Hexanuclear Cluster Research Articles

Facile one-pot synthesis of photoresponsive Cu1.8S and CuInS2 nanostructures aided by Cu-pyrimidylthiolate molecular precursor

Copper-based binary and ternary sulfides have attracted significant attention due to their excellent photo-physical properties, making them highly promising for high-performance energy harvesting and storage devices. This study focuses on the synthesis and structural characterization of an air-stable hexanuclear Cu-pyrimidylthiolate cluster complex which serves as an efficient single-source precursor for the preparation of Cu1.8S nanocrystals. Furthermore, coupling the molecular precursor with suitable indium source resulted in a facile one-pot pathway for the preparation of technologically important, copper-based ternary CuInS₂, nanocrystals. The crystal structure, phase purity, and compositions of the nanostructures were confirmed using PXRD, XPS, EDS, and area elemental mapping. Electron microscopic studies revealed the formation of polygonal and hexagonal morphology with varied size in Cu1.8S and CuInS₂ nanocrystals respectively. UV-Vis diffuse reflectance spectroscopy showed a slight blue shift in the band gap of the nanostructures compared to their bulk counterparts which can be attributed to quantum confinement or surface lattice distortion effects. The band gap of the pristine nanocrystals along with high photocurrent and stable photo-switching characteristics suggest that they can serve as suitable electrode material for optoelectronic and photodetector devices.

Synthesis of an Organotin S‐thiobenzoylthioglycolate Complex and its Application as a Single Source Precursor to SnS2 Thin Film

AbstractS‐thiobenzoylthioglycolic acid possessing two sulfur and two oxygen atoms was used to synthesize an oxoorganotin(IV) carboxylate molecule, [BuSn(O)(O2CCH2SC(S)Ph)]6. The molecule is a hexanuclear cluster that has been characterized structurally by single‐crystal X‐ray diffraction analysis. The complex was used as a single‐source precursor to prepare a thin film of SnS2 by the chemical vapor deposition technique. The distinct triangular formations of SnS2 were characterized by spectral and microscopic measurements. Well‐defined boundaries and considerable sizes of SnS2 structures have been identified.

Metal-Organic Framework Functionalized Chitosan/Pectin Membranes for Solar-Driven Photo-Oxidation and Adsorption of Arsenic

The presence of arsenic as neutral arsenite and oxoanionic arsenate species are a worldwide issue that requires an effective remediation technology capable to remove both AsIII and AsV from water. In this research we propose the assembly of a membrane build up from chitosan/pectin (CHIPEC) composite biopolymer and the UiO-66-NH2 porous and photo-active metal–organic framework. CHIPEC@UiO-66-NH2 membrane integrates porosity, adsorptive capacity, and activity to photo-oxidize and adsorb AsIII and AsV species. Nanometric-sized UiO-66-NH2 was synthetized and homogeneously distributed within the CHIPEC matrix, achieving a composite membrane with optical physico-chemical and optical properties (band gap of 2.91 eV) suitable to be applied on photooxidation of AsIII and adsorption of AsV. Under optimal conditions, maximum adsorption capacities (Qmax) values of 254 and 168 mg g−1 were reached for AsIII adsorption by MOF and membrane, respectively. Notably, for AsV adsorption, Qmax values of 268 and 335 mg g−1 were reached for powdered and immobilized MOF, respectively. Moreover, the membrane keeps most of its activity for AsV adsorption when employed in surface and groundwater matrixes. Further, the efficiently of UiO-66-NH2 to photo-oxidize AsIII to AsV, subsequently adsorbing the arsenate oxyanions, is improved by a factor of five when is integrated into the polymer. A detailed multi-step mechanism for the arsenic transformation and adsorption in CHIPEC@UiO-66-NH2 has been proposed on the basis of the anionic exchange at Zr hexa-nuclear clusters and amino groups in the MOF. Overall, MOF-biopolymeric composite has been proved as a straightforward, efficient, low-cost, and environmentally friendly solution for detoxifying arsenic in surface and underground water.

New Data on the Reactions of Zirconium and Hafnium Tetrachlorides with Aliphatic Acids

The reaction of ZrCl4 or HfCl4 with excess 2-methylpropanoic acid when boiling under reflux has been studied. The formation of polynuclear Zr and Hf complexes of the composition M2O(i-C3H7CO2)6 during prolonged reflux of the reaction mixtures was found. The complexes are very sensitive to hydrolysis, forming hexanuclear [M6(O)4(OH)4(i-C3H7CO2)12]. The reactions have a general character for aliphatic acids and can be used as an alternative to the known methods for the synthesis of polynuclear carboxylate clusters of Group 4 metals. The crystal and molecular structures of previously undescribed {[Hf6(μ3-O)4(μ3-OH)4(i-C3H7CO2)12(H2O)]·3i-C3H7COOH} have been determined. The molecular structure is a completely asymmetric hexanuclear cluster containing six Hf(IV) atoms united by a 4:4 μ3-O/OH system of bridges, and stabilized by twelve 2-methylpropanoate ligands, eight of which are bidentate bridging, three are chelating, and one is monodentate. The crystal structure of the complex includes three independent solvating 2-methylpropanoic acid molecules. The obtained IR spectroscopy data make it possible to determine the type of complexes in the reaction mixture. The results of the study may be useful for improving the catalytic systems for ethylene oligomerization.

A (3,12)-connected metal-organic framework based on hexanuclear zinc cluster for iodine capture

The adsorption of discharged radioactive iodine is considered an important method to address this environmental problem. Metal-organic framework (MOF) materials are expected to be potential materials for capturing iodine. In this work, a new zinc-based MOF, namely [Zn6(OH)6(DMTDC)3(TPB)]·0.5DMF (JOU-31), was successfully prepared under solvothermal condition (H2DMTDC = 3,4-dimethylthieno [2,3-b]thiophene-2,5-dicarboxylic acid, TPB = 1,3,5-tris(4-pyridyl)benzene, DMF = N,N-Dimethylformamide). Structural analyses revealed that JOU-31 was a three-dimensional porous structure based on hexanuclear zinc-oxide clusters. Topologically, the framework of JOU-31 can be simplified to a (3,12)-connected net with new Schläfli symbol of {43·630}{43}2. Due to its large specific surface area, abundant electron-rich N/S sites, and high stability, JOU-31 was applied to capture iodine. The saturated iodine adsorption capacity of JOU-31 in n-hexane solution was 822 mg g−1. In addition, the interaction mechanism between JOU-31 and the adsorbed iodine was further explored in detail. This work provides a valuable clue for the preparation of new MOFs for iodine adsorption.

Unveiling the contribution of hexanuclear clusters for highly selective glucose conversion on Metal–Organic frameworks

With the growing demand for sustainable energy, developing new technologies based on biomass has caused deep interest. Glucose conversion into fructose is a crucial step in the sustainable biorefinery industry. Metal–organic frameworks with abundant active metal centers have shown potential, but their specific contribution is not yet fully understood. In this study, mesoporous Zr-NU-1008 with hexanuclear clusters (M6) exhibited a higher glucose conversion of 54.7 % with a fructose selectivity of 85.3 % under optimized conditions compared with its hafnium counterpart, highlighting the significance of strong Lewis acidity of metal species. By adjusting the amount of the capped formate on the hexanuclear zirconium (IV) cluster (Zr6) of Zr-NU-1008, a positive correlation with the catalytic activity was realized, suggesting the lability of the capping modulator during catalysis, which enables tuning the activity by manipulating the capping modulator. Further saturating the Zr6 cluster with the electron-withdrawing trifluoroacetate modulator achieved an excellent glucose conversion of 63.3 % with a superior fructose selectivity of 86.0 %. Besides, the recovered catalyst can be easily regenerated by reinstalling the modulator on the M6 cluster, restoring its catalytic activity.

Amino-functionalized rare earth hexanuclear cluster based MOFs for CO2/CH4 separation

Climate pollution and global warming caused by greenhouse gases have become one of our toughest environmental challenges. CO2 capture and separation from natural gas can effectively reduce CO2 emissions and improve energy efficiency, accordingly, it is a serious challenge faced by industrial separation and scientific research to effectively reduce the carbon dioxide concentration in natural gas pipeline transportation and achieve the acquisition of high-purity methane (>99.5 %). In this study, three stable hexanuclear microporous rare earth cluster-based MOFs (Sm-BDC-NH2, Er-BDC-NH2, Y-BDC-NH2) were successfully synthesized. The selectivity of CO2/CH4 was improved by the introduction of amino groups to achieve better CO2/CH4 separation performance, which was proved by dynamic penetration experiments.

Yttrium-based metal-organic frameworks built on hexanuclear clusters.

Yttrium-based metal-organic frameworks built on hexanuclear clusters (Y6-MOFs) represent an important subgroup of MOFs that are assembled from Y6 clusters and diverse organic linkers, featuring a variety of topologies. Due to the robust Y-O bonds and high connectivity of hexanuclear SBUs, Y6-MOFs are generally thermally stable and resistant to water. Additionally, their pore structures are highly tunable through the practice of the reticular chemistry strategy, resulting in excellent performance in gas adsorption and separation related applications. Y6-MOFs are structurally analogous to Zr6-MOFs; however, the existence of charge-balancing cations in Y6-MOFs serves as an additional pore structure regulator, enhancing their tailorability with respect to pore shape and dimensions. In this Frontier article, we summarize the main advances in the design and synthesis of Y6-MOFs, with a particular focus on the precise engineering of their pore structure for gas separation. Future directions of research efforts in this field are also discussed.

Can Re cluster complexes be an efficient catalyst for hydrogen evolution reaction? Insights from experiments and computations.

To date, researchers in chase of economic cost-efficiency are faced with the problem of developing effective catalysts for water splitting without the use of platinoids. Herein, catalytic properties of hexanuclear rhenium cluster complexes are investigated in application to the hydrogen evolution reaction (HER). A paste composite electrode containing the cluster complexes was obtained, producing a current density of 10 mA cm-2 at an extraordinarily low overpotential of 90 mV (RHE). The {Re6Se8}-based complexes have shown very favorable reaction kinetics via 102 mV dec-1 value of the Tafel slope for HER reaction within the composition of the paste electrode. Model calculations of kinetic parameters using density functional theory also support the experimental findings. This work underscores the perspectivity of rhenium cluster compounds in HER and opens a promising avenue toward the practical implementation of hydrogen production through electrochemical water splitting.

Heterometallic Cu−Ca/Ba MOFs of 2‐Mercaptonicotinic Acid for Fast Sensing of Fe3+, Cr2O72−/CrO42− in Water

AbstractTwo heterometallic Cu−Ca/Ba metal organic frameworks (MOFs), {[Ca(H2O)6][Cu6Ca2(mna)6(H2O)6] ⋅ 6H2O}n (1) and {[(Cu6Ba3(mna)6(H2O)8] ⋅ 6H2O}n (2), were synthesized by using 2‐mercaptonicotinic acid (H2mna) as ligand via liquid‐liquid diffusion method. The frameworks of compounds 1 and 2 are both adopts hexanuclear copper cluster of [Cu6(mna)6]6− as building units. In 1, the two‐dimensional (2D) structure is formed by the linkage between [Cu6(mna)6]6− and monomeric Ca2+, while the three‐dimensional (3D) framework of 2 is constructed by [Cu6(mna)6]6− and trimer of Ba2+. Furthermore, compounds 1 and 2 show excellent photoluminescence with red emitting around 700 nm. Luminescent studies reveal that 1 can serve as a probe for the rapid detection of Fe3+, Cr2O72− and CrO42− ions in water with remarkable selectivity even in the presence of other analogous ions.

Expanding the Coordination of f-Block Metals with Tris[2-(2-methoxyethoxy)ethyl]amine: From Molecular Complexes to Cage-like Structures.

Low-valent f-block metals have intrinsic luminescence, electrochemical, and magnetic properties that are modulated with ligands, causing the coordination chemistry of these metals to be imperative to generating critical insights needed to impact modern applications. To this end, we synthesized and characterized a series of twenty-seven complexes of f-metal ions including EuII, YbII, SmII, and UIII and hexanuclear clusters of LaIII and CeIII to study the impact of tris[2-(2-methoxyethoxy)ethyl]amine, a flexible acyclic analogue of the extensively studied 2.2.2-cryptand, on the coordination chemistry and photophysical properties of low-valent f-block metals. We demonstrate that the flexibility of the ligand enables luminescence tunability over a greater range than analogous cryptates of EuII in solution. Furthermore, the ligand also displays a variety of binding modes to f-block metals in the solid state that are inaccessible to cryptates of low-valent f-block metals. In addition to serving as a ligand for f-block metals of various sizes and oxidation states, tris[2-(2-methoxyethoxy)ethyl]amine also deprotonates water molecules coordinated to trivalent triflate salts of f-block metal ions, enabling the isolation of hexanuclear clusters containing either LaIII or CeIII. The ligand was also found to bind more tightly to YbII and UIII in the solid state compared to 2.2.2-cryptand, suggesting that it can play a role in the isolation of other low-valent f-block metals such CfII, NpIII, and PuIII. We expect that our findings will inspire applications of tris[2-(2-methoxyethoxy)ethyl]amine in the design of light-emitting diodes and the synthesis of extremely reducing divalent f-block metal complexes that are of interest for a wide range of applications.

Hyperconjugative Aromaticity-Based Circularly Polarized Luminescence Enhancement in Polyaurated Heterocycles.

Hyperconjugative aromaticity (HA) frequently appears in metalla-aromatics, but its effect on photophysical properties remains unexplored to date. Herein, we reveal two different HA scenarios in nearly isostructural triaurated indolium and benzofuranylium compounds. The biased HAs show a discernible effect on the spatial arrangement of metal atoms and thus tailor metal parentage in frontier orbitals and the HOMO-LUMO energy gap. Theoretical calculations and structural analyses demonstrate that HA not only influences the degree of electron delocalization over the trimetalated aromatic rings but also affects π-coordination of Au(I) and intercluster aurophilic interaction. Consequently, the triaurated benzofuranylium complex shows better photoluminescence performance (quantum yield up to 49.7%) over the indolium analogue. Furthermore, four pairs of axially chiral bibenzofuran-centered trinuclear and hexanuclear gold clusters were purposefully synthesized to correlate their HA-involved structures with the chiroptical response. The triaurated benzofuranylium complexes exhibit strong circular dichroism (CD) response in solution but CPL silence even in solid film. In contrast, the hexa-aurated homologues display strong CD and intense CPL signals in both aggregated state and solid film (luminescence anisotropy factor glum up to 10-3). Their amplified chiroptical response is finally ascribed to the dominant intermolecular exciton couplings of large assemblies formed through the HA-tailored aggregation of hexanuclear compounds.

Multinuclear Zinc-Magnesium Hydroxide Carboxylates: A Predesigned Model System for Copolymerization of CO2 with Epoxides.

Among numerous catalysts in the ring-opening copolymerization of epoxides with carbon dioxide (CO2), zinc dicarboxylate complexes are the most common type, and in the family of metal-based homogeneous catalysts, zinc and magnesium complexes have attracted widespread attention. We report on the synthesis and structural characterization of a zinc-magnesium benzoate framework templated by the central hydroxide anion with μ3-κ2:κ2:κ2 coordination mode, [ZnMg2(μ3-OH)(O2CPh)5]n (n = 1 or 2). The resulting heterometallic system forms stable Lewis acid-base adducts with tetrahydrofuran (THF) and cyclohexene oxide (CHO), which crystallize as the hexanuclear zinc-magnesium hydroxide carboxylate cluster [ZnMg2(μ3-OH)(O2CPh)5(L)2]2 (L = THF or CHO). Their X-ray crystal structure analysis revealed that the Zn center prefers 4-fold coordination and the Mg centers demonstrated the ability to accommodate higher coordination numbers, and as a result, the heterocyclic molecules are exclusively bonded to 6-fold Mg atoms. The heteronuclear carboxylate aggregates appeared active in the copolymerization reaction at elevated temperatures to produce an alternating poly(cyclohexene carbonate).

A robust photo-responsive zirconium metal-organic framework for tailorable CO2 capture

Photo-responsive adsorbents (PRAs) have attracted much attention due to their energy efficiency for controllable gas capture. However, the construction of robust PRAs is still full of challenges. In this project, we report the construction of azobenzene-modified UiO-67, namely Azo-U, consisted of hexa-nuclear zirconium clusters and azobenzene derivative ligand Azo-H2BPDC. The single crystal X-ray diffraction (SCXRD) analysis demonstrates that Azo-U shows analogous structures to UiO-67 and the specific surface area is up to 1327 m2·g−1 derived from N2 uptake property at 77 K. The incorporation of Azo-H2BPDC imparts Azo-U with reversible photo-responsive properties. Considering its high porosity and photo-responsive properties, Azo-U was evaluated for controllable CO2 capture and the regulation efficiency can be up to 25.5%. Such a photo-controllable CO2 capacity of Azo-U is further confirmed by density functional theory (DFT) and Grand Canonical Monte Carlo calculation. Besides, the regulation efficiency can be well-preserved upon alternative ultraviolet and visible light irradiation. Moreover, Azo-U possesses good stability under aqueous solutions of different pH values (1.0 to 11.0). This study might shed light on the design and fabrication of target-specific PRAs to meet the various demands.

Yolk-Shell and Hollow Zr/Ce-UiO-66 for Manipulating Selectivity in Tandem Reactions and Photoreactions.

One of the hallmarks of multicomponent metal-organic frameworks (MOFs) is to finely tune their active centers to achieve product selectivity. In particular, obtaining bimetallic MOF hollow structures with precisely tailored redox centers under the same topology is still challenging despite a recent surge of such efforts. Herein, we present an engineering strategy named "cluster labilization" to generate hierarchically porous MOF composites with hollow structures and tunable active centers. By partially replacing zirconium with cerium in the hexanuclear clusters of UiO-66, unevenly distributed yolk-shell structures (YSS) were formed. Through acid treatment or annealing of the YSS precursor, single-shell hollow structures (SSHS) or double-shell hollow structures (DSHS) can be obtained, respectively. The active centers in SSHS and DSHS differ in their species, valence, and spatial locations. More importantly, YSS, SSHS, and DSHS with distinct active centers and microenvironments exhibit tunable catalytic activity, reversed selectivity, and high stability in the tandem reaction and the photoreaction.

Structural and theoretical investigations of a novel hexanuclear Lanthanum (III) cluster self-assembled through a functionalized β-diketone ligand via atmospheric CO2 fixation

Trapping atmospheric carbon-di-oxide (CO2) by lanthanide oxo-hydroxo clusters continuously receives a great deal of attention from the viewpoint of environmental concerns. Functionalized β-diketone ligands plays an important role in assembling lanthanide oxo-hydroxo clusters. Reaction between LaCl3 6H2O and phenolic β-diketone ligand 1-(2‑hydroxyl phenyl)-3-phenyl-1,3propanedione (HO-DBM) in methanol solvent in presence of triethylamine base yielded a novel hexanuclear cluster [La6(O-DBM)6 (HO-DBM)4 (μ3OH) (μ2OH2) (HCO3) (OH2)2 (MeOH)2] (1). The compound has been structurally characterized by single crystal X-ray diffraction analysis, it reveals that 1 consist of a La6 assembly template by (µ4HCO3)− anion. It was anticipated that the bicarbonate anion that bridge lanthanum units is introduced via spontaneous fixation of atmospheric carbon dioxide in the basic medium. Interestingly the bicarbonate anion exhibits a new bridging mode µ4-η1: η1: η1: η1. We applied the fundamental concept of bond valance sum (BVS) method in establishing the level of protonation of the various oxygen atoms in this cluster including water, hydroxide, bicarbonate, methanol and ligand. The values obtained for the title compound totally validate the crystal structure. Further the stability of the structure has been investigated by theoretical studies, the geometrical parameters (bond length and bond angles) are in line with the experimental observation.

Investigation of the Plutonium(IV) Interactions with Two Variants of the EF-Hand Ca-Binding Site I of Calmodulin.

Due to its presence in the nuclear industry and its strong radiotoxicity, plutonium is an actinide of major interest in the event of internal contamination. To improve the understanding of its mechanisms of transport and accumulation in the body, the complexation of Pu(IV) to the most common protein calcium-binding motif found in cells, the EF-hand motif of calmodulin, was investigated. Visible and X-ray absorption spectroscopies (XAS) in solution made it possible to investigate the speciation of plutonium at physiological pH (pH 7.4) and pH 6 in two variants of the calmodulin Ca-binding site I and using Pu(IV) in different media: carbonate, chloride, or nitrate solutions. Three different species of Pu were identified in the samples, with formation of 1:1 Pu(IV):calmodulin peptide complexes, Pu(IV) reduction, and formation of peptide-mediated Pu(IV) hexanuclear cluster.

Linker Vacancy Engineering of a Robust ftw-type Zr-MOF for Hexane Isomers Separation.

Discrimination of physically similar molecules by porous solids represents an important yet challenging task in industrially relevant chemical separations. Precisely controlled pore dimension and/or tailored pore surface functionality are crucial to achieve high-efficiency separation. Metal-organic frameworks (MOFs) are promising candidates for these challenging separations in light of their structural diversity as well as highly adjustable pore dimension/functionality. We report here a microporous, ftw-type Zr-based MOF structure, HIAM-410 (HIAM=Hoffmann Institute of Advanced Materials), built on hexanuclear Zr6 cluster and pyrene-1,3,6,8-tetracarboxylate (ptc4- ). Its crystallographic structure has been determined using continuous rotation electron diffraction (cRED) technique combined with Rietveld refinement against powder X-ray diffraction data, aided by low-dose high-resolution transmission electron microscopy (HRTEM) imaging. The compound features exceptional framework stability that is comparable to the prototype MOF UiO-66. Interestingly, the linker vacancies in the pristine MOF structure could be partially restored by post-synthetic linker insertion. Its separation capability of hexane isomers is enhanced substantially upon the linker vacancy engineering. The restored structure exhibits efficient splitting of monobranched and dibranched hexane isomers at both room temperature and industrially relevant temperature.

Linker Vacancy Engineering of a Robust ftw‐type Zr‐MOF for Hexane Isomers Separation

AbstractDiscrimination of physically similar molecules by porous solids represents an important yet challenging task in industrially relevant chemical separations. Precisely controlled pore dimension and/or tailored pore surface functionality are crucial to achieve high‐efficiency separation. Metal‐organic frameworks (MOFs) are promising candidates for these challenging separations in light of their structural diversity as well as highly adjustable pore dimension/functionality. We report here a microporous, ftw‐type Zr‐based MOF structure, HIAM‐410 (HIAM=Hoffmann Institute of Advanced Materials), built on hexanuclear Zr6 cluster and pyrene‐1,3,6,8‐tetracarboxylate (ptc4−). Its crystallographic structure has been determined using continuous rotation electron diffraction (cRED) technique combined with Rietveld refinement against powder X‐ray diffraction data, aided by low‐dose high‐resolution transmission electron microscopy (HRTEM) imaging. The compound features exceptional framework stability that is comparable to the prototype MOF UiO‐66. Interestingly, the linker vacancies in the pristine MOF structure could be partially restored by post‐synthetic linker insertion. Its separation capability of hexane isomers is enhanced substantially upon the linker vacancy engineering. The restored structure exhibits efficient splitting of monobranched and dibranched hexane isomers at both room temperature and industrially relevant temperature.

Ortho Effects of Tricarboxylate Linkers in Regulating Topologies of Rare-Earth Metal-Organic Frameworks.

A linker design strategy is developed to attain novel polynuclear rare-earth (RE) metal-organic frameworks (MOFs) with unprecedented topologies. We uncover the critical role of ortho-functionalized tricarboxylate ligands in directing the construction of highly connected RE MOFs. The acidity and conformation of the tricarboxylate linkers were altered by substituting with diverse functional groups at the ortho position of the carboxyl groups. For instance, the acidity difference between carboxylate moieties resulted in forming three hexanuclear RE MOFs with novel (3,3,3,10,10)-c wxl, (3,12)-c gmx, and (3,3,3,12)-c joe topologies, respectively. In addition, when a bulky methyl group was introduced, the incompatibility between the net topology and ligand conformation guided the co-appearance of hexanuclear and tetranuclear clusters, generating a novel 3-periodic MOF with a (3,3,8,10)-c kyw net. Interestingly, a fluoro-functionalized linker prompted the formation of two unusual trinuclear clusters and produced a MOF with a fascinating (3,8,10)-c lfg topology, which could be gradually replaced by a more stable tetranuclear MOF with a new (3,12)-c lee topology with extended reaction time. This work enriches the polynuclear clusters library of RE MOFs and unveils new opportunities to construct MOFs with unprecedented structural complexity and vast application potential.