Mixed-ligand Strategy Research Articles

Phosphinous Acid-Phosphinito Tetra-Icosahedral Au52 Nanoclusters for Electrocatalytic Oxygen Reduction.

While the formation of superatomic nanoclusters by the three-dimensional assembly of icosahedral units was predicted in 1987, the synthesis and structural determination of such clusters have proven to be incredibly challenging. Herein, we employ a mixed-ligand strategy to prepare phosphinous acid-phosphinito gold nanocluster Au52(HOPPh2)8(OPPh2)4(TBBT)16 with a tetra-icosahedral kernel. Unlike expected, each icosahedral Au13 unit shares one vertex gold atom with two adjacent units, resulting in a "puckered" ring shape with a nuclearity of 48 in the kernel. The phosphinous acid-phosphinito ligand set, which consists of two phosphinous acids and one phosphinito motif, has strong intramolecular hydrogen bonds; the π-π stacking interactions between the phosphorus- and sulfur-based ligands provide additional stabilization to the kernel. Highly stable Au52(HOPPh2)8(OPPh2)4(TBBT)16 serves as an effective electrocatalyst in the oxygen reduction reaction. Density functional theory calculations suggest that the phosphinous acid-phosphinito ligands provide the most active sites in the electrochemical catalysis, with O* formation being the rate-determining step.

Metal-organic frameworks with mixed-ligands strategy as heterogeneous nucleation center to assist crystallization for efficient and stable perovskite solar cells

Deep-level defects and random oriented configuration in perovskite crystallization process would cause the nonradiative recombination and further affect the performance of perovskite solar cells (PSCs). Herein, two metal-organic frameworks (MOFs) with tunable Lewis-base passivation sites have been constructed (Cd-Httb and Cd-Httb-BDC, Httb = 5-(4-(1H-1,2,4-triazole-1-yl)benzyl)-1h-tetrazole, BDC = 1,4-dicarboxybenzene) to eliminate deep-level defects and simultaneously as nanostructured heterogeneous nucleation seed to assist the growth of large-grained perovskite films. Compared with the control and Cd-Httb, Cd-Httb-BDC designed with mix-ligands strategy exhibited the enhanced inducted effect on the crystallization and nucleation of high-quality perovskite films during annealing process. Consequently, the resultant Cd-Httb-BDC-modified device achieved higher power conversion efficiency (PCE) (22.18%) than the control (20.89%) and Cd-Httb (21.56%). Meanwhile, the unencapsulated Cd-Httb-BDC-modified device still maintained 90% of initial PCE after 1500 h in ambient conditions and exhibited enhanced thermal stability (85 °C in N2 atmosphere). This work presented a successful example of mix-ligands strategy on construction of high-quality MOF-assisted perovskite films for high-efficient and stable PSCs.

Synthesis, characterization and crystal structure of two nickel-based metal-organic frameworks with electrocatalytic activity

Two three-dimensional (3D) nickel-based metal-organic frameworks (Ni(II)-MOFs), {[Ni(adc)(phen)(H2O)]}n (1, H2adc = 9,10-anthracenedicarboxylic acid, phen = 1,10-phenanthroline) and {[Ni(adc)(bpy)]}n (2, bpy = 4,4’-bipyridine), were synthesized via a mixed-ligand strategy under hydrothermal and solvothermal conditions. MOF 1 could be simplified as a binodal tfc topology, while 2 possesses a three-fold interpenetrated framework, which is composed of a 4-connected dia network. The phase purity, molecular vibrations, and thermal stability of 1 and 2 have been characterized by powder X-ray diffraction (PXRD), infrared spectroscopy (IR), and thermogravimetric analysis (TG). Further electrochemical experiments reveal that 1 and 2 exhibit good methanol/ethanol oxidation (MOR/EOR) activities, with the optimal current density reaching up to 21.2 (EOR: 25.3) and 15.8 (EOR: 15.3) mA cm−2, respectively.

Metal-organic frameworks derived from chalcone dicarboxylic acid: New topological characters and initial catalytic properties

Two metal–organic frameworks, [Ag2L(bpy)0.5]n (1) and [CoL(bpy)]n (2), were successfully assembled through mixed-ligands strategy with different metal resource. Remarkably, both MOFs manifest multi-nuclear metal units as nodes and diverse topological structures. Compound 1 is an infinite two-dimensional layer structure with unsaturated four-nuclear silver unit nodes. While compound 2 exhibits a novel three-dimensional structure. The heterogeneous catalysis efficiency of the MOFs towards cycloaddition of N-methyl propargylamine with CO2 has been explored, and compound 1 displays higher catalytic activity derived from bare Lewis acid silver active site.

Synthesis, Structure, and Heterogeneous Catalysis of a Series of Structurally Diverse Coordination Polymers Based on 5-Nitroisophthalate

Four new coordination polymers have been synthesized based on a mixed-ligand strategy, viz., [Cu(4-ABPT)(HNIPA)2H2O]·H2O, SSICG-1; [Cu2(4-ABPT)2(HNIPA)4]·H2O, SSICG-2; [Ni(4-ABPT)(NIPA)H2O], SSICG-3; and [Zn2(ATRZ)2(NIPA)], SSICG-4 (4-ABPT = 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine, H2NIPA = 5-nitroisophthalic acid, and ATRZ = 3-amino-1,2,4-triazole, SSICG stands for the Solid State and Inorganic Chemistry Group at IIT Patna). The copper compounds are one-dimensional, whereas the nickel and zinc compounds are two-dimensional layer compounds. SSICG-3 possesses 4,4-net topology with a Schläfli symbol 44.62, whereas SSICG-4 exhibits a 3,3-net (fes) topology with a Schläfli symbol 4.82. SSICG-1 and SSICG-3 have active metal sites due to the presence of replaceable coordinated water molecules and exhibits efficient catalytic activity for one-pot CO2 cycloadditions. The conversions of SSICG-1 and SSICG-3 for CO2 cycloaddition are 87 and 95% (turnover numbers (TON) of 174 and 190), respectively. The kinetic studies, substrate scope, recyclability, catalyst amount, and temperature dependence studies of the CO2 cycloaddition reaction are discussed. These structurally diverse coordination polymers could contribute to broadening the scope of mixed-ligand coordination polymers for their applications in heterogeneous catalysis.

Green and Large-Scale Preparation of Chiral Metal-Organic Frameworks via Mechanochemistry.

It is a significant challenge to construct chiral metal-organic frameworks (CMOFs) by developing a facile and green preparation strategy. In this work, CMOFs were first synthesized via a mechanochemical process by combining a truncated mixed ligand strategy and defect engineering theory. The simple, green, and rapid construction strategy could solvent-freely harvest gram-scale CMOFs with a hierarchical micro/mesoporous structure. The as-synthesized CMOFs were evaluated by Aldol asymmetric catalysis and exhibited excellent catalytic performance (conversion was up to 97.1%, the ee value was 44.3%, and the activity was still good after 5 cycles).

Synthesis of Hierarchical-Porous Fluorinated Metal-Organic Frameworks with Superior Toluene Adsorption Properties.

Constructing metal-organic frameworks (MOFs) with high volatile organic compounds (VOCs) adsorption capacity and excellent water resistance remain challenging. Herein, a monocarboxylic acid-assisted mixed ligands strategy was designed to synthesize a novel fluorinated MOFs, MIL-53 (Al). The monocarboxylic acid promoted crystallization and produced abundant crystal defects, which increased pore volume. Moreover, the competitive coordination between tetrafluoroterephthalic acid and 1,4-dicarboxybenzene was moderated by monocarboxylic modulators, significantly improving the hydrophobicity. The toluene uptake of the optimal sample reached 254.85 mg g-1 under humid conditions, increased by 33.56 % of MIL-53(Al), and the QWet /QDry (the ratio of adsorption quality under wet to adsorption quality under dry) was 0.92, remarkably surpassing that of origin MIL-53 (0.72). The recycle experiment showed superior reusability with no performance degradation after 10 recycle under RH=50 % (relative humidity). The adsorptive kinetic and thermodynamic analysis proves that the adsorption process is controlled by surface mono-layer adsorption and pore diffusion. The fluorine group affects the internal diffusion, which weakens the transfer rate. This strategy opens a new prospect of obtaining hierarchical functional MOFs for meeting the VOCs uptake under the practical application.

Boosting the CO2/N2 selectivity of MMMs by vesicle shaped ZIF-8 with high amino content

The amino functionalization of MOFs has been verified to be effective in improving the selective permeation of CO2. However, the introduction of amino groups into ZIF-8 by mixed ligands strategy is hard to achieve due to the high steric hindrance of benzene ring in 2-aminobenzimidazole ligand, resulting in insufficient content of amino groups. Therefore, in this work, polystyrene-acrylate (PSA) template is proposed to provide abundant adsorption and reaction sites for the rapid synthesis of NH2-ZIF-8 with high content of 2-aminobenzimidazole. Furthermore, the incomplete etching strategy is used to construct PSA modified hollow NH2-ZIF-8 nanospheres (PHNZ). Importantly, the thickness of PSA layer and the hollow size are adjusted by the etching time, as revealed by the SEM and TEM images. In this PHNZ, the modified PSA can provide good interface compatibility between PHNZ and Pebax matrix to enhance the CO2 selectivity, while the hollow structure can reduce the mass transfer resistance and improve the gas permeability. Moreover, the introduced amino groups can enhance the CO2 affinity of PHNZ and further improve the CO2/N2 selectivity of the PHNZ-based mixed matrix membranes (MMMs). Benefiting from the synergy of good interface compatibility and enhanced CO2 affinity from the amino groups, the PHNZ/Pebax MMMs present greatly improved CO2/N2 selectivity in contrast with pure Pebax and NH2-ZIF-8 based membranes. Besides, as the etching time increases, the PHNZ-2 and PHNZ-3 based MMMs present a higher CO2 permeability than that of NH2-ZIF-8 based MMM, revealing the significance of the hollow structure. The PHNZ-2/Pebax MMM with filler loading of 10 wt% expresses the best gas separation performance with the CO2 permeability of 121.9 Barrer and CO2/N2 selectivity of 96.6, respectively, showing an increase of 54.7 % and 98.0 % in contrast with pure Pebax membrane. Meanwhile, this CO2 separation performance is far beyond the Robeson upper bound in 2008 and close to the McKeown upper bound in 2019, demonstrating that the proposed PHNZ displays a promising and competitive potential in MMM based CO2 capture.

Fine tuning the relaxation dynamics of mononuclear Dy(III) complexes by auxiliary ligand

Two new mononuclear Dy(III) compounds [Dy(H2O)4(Htpy)(dfa)]·2Cl (1) and [Dy(CH3OH)(Htpy)(NO3)(tma)2]·CH3OH (2) (Htpy = 4′-(4-Hydroxyphenyl)-2,2′:6′,2″-terpyridine, Hdfa = difluoroacetic acid, Htma = trimethylacetic acid) were successfully prepared by mixed-ligand strategy. Structurally, the substitution of different carboxylate ligand in 1 and 2 induces insignificant structural distortion, but causes large difference in magnetic behavior. Analysis results reveal that compound 2 shows better SMM behaviour than 1 as a result of the ferromagnetic coupling and the shorter Dy-O bond as well as a pronounced bond length difference, in which bond length distribution becomes more predominant.

Designing Multicomponent Metal–Organic Frameworks with Hierarchical Structure-Mimicking Distribution for High CO2 Capture Performance

By utilizing a mixed-ligand strategy, a novel multicomponent Cu-metal-organic framework (MOF) (JLU-MOF107) has been successfully synthesized. JLU-MOF107 has an unusual hierarchical structure-mimicking distribution structure. The triangular 4,4',4″-benzene-1,3,5-triyl-tribenzoate (BTB) ligand and the binuclear Cu cluster form a threefold interpenetration layer, while the linear ligand 1,4-phenylene-4,4'-bis(1,2,4-triazole) (p-tr2ph) and tetranuclear Cu cluster form a noninterpenetration pillared-layer structure. Then, the two types of layers are connected by tetranuclear Cu clusters to construct the final sandwichlike framework. JLU-MOF107 exhibits good water and humidity stability. Due to the presence of various active sites and pores, JLU-MOF107 shows an outstanding performance for CO2 capture (171.0 cm3 g-1 at 273 K). Density functional theory (DFT)-based calculations further prove the interactions between CO2 molecules and multiple active sites. The innovative synthesis of this multicomponent structure offers a new perspective on making hierarchical porous materials and multifunctional MOFs.

Mixed-Ligand Strategy for the Creation of Hierarchical Porous ZIF-8 for Enhanced Adsorption of Copper Ions.

The adsorption of heavy metals using metal–organic framework-based adsorption technology has been pointed out as a promising technique for the removal of these toxic elements from water. However, their adsorption capacity needs to be enhanced. Thus, the current work reports the effect of using a mixed-ligand strategy on the MOF framework and its effect on the removal of copper ions from water by adding terephthalic acid (BDC) linker to the ZIF-8precursors (2-methylimidazole (mI) and Zn2+) under solvothermal synthesis, leading to the formation of a hierarchical microporous mesoporous MOF, named Zn-mI-BDC, which was characterized by SEM, EDX, XRD, TGA, BET, and FTIR. As a result, all of these techniques revealed that the addition of a controlled amount of BDC did not alter the crystallinity of ZIF-8, resulting in the creation of a pore size of 4.2 nm. The new hierarchical porous MOF was tested for the adsorption of copper and exhibited an enhanced adsorption capacity compared to pristine ZIF-8 and many other standard adsorbents. The adsorption isotherm matched well with the Langmuir isotherm model, suggesting that the adsorption process chemisorption had a dominant role in the adsorption of Cu2+ species. Therefore, the current work is considered as an important step toward the use of a mixed-ligand strategy in enhancing the adsorption capacity of heavy metals using MOF materials.

Amine and fluorine co-functionalized MIL-101(Cr) synthesized via a mixed-ligand strategy for CO2 capture under humid conditions

The selective capture of CO2 in humid conditions on metal–organic frameworks is challenging due to competitive adsorption of H2O and CO2 on the active sites. Herein, amine and fluorine co-functionalized MIL-101(Cr) was synthesized and evaluated for use as CO2 adsorbent to overcome this issue. MIL-101(Cr)–NH2-F0.5 (CrA-F0.5) was prepared using a mixed-ligand strategy, and contains 2.9% nitrogen and 0.5% fluorine while maintaining the MIL-101(Cr) structure. Numerically, one 4F ligand per 20 amino ligands was included in the CrA-F0.5 structure. The calculated selectivity for CO2/N2 of CrA-F0.5 is 108 (CO2/N2 = 15/85) at 20 ℃ and 1 bar, and this value was 3.7 and 2.1 times higher than that of MIL-101(Cr) and MIL-101(Cr)–NH2, respectively. The results of CrA-F0.5 adsorption of CO2 indicated that amine and fluorine groups served as adsorptive sites for CO2 in this structure. The moderate isosteric heat of CO2 adsorption value (45 kJ mol−1) of CrA-F0.5 merits in desorption of CO2. The result of a hydrophobicity index test, indicated that CrA-F0.5 was 2.5 times hydrophobic than MIL-101(Cr)–NH2. In a CO2 and N2 breakthrough test, compared to the dry condition, the CO2 breakthrough time at 30 ℃ and 1 bar was reduced by 40% for MIL-101(Cr)–NH2 and by 10% for CrA-F0.5 in 60% relative humidity. The CO2 and N2 breakthrough results under humid conditions were consistent with the hydrophobicity index value, and the excellent water repellency of CrA-F0.5 was confirmed. CrA-F0.5 is considered a candidate suitable for CO2 adsorbent in an actual post-combustion CO2 adsorption process.

A Mixed-Ligand Strategy to Modulate P3HT Regioregularity for High-Efficiency Solar Cells

A Mixed-Ligand Strategy to Modulate P3HT Regioregularity for High-Efficiency Solar Cells

Mixed-Linker Metal-Organic frameworks for carbon and hydrocarbons capture under moist conditions

• MOF-801-FA were synthesised via utilizing a mixed-ligand strategy. • Gas adsorption was boosted, e.g., a 2.5-fold increase for methane capture. • Prominent IAST selectivities were witnessed for CH 4 /N 2 and CO 2 /N 2 mixture. • MOF-801-FA reveal clean and sharp separations in a high relative humidity. The capture of carbon and hydrocarbons is significant to the utilization of valuable resources and the mitigation of global warming, but achieving high gas capacity and selectivity at the same time remains a challenge, especially in the presence of high humidity. In this regard, based on the building block of MOF-801, MOF-801-FA structures were synthesized with high quality and few defects through a mixed-ligand strategy, in which formate ligands were introduced into the framework apart from fumarate ligands. This brought about tremendous increases in gas adsorption capacity, e.g., ca. 2.5-fold and 1.1-fold enhancement occurred to the adsorption of CH 4 and CO 2 in MOF-801-Hf-FA than MOF-801-Hf at 298 K and 1 bar. Besides, prominent IAST selectivities were also witnessed in MOF-801-FA, higher than those in the pristine MOFs, for CH 4 /N 2 and CO 2 /N 2 mixtures under ambient conditions. We then confirmed the efficient performance of MOF-801-FA for real CH 4 /N 2 and CO 2 /N 2 mixtures using the breakthrough experiments and following cycling tests, even in a relative humidity of 90%. Thus, the mixed-linker strategy was demonstrated effective to tune the structures of MOFs, and boost their performance in gas adsorption and separation. The results also showed that, with high capacities for CH 4 and CO 2 , superior selectivities over N 2 , desirable water resistance and facile regeneration, MOF-801-M−FA (M = Zr or Hf) are promising candidates for capturing CH 4 and CO 2 from N 2 in industry.

Mixed-Linker Strategy for the Construction of Metal-Organic Framework Combined with Dyes toward Alcohol Detection.

Herein, a N-rich metal-organic framework (MOF) with four kinds of cages, Zn4(ade)2(TCA)2(H2O) (NENU-1000, Hade = adenine, H3TCA = 4,4',4″-tricarboxytriphenylamine, NENU = Northeast Normal University), was prepared by the mixed-ligand strategy. Cationic dyes can be selectively absorbed by NENU-1000 at proper concentrations, but not neutral and anionic dyes, which perhaps can be assigned to the N-rich neutral framework of NENU-1000. When NENU-1000 was introduced to a relatively lower concentration of cationic dye solutions (e.g., rhodamine B or basic red 2), the colors of these systems faded quickly. Furthermore, the faded solutions can be used for the detection of methanol and other small alcohol molecules with either the naked eye or common UV-vis spectra. The effect of the length of carbon chain, the position of the -OH group, and the number of the hydroxyl group of the alcohols was explored for the color development rate. In addition, the performance of NENU-1000 in iodine sorption and release was also studied.

Utilization of a Mixed-Ligand Strategy to Tune the Properties of Cuboctahedral Porous Coordination Cages.

Ligand functionalization has been thoroughly leveraged to alter the properties of paddlewheel-based coordination cages where, in the case of ligand-terminated cages, functional groups are positioned on the periphery of synthesized cages. While these groups can be used to optimize solubility, porosity, crystal packing, thermal stability toward desolvation, reactivity, or optical activity, optimization of multiple properties can be challenging given their interconnected nature. For example, installation of functional groups to increase the solubility of porous cages typically has the effect of decreasing their porosity and stability toward thermal activation. Here we show that mixed-ligand cages can potentially address these issues as the benefits of various functional groups can be combined into one mixed-ligand cage. We further show that although ligand exchange reactions can be employed to obtain mixed ligand copper(II)-based cages, direct synthesis of mixed-ligand products is necessary for molybdenum(II) paddlewheel-based cages as these substitutionally inert clusters are resistant to ligand exchange. We ultimately show that highly soluble, highly porous, and thermally stable cuboctahedral cages are isolable by this strategy.

A 3D Co(II) compound: Crystal structure and protective activity on chronic nephritis

In the current study, via applying a mixed-ligand strategy, a Co(II) coordination polymer that is, {[Co4(3-dpyb)2 (odpa)2(H2O)3]·4H2O}n (1) [where 3-dpyb is N,N′-bis(3-pyridinecarboxamide)-1,4-butane, and H4odpa represents 4,4′-oxydiphthalic acid] is produced through reaction between two organic ligands and Co(NO3)2·6H2O in the water and DMF mixed solvents. For the treatment of chronic nephritis, real time RT-PCR is employed for measuring the AMPK signaling pathway activation, and ELISA detection kit is applied to evaluate inflammatory cytokines content released into plasma. Computer simulation has revealed that the activity of the proposed candidate is only from the carboxyl function groups, however, nitrogen atoms from both amide and pyridine groups only showed limited activity to the protein.

RETRACTED: Two photoluminescent Zn(II) complexes: Protection evaluation against cancer disease by reducing activation of PI3K/Akt signaling pathway

• Two novel compounds based on Zn(II) was prepared. • The above compounds’ solid luminescent emission spectra show intense L 2− ligand-centered emission bands at room temperature. • For treating the cancer disease, real time RT-PCR was exploited for detecting PI3K/Akt signaling pathway activation in myocardium. Through utilizing a mixed-ligand strategy, two novel compounds based on Zn(II), that is [Zn(L)(bpe)] n ·5n(H 2 O) ( 1 ) and [Zn(L)(bpp)] n ( 2 ) (H 2 L is =5-(1-oxoisoindolin-2-yl)isophthalic acid, bpe is 1,2-bis(4-pyridyl)ethane, and bpp is 1,3-bis(4-pyridyl)propane), are solvothermally generated via tuning the auxiliary N-donor ligand. The above compounds’ solid luminescent emission spectra show intense L 2− ligand-centered emission bands at room temperature. For treating the cancer disease, real time RT-PCR was exploited for detecting PI3K/Akt signaling pathway activation in myocardium. In addition to this, the flow cytometry was employed for measuring the percentage of the apoptotic cancer cells.

Stable bifunctional ZnII-based sensor toward acetylacetone and l-histidine via a fluorescence red shift and turn-on effect

A ZnII-based coordination polymer was synthesized by a mixed-ligand strategy, and it could be viewed as the first bifunctional fluorescent sensor with good stability for acac and l-His via a fluorescence red shift and enhancement.

Opening magnetic hysteresis via improving the planarity of equatorial coordination by hydrogen bonding.

Through a mixed-ligand strategy, the structural change from a discrete dinuclear DyIII cluster to a one-dimensional polymeric chain was achieved, maintaining the two magnetic entities with the same {Dy(dppbO2)2(H2O)5} (dppbO2 = 1,4-butylenebis(diphenylphosphine oxide)) core structure. Since the hydrogen bonding between the equatorial coordinated water molecules and the guests/solvents/anions is distinct, the local geometry and the equatorial planarity of the first coordination sphere of the central DyIII ion become slightly different caused by the second coordination sphere. As a result, the dinuclear compound shows typical butterfly-shaped hysteresis loops, while it significantly opens at zero magnetic field up to 11 K for the 1D polymer, which is unprecedented in coordination polymers. Our experimental observations and theoretical analysis indicate that the hydrogen bonding leads to the fine-tuning of certain bond lengths and angles of the coordination environment, as well as the crystal field to a certain extent, revealing that the second coordination sphere affects the first coordination sphere by hydrogen bonding.