Simple Organic Ligands Research Articles

Band Structure Engineering in 2D Metal-Organic Frameworks.

The design of 2D metal-organic frameworks (2D MOFs) takes advantage of the combination of the diverse electronic properties of simple organic ligands with different transition metal (TM) centers. The strong directional nature of the coordinative bonds is the basis for the structural stability and the periodic arrangement of the TM cores in these architectures. Here, direct and clear evidence that 2D MOFs exhibit intriguing energy-dispersive electronic bands with a hybrid character and distinct magnetic properties in the metal cores, resulting from the interactions between the TM electronic levels and the organic ligand π-molecular orbitals, is reported. Importantly, a method to effectively tune both the electronic structure of 2D MOFs and the magnetic properties of the metal cores by exploiting the electronic structure of distinct TMs is presented. Consequently, the ionization potential characteristic of selected TMs, particularly the relative energy position and symmetry of the 3d states, can be used to strategically engineer bands within specific metal-organic frameworks. These findings not only provide a rationale for band structure engineering in 2D MOFs but also offer promising opportunities for advanced material design.

Quasi-FeCo-MOF/CoS amorphous Nanosheets: A stable and highly active catalyst for electrocatalytic water splitting and monosaccharide oxidation

Quasi-metal organic frameworks (quasi-MOFs) are intermediate materials between pristine MOFs and metal compounds, possessing unusual structures and properties, which makes them promising porous materials. However, their synthesis remains challenging due to the absence of reliable design strategies. Here, we propose a novel solvent-thermal synthesis strategy for preparing quasi-FeCo-MOF/CoS amorphous nanosheet composites. The strategy involves the use of high-coordination metal ions and simple organic ligands, followed by a simple solvent-thermal treatment to induce quasi-MOF formation. The formation of CoS not only transforms the original crystal structure of FeCo-MOF into amorphous nanosheets but also imparts structural stability to the composite material. Furthermore, density functional theory (DFT) calculations reveal the catalytic mechanism, demonstrating that the introduction of CoS can adjust the d-band center of the composite material, optimizing adsorption free energy and reducing its overpotential. This method significantly enhances the electrocatalytic activity of the composite material in alkaline and neutral solutions. Notably, the optimized composite material (FeCo-MOF/CoS-2/FF) exhibits low overpotentials of 142 mV and 55 mV (at 10 mA cm−2) for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, and achieved a current density of 10 mA cm−2 with a low overpotential of 1.391 V for HER and monosaccharide oxidation (MOR) using FeCo-MOF/CoS-2/FF. This method provides new insights and perspectives for developing highly active and stable catalysts and is expected to advance the development of electrocatalytic water splitting technology.

A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]anes and Selectively Bind Fluorinated Steroids.

Simple organic ligands can self-assemble with metal ions to generate metal-organic cages, whose cavities bind guests selectively. This binding may enable new methods of chemical separation or sensing, among other useful functions. Here we report the preparation of a CuI6L4 pseudo-octahedral metal-organic cage, the ligands of which self-assemble from simple organic building blocks. Temperature, solvent, and the presence of different guests governed which structure predominated from a dynamic mixture of cage diastereomers with different arrangements of right- or left-handed metal vertices. Dissolution in dimethyl sulfoxide or the binding of tetrahedral guests led to a chiral tetrahedral T-symmetric framework, whereas low temperatures favored the achiral S4-symmetric diastereomer. Tetrahedral guests with long arms were encapsulated to form mechanically bonded suit[4]anes, with guest arms protruding out through host windows. The cage was also observed to bind fluorinated steroids, an important class of drug molecules, but not non-fluorinated steroids, providing the basis for new separation processes.

Selective catalytic hydrogenation of 5-hydroxymethylfurfural over silica supported FeCoNiCuRu high-entropy alloy nanoparticles

A simple organic ligand chelate-assisted thermal-reduction method provides a universal strategy for generating high-entropy alloy (HEA) nanoparticles catalysts with uniformly dispersed particles for efficient catalytic hydrogenation.

Two Dual-Function Zr/Hf-MOFs as High-Performance Proton Conductors and Amines Impedance Sensors.

In the field of sensing, finding high-performance amine molecular sensors has always been a challenging topic. Here, two highly stable 3D MOFs DUT-67(Hf) and DUT-67(Zr) with large specific surface areas and hierarchical pore structures were conveniently synthesized by solvothermal reaction of ZrCl4/HfCl4 with a simple organic ligand, 2,5-thiophene dicarboxylic acid (H2TDC) according to literature approach. By analyzing TGA data, it was found that the two MOFs have defects (unsaturated metal sites) that can interact with substrates (H2O and volatile amine gas), which is conducive to proton transfer and amine compound identification. Further experiments showed that at 100 °C and 98% relative humidity (RH), the optimized proton conductivities of DUT-67(Zr) and DUT-67(Hf) can reach the high values of 2.98 × 10-3 and 3.86 × 10-3 S cm-1, respectively. Moreover, the room temperature sensing characteristics of MOFs' to amine gases were evaluated at 68, 85 and 98% RHs, respectively. Impressively, the prepared MOFs-based sensors have the desired stability and higher sensitivity to amines. Under 68% RH, the detection limits of DUT-67(Zr) or DUT-67(Hf) for volatile amine gases were 0.5 (methylamine), 0.5 (dimethylamine) and 1 ppm (trimethylamine), and 0.5 (methylamine), 0.5 (dimethylamine) and 0.5 ppm (trimethylamine), respectively. As far as we know, this is the best performance of ammonia room temperature sensors in the past proton-conductive MOF sensors.

Complexation of uranyl with benzoic acid in aqueous solution at variable temperatures: potentiometry, spectrophotometry and DFT calculations.

Investigation of the fundamental coordination chemistry between U(VI) and simple organic ligands is important to understand the chemical behavior of U(VI) in the natural environment and separation processes. In this work, the complexation of U(VI) with a common carboxylic acid, benzoic acid, has been systematically investigated through potentiometry, spectrometry and DFT calculations. Three successive complexes (UO2L+, UO2L2 and UO2L3-, L = benzoate ion) between U(VI) and benzoic acid are successfully identified in aqueous solution and their corresponding thermodynamic parameters (stability constant, enthalpy and entropy) are determined. Notably, this is the first time that the previously missing 1 : 2 and 1 : 3 (U to L) complexes in aqueous solution and their complexation thermodynamics have been reported, which would aid in more accurate prediction of the chemical behavior of U(VI) in the presence of benzoic acid. Moreover, the structures of the complexes are elucidated using DFT calculations, which show that benzoic acid coordinates to U(VI) in a bidentate form in all the complexes.

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand.

Employing 4-ethynylaniline as a simple organic ligand we were able to prepare the stable trans-bis(acetylide)platinum(II) complex [Pt(L1)2(PBu3)2] as a linear metalloligand. The reaction of this metalloligand with iron(II) cations and pyridine-2-carbaldehyde according to the subcomponent self-assembly approach yielded decanuclear heterobimetallic tetrahedron [Fe4Pt6(L2)12](OTf)8. Thus, combination of these two design concepts – the subcomponent self-assembly strategy and the complex-as-a-ligand approach – ensured a fast and easy synthesis of large heterobimetallic coordination cages of tetrahedral shape with a diameter of more than 3 nm as a mixture of all three possible T-, S4- and C3-symmetric diastereomers. The new complexes were characterized by NMR and UV–vis spectroscopy and ESI mass spectrometry. Using GFN2-xTB we generated energy-minimized models of the diastereomers of this cage that further corroborated the results from analytical findings.

Double ligand MOF-derived pomegranate-like Ni@C microspheres as high-performance microwave absorber

Metal-organic framework (MOF)-derived functional composites have received extensive attention, especially in microwave absorption (MA) materials. However, the delicate design of the spatial structure, designed components, and heterojunction interfaces of MOF derivatives remains a great challenge in the MA application. Herein, a simple double organic ligand strategy and controllable pyrolysis treatment were used to regulate the Ni-MOF derived pomegranate-like Ni@C Microspheres. Their morphology and crystallization can be accurately controlled by a simple hydrothermal method. After pyrolysis, hierarchical magnetic-carbon Ni@C microspheres were obtained which consists of many nickel-carbon core–shell units within the carbon layer. MOF-derived Ni@C microspheres possessed plentiful interfaces, unique three-dimensional conduction network, and magnetic-dielectric synergy system. The pomegranate-like Ni@C microspheres shown excellent microwave absorption performance of a maximum reflection loss (−46.9 dB at 3.5 mm), which can be attributed to the dielectric attenuation, magnetic loss, and matched impedance. Precision regulation of MOF precursors and MOF derivatives provide a novel platform of magnetic-dielectric Ni@C composites that offers excellent MA applications.

Zinc metal–organic framework with 3-pyridinecarboxaldehyde and trimesic acid as co-ligands for selective detection of Cr (VI) ions in aqueous solution

There is an increasing need for the development of probes for the detection of hexavalent chromium since it is a known carcinogen, which can cause adverse effects on human health. Metal-organic frameworks (MOFs) have shown successful detection and removal of hazardous substances from aqueous media. This work presents the use of simple organic ligands such as 3-pyridinecarboxaldehyde and trimesic acid with Zn(II) ion to fabricate a new MOF that exhibits sensitive and selective luminescence quenching response towards CrO4 2− and Cr2O7 2− species in aqueous solution. The MOF showed a detection limit of 0.67 μM (0.078 ppm) as CrO4 2− species and 1.91 μM (0.41 ppm) as Cr2O7 2− species. Results reveal that the as-synthesized MOF could serve as a good luminescent sensor for CrO4 2− and Cr2O7 2− species in the contaminated aqueous phase.

Impact of Training Through Research on the Evolution of Contemporary Teaching Technology

The orientation of the education system towards technologies based on training through research presents an objective not only educational, but also socio-economic, because the challenges of the future society are largely related to the elaboration of new materials, more efficient ones than the existing analogies. The educational system has the task of developing competencies from the first steps to the university level: research, education, and entrepreneurship. In order to achieve this goal, it is necessary to develop evolutionary strategies from traditional to innovative education, with the application of developed products in different fields, in order to generate performant and ergonomic technologies. It is important for the scientific study to have relevant goals by applying the obtained results in order to solve real problems in everyday life, agriculture, material science, etc. As a model, it is proposed to study the synthesis process of coordinating compounds, analysis of composition, structure and determination of the practical application domains based on the manifested biological and physical properties. For the university level, as an exercise in the research competence, it is proposed to obtain and analyze some coordinating compounds based on transition metals. In order to achieve multi-level interdisciplinary studies, the starting point is the interaction of simple salts and organic ligands that lead to highly complex chemical compounds, composition study, molecular structure, and practical implementation based on useful properties. An important role in the manifestation of the properties of metallo-complexes is also played by the ligands in their composition which, due to the large set of donor atoms, create stable complexes different in composition, structure and properties with transition metal ions. Biologically active substances included in the complexes of metals as ligands substantially increase their effectiveness. After developing the research competence which results in the students synthesizing to assemble new coordinating compounds, it is necessary to move from the oriented, guided synthesis stage to that of creating new molecular models based on their own ideas. At this level it becomes obvious the manifestation of creativity and the spirit of initiative which can end with the development of innovation competence – the supreme product of the educational process, which offers the future specialists the freedom of creation, the independence and the confidence in their own orientation skills in the issues regarding the professional field.

Copper(I) bromide coordinated by the ionic liquid 1‐[(diethyl amine)amine]ethyl‐3‐methyl imidazolium chloride to catalyze the atom transfer radical polymerization of methyl methacrylate in 1‐allyl‐3‐methyl imidazolium chloride

ABSTRACTA coordinating ionic liquid (IL), 1‐[(diethyl amine)amine]ethyl‐3‐methyl imidazolium chloride ([N3MIM]Cl), was prepared as an alternative to a simple organic ligand to coordinate to copper(I) bromide (CuBr). We, thereby, obtained a novel catalyst for atom transfer radical polymerization (ATRP) reactions. This catalyst was applied to the ATRP of methyl methacrylate in the IL 1‐allyl‐3‐methyl imidazolium chloride ([AMIM]Cl). The chemical structures of the ILs obtained were confirmed by Fourier transform infrared spectroscopy, mass spectrometry, and 1H‐NMR analyses. The coordination ability of [N3MIM]Cl was assessed by cyclic voltammetry, and the redox potential of [N3MIM]Cl–CuBr was −0.507 V. The [N3MIM]Cl–CuBr complex was expected to be a markedly more active catalyst than the amine DETA–CuBr complex. The coordination mode toward CuBr was also examined. The [N3MIM]Cl–CuBr catalyst system showed good controllability in the aforementioned ATRP reaction in [AMIM]Cl. The Cu catalyst was easily separated from the obtained polymer with the coordinating IL as a ligand. Consequently, the coordinating IL overcame the shortcomings of traditional organic ligands, such as poor compatibility with IL media and poor separation of the catalyst from the polymer; this makes it highly promising for applications in the ATRP field. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45484.

“Cascade recognition” of Cu2+ and H2PO4− with high sensitivity and selectivity in aqueous media based on the effect of ESIPT

Organic molecular sensors have the advantage of being used through easy, fast, economical and reliable optical methods for detecting toxic metal ions in the environment. In the present work, a simple but specific organic ligand N,N-(3,3′-dimethyl biphenyl)-bis(4-diethylaminosalicyladimine) (Q2) was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). Q2 can be regarded as a colorimetric and fluorescent sensor for relay recognition of Cu2+ and H2PO4− in DMSO/H2O (8:2, v/v) HEPES buffer solutions. Moreover, sensor Q2 showed a highly sensitive and selective response towards Cu2+ and H2PO4− over other metal ions and anions. Particularly, the fluorescence “ON–OFF–ON” responding circle could be repeated over 4 times by the sequential addition of Cu2+ and H2PO4−. Notably, the actual usage of sensor Q2 was further demonstrated by test kits and silica gel plates. The fluorescence changes of Q2 upon the addition of Cu2+ and H2PO4− were utilized as an INHIBIT logic gate at the molecular level, using Cu2+ and H2PO4− as chemical inputs and the fluorescence intensity signal as the output.

Magnesite growth inhibition by organic ligands: An experimental study at 100, 120 and 146 °C

It has been proposed that simple organic ligands, which accelerate Mg-silicates dissolution, could be used to accelerate CO2 mineral sequestration through mineral carbonation. The influence of these ligands on magnesite growth has however never been quantified.In this work, we investigated the influence of three organic ligands: oxalate, citrate and EDTA on magnesite growth in alkaline conditions and at hydrothermal temperatures (100, 120 and 146°C) using mixed flow reactors. We show that the studied carboxylates decrease magnesite growth rates, due to two converging mechanisms:–Complexation of Mg2+ in solution, which decreases the saturation state of the solution. This effect was carefully taken into account by using a thermodynamic database relevant for the studied system. EDTA being the stronger chelate of the three investigated ligands, it has the strongest influence on solution saturation state.–Adsorption of the ligand on magnesite surface growth sites, which decreases the kinetic rate constant of magnesite growth. We observed the following inhibition effectiveness of investigated organic ligands: citrate>EDTA>oxalate.While citrate exerts the strongest growth inhibition due to adsorption, it does not apparently lead to a complete interruption of magnesite growth. Preliminary adsorption experiments suggest that citrate adsorbs to active growth sites at the mineral surface with a much higher affinity than for the bulk of the surface.Using experimentally retrieved magnesite growth rate laws and published forsterite (Mg2SiO4) dissolution rate law, we performed simple numerical simulations to estimate the overall influence of the investigated ligands on the carbonation rates of forsterite. We observe that all ligands will clearly be detrimental to forsterite carbonation rates in typical conditions foreseen for Mg-silicates mineral carbonation. Their use may be positive for the carbonation of less reactive Mg-silicate minerals, but the delayed formation of magnesite could as well trigger the formation of secondary Mg-bearing phases which would reduce the maximal carbonation extent.

Effect of loading on the nature of the REE–humate complexes as determined by Yb3+ and Sm3+ LIII-edge EXAFS analysis

Humic substances are major natural complexing agents that strongly influence the cycling of metal cations in the environment. The metal to humic acid (HA) concentration ratio (metal loading) can significantly impact the overall HA complexation properties in natural soils and waters. At low metal loading, cations bind to strong multi-carboxylate or -phenolate sites of HA. In addition, these strong sites might contain soft Lewis bases such as N or S, the contribution of which is still a matter of debate. Based on the possible ability of Rare Earth Elements (REE) to trace HA binding properties, the present study aimed at evaluating the influence of REE-loading on the HA binding mechanisms of two hard Lewis acids, Sm3+ and Yb3+. Extended X-ray Absorption Fine Structure (EXAFS) at the Sm and Yb LIII edge was used to analyze the local coordination of these intermediate and heavy REE ions, respectively, in a low and a high REE-loading HA sample. Data were interpreted by comparison with EXAFS data for a series of aqueous REE complexes with iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and a carboxylic-grafted resin. In all these samples, both a Yb–O (~2.31Å) and a Yb–N (~2.50Å) backscattering path could be identified in the first coordination shell of Yb. At low REE loading, the first coordination shell around the Yb bond to HA is described by a single Yb–O backscattering path, i.e. the presence of N could not be evidenced. By contrast, the carboxylic-grafted resin exhibits both a short (2.31Å) and a long Yb–O average distance (2.44Å), suggesting the coordination of carboxylate is bidentate. The Fourier transform of the high loading HA samples exhibits a broad first shell peak possibly described by two Yb–O distances (2.29 and 2.43Å) suggesting two coordination modes of the carboxylic groups. Different Yb–HA complex structures can therefore be observed at different metal loadings. Unfortunately, the Sm EXAFS spectra could only be recorded up to k=10Å−1. There was no evidence of either a clear difference between the metal loadings or with Yb–HA complex structures. A comparison between the EXAFS results, PHREEQC-Model VI simulations, and the pattern of the REE complexation constants with simple organic ligands (REE:ligand 1:1 and 1:2 complexes) provides evidence that, at high loading, REE are bound to HA through bi-ligand complexes without any chelation effect in which REE may potentially act as a cation bridge between two organic molecules. At low loading, the fact that N could not be detected in the Yb first shell suggests that, at low loading, Yb binds to O-containing groups of HA rather than N-containing groups. This may call into question the definition of HA strong sites for REE binding such as soft Lewis base-containing sites.

Selective Sorption of Actinides by Titania Nanoparticles Covalently Functionalized with Simple Organic Ligands

Although current and proposed reprocessing of used nuclear fuel is performed predominantly by solvent extraction processes, solid phase sorbent materials have many advantages including the ability to avoid production of large volumes of organic waste. Therefore, three titania nanoparticle based sorbent materials have been developed, functionalized with organic ligands designed to impart selectivity for elements relevant to important separations at the back end of the nuclear fuel cycle. A novel, simplified method of covalent functionalization to the titania surface has been utilized, and the resulting materials have been shown to be hydrolytically stable at pH 2. The sorption behavior of these organofunctionalized titania materials was investigated over a wide pH range with a selection of elements including fission products and actinides. Titania nanoparticles functionalized with an amine or phosphate moiety were able to demonstrate exclusive extraction of uranium under optimized conditions. Titania nanoparticles functionalized with a picolinamide moiety exhibited superior minor actinide sorption properties, in terms of both efficiency and selectivity, to solvent extraction processes using similar organic moieties. As such, organo-functionalized titania materials as solid phase sorbents show promise as a future alternative to solvent extraction processes for nuclear separations.

ChemInform Abstract: Tetrametallic Molecular Catalysts for Photochemical Water Oxidation

AbstractReview: 88 refs.

Tetrametallic molecular catalysts for photochemical water oxidation

Among molecular water oxidation catalysts (WOCs), those featuring a reactive set of four multi-redox transition metals can leverage an extraordinary interplay of electronic and structural properties. These are of particular interest, owing to their close structural, and possibly functional, relationship to the oxygen evolving complex of natural photosynthesis. In this review, special attention is given to two classes of tetrametallic molecular WOCs: (i) M(4)O(4) cubane-type structures stabilized by simple organic ligands, and (ii) systems in which a tetranuclear metal core is stabilized by coordination of two polyoxometalate (POM) ligands. Recent work in this rapidly evolving field is reviewed, with particular emphasis on photocatalytic aspects. Special attention is given to studies addressing the mechanistic complexity of these systems, sometimes overlooked in the rush for oxygen evolving performance. The complementary role of molecular WOCs and their relationship with bulk oxides and heterogeneous catalysis are discussed.

Using capillary electrophoresis to separate trivalent f-elements based on their speciation when complexed with simple organic ligands

Capillary electrophoresis (CE) is a useful method for rapid separations of metal cations. Under ideal conditions, CE can provide complete separation of the trivalent lanthanides in less than 10 min. Simple organic ligands must be included in the electrolyte matrix to achieve good resolution between the cations. In this paper, we demonstrate how to use complexation constants from the literature to design separation protocols for the trivalent f-elements.

Speciation of Molybdenum(VI)-Citric Acid Complexes in Aqueous Solutions

The chemistry of molybdenum(VI) (Mo 6+ ) encounters very complex pathways even when reacting with the simplest of ligands (the aqua ligand). Citric acid (Cit) is considered to be a simple organic ligand. From our efforts to study citric acid with a variety of metal ions (Hamada et al. 2003 [41] and Hamada et al. 2006) a di-hydrolytic complex (or dihydroxo complex) of the Mo 6 + : Cit system has been observed using both a speciation computer program and potentiometric titrations in aqueous solutions at 25°C. The speciation diagrams show that the percentage of formation of this di-hydrolytic complex species overshadows the percentage of formation of the individual free citric acid species. We have taken into account the presence of the following species: the mononuclear species Mo(H −1 Cit), Mo(H −1 Cit)(OH), and Mo(H −1 Cit)(OH) 2 , and the di-nuclear Mo 2 (H −1 Cit)(OH) 2 complex. Among all complexes taken into account, only the di-hydrolytic complex Mo(H −1 Cit)(OH) 2 has been detected in appreciable percentages. The UV-vis titrations performed at different pH values are in a good agreement with the chemistry literature. Further experimental and theoretical studies are underway in this area.

Radioactive contaminants in the subsurface: the influence of complexing ligands on trace metal speciation

Equilibrium thermodynamics is one of the pillars which support safety analyses of repositories for radioactive waste. The research summarized in this review deals with approaches to resolve the problems related to thermodynamic equilibrium constants and solubility of solid phases in the field of radioactive waste management. The results have been obtained at the Paul Scherrer Institut between 1995 and 2005 and comprise the scientific basis of the author’s habilitation thesis in the field of nuclear environmental chemistry. The topics are grouped according to three different levels of problem solving strategies: (1) Critical and comprehensive reviews of the available literature, which are necessary in order to establish a reliable chemical thermodynamic database that fulfils the requirements for rigorous modeling of the behavior of the actinides and fission products in the environment. (2) In many case studies involving inorganic and simple organic ligands a serious lack of reliable thermodynamic data is encountered. There, a new modeling approach to estimate the effects of these missing data was applied. This so called “backdoor approach” begins with the question, “What total concentration of a ligand is necessary to significantly influence the speciation, and hence the solubility, of a given trace metal?” (3) In the field of natural organics, mainly humic and fulvic acids, we face an ill-defined problem concerning the molecular structure of the ligands. There, a pragmatic approach for performance assessment purposes was applied, the “conservative roof” approach, which does not aim to accurately model all experimental data, but allows estimates of maximum effects on metal complexation by humic substances to be calculated.