Transition Metal Series Research Articles

Room-Temperature Methane Conversion by Graphene-Confined Single Iron Atoms

Summary Direct conversion of methane to high-value-added chemicals is a major challenge in catalysis, which usually requires high-energy input to overcome the reaction barrier. We report that graphene-confined single Fe atoms can be used as an efficient non-precious catalyst to directly convert methane to C1 oxygenated products at room temperature. A series of graphene-confined 3d transition metals (Mn, Fe, Co, Ni, and Cu) were screened, yet only single Fe atoms could catalyze the methane conversion. Combining in operando time-of-flight mass spectrometry, 13C nuclear magnetic resonance, and density functional theory calculations, we found that methane conversion proceeds on the O–FeN4–O active site along a radical pathway to produce CH3OH and CH3OOH first, and then the generated CH3OH can be further catalyzed to form HOCH2OOH and HCOOH at room temperature.

Influence of dilute solute substitutions in Ni on its generalized stacking fault energies and ductility

We determine effects of substitutional solutes belonging to 3d, 4d and 5d transition metal (TM) series on volume, intrinsic stacking fault energy (ISFE), unstable stacking fault energy (USFE) and ductility parameter of Ni using first-principles calculations based density functional theory (DFT), considering both ferromagnetic (spin-polarized) and non-magnetic states of Ni. For each of the TM series, we find that volume exhibits a minimum for substitutional elements with half-filled d-orbitals (5 d-electrons). Reduction in ISFE of Ni is seen with all the solute additions except for Pd (in the non-magnetic case). Inclusion of spin-polarization has a pronounced effect on the fault energies and results in increase in both ISFE as well as USFE. In the non-magnetic case, USFE exhibits maxima for alloying with elements having five electrons in d-orbital. Except for Zr and Pd, substitution of other elements enhanced cleavage energy of Ni. Differences in the fault energies on alloying have been explained based on the electronic structure of the alloys. There exists a correlation between change in volume and change in USFE with substitutional alloying. It is envisaged that the exhaustive data generated here would not only form necessary input to multi-scale microstructural modeling, but also help in evolving simple recipes for design of new alloys.

Engineered Electrolyte-Electrocatalyst Nanocomposites for Enhanced CO2 Electroreduction

The development of a viable approach to capture, store, and convert carbon dioxide into fuels and chemicals may offer a means to mitigate climate change while also creating value added commodity chemicals. Critical bottlenecks in existing technologies that have impeded commercialization of CO2 electrosynthesis include catalysts with high overpotentials and limited selectivities. Furthermore, current approaches often employ PEM-based electrolyzers that suffer from low CO2 solubility in acidic aqueous solutions, limiting mass transport and reaction rates, or AEM-based systems which have much higher CO2 solubilites in alkaline electrolytes, but have the added problem of membrane poisoning by bicarbonate and carbonate. We have recently developed an electrochemical reactor that overcomes many of the shortcomings that have limited the above technologies. Our preliminary results suggest that onset potentials for CO2 reduction are more than 200 mV lower than with current densities in excess of 150 mA/cm2 at -1 V vs RHE. We have examined several cathode electrocatalysts and some of the most promising include a series of nanostructured mixed and/or doped transition metal and main group metal oxides that also suppress the hydrogen evolution reaction. We will present detailed electrochemical and structural studies and will comment on possible reaction mechanisms as well as the key features of the reactor that enable the enhanced kinetics.

Spectra Characterization, In vitro Evaluation of Antibacterial and Hemolytic Activity of Novel Ligand 5-(5-{(2Z)-2-[(2-Hydroxynaphthalen-1- yl)Methylidene]Hydrazinyl}-1,3,4-Oxadiazol-2-yl)Benzene-1,2,3-Triol with some its Transition Metal Complexes

A new series of transition metal (Cr(III), Co(II), Ni(II)and Cu(II) complexes of ligand 5-(5-{(2Z)-2-[(2- hydroxynaphthalen-1- yl)methylidene]hydrazinyl}-1,3,4-oxadiazol-2-yl)benzene-1,2,3-triol were synthesized and evaluated for its biological activities. A ligand was synthesized by reaction propyl gallate and hydrazine hydrate in presence of ethanol to give 3, 4, 5- trihydroxybenzohydrazide followed by reaction with potassium hydroxide and carbon disulfide, the resultant was mixed with hydrazine hydrate to produce the ligand. The newly synthesized compounds were characterized by Fourier transform infrared (FTIR)Spectroscopy, Nuclear Magnetic Resonance Spectroscopy (1H NMR), elemental analyses (C, H, N), mass spectral, conductivity measurement, and magnetic susceptibility data. The Hyperchem 7.51 program have been used to draw the ligand geometry optimization and then study the electrostatic potential that given right data about the active site. Antibacterial activity and hemolysis assay of prepared compounds were studied. Antibacterial activity was carried out against Escherichia coli, Salmonella, and Staphylococcus aureus with test compounds at four concentrations of (50,100,250,500μg/ml). Erythromycin was the standard drug utilize. Some of these compounds showed good efficacy, while others ranged from medium to small.

The surface energy and stress of metals

We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

Synthesis, crystal structure, theoretical studies and biological properties of three novel trigonal prismatic Co(II), Ni(II) and Cu(II) macroacyclic Schiff base complexes incorporating piperazine moiety

Abstract Trigonal-prismatic structures among different transition metal complexes according to the Cambridge Structural Database (CSD) are rare. The number of trigonal prisms throughout the transition-metal series is less than 1% of all six-coordinate metal centers and only 0.4% of cobalt complexes. Herein we report a novel macroacyclic Schiff base complexes incorporating piperazine moiety with Trigonal-Prismatic coordination were prepared via the metal templated of the 2,2′-(piperazine-1,4-diylbis(methylene))dianiline (A) and 2-formylpyridinein the presence of appropriate Co(II), Ni(II) and Cu(II) metal ions in methanolic/ethanolic solution. The complexes were characterized by elemental analysis, mass spectrometry and FT-IR. Also, the crystal structure of [CoL](ClO4)2·(H2O) complex was obtained by single-crystal X-ray crystallography. An interesting point in this report is the trigonal prismatic coordination for complexes that is the first for Schiff-base complexes containing piperazine moiety. Furthermore, these newly synthesized complexes were evaluated for their in vitro antioxidant and antibacterial activities by using scavenging effects on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and disc diffusion methods, respectively. Based on the resulting experimental data, these compounds exhibited good biological activities. The geometry of [ML]2+ (M = Co, Ni, Cu) complexes have been also optimized at the BP86/def2-SVP level of theory. Furthermore the nature of M ← L (M = Co, Ni, Cu) bonds in the complexes have been studied with the help of NBO and Energy decomposition analysis (EDA). Results showed that the nature of metal-ligand bonds is more covalent (orbital term) with a contribution of about 53.4–62.8% in total interaction energy.

Quantification of Olivine Using Fe Lα in Electron Probe Microanalysis (EPMA).

Quantification of first series transition metal Lα X-rays is hampered by absorption and in some cases transition probabilities (fluorescence yields) varying with chemical bonding. Compound mass absorption coefficients for Fe Lα were measured in the olivine solid solution series [Forsterite (Mg2SiO4) to Fayalite (Fe2SiO4)] and the mass absorption coefficients for Fe Lα absorbed by Fe were calculated. The mass absorption coefficients vary systematically between Fo83 and Fo0. Using the measured mass absorption coefficients for both standard and unknown and by correcting for a systematic discrepancy, consistent with varying partial fluorescence yields, a good agreement between calculated k-ratios and measured k-ratios is achieved. The systematic variations allow quantification of unknown k-ratios. The described method of quantification requires modification of matrix correction routines to allow standards and unknowns to have different mass absorption coefficients, and to incorporate solid solution mass absorption coefficients and partial fluorescence yield corrections derived from regression of experimental data.

Synergistic Improvement in Charge Overpotential of Li–O2 Batteries by Oxidized Carbon Nanotubes and Cobalt Nitride Composites

Bifunctional electrocatalysts are important to optimize the overpotential in Li–O2 battery cycles. Catalysts with a size distribution in the nanometer range perform efficiently because of the availability of numerous active sites. Carbonaceous composites of materials derived from transition metal series are exploited as bifunctional catalysts for oxygen reactions in the Li–O2 batteries. Cobalt nitride (Co4N) as predicted by density functional theory is believed to possess metallic properties. In this study, we have examined the viability of Co4N nanoparticles to oxygen reactions in Li–O2 batteries. Oxidized multiwall carbon nanotubes are further added to Co4N nanoparticles to form a composite. Structural characterizations reveal that nanoparticles arranged conformally around the nanotubes, creating active centers for both oxygen evolution and reduction through the nanotube as a charge-transport channel. Electrochemical measurements for Li–O2 characteristics are performed on both pristine and composite cat...

Magnetic Chern Insulators in a monolayer of Transition Metal Trichalcogenides

A monolayer of transition metal trichalcogenides has received a lot of attention as potential two dimensional magnetic materials. The system has a honeycomb structure of transition metal ions, where both spin-orbit coupling and electron correlation effect play an important role. Here, motivated by these transition metal series with effective doping or mixed valence case, we propose the possible realization of magnetic Chern insulators at quarter filled honeycomb lattice. We show that the interplay of intrinsic spin-orbit coupling and electron correlation opens a wide region of ferromagnetic Chern insulating phases in between metals and normal insulators. Within the mean field approximation, we present the phase diagram of a quarter filled Kane-Mele Hubbard model and also discuss the effects of Rashba spin-orbit coupling and nearest neighbor interactions on it.

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MN4C4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical prediction of MN4C4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.

Single transition metal atom embedded into a MoS2 nanosheet as a promising catalyst for electrochemical ammonia synthesis.

The electrochemical reduction of N2 to NH3 (NRR) under ambient conditions is significant for sustainable agriculture. Here, by means of density functional theory (DFT) computations, the potential of a series of single transition metal (TM) atoms embedded into a MoS2 monolayer with an S-vacancy (TM/MoS2) as electrocatalysts for NRR was systematically investigated. Our DFT results revealed that among all these considered candidate catalysts, the single Mo atom embedded into the MoS2 nanosheet was found to be the most active catalyst for NRR with an onset potential of -0.53 V, in which the hydrogenation of the adsorbed N2* to N2H* is the potential-determining step. The high stabilization of the N2H* species is responsible for the superior performance of the embedded Mo atom for the NRR, which is well consistent with its d-band center. Our findings may facilitate the further design of single-atom electrocatalysts with high efficiency for NH3 synthesis at room temperature.

Ab Initio Monte Carlo Simulations of the Acidic Dissolution of Stainless Steels: Further Insights into the Mechanisms

Using Ab initio based Monte Carlo simulation techniques (AbMC), dissolution kinetics in acidic media was evaluated for different stainless steels (SS) as a function of their chemical composition, with particular attention paid to the role of transition metals series (TM). The elementary dissolution events at the atomic scale were treated as stochastic processes, from which dissolution probabilities were deduced. Two determining factors emerge as critical for the control of dissolution kinetics: the bonding energy of an alloying element in the SS matrix and its standard electrochemical potential. The first reflects the ability of an element to form stronger (Mo, Nb, Ni etc.) or weaker (Cr, Cu, Sn etc.) bonding than Fe, and the second refers to its facility to dissolve under an applied potential. High bonding energies and high standard potentials lead to a strong dissolution resistance (Mo), whereas low bonding energies and low standard potentials induce high dissolution kinetics (Sn). The intermediate situations: high-bonding energy and low standard potential (Nb) or low bonding energy and high standard potential (Cu) usually lead to moderate dissolution regimes with a strong impact on the dissolution mechanisms.

Synthesis and Characterization of FeІІ , CoІІ , NiІІ , CuІІ and ZnІІ Complexes With Dithiocarbamate and N-Donor Ligands

New complexes of first series of transition metals with P-amino benzene dithiocarbamate of the general formula [M(PABdtc)2] and [ M(PABdtc)2(L)n] M=Fe( ІІ ),Co( ІІ ),Ni( ІІ ) ,Cu(ІІ) and Zn (ІІ). PABdtc = Paraamino benzene dithiocarbamate ,n=2 when L= Py,ɣ-Pic,iso qunoline ,3,5lutidine n=1when L=1,10-phenanthroline, en, 2,-2bipy.and the type(R)4N[Ni(PABdtc)3] R= methyl, ethyl are prepared. Physico chemical characterization of these complexes was applied using magnetic susceptibility measurements, molar conductance , Infrared and electronic spectra, Metal content measurements, molar conductance indicate complexes of the type [M(PABdtc)2] and [M(PABdtc)2(L)n] are non-electrolyte while complexes of the type (R)4N[Ni(PABdtc)3] are 1:1 electrolyte. Magnetic moment and electronic spectra indicate that the complexes of the type [M(PABdtc)2] are tetrahedral geometry while the complexes of the type [M(PABdtc)2(L)n] and (R)4N[Ni(PABdtc)3] have octahedral geometry

First-Row-Transition Ion Metals(II)-EDTA Functionalized Magnetic Nanoparticles as Catalysts for Solvent-Free Microwave-Induced Oxidation of Alcohols

A series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA), as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs) was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4@EDTA-M2+ [M = Mn2+ (1), Fe2+ (2), Co2+ (3), Ni2+ (4), Cu2+ (5) or Zn2+ (6)] were characterized by FTIR (Fourier Transform Infrared) spectroscopy, powder XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectrometer), VSM (Vibrating Sample Magnetometer) and TGA (Thermal Gravity Analysis). The application of the magnetic NPs towards the microwave-assisted oxidation of several alcohol substrates in a solvent-free medium was evaluated. The influence of reaction parameters such as temperature, time, type of oxidant, and presence of organic radicals was investigated. This study demonstrates that these MNPs can act as efficient catalysts for the conversion of alcohols to the corresponding ketones or aldehydes with high selectivity and yields up to 99% after 2 h of reaction at 110 °C using t-BuOOH as oxidant. Moreover, they have the advantage of being magnetically recoverable catalysts that can be easily recycled in following runs.

Optical activity of Co-porphyrin in the light of IR and Raman spectroscopy: A critical DFT investigation

A critical investigation on the structure, electronic properties and optical activities of a series of transition metal doped porphyrins (TMP; TM=Fe, Co, Ni) in the light of infrared and Raman spectroscopy is performed, under density functional formalism. The structure and electronic properties are studied in terms of ionization potential, electron affinity, chemical hardness (η), binding energies of the transition metals (BETM) etc. The origin of the optical activities, especially the visibly active cobalt porphyrin is addressed through critical study on their infrared and Raman spectra. The information availed from the spectral analysis will certainly ease their possible synthesis and useful applications in the sensor and optoelectronic domains.

Copper(II) and zinc(II) dinuclear enzymes model compounds: The nature of the metal ion in the biological function

First series transition metals are used abundantly by nature to perform catalytic transformations of several substrates. Furthermore, the cooperative activity of two proximal metal ions is common and represents a highly efficient catalytic system in living organisms. In this work three dinuclear μ-phenolate bridged metal complexes were prepared with copper(II) and zinc(II), resulting in a ZnZn, CuCu and CuZn with the ligand 2-ethylaminodimethylamino phenol (saldman) as model compounds of superoxide dismutase (CuCu and CuZn) and metallo-β-lactamases (ZnZn). Metals are coordinated in a μ-phenolate bridged symmetric system. Cu(II) presents a more distorted structure, while zinc is very symmetric. For this reason, [CuCu(saldman)] shows higher water solubility and also higher lability of the bridge. The antioxidant and hydrolytic beta-lactamase-like activity of the complexes were evaluated. The lability of the bridge seems to be important for the antioxidant activity and is suggested to because of [CuCu(saldman)] presents a lower antioxidant capacity than [CuZn(saldman)], which showed to present a more stable bridge in solution. The hydrolytic activity of the bimetallic complexes was assayed using nitrocefin as substrate and showed [ZnZn(saldman)] as a better catalyst than the Cu(II) analog. The series demonstrates the importance of the nature of the metal center for the biological function and how the reactivity of the model complex can be modulated by coordination chemistry.

Importance of the ligand basis set in ab initio thermochemical calculations of transition metal species

The impact of basis set choice has been considered for a series of transition metal (TM) species. The need for higher level correlation consistent basis sets on both the metal and ligand has been investigated, and permutations in the pairings of basis set used for TM’s and basis set used for ligands can lead to effective routes to complete basis set (CBS) limit extrapolations of thermochemical energetics with little change in thermochemical predictions as compared to those resulting from the use of traditional basis set pairings, while enabling computational cost savings. Basis set superposition errors (BSSE) that can arise have also been considered.

Computational Design Principles of Two-Center First-Row Transition Metal Oxide Oxygen Evolution Catalysts

Computational screens for oxygen evolution reaction (OER) catalysts based on Sabatier analysis have seen great success in recent years; however, the concept of using chemical descriptors to form a reaction coordinate has not been put under scrutiny for complex systems. In this paper, we examine critically the use of chemical descriptors as a method for conducting catalytic screens. Applying density functional theory calculations to a two-center metal oxide model system, we show that the Sabatier analysis is quite successful for predicting activities and capturing the chemical periodic trends expected for the first-row transition metal series, independent of the proposed mechanism. We then extend this analysis to heterodimer metallic systems—metal oxide catalysts with two different catalytically active metal centers—and find signs that the Sabatier analysis may not hold for these more complex systems. By performing a principal component analysis on the computed redox potentials, we show (1) that a single c...

NMR, ESR, NQR and IR Studies of Paramagnetic Macrocyclic Complexes of 1st Transition Series Metal Ions Exhibiting MLCT Phenomenon: A DFT Application. Part: III. Tris (2, 2- bipyridine) Complexes

NMR, ESR, NQR and IR Studies of Paramagnetic Macrocyclic Complexes of 1st Transition Series Metal Ions Exhibiting MLCT Phenomenon: A DFT Application. Part: III. Tris (2, 2- bipyridine) Complexes

Polymer complexes. LXVII: electrical conductivity and thermal properties of polymer complexes of quinoline azo dye

A novel series of divalent transition metals (Cu2+, Co2+ and Ni2+) polymer complexes of azo ligand named 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-8-hydroxyquinoline (Q) have been synthesized. The azo quinoline ligand (Q) and polymer complexes are characterized by various physicochemical techniques. The thermal properties of the ligand and its isolated polymer complexes are studied using thermogravimetric analysis. The physicochemical investigations elucidate that the azo ligand acts as a neutral bis(bidentate) ligand. The polymer complexes are found to be octahedral geometry. The change in the ac electrical conductivity, loss tangent and dielectric properties are studied upon heating in temperature region 298–550 K and frequency ranging from 0.1 to 100 kHz, moreover, the mechanism of conduction is determined. The electrical conductivity studies indicate that the ligand (Q) and polymer complexes have the semiconducting behavior. The correlated barrier hopping is the dominant conduction mechanism for all samples.