This excellent structural stability was further illustrated from the perspective of thermal decomposition kinetics. The luminescence properties were investigated, showing that complex 1 displays high sensitivity and selectivity for detecting Fe3+ and Cr2O72- ions in aqueous solutions via luminescence quenching effects.

Two tetranuclear Cd-based metal–organic frameworks for sensitive sensing of TNP/Fe3+ in aqueous media and gas adsorption

Two Cd-MOFs were solvothermally synthesized by mixed-ligand strategy. 1 has the largest adsorption selectivity for CO2. Furthermore, 1 and 2 present sensitive sensing for TNP/Fe3+ in water or soil samples.

A mixed-ligand strategy regulates thorium-based MOFs.

Two novel thorium-based organic frameworks (Th-IHEP-5 and Th-IHEP-6) were assembled from a hexanuclear thorium cluster, porphyrin derivative ligand and linear carboxylic acid ligands via a mixed-ligand strategy. As a stable heterogeneous catalyst, Th-IHEP-5 exhibited high photocatalytic activity for the oxidation of 2-chloroethyl ethyl sulfide (CEES) and the fixation of CO2. The good catalytic effect is attributed to the large conjugated system of porphyrin and the photosensitizer enhancing effects of bipyridine.

Two Co(II) and Zn(II) coordination polymers: structural characterization and anticancer activity against nasopharyngeal carcinoma

By employing a mixed-ligand strategy, two new coordination polymers with the chemical formulae [Co(4-bptzh)(1,3-BDC)] (1) and [Zn(4-bptzp)(1,3-BDC)]n (2) are hydrothermally synthesized using two flexible bis(pyridyl-tetrazole) ligands (4-bptzh = 1,4-bis(5-(4-pyridyl)tetra­zolyl)hexane, 4-bptzp = 1,4-bis(5-(4-pyridyl)tetrazolyl)propane) and 1,3-benzenedicarboxylic acid (1,3-H2BDC). Both complexes are characterized by single crystal X-ray diffraction along with the elemental analysis. Furthermore, the inhibitory effect of compounds 1 and 2 against CNE-1 nasopharyngeal cancer cells are evaluated in vitro. Firstly, the antiproliferation activity of compounds 1 and 2 against cancer cells is assessed by the CCK-8 assay. Then, the cancer cell apoptosis is measured with the Annexin V-FITC/PI apoptosis assay by flow cytometry.

A new mixed-ligand Ni(II) complex: crystal structure, protective and anti-inflammatory activity of its nanoparticles on acute viral myocarditis by reducing the release of inflammatory cytokines TNF-α and IL‐1β

By means of the mixed-ligand strategy, a new Ni(II)-bearing coordination complex [Ni(pda)(bimb)(H2O)](H2O)1.5 (1, bimb = 6,6'-bis(1H-benzo[d]imidazol-2-yl)-2,2'-bipyridine, H2pda = 4,4'-(pyridine-2,6-diyl)dibenzoic acid) is successfully obtained by the reaction of Ni(NO3)2×6H2O, bimb, and H2pda under hydrothermal reaction conditions. Furthermore, the nanoparticles of 1 (nano 1) with a size distribution of around 160 nm can be produced via a grinding method. In the section of biological research, we describe the anti-inflammatory activity of nano 1 on the acute viral myocarditis model. In the CVB3-induced acute viral myocarditis model, the treatment effect of nano 1 is evaluated by determining the mice survival rate and the CVB3 titer. The anti-inflammatory activity of nano 1 is determined by the ELISA assay of TNF-a and IL-1b levels in plasma.