Dielectric Properties Investigation of Metal–Insulator–Metal (MIM) Capacitors

This study presents the construction and dielectric properties investigation of atomic-layer-deposition Al₂O₃/TiO₂/HfO₂ dielectric-film-based metal–insulator–metal (MIM) capacitors. The influence of the dielectric layer material and thickness on the performance of MIM capacitors are also systematically investigated. The morphology and surface roughness of dielectric films for different materials and thicknesses are analyzed via atomic force microscopy (AFM). Among them, the 25 nm Al₂O₃-based dielectric capacitor exhibits superior comprehensive electrical performance, including a high capacitance density of 7.89 fF·µm⁻², desirable breakdown voltage and leakage current of about 12 V and 1.4 × 10⁻¹⁰ A·cm⁻², and quadratic voltage coefficient of 303.6 ppm·V⁻². Simultaneously, the fabricated capacitor indicates desirable stability in terms of frequency and bias voltage (at 1 MHz), with the corresponding slight capacitance density variation of about 0.52 fF·µm⁻² and 0.25 fF·µm⁻². Furthermore, the mechanism of the variation in capacitance density and leakage current might be attributed to the Poole–Frenkel emission and charge-trapping effect of the high-k materials. All these results indicate potential applications in integrated passive devices.     

Redox Potential and Crystal Chemistry of Hexanuclear Cluster Compounds

Most of TM₆-cluster compounds (TM = transition metal) are soluble in polar solvents, in which the cluster units commonly remain intact, preserving the same atomic arrangement as in solids. Consequently, the redox potential is often used to characterize structural and electronic features of respective solids. Although a high lability and variety of ligands allow for tuning of redox potential and of the related spectroscopic properties in wide ranges, the mechanism of this tuning is still unclear. Crystal chemistry approach was applied for the first time to clarify this mechanism. It was shown that there are two factors affecting redox potential of a given metal couple: Lever’s electrochemical parameters of the ligands and the effective ionic charge of TM, which in cluster compounds differs effectively from the formal value due to the bond strains around TM atoms. Calculations of the effective ionic charge of TMs were performed in the framework of bond valence model, which relates the valence of a bond to its length by simple Pauling relationship. It was also shown that due to the bond strains the charge depends mainly on the atomic size of the inner ligands.     

Tunable Ammonia Adsorption within Metal–Organic Frameworks with Different Unsaturated Metal Sites

Ammonia (NH₃) emissions during agricultural production can cause serious consequences on animal and human health, and it is quite vital to develop high-efficiency adsorbents for NH₃ removal from emission sources or air. Porous metal–organic frameworks (MOFs), as the most promising candidates for the capture of NH₃, offer a unique solid adsorbent design platform. In this work, a series of MOFs with different metal centers, ZnBTC, FeBTC and CuBTC, were proposed for NH₃ adsorption. The metal centers of the three MOFs are coordinated in a different manner and can be attacked by NH₃ with different strengths, resulting in different adsorption capacities of 11.33, 9.5, and 23.88 mmol/g, respectively. In addition, theoretical calculations, powder XRD patterns, FTIR, and BET for the three materials before and after absorption of ammonia were investigated to elucidate their distinctively different ammonia absorption mechanisms. Overall, the study will absolutely provide an important step in designing promising MOFs with appropriate central metals for the capture of NH₃.     

A Paradigmatic Approach to Find the Valency-Based K-Banhatti and Redefined Zagreb Entropy for Niobium Oxide and a Metal–Organic Framework

Entropy is a thermodynamic function in chemistry that reflects the randomness and disorder of molecules in a particular system or process based on the number of alternative configurations accessible to them. Distance-based entropy is used to solve a variety of difficulties in biology, chemical graph theory, organic and inorganic chemistry, and other fields. In this article, the characterization of the crystal structure of niobium oxide and a metal–organic framework is investigated. We also use the information function to compute entropies by building these structures with degree-based indices including the K-Banhatti indices, the first redefined Zagreb index, the second redefined Zagreb index, the third redefined Zagreb index, and the atom-bond sum connectivity index.     

Metal–Organic Frameworks–Based Memristors: Materials,Devices, and Applications

Facing the explosive growth of data, a number of new micro-nano devices with simple structure, low power consumption, and size scalability have emerged in recent years, such as neuromorphic computing based on memristor. The selection of resistive switching layer materials is extremely important for fabricating of high performance memristors. As an organic-inorganic hybrid material, metal-organic frameworks (MOFs) have the advantages of both inorganic and organic materials, which makes the memristors using it as a resistive switching layer show the characteristics of fast erasing speed, outstanding cycling stability, conspicuous mechanical flexibility, good biocompatibility, etc. Herein, the recent advances of MOFs-based memristors in materials, devices, and applications are summarized, especially the potential applications of MOFs-based memristors in data storage and neuromorphic computing. There also are discussions and analyses of the challenges of the current research to provide valuable insights for the development of MOFs-based memristors.     

Is it True That the Normal Valence‐Length Correlation Is Irrelevant for Metal–Metal Bonds?

The most intriguing feature of metal–metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal–metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)_n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation.     

Synthesis and Biomedical Applications of Highly Porous Metal–Organic Frameworks

In this review, aspects of the synthesis, framework topologies, and biomedical applications of highly porous metal–organic frameworks are discussed. The term “highly porous metal–organic frameworks” (HPMOFs) is used to denote MOFs with a surface area larger than 4000 m² g⁻¹. Such compounds are suitable for the encapsulation of a variety of large guest molecules, ranging from organic dyes to drugs and proteins, and hence they can address major contemporary challenges in the environmental and biomedical field. Numerous synthetic approaches towards HPMOFs have been developed and discussed herein. Attempts are made to categorise the most successful synthetic strategies; however, these are often not independent from each other, and a combination of different parameters is required to be thoroughly considered for the synthesis of stable HPMOFs. The majority of the HPMOFs in this review are of special interest not only because of their high porosity and fascinating structures, but also due to their capability to encapsulate and deliver drugs, proteins, enzymes, genes, or cells; hence, they are excellent candidates in biomedical applications that involve drug delivery, enzyme immobilisation, gene targeting, etc. The encapsulation strategies are described, and the MOFs are categorised according to the type of biomolecule they are able to encapsulate. The research field of HPMOFs has witnessed tremendous development recently. Their intriguing features and potential applications attract researchers’ interest and promise an auspicious future for this class of highly porous materials.     

Linker Functionalization Strategy for Water Adsorption in Metal–Organic Frameworks

Water adsorption in metal–organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be −12.7 Kcal/mol for the -OSO₃H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm³/cm³ for all candidates, classifying them among the top performing materials for water harvesting.     

A New Microporous Lanthanide Metal–Organic Framework with a Wide Range of pH Linear Response

Lanthanide metal–organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4′,4″-s-triazine-2,4,6-triyltribenzoate (H₃TATB) as an organic ligand, coordinated with lanthanide ions (Eu³⁺/Tb³⁺), and synthesized a new metal–organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH⁻ and ligand (TATB³⁻) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0–14), which can be used as a potential fluorescence sensing material for pH detection.     

Fluorescein Hydrazide-Appended Metal–Organic Framework as a Chromogenic and Fluorogenic Chemosensor for Mercury Ions

In this work, we prepared a fluorescein hydrazide-appended Ni(MOF) (Metal–Organic Framework) [Ni₃(BTC)₂(H₂O)₃]·(DMF)₃(H₂O)₃ composite, FH@Ni(MOF). This composite was well-characterized by PXRD (powder X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), N₂ adsorption isotherm, TGA (thermogravimetric analysis), XPS (X-ray photoelectron spectroscopy), and FESEM (field emission scanning electron microscopy). This composite was then tested with different heavy metals and was found to act as a highly selective and sensitive optical sensor for the Hg²⁺ ion. It was found that the aqueous emulsion of this composite produces a new peak in absorption at 583 nm, with a chromogenic change to a pink color visible to the naked eye upon binding with Hg²⁺ ions. In emission, it enhances fluorescence with a fluorogenic change to green fluorescence upon complexation with the Hg²⁺ ion. The binding constant was found to be 9.4 × 10⁵ M⁻¹, with a detection limit of 0.02 μM or 5 ppb. This sensor was also found to be reversible and could be used for seven consecutive cycles. It was also tested for Hg²⁺ ion detection in practical water samples from ground water, tap water, and drinking water.     

Multiple Metal–Metal Bond or No Bond? The Electronic Structure of V2O2

Detailed knowledge of the electronic structure of vanadium oxide clusters provides the basis for understanding and tuning their significant catalytic properties. However, already for the simple four‐atom V₂O₂ molecule, there are contradictory reports in the literature regarding the electronic ground state and a possible vanadium–vanadium bond. We herein show through a combination of experimental (matrix isolation) studies and theoretical results that there is a multiple vanadium–vanadium bond in this benchmark vanadium oxide molecule.     

f‐Element–Metal Bonding and the Use of the Bond Polarity To Build Molecular Intermetalloids

Metal–metal bonding in heterobimetallic complexes is of fundamental interest due to its implications to both bonding theory and new reactivities. In this Concept, structurally authenticated molecular compounds with direct bonds between rare‐earth metals or actinoids and transition or main group metals are summarized. Special attention is given to the use of bond polarity as a tool for designing molecular intermetalloids incorporating rare‐earth atoms and transition metals.     

Beyond Pristine Metal–Organic Frameworks: Preparation of Hollow MOFs and Their Composites for Catalysis,Sensing, and Adsorption Removal Applications

Metal–organic frameworks (MOFs) have been broadly applied to numerous domains with a substantial surface area, tunable pore size, and multiple unsaturated metal sites. Recently, hollow MOFs have greatly attracted the scientific community due to their internal cavities and gradient pore structures. Hollow MOFs have a higher tunability, faster mass-transfer rates, and more accessible active sites when compared to traditional, solid MOFs. Hollow MOFs are also considered to be candidates for some functional material carriers. For example, composite materials such as hollow MOFs and metal nanoparticles, metal oxides, and enzymes have been prepared. These composite materials integrate the characteristics of hollow MOFs with functional materials and are broadly used in many aspects. This review describes the preparation strategies of hollow MOFs and their composites as well as their applications in organic catalysis, electrochemical sensing, and adsorption separation. Finally, we hope that this review provides meaningful knowledge about hollow-MOF composites and their derivatives and offers many valuable references to develop hollow-MOF-based applied materials.     

Metalloporphyrin Metal–Organic Frameworks: Eminent Synthetic Strategies and Recent Practical Exploitations

The emergence of metal–organic frameworks (MOFs) in recent years has stimulated the interest of scientists working in this area as one of the most applicable archetypes of three-dimensional structures that can be used as promising materials in several applications including but not limited to (photo-)catalysis, sensing, separation, adsorption, biological and electrochemical efficiencies and so on. Not only do MOFs have their own specific versatile structures, tunable cavities, and remarkably high surface areas, but they also present many alternative procedures to overcome emerging obstacles. Since the discovery of such highly effective materials, they have been employed for multiple uses; additionally, the efforts towards the synthesis of MOFs with specific properties based on planned (template) synthesis have led to the construction of several promising types of MOFs possessing large biological or bioinspired ligands. Specifically, metalloporphyrin-based MOFs have been created where the porphyrin moieties are either incorporated as struts within the framework to form porphyrinic MOFs or encapsulated inside the cavities to construct porphyrin@MOFs which can combine the peerless properties of porphyrins and porous MOFs simultaneously. In this context, the main aim of this review was to highlight their structure, characteristics, and some of their prominent present-day applications.     

Preparation and Characterization of Magnetic Metal–Organic Frameworks Functionalized by Ionic Liquid as Supports for Immobilization of Pancreatic Lipase

Enzymes are difficult to recycle, which limits their large-scale industrial applications. In this work, an ionic liquid-modified magnetic metal–organic framework composite, IL-Fe₃O₄@UiO-66-NH₂, was prepared and used as a support for enzyme immobilization. The properties of the support were characterized with X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectra, transmission electron microscopy (TEM), scanning electronic microscopy (SEM), and so on. The catalytic performance of the immobilized enzyme was also investigated in the hydrolysis reaction of glyceryl triacetate. Compared with soluble porcine pancreatic lipase (PPL), immobilized lipase (PPL-IL-Fe₃O₄@UiO-66-NH₂) had greater catalytic activity under reaction conditions. It also showed better thermal stability and anti-denaturant properties. The specific activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ was 2.3 times higher than that of soluble PPL. After 10 repeated catalytic cycles, the residual activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ reached 74.4%, which was higher than that of PPL-Fe₃O₄@UiO-66-NH₂ (62.3%). In addition, kinetic parameter tests revealed that PPL-IL-Fe₃O₄@UiO-66-NH₂ had a stronger affinity to the substrate and, thus, exhibited higher catalytic efficiency. The results demonstrated that Fe₃O₄@UiO-66-NH₂ modified by ionic liquids has great potential for immobilized enzymes.     

A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal–Organic Frameworks for Visual Detection of Uric Acid

As an important biomarker in urine, the level of uric acid is of importance for human health. In this work, a Cu(II) functionalized metal–organic framework (Cu²⁺@Tb-MOFs) is designed and developed as a novel fluorescence probe for wide-range uric acid detection in human urine. The study shows that this fluorescence platform demonstrated excellent pH-independent stability, high water tolerance, and good thermal stability. Based on the strong interaction between metal ions and uric acid, the designed Cu²⁺@Tb-MOFs can be employed as efficient turn-on fluorescent probes for the detection of uric acid with wide detection range (0~10⁴ µM) and high sensitivity (LOD = 0.65 µM). This probe also demonstrates an anti-interference property, as other species coexisted, and the possibility for recycling. The sensing mechanisms are further discussed at length. More importantly, we experimentally constructed a molecular logic gate operation based on this fluorescence probe for intelligent detection of uric acid. These results suggest the Cu(II) functionalized metal–organic framework can act as a prominent candidate for personalized monitoring of the concentration of uric acid in the human urine system.     

Synthesis and the Crystal Structure of a New Chiral 1D Metal–Organic Coordination Polymer Based on L-Prolineamide-Substituted Diarylacetylenedicarboxylic Acid Derivative

The new homochiral 1D metal–organic coordination polymer [Cu₂(EDPB)•H₂O]_n was synthesized starting from the original 3,3′-ethyne-1,2-diylbis[6-(L-prolylamino)benzoic acid] (H₄EDPB). The unique crystal structure of the new compound was established by powder X-ray diffraction. The [Cu₂(EDPB)•H₂O]_n system shows catalytic activity and enantioselectivity in a Henry reaction of p-nitrobenzaldehyde with nitromethane.