Search Results (16)

HKUST-1 (HKUST = Hong Kong University of Science and Technology) is one of the most recognized metal-organic frameworks (MOFs) based on copper and trimesate, extensively studied for a variety of applications, such as gas storage, separation, adsorption, electrocatalysis, drug delivery, sensor and photodegradation, etc. In this work, we introduce a novel nanofused HKUST-1, referred to as N-CuBTC (BTC = trimesate), which has been synthesized with the hydrothermal method at room temperature (typical synthesis temperature is from 80~120 °C). The resulting N-CuBTC features an irregular particle morphology, with numerous crystals clustering together and edges that have fused, creating a hierarchical pore structure. In contrast to the traditional micro-sized octahedral HKUST-1 (named as M-CuBTC), N-CuBTC displays a unique clumped morphology, where the HKUST-1 crystals are seamlessly integrated into a cohesive structure. This innovative formation significantly enhances mass transfer capabilities and porosity accessibility. Consequently, N-CuBTC demonstrates markedly improved catalytic performance in the cyanosilylation of aldehydes. Full article

Introduction/Objectives: Since the biological activities and toxicities of ‘foreign’ and/or excess levels of metal ions are predominantly determined by their precise molecular nature, here we have employed high-resolution ¹H NMR analysis to explore the ‘speciation’ of paramagnetic Ni(II) ions in human saliva, a potentially rich source of biomolecular Ni(II)-complexants/chelators. These studies are of relevance to the in vivo corrosion of nickel-containing metal alloy dental prostheses (NiC-MADPs) in addition to the dietary or adverse toxicological intake of Ni(II) ions by humans. Methods: Unstimulated whole-mouth human saliva samples were obtained from n = 12 pre-fasted (≥8 h) healthy participants, and clear whole-mouth salivary supernatants (WMSSs) were obtained from these via centrifugation. Microlitre aliquots of stock aqueous Ni(II) solutions were sequentially titrated into WMSS samples via micropipette. Any possible added concentration-dependent Ni(II)-mediated pH changes therein were experimentally controlled. ¹H NMR spectra were acquired on a JEOL JNM-ECZ600R/S1 spectrometer. Results: Univariate and multivariate (MV) metabolomics and MV clustering analyses were conducted in a sequential stepwise manner in order to follow the differential effects of increasing concentrations of added Ni(II). The results acquired showed that important Ni(II)-responsive biomolecules could be clustered into distinguishable patterns on the basis of added concentration-dependent responses of their resonance intensities and line widths. At low added concentrations (71 µmol/L), low-WMSS-level N-donor amino acids (especially histidine) and amines with relatively high stability constants for this paramagnetic metal ion were the most responsive (severe resonance broadenings were observed). However, at higher Ni(II) concentrations (140–670 µmol/L), weaker carboxylate O-donor ligands such as lactate, formate, succinate, and acetate were featured as major Ni(II) ligands, a consequence of their much higher WMSS concentrations, which were sufficient for them to compete for these higher Ni(II) availabilities. From these experiments, the metabolites most affected were found to be histidine ≈ methylamines > taurine ≈ lactate ≈ succinate > formate > acetate ≈ ethanol ≈ glycine ≈ N-acetylneuraminate, although they predominantly comprised carboxylato oxygen donor ligands/chelators at the higher added Ni(II) levels. Removal of the interfering effects arising from the differential biomolecular compositions of the WMSS samples collected from different participants and those from the effects exerted by a first-order interaction effect substantially enhanced the statistical significance of the differences observed between the added Ni(II) levels. The addition of EDTA to Ni(II)-treated WMSS samples successfully reversed these resonance modifications, an observation confirming the transfer of Ni(II) from the above endogenous complexants to this exogenous chelator to form the highly stable diamagnetic octahedral [Ni(II)-EDTA] complex (K_stab = 1.0 × 10¹⁹ M⁻¹). Conclusions: The results acquired demonstrated the value of linking advanced experimental design and multivariate metabolomics/statistical analysis techniques to ¹H NMR analysis for such speciation studies. These provided valuable molecular information regarding the identities of Ni(II) complexes in human saliva, which is relevant to trace metal ion speciation and toxicology, the in vivo corrosion of NiC-MADPs, and the molecular fate of ingested Ni(II) ions in this biofluid. The carcinogenic potential of these low-molecular-mass Ni(II) complexes is discussed. Full article

This work presents the synthesis and characterization of materials that contain Sn metal clusters formed by ligands of trimesic acid (Sn-BTC) or 5-sulfobenzene-1,3-dicarboxylic acid (Sn-H₃-5-SIP). These catalysts were used to convert levulinic acid with ethanol to produce ethyl levulinate under mild reaction conditions. The characterization results confirmed that Sn is mainly present in the cassiterite crystalline phase with a tetragonal rutile structure in octahedral and tetrahedral coordination in the materials. The assembly of trimesic acid (a hard base) with metal species (Sn) results in the formation of acid and thermally stable metal–organic frameworks. The use of 5-sulfobenzene-1,3-dicarboxylic acid instead of trimesic acid in the synthesis incorporates sulfonic groups in the material, enhancing the total acidity of the Sn-H₃-5-SIP catalyst compared to the Sn-BTC material. The Sn-H₃-5-SIP catalyst exhibited the highest catalytic activity when converting levulinic acid with ethanol, resulting in a turnover frequency (TOF) of 0.0495 s⁻¹, which is a 50% increase compared to the TOF of the Sn-BTC catalyst (0.0329 s⁻¹). This result can be attributed to its higher concentration of acid sites (2.23 ± 0.05 mmol H⁺/g_cat) and specific area (139 m²/g). Thus, materials containing tin metal clusters and sulfonic groups are promising materials that could be used as catalysts for synthesizing ethyl levulinate under mild reaction conditions. Full article

Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu₁₂Pb₂O₁₅Br₂, and cubic Fm$\overline{3}$m symmetry: a = 9.2407(9) Å; V = 789.1(2) ų; Z = 2. Eddavidite is the bromine analog of murdochite, Cu₁₂Pb₂O₁₅Cl₂, with which it forms a solid solution series. The type locality is the Southwest mine, Bisbee, Cochise County, Arizona, U.S.A. Eddavidite also occurs in the Ojuela mine, Mapimí, Durango, Mexico. Eddavidite occurs as domains within mixed murdochite–eddavidite crystals. The empirical formula, normalized to 12 Cu apfu, is Cu₁₂(Pb_1.92Fe_0.06Si_0.06)(O_15.08F_0.02)-(Br_0.99Cl_0.89☐_0.12). Type locality samples contain up to 67% eddavidite component, while Ojuela mine samples contain up to 62%. Mixed eddavidite–murdochite crystals show forms {100} and {111}; the habit grades from cubic through cuboctahedral to octahedral. Mixed eddavidite–-murdochite crystals exhibit good cleavage on {111}. Eddavidite is black, opaque with submetallic luster, and visually indistinguishable from intergrown murdochite. Its Mohs hardness is 4; d_meas. = 6.33 g/cm³, d_calc. = 6.45 g/cm³. The crystal structure, refined to R = 0.0112, consists of corner-sharing square planar CuO₄ units, arranged in Cu₁₂O₂₄ metal oxide clusters, which encapsulate Br atoms. PbO₈ cubes share edges with Cu₁₂O₂₄ clusters in a continuous framework. Eddavidite incorporates bromine remaining after desiccation of paleo-seawater at its two known localities, which were both once situated along the Western Interior Seaway. Full article

The chemistry of transition metal clusters has been intensively developed in the last decades, leading to the preparation of a number of compounds with promising and practically useful properties. In this context, the present work demonstrates the preparation and study of the reactivity, i.e., the possibility of varying the ligand environment, of new square pyramidal molybdenum chalcogenide clusters [{Mo₅(μ₃-S)ⁱ₄(μ₄-S)ⁱ(μ-pz)ⁱ₄}(pzH)^t₅]^1+/2+ (pzH = pyrazole, i = inner, t = terminal). The one-step synthesis starting from the octahedral Mo₆Br₁₂ cluster as well as the substitution of the apical pyrazole ligand or the selective bromination of the inner pyrazolate ligands were demonstrated. All the obtained compounds were characterized in detail using a series of physicochemical methods both in solid state (X-ray diffraction analysis, etc.) and in solution (nuclear magnetic resonance spectroscopy, mass spectrometry, etc.). In this work, redox properties and absorption in the ultraviolet-visible and near-infrared region of the obtained compounds were studied. Full article

The tetranuclear iron(III) compounds [Fe₄(μ₃-O)₂(μ-L^Z)₄] (1–3) were obtained by reaction of FeCl₃ with the shortened salen-type N₂O₂ tetradentate Schiff bases N,N’-bis(salicylidene)-o-Z-phenylmethanediamine H₂L^Z (Z = NO₂, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe₄ bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe₄(μ₃-O)₂} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Fe_b, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Fe_w. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe₄(μ₃-O)₂} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1–3. Full article

The propensity of 4-hydroxybenzhydrazone-related ligands derived from 3-methoxysalicylaldehyde (H₂L^3OMe), 4-methoxysalicylaldehyde (H₂L^4OMe), and salicylaldehyde (H₂L^H) to act as chelating and/or bridging ligands in Ni(II) complexes was investigated. Three clusters of different nuclearities, [Ni₃(L^3OMe)₂(OAc)₂(MeOH)₂]∙2MeOH∙MeCN (1∙2MeOH∙MeCN), [Ni₂(HL^4OMe)(L^4OMe)(OAc)(MeOH)₂]∙4.7MeOH (2∙4.7MeOH), and [Ni₄(HL^H)₂(L^H)₂(OAc)₂]∙4MeOH·0.63H₂O·0.5MeCN·HOAc (3∙4MeOH·0.63H₂O·0.5MeCN·HOAc), were prepared from Ni(OAc)₂∙4H₂O and the corresponding ligand in the presence of Et₃N. The hydrazones in these acetato- and phenoxido-bridged clusters acted as singly or doubly deprotonated ligands. When pyridine was used, mononuclear complexes with the square-planar geometry seemed to be favoured, as found for complexes [Ni(L^3OMe)(py)] (4), [Ni(L^4Ome)(py)] (5) and [Ni(L^H)(py)] (6). Ligand substituent effects and the stability of square-planar complexes were investigated and quantified by extensive quantum chemical analysis. Obtained results showed that standard Gibbs energies of binding were lower for square-planar than for octahedral complexes. Starting from [MoO₂(L)(EtOH)] complexes as precursors and applying the metal-exchange procedure, the mononuclear complexes [Ni(HL^3OMe)₂]∙MeOH (7∙MeOH) and [Ni(HL^H)]∙2MeOH (9∙2MeOH) and hybrid organic–inorganic compound [Ni₂(HL^4OMe)₂(CH₃OH)₄][Mo₄O₁₀(OCH₃)₆] (10) were achieved. The octahedral complexes [Ni(HL)₂] (7–9) can also be obtained by the direct synthesis from Ni(Oac)₂∙4H₂O and the appropriate ligand under specific reaction conditions. Crystal and molecular structures of 1∙2MeOH∙MeCN, 2∙4.7MeOH, 3∙4MeOH∙0.63H₂O∙0.5MeCN∙HOAc, 4, 5, 9∙2MeOH, and 10 were determined by the single-crystal X-ray diffraction method. Full article

New nanocomposite materials with UV-NIR blocking properties and hues ranging from green to brown were prepared by integrating inorganic tantalum octahedral cluster building blocks prepared via solid-state chemistry in a PMMA matrix. After the synthesis by the solid-state chemical reaction of the K₄[{Ta₆Brⁱ₁₂}Br^a₆] ternary halide, built-up from [{Ta₆Brⁱ₁₂}Br^a₆]⁴⁻ anionic building blocks, and potassium cations, the potassium cations were replaced by functional organic cations (Kat⁺) bearing a methacrylate function. The resulting intermediate, (Kat)₂[{Ta₆Brⁱ₁₂}Br^a₆], was then incorporated homogeneously by copolymerization with MMA into transparent PMMA matrices to form a brown transparent hybrid composite Ta@PMMA_brown. The color of the composites was tuned by controlling the charge and consequently the oxidation state of the cluster building block. Ta@PMMA_green was obtained through the two-electron reduction of the [{Ta₆Brⁱ₁₂}Br^a₆]²⁻ building blocks from Ta@PMMA_brown in solution. Indeed, the control of the oxidation state of the Ta₆ cluster inorganic building blocks occurred inside the copolymer, which not only allowed the tuning of the optical properties of the composite in the visible region but also allowed the tuning of its UV and NIR blocking properties. Full article

The generation of hydrogen (H₂) using sunlight has become an essential energy alternative for decarbonization. The need for functional nanohybrid materials based on photo- and electroactive materials and accessible raw materials is high in the field of solar fuels. To reach this goal, single-step synthesis of {Ta₆Brⁱ₁₂}@GO (GO = graphene oxide) nanohybrids was developed by immobilization of [{Ta₆Brⁱ₁₂}Br^a₂(H₂O)^a₄]·4H₂O (i = inner and a = apical positions of the Ta₆ octahedron) on GO nanosheets by taking the advantage of the easy ligand exchange of the apical cluster ligands with the oxygen functionalities of GO. The nanohybrids were characterized by spectroscopic, analytical, and morphological techniques. The hybrid formation enhances the yield of photocatalytic H₂ from water with respect to their precursors and this is without the presence of precious metals. This enhancement is attributed to the optimal cluster loading onto the GO support and the crucial role of GO in the electron transfer from Ta₆ clusters into GO sheets, thus suppressing the charge recombination. In view of the simplicity and versatility of the designed photocatalytic system, octahedral tantalum clusters are promising candidates to develop new and environmentally friendly photocatalysts for H₂ evolution. Full article

The antagonism between global energy needs and the obligation to slow global warming is a current challenge. In order to ensure sufficient thermal comfort, the automotive, housing and agricultural building sectors are major energy consumers. Solar control materials and more particularly, selective glazing are part of the solutions proposed to reduce global energy consumption and tackle global warming. In this context, these works are focused on developing new highly ultraviolet (UV) and near-infrared (NIR) absorbent nanocomposite coatings based on K₄[{Nb_6-xTa_xXⁱ₁₂}X^a₆]. (X = Cl, Br, 0 ≤ x ≤ 6) transition metal cluster compounds. These compounds contain cluster-based active species that are characterized by their strong absorption of UV and NIR radiations as well as their good transparency in the visible range, which makes them particularly attractive for window applications. Their integration, by solution processes, into a silica-polyethylene glycol or polyvinylpyrrolidone matrices is discussed. Of particular interest is the control and the tuning of their optical properties during the integration and shaping processes. The properties of the solutions and films were investigated by complementary techniques (UV-Vis-NIR spectrometry, ESI-MS, SEM, HRTEM, etc.). Results of these works have led to the development of versatile solar control coatings whose optical properties are competitive with commercialized material. Full article

We present a molecular mechanics force field in AMBER format for the mixed-valence manganese vanadium oxide cluster [Mn${}_4$V${}_4$O${}_{17}$(OAc)${}_3$]${}^{3-}$—a synthetic analogue of the oxygen-evolving complex that catalyzes the water oxidation reaction in photosystem II—with parameter sets for two different oxidation states. Most force field parameters involving metal atoms have been newly parametrized and the harmonic terms refined using hybrid quantum mechanics/molecular mechanics reference simulations, although some parameters were adapted from pre-existing force fields of vanadate cages and manganese oxo dimers. The characteristic Jahn–Teller distortions of d${}^4$ Mn${}^{\mathrm{III}}$ ions in octahedral environments are recovered by the force field. As an application, the developed parameters have been used to calculate the redox potential of the [Mn${}^{\mathrm{III}}$Mn${}_3^{\mathrm{IV}}$] ⇌ [Mn${}_4^{\mathrm{IV}}$]+e${}^{-}$ half-reaction in acetonitrile by means of Marcus theory. Full article

The effective ionic charges of lead-free perovskite dielectric complex compounds were investigated with molecular orbital calculation. The base model was a double perovskite cluster that consisted of octahedral oxygen cages with a transition metal ion of titanium, niobium, or zirconium located at each of their centers, and alkali and/or alkaline earth metal ions located at the body center, corners, edge centers, or face centers of the cluster. The results showed significant covalent bonds between the transition metals and the oxygens, and the alkali metals, especially sodium and oxygen. On the other hand, the alkaline earth metals have weak covalency. Calculation was also performed with the replacement of some of the oxygens with chlorine or fluorine; such replacement enhances the covalency of the transition metals. These trends provide good guidelines for the design properties of lead-free perovskite piezoelectrics based on ubiquitous sodium use. Full article

The self-assembly reaction between NiI₂, benzoic acid (PhCO₂H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH₂), in the presence of the organic base triethylamine (NEt₃), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear [Ni₁₂I₂(OH)₆(O₂CPh)₅(nacb)₅(H₂O)₄(MeCN)₄]I (1) cluster compound in ~30% yield. Complex 1 has a cage-like conformation, comprising twelve distorted, octahedral Ni^II ions that are bridged by five μ₃-OH⁻, one μ-OH⁻, an I⁻ in 55% occupancy, five PhCO₂⁻ groups (under the η¹:η¹:μ, η¹:η²:μ₃ and η²:η²:μ₄ modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb²⁻ groups. The overall {Ni₁₂} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni₃} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH₂ chelate, and a rare example of polynuclear Ni^II complex containing coordinating I⁻ ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Ni^II ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb²⁻ chelate in the presence of Ni^II metal ions, and the ability of this ligand to adopt a variety of different bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties. Full article

Thin and transparent Mo₆ cluster films with significant optical properties were prepared on indium tin oxide (ITO)-coated glass plates from the suspension of Cs₂Mo₆Br₁₄ cluster precursors dispersed in methyl-ethyl-ketone (MEK) by an electrophoretic deposition (EPD) process. Two kinds of polydimethylsiloxanes (PDMS); i.e., KF-96L-1.5CS and KF-96L-2CS corresponding to the kinetic viscosity of 1.5 and 2 centistokes, respectively, were selected to topcoat the Mo₆ cluster film after the EPD. The influence of the PDMS on the durability, chemical compatibility and light absorption property of Mo₆ cluster films were characterized by means of field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. The stabilized PDMS-coated Mo₆ cluster film could be stored for more than 6 months under ambient conditions. Full article

Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re₃Cl₉, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses. Full article