Variable Oxidation States Research Articles

Back donation, intramolecular electron transfer and N-O bond scission targeting nitrogen oxyanion reduction: how can a metal complex assist?

A density functional theory exploration studies a range of ancillary coordinated ligands accompanying nitrogen oxyanions with the goal of promoting back donation towards varied nitrogen oxidation states. Evaluation of a suite of Ru and Rh metal complexes reveals minimum back donation to the κ1-nitrogen oxyanion ligand, even upon one-electron reduction. This reveals some surprising consequences of reduction, including redox activity at pyridine and nitrogen oxyanion dissociation. Bidentate nitrate was therefore considered, where ancillary ligands enforce geometries that maximize M-NOx orbital overlap. This strategy is successful and leads to full electron transfer in several cases to form a pyramidal radical NO32- ligand. The impact of ancillary ligand on degree of nitrate reduction is probed by comparing the powerful o-donor tris-carbene borate (TCB) to a milder donor, tris-pyrazolyl borate (Tp). This reveals that with the milder Tp donor, nitrate reduction is only seen upon addition of a Lewis base. Protonation of neutral and anionic (TCB)Ru(κ2-NO3) at both terminal and internal oxygens reveals exergonic N-O bond cleavage for the reduced species, with one electron coming from Ru, yielding a RuIII hydroxide product. Comparison of H+ to Na+ electrophile shows weaker progress towards N-O bond scission. Finally, calculations on (TCB)Fe(κ2-NO3) and [(TCB)Fe(κ2-NO3)]- show that electron transfer to nitrate is possible even with an earth abundant 3d metal.

Microwave radiated comparative growths of vanadium pentoxide nanostructures by green and chemical routes for energy storage applications

Supercapcitors are prominent energy storage devices an account of its high-power density, long cycle life and superior rate capability. Metal oxides play an important role in energy storage devices, while vanadium pentoxide is most promising due to variable oxidation states, wide potential window, unique layer structure etc. In general, specific capacitance of a vanadium pentoxide is very low due to poor ionic diffusivity and electrical conductivity but can improve drastically by encapsulating vanadium pentoxide with metals or carbonaceous materials or by decreasing the size to nanoscale or by modifying the morphology. On the other hand, the methodologies employed play a crucial role in increasing specific capacitance of a particular compound. Here we report a microwave assisted synthesis of vanadium pentoxide nanoparticles by green and chemical synthetic approach. The prepared samples were characterized by UV–Vis spectroscopy, Fourier-Transform Infrared spectroscopy, X-ray diffraction studies, Scanning Electron Microscope and Energy Dispersive Spectroscopy. The major peak in Uv–vis spectra confirms six-fold coordination state of V+5 with square pyramidal configuration. FTIR and XRD analysis concludes orthorhombic structure of synthesized nanoparticles with crystal size ranging from 20 to 25 nm. The anions and cations of an electrolyte is also play a crucial role in determination of specific capacitance of a particular materials and is in the order of 2 M KOH > 2 M LiOH > 2 M Na2SO4 > 2 M NaOH and are in accordance with hydration sphere radius, solvated ion size, ion shape and conductivity of particular ion. On the other hand calcinations temperature and concentration of specific electrolyte play a crucial role in determination of specific capacitance of a particular materials and is as follows 6 M KOH (600 °C) > 6 M KOH (400 °C) > 2 M KOH (600 °C) > 2 M KOH (400 °C). The V2O5-green modified electrode is showing excellent electrochemical performance than V2O5-chemical modified electrodes due to less agglomeration of oxide, high percentage of vanadium over the surface leads high intercalation and de-intercalation of K+ ions from electrolyte into V2O5 lattices.

A novel high-performance and energy-efficient RRAM device with multi-functional conducting nanofilaments

Resistive random access memory (RRAM) is a potential nonvolatile memory to apply in large-scale integration systems due to its high switching speed and cost-effective priority. Transition metal oxides have been utilized as the switching layer owing to the stable structure and variable oxidation state of transition metals. In this work, a functional RRAM device (Pt/AlOx/ZnO/Ti) was fabricated, and the resistive switching process could be well controlled by the voltage supply. The device exhibited low power consumption (0.586 nW for SET, 0.596 nW for RESET, and forming free), self-current compliance in LRS (106 Ω with approximately 10−5 A), and high cycling endurance (up to 3 ×103 times). The switching mechanism has been discussed in detail and comprehensively analyzed by scanning transmission electron microscope (STEM) and electrons energy loss spectrum (EELS). The results provide strong evidence of the continuous oxygen vacancy filaments in ZnO and discontinuous oxygen-deficient regions in AlOx. The switching mechanism for complex structure RRAM is verified and a potential candidate selection with excellent electrical properties is demonstrated.

Turn‐off Fluorescent Sensing of Energetic Materials using Protonic Acid doped Polyaniline: A Spectrochemical Mechanistic Approach

The trace detection of energetic materials (EMs) is a challenge due to the very low vapor pressure possessed by these compounds. Polyaniline (PAni) possesses variable oxidation and reduction states, which makes it strike different from other conducting polymers in understanding the mechanism of fluorophore‐analyte interaction leads to the designing of selectivity and sensitivity of analytes; also, fluorophore as a sensing device. The present work is aimed at trace detection of some very prominent EMs; nitroarenes viz., 1,3,5‐trinitroperhydro‐1,3,5‐triazine (RDX), trinitrotoluene (TNT); nitramines viz., hexanitrohexaazaisowurtzitane (CL‐20) and nitro ester viz., pentaerithroltetraniterate (PETN) employing para‐toluenesulfonic acid as a dopant for PAni nanofibers (P‐PAni). The P‐PAni helps overcome the dual difficulties of PAni, i.e., solubility and removal of π stacking when dimethylformamide (DMF) is used as a solvent. P‐PAni showed good quenching response and selectivity towards EMs, with the LOD being the best for CL‐20 (0.717 μM·L–1). The sensing studies further collaborated with the Cyclic Voltammetry, FTIR and Raman Spectroscopy studies gave a detailed understanding of the bipolaron‐polaron transition mechanism accompanying the electron transfer process in the fluorescence quenching study.

One-Step Solvothermal Preparation of Mn-Doped VO2(B) Nanosheets for High-Performance Supercapacitors

Pure and Mn-doped VO2(B) nanosheets were prepared using a simple one-step solvothermal reaction with V2O5 and H2O2 as precursors with Mn(CH3COO)2·4H2O added directly into the precursor solution to obtain the Mn-doped variant. The powder morphology, local structures and cation oxidation states were investigated using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), high-energy X-ray scattering, X-ray absorption near edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties were studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The Mn-doped VO2(B) nanosheet sample, comprising a mixed phase of two polymorphs of VO2, exhibits 80% higher capacitance at 2 mV s−1 scan rate, 2X smaller charge transfer resistance, and much improved cyclic stability compared with pure VO2(B). The improved electrochemical response is attributed to the enhanced mass transfer kinetics due to slightly differing microstructures and formation of more varied oxidation states of the V and Mn ions such that the charged defects increase the electrical conductivity and charge transfer efficiency.

Synthesis of β-Mn2V2O7 Anode Materials Using Facile Green Strategy for High Performance Rechargeable Lithium Ion Batteries

Vanadium-based mixed metal oxides are of interest because of their high energy density, variable oxidation states, and high specific capacities.Within the family of manganese vanadium oxides, earth abundant β-Mn2V2O7 (MnVO) has attracted considerable attention because of its fascinating crystal structures with key building blocks of several extended M-O and V-O polyhedral units.Herein we report the β-Mn2V2O7 (MnVO) were synthesized by a simple and cost-effective zeolitic imidazolate frame- work precipitation technique using water as the sole solvent and reported for excellent electrochemical Li storage properties. The anode delivers specific capacities of 868 and 751 mAh g-1 at rates of 500 and 2000 mAh g-1 after 180 and 400 cycles, respectively.

Diuranium(IV) Carbide Cluster U2C2 Stabilized inside Fullerene Cages

Novel actinide cluster fullerenes, U2C2@I h(7)-C80 and U2C2@D 3h(5)-C78, were synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, UV-vis-NIR , Raman spectroscopy, IR spectroscopy, as well as density functional and multireference wavefunction calculations. The encapsulated U2C2 is the first example of a uranium carbide cluster featuring two U centers bridged by a C≡C unit. The U-C bond distances in these U2C2 clusters are in the range between 2.130-2.421 Å. While the U2C2cluster in U2C2@C80 adopts a butterfly-shaped geometry with a U-C2-U dihedral angle of 112.716 °and a U-U distance of 3.855 Å, the U-U distance in U2C2@C78 is 4.164 Å and the resulting U-C2-U dihedral angle is increased to 149.084 °. The combined experimental and quantum-chemical results suggest that the formal U oxidation state is +IV in the U2C2 cluster, and each U center transfers three electrons to the C2n cage and one electron to C2. Different from the strong U=C covalent bonding reported for U2C@C80, the U-C bonds in U2C2 are less covalent and predominantly ionic. The C-C triple bond is somewhat weaker than in HCCH and the C-C -bonds undergo donation bonding with the U centers. This study demonstrates that the combination of the unique encapsulation effect of fullerene cages and the variable oxidation states of actinide elements can lead to the stabilization of novel actinide clusters which are not accessible by conventional synthetic methods. Figure 1

Insights into the role of surface functional species in Cu-Mn-O thin film catalysts for N2O decomposition

Efficient N2O decomposition using catalytic materials has been gaining attention for long time. Catalytic materials based on noble metals have proved good feasibility; however, their applications are restricted because of the high cost and limited resources. Herein, low-cost catalysts based on copper manganese oxides were synthesized by chemical vapor deposition technique for N2O decomposition. The obtained catalysts were characterized to identify the structure, morphology, composition and arrangement of formed species. The results showed that the particles are getting agglomerated when increasing Mn content, which could be due to the difference in growth and crystallization rates of Cu and Mn. XPS analysis exhibited the existence of several active species such as, Cu and Mn cations, hydroxides and metal carbonates. The ratio of Cu/Mn in bulk is found to be in correlation with the catalytic activity. The catalytic tests of N2O decomposition revealed good activity of all catalysts, and the quality and quantity of the formed surface species have dramatic effect on the activity of the catalysts. When doping by Mn to promote the catalytic activity, formed Cu(OH)2 species at catalysts’ surface appeared to be good promoters in the studied reaction of N2O decomposition by C3H6. However, the existence of Cu metal, as more reduced Cu state, at the surface of catalysts is appeared to decrease the catalytic activity, which may play an inhibitor role in this studied reaction. In addition, Cu auger peak identification revealed the existence of Cu cations with varied oxidation states, leading to establish a correlated sequence of Cu1+>Cu2+>Cu0 with the catalytic activity. This approach of fine-tuning the surface formed species could lead to enhance the performance of other catalysts in different applications.

Conformational Analysis of Acyclic α-Fluoro Sulfur Motifs.

Bioactive small molecules containing α‐fluoro sulfur motifs [RS(O)nCH2F] are appearing with increasing frequency in the pharmaceutical and agrochemical sectors. Prominent examples include the anti‐asthma drug Flovent® and the phenylpyrazole insecticide pyrafluprole. Given the popularity of these structural units in bioactive small molecule design, together with the varying oxidation states of sulfur, a conformational analysis of α‐fluoro sulfides, sulfoxides, and sulfones, would be instructive in order to delineate the non‐covalent interactions that manifest themselves in structure. A combined crystallographic and computational analysis demonstrates the importance of hyperconjugative donor‐acceptor interactions in achieving acyclic conformational control. The conformational disparity in the syn‐ and anti‐diastereoisomers of α‐fluorosulfoxides is particularly noteworthy.

Investigation of dielectric, magnetic and impedance spectroscopic properties of CaCu3-XMnXTi4-XMnXO12 (X = 0.10) nano-ceramic synthesized through semi-wet route

This communication reports a detail study on manganese (Mn) doping in CaCu3Ti4O12 (CCTO) ceramic (simultaneously doping copper and titanium site) with the help of X-ray Photoelectron Spectroscopy ( XPS), High Resolution - Scanning Electron Microscopy ( HR-SEM), High Resolution- Transmission Electron Microscopy (HR-TEM ) and Raman spectra. The doping of manganese in CCTO ceramic, the dielectric constant was largely decreased due to Mn exist variable oxidation state like Mn+2, Mn+3and Mn+4 due to this reason the grains (GB) and grain boundaries (GBs) slightly behave conducting nature. Raman spectra show the existence of copper oxide and manganese oxide presence in the grain and grain boundary of CaCu2.9Mn0.1Ti3.9Mn0.1O12 (CCMTMO) ceramic. The novelty of Mn-doped CCTO ceramic is that the tangent loss also decreases largely as compared to CCTO ceramic. The dielectric constant and tangent loss of CCMTMO ceramic 375 and 0.3 at 10 Hz temperature, respectively. CCMTMO ceramic is very useful for microelectronic devices. The polycrystalline nature of CCMTMO was to be studied with the help of X-ray diffraction (XRD), HR-SEM, HR-TEM, and Magnetic Property Measurement System (MPMS, Quantum Design). The elemental analysis and oxidation state was confirmed by (Energy Diffraction X-ray) EDX and XPS respectively. The elements were found to be their required stoichiometric and oxidation state. The impedance and modulus spectroscopy also studied.

Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application.

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

Polymer-Supported Phosphoric, Phosphonic and Phosphinic Acids-From Synthesis to Properties and Applications in Separation Processes.

Efficient separation technologies are crucial to the environment and world economy. The challenge posed to scientists is how to engineer selectivity towards a targeted substrate, especially from multicomponent solutions. Polymer-supported reagents have gained a lot of attention in this context, as they eliminate a lot of inconveniences concerning widely used solvent extraction techniques. Nevertheless, the choice of an appropriate ligand for immobilization may be derived from the behavior of soluble compounds under solvent extraction conditions. Organophosphorus compounds play a significant role in separation science and technology. The features they possess, such as variable oxidation states, multivalence, asymmetry and metal-binding properties, highlight their status as a unique and versatile class of compounds, capable of selective separations proceeding through different mechanisms. This review provides a detailed survey of polymers containing phosphoric, phosphonic and phosphinic acid functionalities in the side chain and covers main advances in the preparation and application of these materials in separation science, including the most relevant synthesis routes (Arbuzov, Perkow, Mannich, Kabachnik-Fields reactions, etc.), as well as the main stages in the development of organophosphorus resins and the most important achievements in the field.

Chitosan supported molybdate nanoclusters as an efficient catalyst for oxidation of alkenes and alcohols

The excellent Lewis acidity and variable oxidation states of molybdate anions for the oxidation reactions was utilized by supporting it on eco-friendly and amply available fishery waste chitosan backbone using a simple “mix and make” methodology. The comprehensive structural analysis was done by FTIR, XRD, FESEM, elemental mapping, TEM and XPS. FESEM and elemental analysis revealed the mono-dispersion of molybdate nanoclusters on the surface of the chitosan. The increase in the molybdate loading increased the size of the clusters without affecting their uniformity over the polymer. This multi-nuclear material showed high catalytic activity towards the liquid phase oxidation of alkenes and alcohols owing to the surface sorption of the molybdate nanoclusters. The oxidation of cycloalkenes gave full conversion with > 90% selectivity towards the corresponding epoxides, while the oxidation of aryl alkenes and alcohols gave good to best results in terms of catalytic activity and selectivity. The catalyst exhibited prominent reusability.

Polyol mediated synthesis of anisotropic ZnO nanomaterials and composite with rGO: Application towards hybrid supercapacitor

Metal oxides nanomaterials are widely investigated for electrode materials of supercapacitor. However, the performance of supercapacitor strongly correlated to the variable oxidation state of metallic ions in metal oxides as well as morphology (shape and size) and porosity of the nanomaterials. Here, we have investigated the role of polyols such as ethylene glycol (EG), diethylene glycol (DEG) and polyethylene glycols (PEG, Mw = 400 and 1000) on the formation of ZnO nanostructures with anisotropicity in morphology. The phase of ZnO and coating with polyol was confirmed by X-ray diffraction and thermogravimetric (TG) analysis. FESEM image reveals nanosphere, nanoassemblies, nanorod, and hexagonal (cup shaped and rigid shaped) morphology of ZnO particles in different dimensions. The specific capacitance of the nanomaterials was measured by cyclic voltammetry method in a three electrodes system with 1 M KCl solution as electrolyte. Hexagonal rigid shaped ZnO gives better capacitance value of (6.42 F/g) followed by hexagonal cup shaped (6.4 F/g), nanoassemblies (5.75 F/g), nanorod (4.03 F/g), and nanosphere (3.67 F/g) at 10 mV/s. Further hexagonal shaped zinc oxide was made composite with reduced graphene oxide (rGO) and interestingly, the composite with 1:2 wt% of rGO to ZnO exhibits excellent specific capacitance of 251.16 F/g at 2 mV/s. Chronopotentiometry analysis indicated good charging and discharging behavior of the composite whereas electrochemical impedance spectroscopy revealed a good charge transfer characteristic.

Structural, dielectric and electrical characteristics of lead-free scandium modified barium iron niobate: Ba(Fe0.5-x ScxNb0.5)O3

Scandium (Sc) modified barium iron niobates (i.e., Ba(Fe0.5-x ScxNb0.5)O3 (x = 0.03,0.05 and 0.07) (BFSN)) were synthesized by using a standard ceramic technology (i.e., high-temperature solid-state reaction of mixed oxide route). The analysis of room temperature X-ray diffraction data shows the monoclinic phase of the materials. The dielectric and impedance parameters were measured in different temperature (250C–500 °C) and frequency (1 kHz-1 MHz) ranges. Detailed study of temperature dependent dielectric constant shows the two anomalies; one may be related to the ferroelectric to paraelectric phase transition at about 249 °C and another at about 368 °C may be due to some extrinsic effects (due to creation of oxygen vacancies for variable oxidation states). The grains and grain boundary contributions in resistive and capacitive characteristics, temperature activated polarization mechanisms are analysed. The Leakage (J ~ E) characteristics illuminate the bulk (ohms due to hopping of charge carriers and, space charge limited) conduction processes of the samples. With the increase in scandium, diffusivity decreases in BFSN compounds.

Identification of the Active Catalyst for Nickel-Catalyzed Stereospecific Kumada Coupling Reactions of Ethers.

A series of nickel complexes in varying oxidation states were evaluated as precatalysts for the stereospecific cross-coupling of benzylic ethers. These results demonstrate rapid redox reactions of precatalysts, such that the oxidative state of the precatalyst does not dictate the oxidation state of the active catalyst in solution. These data provide the first experimental evidence for a Ni0 -NiII catalytic cycle for a stereospecific alkyl-alkyl cross-coupling reaction, including spectroscopic analysis of the catalyst resting state.

Ruthenium: Past and Present

This article provides information on one of the most interesting elements in the D.I. Mendeleev Periodic Table - ruthenium, discovered 175 years ago by the outstanding Russian chemist Karl Karlovich Klaus. Its most important physical properties, a variety of oxidation states, and a tendency to form countless compounds have been noted, mocking it unique and indispensable in all areas of science, technology, and in society. We have taken into consideration the structure of ruthenium consumption today as well as a few prospects for its future use.

Influence of structure on catalytic activity of nano - manganese oxide

Nano-oxides of manganese synthesized from the radiolytic reduction of permanganate (MnO4-) medium at varying pH in ambient temperature showed differences in structural properties. In the present communication, we report the effect of variance in the structural morphology on the hetero-catalytic activity of manganese nano-oxides. Applications of these radiolytically generated manganese nano-oxides, as catalysts were tested by monitoring the decomposition of H2O2 and N2H4 solutions at room temperature and suitable mechanism has been proposed. The catalytic decomposition rates of H2O2 and N2H4 solutions increased in the presence of oxides formed from the radiolysis of alkaline permanganate solutions. The kinetics of the catalytic activity of the nano-oxides was correlated with their high surface area, large pore volume, adsorbed –OH groups, varying oxidation states of Mn, and their microstructures.

Collagen stabilization using ionic liquid functionalised cerium oxide nanoparticle

Nanoparticles owing to their size have a substantial influence on the biological behavior of collagen, thereby opening new channels to unfold the propensity of nanoparticles in terms of collagen stabilization. The present study aims to synthesize and characterize cerium oxide nanoparticles and to investigate their crosslinking efficiency on collagen. Cerium oxide nanoparticles, known biocatalysts, form an effective oxidation system due to their variable oxidation state. Ionic liquid functionalizes cerium oxide nanoparticles (IL-CONP) have been synthesis by the sonication method and characterizes using techniques such as Dynamic Light Scattering, and X-ray Diffraction. The hydrodynamic diameter, Zeta potential and polydispersity index of nanoparticles is 192.3 ± 2.14 nm, −13.76 ± 1.5 mV and 0.387, respectively. Changes in the secondary structure of collagen upon treatment with increasing concentration of IL-CONP indicate conformational modifications at the molecular level. Differential scanning calorimetry studies on rat tail tendon collagen fibers with IL-CONP indicate an increase in thermal stability of collagen from 61 to 87 °C. Thus, cerium oxide-based nanoparticle crosslinking invokes a considerable array of interest as a potential crosslinking agent for collagen.

Computational Screening of Metal–Organic Framework-Supported Single-Atom Transition-Metal Catalysts for the Gas-Phase Hydrolysis of Nerve Agents

Recent studies have suggested that the gas-phase hydrolysis of nerve agents by Zr-based metal–organic frameworks (MOFs) may be limited by product inhibition resulting from strong bidentate binding of the hydrolysis products to the Zr6-nodes. A potential method to avoid this problem is to deposit single-atom catalysts on the nodes so that the products bind in a more favorable monodentate mode. Such catalytic active sites can be characterized with atomic precision, enabling detailed computational mechanistic studies. Thus, we used density functional theory to perform a comprehensive screening of single-atom transition-metal catalysts, in varying oxidation states, deposited on NU-1000 nodes for the gas-phase hydrolysis of the nerve agent sarin. By calculating the complete reaction pathways for M–NU-1000 systems, we discovered that the highest reaction barrier varies between catalysts, highlighting the need to consider more than a single reaction step when screening a large number of diverse materials. The si...