First-row Transition Metal Research Articles

Recent Advances in Hydrogen Evolution Reaction Using First-Row Transition Metal Complexes as Catalyst

The precise use of an electrocatalyst for the HER reaction mainly depends on synthesis cost, durability, and over potential. Recently there is promising research for electrocatalyst synthesis using first-row transition metals. Working towards this herein we present synthesis, physio-chemical characterization, and hydrogen evolution activity of amino guanidium metal naphthoate complexes. The obtained electrocatalysts were characterized by element analysis, IR spectra, UV-Visible spectroscopy, TG-DTA, and powder-XRD. The thermal behavior of these compounds has been studied by simultaneous TG-DTA techniques. The isomorphic nature of the metal complexes is evident from powder-XRD data.

Single-Source Deposition of Mixed-Metal Oxide Films Containing Zirconium and 3d Transition Metals for (Photo)electrocatalytic Water Oxidation.

The fabrication of mixed-metal oxide films holds promise for the development of practical photoelectrochemical catalyst coatings but currently presents challenges in terms of homogeneity, cost, and scalability. We report a straightforward and versatile approach to produce catalytically active zirconium-based films for electrochemical and photoelectrochemical water oxidation. The mixed-metal oxide catalyst films are derived from novel single-source precursor oxide cage compounds containing Zr with first-row transition metals such as Co, Fe, and Cu. The Zr-based film doped with Co on fluorine-doped tin oxide (FTO)-coated glass exhibits the highest electrocatalytic O2 evolution performance in an alkaline medium and an operational stability above 18 h. The deposition of this film onto a BiVO4 photoanode significantly enhances its photoelectrochemical activity toward solar water oxidation, lowering the onset potential by 0.12–0.21 V vs reversible hydrogen electrode (RHE) and improving the maximum photocurrent density by ∼50% to 2.41 mA cm–2 for the CoZr-coated BiVO4 photoanodes compared to that for bare BiVO4.

Enhanced hydrogen evolution by using ternary nanocomposites of mesoporous carbon nitride/black phosphorous/transition metal nanoparticles (m-gCN/BP-M; M = Co, Ni, and Cu) as photocatalysts under visible light: A comparative experimental and theoretical study

The effect of first-row transition metal nanoparticles as co-catalysts on the activity of mesoporous graphitic carbon nitride (m-gCN) and black phosphorous (BP) heterojunctions (m-gCN/BP) in the photocatalytic hydrogen evolution reaction (HER) is investigated comparatively. Three m-gCN/BP-M (M: Co, Ni, and Cu) ternary nanocomposites were prepared via wetness impregnation and chemical reduction of metal precursors on as-prepared m-gCN/BP binary heterojunctions. The photocatalytic HER activities of m-gCN, m-gCN/BP, m-gCN/BP-Ni, m-gCN/BP-Co, and m-gCN/BP-Cu nanocomposites were determined to be 0.233, 0.330, 0.442, 0.326, and 0.223 mmol g−1 h−1, respectively, under visible light illumination. These results revealed that type of transition metal NPs as co-catalysts have considerable effect on the activity of m-gCN/BP heterojunctions in the photocatalytic HER, among which m-gCN/BP-Ni is the best one. The DFT calculations performed on the nanocomposites revealed that m-gCN/BP-Ni possesses the lowest band gap and the highest visible light absorption resulting in the highest photocatalytic activity in HER.

First-Row Transition Metal Antimonates for the Oxygen Reduction Reaction.

The development of inexpensive and abundant catalysts with high activity, selectivity, and stability for the oxygen reduction reaction (ORR) is imperative for the widespread implementation of fuel cell devices. Herein, we present a combined theoretical-experimental approach to discover and design first-row transition metal antimonates as excellent electrocatalytic materials for the ORR. Theoretically, we identify first-row transition metal antimonates─MSb2O6, where M = Mn, Fe, Co, and Ni─as nonprecious metal catalysts with good oxygen binding energetics, conductivity, thermodynamic phase stability, and aqueous stability. Among the considered antimonates, MnSb2O6 shows the highest theoretical ORR activity based on the 4e- ORR kinetic volcano. Experimentally, nanoparticulate transition metal antimonate catalysts are found to have a minimum of a 2.5-fold enhancement in intrinsic mass activity (on transition metal mass basis) relative to the corresponding transition metal oxide at 0.7 V vs RHE in 0.1 M KOH. MnSb2O6 is the most active catalyst under these conditions, with a 3.5-fold enhancement on a per Mn mass activity basis and 25-fold enhancement on a surface area basis over its antimony-free counterpart. Electrocatalytic and material stability are demonstrated over a 5 h chronopotentiometry experiment in the stability window identified by theoretical Pourbaix analysis. This study further highlights the stable and electrically conductive antimonate structure as a framework to tune the activity and selectivity of nonprecious metal oxide active sites for ORR catalysis.

Modulated Antimicrobial Activity and Drug-Protein Interaction Ability of Zinc Oxide and Cadmium Sulfide Nanoparticles: Effect of Doping with Few First-Row Transition Metals

Modulated Antimicrobial Activity and Drug-Protein Interaction Ability of Zinc Oxide and Cadmium Sulfide Nanoparticles: Effect of Doping with Few First-Row Transition Metals

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Computational analysis of the optical response of ZnSe with d-orbital defects

The doping of wide band-gap semiconducting ZnSe by transition metal (TM) atoms finds applications from mid-infrared lasing, sensing, photoelectrochemical cells, to nonlinear optics. Yet understanding the response of these materials at the atomic and electronic level is lacking, particularly in comparing a range of TM dopants, which were studied primarily by phenomenological crystal-field theory. In this work, to investigate bulk ZnSe singly doped with first-row TM atoms, specifically Ti through Cu, we applied a first-principles approach and crystal-field theory to explain the origin of the infrared absorption. We show that the use of an appropriate exchange–correlation functional and a Hubbard U correction to account for electron correlation improved the determination of the electronic transitions in these systems. We outline an approach for the calculation of the crystal-field splitting from first-principles and find it useful in providing a measure of dopant effects, also in qualitative comparison to our experimental characterization for ZnSe doped with Fe, Cr, and Ni. Our calculated absorption spectra indicate absorption signatures in the mid-infrared range, while the absorption in the visible portion of the spectrum is attributed to the ZnSe host. Our calculations will potentially motivate further experimental exploration of TM-doped ZnSe. Finally, the methods used here provide a route towards computational high-throughput screening of TM dopants in III–V materials through a combination of the electronic band structure and crystal-field theory.

Reactivity between late first-row transition metal halides and the ligand bis(2-pyridylmethyl)disulfide: Vibrantly-colored compounds with variable molecular geometries influenced by metal-sulfur interactions

The reactivity between late first-row transition metal halides and the disulfide-containing ligand bis(2-pyridylmethyl)disulfide was examined. From this survey, a series of mononuclear, four- and five-coordinate metal compounds were prepared and characterized. Single-crystal X-ray diffraction was employed to analyze the molecular structures in the solid state. The four-coordinate, tetrahedral compounds adopt either the form MLX2 (M = Zn; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the disulfide ligand is coordinated in a bidentate fashion by two nitrogen donors, or MLX (M = Cu; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the ligand is tridentate, coordinating via one sulfur and two nitrogen donors. The five-coordinate metal compounds, though varying significantly with regard to molecular geometry due to metal-sulfur interaction strength, adopt the form MLX2 (M = Zn, Cu, Co; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) with the ligand serving as a tridentate scaffold employing one sulfur and two nitrogen donors. The crystal structures ZnLCl2•CHCl3 and ZnLBr2•CHCl3 are isomorphous as are the structures ZnLCl2•CH2Cl2, ZnLBr2•CH2Cl2, and CoLBr2•CH2Cl2. The crystal structure of CoLCl2 is a kryptoracemate, having an enantiomeric pair within the asymmetric unit. Although chemically-identical, both hands of CoLCl2 have strikingly different Co–S distances: 2.599(2) versus 2.755(2) Å. Based on the X-ray crystal structures, the choice of halide does not appear to significantly influence the molecular geometry. For the solvated crystal structures, the identity of the solvent molecule has a drastic effect on the metal-sulfur distances. Compounds that contain metal-sulfur coordination do not appreciably affect the disulfide bond, as determined by X-ray crystallography and Raman spectroscopy. In addition to the standard analytical methods, variable-temperature NMR and UV–vis–NIR spectroscopy was utilized to gain insight into the solution behavior of the vibrantly-colored compounds.

Aberrant Cerebral Iron Trafficking Co-morbid With Chronic Inflammation: Molecular Mechanisms and Pharmacologic Intervention.

The redox properties that make iron an essential nutrient also make iron an efficient pro-oxidant. Given this nascent cytotoxicity, iron homeostasis relies on a combination of iron transporters, chaperones, and redox buffers to manage the non-physiologic aqueous chemistry of this first-row transition metal. Although a mechanistic understanding of the link between brain iron accumulation (BIA) and neurodegenerative diseases is lacking, BIA is co-morbid with the majority of cognitive and motor function disorders. The most prevalent neurodegenerative disorders, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple System Atrophy (MSA), and Multiple Sclerosis (MS), often present with increased deposition of iron into the brain. In addition, ataxias that are linked to mutations in mitochondrial-localized proteins (Friedreich's Ataxia, Spinocerebellar Ataxias) result in mitochondrial iron accumulation and degradation of proton-coupled ATP production leading to neuronal degeneration. A comorbidity common in the elderly is a chronic systemic inflammation mediated by primary cytokines released by macrophages, and acute phase proteins (APPs) released subsequently from the liver. Abluminal inflammation in the brain is found downstream as a result of activation of astrocytes and microglia. Reasonably, the iron that accumulates in the brain comes from the cerebral vasculature via the microvascular capillary endothelial cells whose tight junctions represent the blood-brain barrier. A premise amenable to experimental interrogation is that inflammatory stress alters both the trans- and para-cellular flux of iron at this barrier resulting in a net accumulation of abluminal iron over time. This review will summarize the evidence that lends support to this premise; indicate the mechanisms that merit delineation; and highlight possible therapeutic interventions based on this model.

Manganese Carbonyl Complexes as Selective Electrocatalysts for CO2 Reduction in Water and Organic Solvents

ConspectusThe electrochemical reduction of CO2 provides a way to sustainably generate carbon-based fuels and feedstocks. Molecular CO2 reduction electrocatalysts provide tunable reaction centers offering an approach to control the selectivity of catalysis. Manganese carbonyl complexes, based on [Mn(bpy)(CO)3Br] and its derivatives (bpy = 2,2′-bipyridine), are particularly interesting due to their ease of synthesis and the use of a first-row earth-abundant transition metal. [Mn(bpy)(CO)3Br] was first shown to be an active and selective catalyst for reducing CO2 to CO in organic solvents in 2011. Since then, manganese carbonyl catalysts have been widely studied with numerous reports of their use as electrocatalysts and photocatalysts and studies of their mechanism.This class of Mn catalysts only shows CO2 reduction activity with the addition of weak Brønsted acids. Perhaps surprisingly, early reports showed increased turnover frequencies as the acid strength is increased without a loss in selectivity toward CO evolution. It may have been expected that the competing hydrogen evolution reaction could have led to lower selectivity. Inspired by these works we began to explore if the catalyst would work in protic solvents, namely, water, and to explore the pH range over which it can operate. Here we describe the early studies from our laboratory that first demonstrated the use of manganese carbonyl complexes in water and then go on to discuss wider developments on the use of these catalysts in water, highlighting their potential as catalysts for use in aqueous CO2 electrolyzers.Key to the excellent selectivity of these catalysts in the presence of Brønsted acids is a proton-assisted CO2 binding mechanism, where for the acids widely studied, lower pKa values actually favor CO2 binding over Mn–H formation, a precursor to H2 evolution. Here we discuss the wider literature before focusing on our own contributions in validating this previously proposed mechanism through the use of vibrational sum frequency generation (VSFG) spectroelectrochemistry. This allowed us to study [Mn(bpy)(CO)3Br] while it is at, or near, the electrode surface, which provided a way to identify new catalytic intermediates and also confirm that proton-assisted CO2 binding operates in both the “dimer” and primary (via [Mn(bpy)(CO)3]−) pathways. Understanding the mechanism of how these highly selective catalysts operate is important as we propose that the Mn complexes will be valuable models to guide the development of new proton/acid tolerant CO2 reduction catalysts.

A New Class of Task-Specific Imidazolium Salts and Ionic Liquids and Their Corresponding Transition-Metal Complexes for Immobilization on Electrochemically Active Surfaces.

Adding to the versatile class of ionic liquids, we report the detailed structure and property analysis of a new class of asymmetrically substituted imidazolium salts, offering interesting thermal characteristics, such as liquid crystalline behavior, polymorphism or glass transitions. A scalable general synthetic procedure for N‐polyaryl‐N’‐alkyl‐functionalized imidazolium salts with para‐substituted linker (L) moieties at the aryl chain, namely [LPh m ImHR]+ (L=Br, CN, SMe, CO2Et, OH; m=2, 3; R=C12, PEG n ; n=2, 3, 4), was developed. These imidazolium salts were studied by single‐crystal X‐ray diffraction (SC‐XRD), NMR spectroscopy and thermochemical methods (DSC, TGA). Furthermore, these imidazolium salts were used as N‐heterocyclic carbene (NHC) ligand precursors for mononuclear, first‐row transition metal complexes (MnII, FeII, CoII, NiII, ZnII, CuI, AgI, AuI) and for the dinuclear Ti‐supported Fe‐NHC complex [(OPy)2Ti(OPh2ImC12)2(FeI2)] (OPy=pyridin‐2‐ylmethanolate). The complexes were studied concerning their structural and magnetic behavior via multi‐nuclear NMR spectroscopy, SC‐XRD analyses, variable temperature and field‐dependent (VT‐VF) SQUID magnetization methods, X‐band EPR spectroscopy and, where appropriate, zero‐field 57Fe Mössbauer spectroscopy.

Porous aromatic frameworks with metallized catecholate ligands for CO2 capture from gas mixtures: A molecular simulation study

Carbon dioxide (CO2) capture from industrial gas mixtures, including flue gas, natural gas, and syngas is very important. Physical adsorption based on porous framework materials is quite promising for CO2 capture. In this work, we systematically investigated the separation performance of CO2 from CO2/N2, CO2/CH4, and CO2/H2 gas mixtures in porous framework materials with metallized catecholate ligands. The results indicated that the metallized catecholate ligands, including alkaline earth metals (Be, Mg, and Ca) and first-row transition metals (Sc to Zn), exhibit significantly effect on CO2 capture in porous framework materials. Specially, the selectivity of CO2 over N2, CH4, and H2 in the PAF-303 containing metallized catecholate ligands at initial pressure can reach up to 939.02 (PAF-303-Zn), 1775.5 (PAF-303-Cr), and 36555.24 (PAF-303-Cr), respectively. Furthermore, the incorporation of several transition metals can result in the revised N2 adsorption over CO2 owing to the strong selective back bonding with the N2 but not the CO2. The above results indicated that the materials containing metallized catecholate ligands are promising candidates for CO2 capture form flue gas, natural gas, and syngas.

NSAID-Based Coordination Compounds for Biomedical Applications: Recent Advances and Developments.

After the serendipitous discovery of cisplatin, a platinum-based drug with chemotherapeutic effects, an incredible amount of research in the area of coordination chemistry has been produced. Other transition metal compounds were studied, and several new relevant metallodrugs have been synthetized in the past few years. This review is focused on coordination compounds with first-row transition metals, namely, copper, cobalt, nickel or manganese, or with zinc, which have potential or effective pharmacological properties. It is known that metal complexes, once bound to organic drugs, can enhance the drugs’ biological activities, such as anticancer, antimicrobial or anti-inflammatory ones. NSAIDs are a class of compounds with anti-inflammatory properties used to treat pain or fever. NSAIDs’ properties can be strongly improved when included in complexes using their compositional N and O donor atoms, which facilitate their coordination to metal ions. This review focuses on the research on this topic and on the promising or effective results that complexes of first-row transition metals and NSAIDs can exhibit.

Synthesis of hierarchical transition metal oxyhydroxides in aqueous solution at ambient temperature and their application as OER electrocatalysts

First-row (3d) transition metal oxyhydroxides have attracted increasing attention due to their various advantages. Although investigating the oxidation mechanism and processing such materials into hierarchical architectures are greatly desired for their further development, it remains unclear how the oxidation state change occurs, and efforts to produce hierarchical oxyhydroxides in compliance with high ecological and economic standards have progressed slowly. Here, we describe a facile one-step coprecipitation route for the preparation of hierarchical CoOOH, NiOOH and MnOOH, which involves the diffusion of NH3 originating from ammonium hydroxide solution into an aqueous solution containing metal ion salts and K2S2O8. Comprehensive characterizations by scanning electron microscope, transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy and in situ pH measurement demonstrated that K2S2O8 induces the oxidation state change of metal ion species after the start of hydrolysis. Meanwhile, it was found that, benefiting from the OH– concentration gradient created by the NH3 diffusion method and the suitable growth environment provided by the presence of K2S2O8 (high nucleation rate and secondary nucleation), the formation of hierarchical oxyhydroxide structures can be realized in aqueous solution at ambient temperature without the use of heat energy and additional structure-directing agents. The hierarchical CoOOH structures are performed as the electrocatalysts for the oxygen evolution reaction in alkaline media, which exhibit good activity with an overpotential of 320 mV at 10 mA cm−2 and a low Tafel slope of 59.6 mV dec–1, outperforming many congeneric electrocatalysts. Overall, our study not only provides important insights to understand the formation mechanism of hierarchical oxyhydroxides, but also opens up new opportunities for the preparation of hierarchical oxyhydroxides via a facile, green and low-cost method.

Amorphous NiSb2O6–x nanofiber: A d-/p-block Janus electrocatalyst toward efficient NH3 synthesis through boosted N2 adsorption and activation

The electrochemical N2 reduction reaction (NRR) is greatly challenged by relatively low faradaic efficiency (FE) owing to fierce competition from the H2 evolution reaction (HER) suffered by the current transition-metal electrocatalysts (d-block elements). Considering the unique electronic structure of group-VA pnictogens (p-block elements) that is complementary to d-block elements in HER suppression, we report a conceptually new Janus electrocatalyst to tackle the selectivity challenge. Specifically, an amorphous NiSb2O6–x nanofiber is synthesized, in which Ni and Sb contribute to a synergistic catalysis pathway for inhibiting the two-electron transfer process of HER as well as activating the adsorbed N2 molecules. Moreover, amorphization is able to produce more oxygen vacancies, thus mimicking the “π back-donation’’ process to promote the NRR performance. Benefiting from this coupled element design and amorphization strategy, the amorphous NiSb2O6–x nanofiber significantly outperforms either component (NiO or Sb2O4) as well as its crystalline counterparts in terms of NH3 yield and FE.

Finding the True Catalyst for Water Oxidation at Low Overpotential in the Presence of a Metal Complex.

The design of molecular-based catalysts for oxygen-evolution reaction (OER) requires more investigations for the true catalyst to be found. First-row transition metal complexes are extensively investigated for OER, but the role of these metal complexes as a true catalyst is doubtful. Some doubts have been expressed about the role of first-row transition metal complexes for OER at high overpotentials (η > 450). Generally, the detection of the true catalyst has so far been focused on high overpotentials (η > 450) because at low overpotentials (η < 450), many methods are not sensitive enough to detect small amounts of heterogeneous catalysts on the electrode surface during the first seconds of the reaction. Ni(II) phthalocyanine-tetra sulfonate tetrasodium (1) is in moderate conditions (at 20-50 °C and pH 5-13) in the absence of electrochemical driving forces, which could make it noteworthy for OER. Herein, the results of OER in the presence of 1 at low overpotentials under alkaline conditions are presented. In addition, in the presence of Ni complexes, using an Fe ion is introduced as a new method for detecting Ni (hydr)oxide under OER. Our experiments indicate that in the presence of a homogeneous OER (pre)catalyst, a deep investigation is necessary to rule out the heterogeneous catalysts formed. Our approach is a roadmap in the field of catalysis to understand the OER mechanism in the presence of a molecular Ni-based catalyst design. Our results shown in this study are likely to open up new perspectives and discussion on many molecular catalysts in a considerable part of the chemistry community.

Delicate Tuning of the Ni/Co Ratio in Bimetal Layered Double Hydroxides for Efficient N2 Electroreduction.

Electroreduction of N2 to NH3 at ambient conditions using renewable electricity is promising, but developing efficient electrocatalysts is still challenging due to the inertness of N≡N bonds. Layer double hydroxides (LDHs) composed of first-row transition metals with empty d-orbitals are theoretically promising for N2 electroreduction (NRR) but rarely reported. Herein, hollow NiCo-LDH nanocages with different Ni/Co ratios were prepared, and their electronic structures and atomic arrangements were critical. The synergetic mechanisms of Ni and Co ions were revealed, and the optimized catalytic sites were proposed. Besides, in-situ Raman spectroscopy and 15 N2 isotopic labeling studies were applied to detect reaction intermediates and confirm the origin of NH3 . As a result, high NH3 yield of 52.8 μg h-1 mgcat -1 and faradaic efficiency of 11.5 % were obtained at -0.7 V, which are top-ranking among Co/Ni-based NRR electrocatalysts. This work elucidates the structure-activity relationship between LDHs and NRR and is instructive for rational design of LDH-based electrocatalysts.

Revisiting Reduction of CO2 to Oxalate with First-Row Transition Metals: Irreproducibility, Ambiguous Analysis, and Conflicting Reactivity.

Construction of higher C≥2 compounds from CO2 constitutes an attractive transformation inspired by nature’s strategy to build carbohydrates. However, controlled C–C bond formation from carbon dioxide using environmentally benign reductants remains a major challenge. In this respect, reductive dimerization of CO2 to oxalate represents an important model reaction enabling investigations on the mechanism of this simplest CO2 coupling reaction. Herein, we present common pitfalls encountered in CO2 reduction, especially its reductive coupling, based on established protocols for the conversion of CO2 into oxalate. Moreover, we provide an example to systematically assess these reactions. Based on our work, we highlight the importance of utilizing suitable orthogonal analytical methods and raise awareness of oxidative reactions that can likewise result in the formation of oxalate without incorporation of CO2. These results allow for the determination of key parameters, which can be used for tailoring of prospective catalytic systems and will promote the advancement of the entire field.

Molecular water oxidation catalysts based on first-row transition metal complexes

Molecular water oxidation catalysts based on first-row transition metal complexes

Enantioselective Radical Reactions Using Chiral Catalysts.

Benefiting from the impressive increase in fundamental knowledge, the last 20 years have shown a continuous burst of new ideas and consequently a plethora of new catalytic methods for enantioselective radical reactions. This review aims to provide a complete survey of progress achieved over this latter period. The first part of this review focuses on the use of chiral organocatalysts, and these include catalysts covalently linked to the substrate and those that interact with the substrate by weaker interactions like hydrogen bonds. The second part of the review is devoted to transition-metal redox catalysis which is organized according to increasing atomic number for the first-row transition metals (Ti, Cr, Fe, Mn, Co, Ni, Cu). Bioinspired manganese- and iron-mediated hydroxylations and oxidations are also discussed. A specific section is dedicated to the reactivity of Ru, Rh, and Ir complexes as Lewis acids with a special focus on complexes chiral at metal. Absorption of photons result in different events such as energy transfer, single-electron transfer, and hydrogen-atom transfer facilitating the formation of radicals. Organocatalysis has been successfully combined with photocatalysts, a reactivity which has opened new pathways enlarging the number of radical precursors available. The merger of photocatalysis with organo- or metalla-photocatalysis has brought novelty and allowed for the discovery of a large number of original transformations. The use of enzyme-catalyzed reactions involving radical intermediates which also largely benefit from visible-light irradiation are included in the review. This review provides a comprehensive inventory of progress in enantioselective radical reactions with a goal of detailing the reaction mechanisms involved in these transformations such that any nonspecialist could find their own creativity to invent yet unknown applications.