Row Transition Metal Research Articles

Recent Advancements in the Anticancer Potentials of First Row Transition Metal Complexes

Recent Advancements in the Anticancer Potentials of First Row Transition Metal Complexes

MII (M = Mn, Fe, Co, Ni and Cu) complexes with a chromone-derived neutral ligand: synthesis, structural characterization, photocatalytic and mycobacterial activity studies

This work provides the coordination chemistry of the resulting compound of 2-(2-furyl)-3-hydroxychromone and nicotinoyl chloride with first row transition metal ions. Good performance in H2 evolution was shown by the copper-containing photocatalyst.

The importance of the bite angle of metal(III) salen catalysts in the sequestration of CO2 with epoxides in mild conditions

Located in the middle of the fever to solve the problem of CO2 emissions in the environment, CO2 sequestration by reaction with epoxides is one of the key tools, as it not only fixes CO2, but also makes it functional by leading to cyclic carbonates. Herein, the results are focused specifically on the formation of cyclic organic carbonates catalyzed by metal-salen complexes, previously achieved with yttrium and scandium, that are compared with those of analogous complexes containing metals from the first transition series, such as cobalt or chromium. Density functional theory (DFT) calculations allow to determine whether this switch of metals will be feasible and provide the basis for instigating future experimental efforts in this regard. The calculations analyzing the structure and electronics of the catalysts allow us to give not only a clear picture of whether these catalysts will be efficient, but also allow us to assess which metal center is the most convenient and/or whether the catalytic reaction will occur under mild conditions. Advanced buried volume calculations with the SambVca packages shed light on the different catalytic pockets of monometallic first row transition metals vs. group III salen complexes. Our predictive catalysis results show that the bite O-M-O angle plays an essential role in the catalysis.

First row transition metal complexes of bis(3,5-dimethyl pyrazolyl)methane: Synthesis, molecular structure and antibacterial properties

A series of nine transition metal complexes was synthesized by reacting bis(3,5-dimethylpyrazolyl)methane (BP) with the respective metal chlorides in 1:1 and 2:1 stochiometric proportions. The complexes were duly characterized by molar conductivity measurement, IR, UV, NMR spectroscopy and elemental analysis. Using X-ray analysis, solid state molecular structures of the complexes C3 and C8 were determined. The molecular structures and the stoichiometry of the obtained complexes were found to be governed by the steric factors of the ligand substituents. The prepared compounds were found to be bactericidal against the four bacterial stains tested, however with high MIC/MBC values.

First row transition metals Fe, Co, Ni, Cu, and Zn analyzed by XPS using monochromatic Ag Lα x rays

XPS spectra of five first row transition metals (Fe, Co, Ni, Cu, and Zn) were obtained using monochromatic Ag Lα radiation. Survey and high resolution photoelectron region (2p, 2s, 3p, and 3s) and x-ray induced Auger spectra were recorded from Ar+ ion cleaned metal foils.

Effects of organic matter complexation on partitioning of transition metals into calcite: Cave-analogue crystal growth experiments

We highlight the potential for first row transition metals to carry paleohydrological signals in speleothems, and argue that these metals constitute valuable proxies for climate reconstructions. Metal availability to speleothems is hypothesised to be restricted by organic complexation, which strongly limits the free ion activity of transition metals (Co2+, Ni2+ and Cu2+) in dripwater, thereby creating a kinetic overprint on metal concentrations and isotope ratios in speleothem calcite.This study presents the results of the first cave-analogue experiments of transition metal partitioning into calcite in the absence and presence of organic ligands. The Geological Microclimate (GeoMic) system establishes homeostatic control of air temperature and atmospheric pCO2 (set to 20 ± 0.1 °C and 1000 ± 10 ppm, respectively), and regulates relative humidity to cave-analogue levels (>90%). Calcite was precipitated from flowing aqueous films on inclined glass plates to assess the effect of prior calcite precipitation (PCP) on metal partitioning. We report speleothem-specific inorganic Kd values for Co, Ni and Cu of ∼4, 1, and 44, respectively. Pronounced PCP effects were observed in Co and Cu in the inorganic experiments, leading to strong reduction in Cu/Ca and Co/Ca, whereas Ni/Ca molar ratios remained constant.Introduction of the organic chelating ligand nitrilotriacetic acid (NTA) overturned the behaviour of all three metals, leading to stable solution Cu/Ca ratios and progressive enrichment of Co/Ca and Ni/Ca ratios as PCP progressed and apparent Kd values <1 for all three metals. This result is confirmed in a Cu-fulvic acid experiment. We show that in the presence of organic ligands with stability constants close to those observed in natural systems, the partitioning of transition metals into calcite is dependent on the fluid residence time and the stability of the metal–ligand complexes. Therefore, drip rate should be the first-order control on transition metal concentrations in stalagmites: opening the way to a novel and potentially quantitative paleohydrological proxy.

Theoretical comparative survey on the structure and electronic properties of first row transition metal substituted Keggin type polyoxometalates

In the present study, molecular geometry, electronic structure, first row transition metal-polyoxometalate interactions, transition metal-H2O bonding, and simulated infrared (IR) spectrum of H2O ligated/unligated transition metal substituted Keggin type polyoxometalates ([PW11O39(MII/MIIOH2)]5-, MII ​= ​Cr, Mn, Fe, Co, Ni, Cu and Zn) have been studied through Density Functional Theory (DFT) calculations. From the results, it has been predicted that the interaction of H2O ligand with MII leads to a stable [PW11O39(MII-H2O)]5- complex, without spin crossing during water attachment. The calculations have also revealed that interaction of H2O ligand with [PW11O39(MII)]5- could be discussed in two different classes: when MII is Cr, Mn and Fe, the H2O molecule interacts directly to MII from O side, while for MII ​= ​Co, Ni, Cu and Zn, the H-bond interaction between H2O and O atoms around the M, leads to the stabilization of POM-H2O system. Moreover, it has been predicted that the binding properties of H2O strikingly depends on axial 3dz2 orbital of MII. In this regard, it has been exhibited that the affinity of H2O for MII in [PW11O39(MII)]5- with a filled 3dz2 orbital, is strongly reduced as measured by increasing in calculated MII-ligand distance. Also, strong contributions of MII 3d as well as the 2p orbitals of five oxygen donor atoms in polyoxometalate cluster results in the bonding interaction between MII and lacunary Keggin polyoxometalate. The DFT-derived IR spectra showed displacement and splitting in four previously known vibrational bands of Keggin-type polyoxometalate, α-[PW12O40]3-, owing to transition metal substitution and H2O ligation.

Recent advances in homogeneous base-metal-catalyzed transfer hydrogenation reactions

Owing to availability of various hydrogen sources, operational simplicity, and mild reaction conditions, catalytic transfer hydrogenation (TH) has emerged as an appealing alternative for the direct hydrogenation reactions with H2 gas. Conventional TH catalysts are based on noble metals, such as Ru, Rh, and Ir, which are toxic and expensive due to their limited availability. Current research in this area is oriented towards the development of more sustainable catalysts utilizing abundant 1st row transition metals with readily accessible ligand platforms. During the past few decades, many novel examples of such systems appeared in the literature, expanding not only the number of catalyst surrogates but also the scope of unsaturated substrates, opening new venues for TH in organic synthesis. This review aims to provide an update on recent advances in homogeneous TH reactions catalyzed by base-metal (Mn, Fe, Co and Ni) complexes. Special attention is paid to selectivity and the mechanisms of such transformations.

Potentiometric determination of stability constants of ternary complexes of first row transition metal ions with ditopic azelaic acid dihydrazide and aspartic acid in aqueous medium

A Chemical speciation study of ternary complexes containing transition metal ions (Mn2+,Co2+,Ni2+, Cu2+ and Zn2+) with a ditopic novel ligand L ​= ​Azelaic acid dihydrazide (AZDH) and X ​= ​l-Aspartic acid of type [MmLlX xHh], (where m ​= ​1, 2; l ​= ​1; x ​= ​1, 2 and h ​= ​−2 to 5) in different ratios of M:L:X ​= ​1:1:1, 1:2:1, 2:1:1and 2:1:2 was carried out using pH -potentiometric method of data acquisition and applied to chemometric modelling methods of analysis. MINIQUAD-75 program was used for the resolution of the plausible species and their corresponding formation constants at 303 ​± ​0.1 ​K, and 0.01 ​M ionic strength. Species concentration distribution diagrams were generated using HySS program. Best-fit chemical models were selected on the basis of statistical parameters like Standard deviation (SD), U (sum of the squares of the residuals in mass balance equations), and chi-square test etc. Relatively stable ternary complexes were evaluated quantitatively using Δlog K formulation. All the formation constants for the species were compared for Irving-Williams order of stability.

First principles investigation on cobalt–tetracyanoquinodimethane monolayer for efficient Bi-functional single atom electrocatalyst

A bi-functional electrocatalyst is a stable and catalytically active material for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the development of which is highly challenging, although essential for application in fuel cells. Herein, the first principle based density functional theory (DFT) computations have been carried out to investigate a series of transition metal-tetracyanoquinodimethane (TM-TCNQ: TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd) monolayer for bi-functional single atom electrocatalyst towards ORR and OER. Amongst various first transition metal row based TCNQ substrates, Cobalt-TCNQ (Co-TCNQ) monolayer was predicted to exhibit best bi-functional catalytic activity. At equilibrium potential (1.23 V, vs RHE), the free energy portraits of Co-TCNQ monolayer for OER in acidic or alkaline media are not completely downhill, measuring an excess potential of 0.6 V, equal to the overpotential, which is needed to be supplied externally to promote the OER activity. On the other hand, an onset potentials of 0.34 V (vs RHE) in acidic media are measured for ORR to proceed. The promising catalytic activity of two dimensional Co-TCNQ monolayer towards ORR and OER as revealed by DFT investigations has been explained in terms of density of states and Bader charge analysis.

Synthesis, Characterization, Antimicrobial and Antioxidant Studies of Co(II), Ni(II), Cu(II) and Zn(II) Metal Complexes with the Ligands 2-{[4-(5-bromo thiophen-2- yl)-6- phenylpyrimidin-2 yl]carbonoimidoyl}phenol Derivatives

A few complexes 2-{[4-(5-bromo thiophen-2-yl)-6-phenyl pyrimidin-2-yl] carbonoimidoyl} phenol [HL5] and 2-{[4-(5-bromo thiophen-2-yl) -6- phenyl pyrimidin-2-yl]carbon imidoyl}-5-methoxyphenol [HL6] with first row transition metal ions have been reported in this paper. The stichiometry of type (1:1) [M(L)]2H2O is analysed by these complexes. Complexes with ligands (HL5 and HL6) of metal ions Co(II), Ni(II), Cu(II) and Zn(II) reveal co- ordination number six, by means of magnetic susceptibility, electronic, IR, 1H NMR, X-ray diffraction and ESR spectrum data. Copper(II) complexes with (HL5) and (HL6) were studied spectrophotometrically at different temperatures having an absorption maxima of 535 nm. The findings demonstrate that copper(II) and (HL5) and (HL6) are combined at pH 5.0 at a molar ratio of 1:1. The stability constants of the complexes were calculated to be 13.06×104, 14.51×104 and 10.40×104 and 13.18x104, 15.06x104, 11.23x104 for (HL5) and (HL6) respectively by Jobs continuous variation method and 0.24×104, 0.57×104, and 0.77×104 and 0.28×104, 0.55×104, 0.79×104 for (HL5) and (HL6) respectively by mole ratio method at 30, 35 and 40°C, respectively. Both ligands and their metal complexes were screened for their antibacterial and antifungal activity by cup plate method and antioxidant activity by using standard DPPH radical scavenging ability method.

High Spin Cobalt Complexes Supported by a Trigonal Tris(Phosphinimide) Ligand.

Terminal, π-basic moieties occupy a prominent position in the stabilization of unusual or reactive inorganic species. The electron-releasing, π-basic properties of phosphinimides (PN) have been employed to stabilize electron-deficient early transition metals and lanthanides. In principle, a ligand field comprised of terminal PN groups should enable access to high-valent states of late first row transition metals. Herein, we report a new class of multidentate phosphinimide ligands to logically explore this hypothesis. Access to such ligands is made possible by a new procedure for the electrophilic amination of rigid, sterically encumbering, multidentate phosphines. Such frameworks facilitate terminal PN coordination to cobalt as demonstrated by the synthesis of a trinuclear CoII3 complex and a homoleptic, three-coordinate CoIII complex. Interestingly, the CoIII complex exhibits an exceedingly rare S = 2 ground state. Combined XRD, magnetic susceptibility, and DFT studies highlight that terminally bound PNs engage in strong dπ-pπ interactions that present a weak ligand field appropriate to stabilize high-spin states of late transition metals.

Searching Ternary Oxides and Chalcogenides as Positive Electrodes for Calcium Batteries

The identification of alternatives to the Lithium-ion battery architecture remains a crucial priority in the diversification of energy storage technologies. Accompanied by the low reduction potential of $\mathrm{Ca^{2+}/Ca}$, -2.87 V vs. SHE, metal-anode-based rechargeable Calcium (Ca) batteries appear competitive in terms of energy densities. However, the development of Ca-batteries lacks high-energy density intercalation cathode materials. Using first-principles methodologies, we screen a large chemical space for potential Ca-based cathode chemistries, with composition of $\mathrm{Ca_iTM_jZ_k}$, where TM is a 1$^{st}$ or 2$^{nd}$ row transition metal and $\mathrm{Z}$ is oxygen, sulfur, selenium or tellurium. 10 materials are selected and their Ca intercalation properties are investigated. We identify two previously unreported promising electrode compositions: the post-spinel $\mathrm{CaV_2O_4}$ and the layered $\mathrm{CaNb_2O_4}$, with Ca migration barriers of $\sim$654 meV and $\sim$785 meV, respectively. Finally, we analyse the geometrical features of the Ca migration pathways across the 10 materials studied and provide an updated set of design rules for the identification of good ionic conductors, especially with large mobile cations.

Microwave assisted synthesis of core-shell Ni-Co/graphene nano sheets and their catalytic activity for methanol electro-oxidation

The improvement of nanostructured architectures the use of less expensive first–row transition metals with high electrocatalytic activity to substitute noble-metal-based electrocatalysts has currently received enormous interest in the discipline of easy and sustainable energy generation technology. Nickel-Cobalt core–shell nanostructures for supported over N-doped graphene nanosheets (Ni@Co/N-GNS) present higher catalytic activity due to presence of increased surface active centers, high surface area and extended reactive zones. Using microwave irradiation, bimetallic Ni@Co nanoparticles are deposited on N-Doped graphene nanosheets. Influence of reactive conditions and composition of metal precursors are studied systematically, these studies revealed that core–shell nanostructures synthesized using 1:1 metal precursors irradiated under microwave for 40 s displayed superior electro catalytic activity towards methanol. XPS, SEM, and EDAX studies are performed to understand physico-chemical properties of Ni@Co/GNS catalyst. It is deduced that thickness, surface characteristics and catalytic properties of Ni@Co deposits could be influenced pointedly by microwave conditions. Core-shell morphology is decidedly of assistance to offer readily accessible active Ni@Co active zones for methanol oxidation reaction, which is evidenced by cyclic voltammetry, Impedance analysis and chronoammperometric studies. The developed catalyst is a therefore a potential electrocatalyst for direct alcohol fuel cells.

Metal complex pigments

AbstractThere are several commercially significant metal complex organic pigments that are based on first row transition metals. The most important of these are the copper phthalocyanine blue and green pigments which find virtually universal use in paints, printing inks, and plastics. These pigments are of such prime importance that they are dealt with separately in three other chapters in this series. This paper describes a group of pigments that are complexes of iron, copper, nickel, and cobalt with polydentate colored ligands of azo, azomethine, oxime, and isoindoline chemical types. The oldest metal complex organic pigment that still finds some use is CI Pigment Green 8, an octahedral oxime iron complex. In the 1970s and 1980s, there was considerable industrial research effort aimed at developing metal complex pigments based on azomethine and isoindoline structures, many of which were found to offer excellent lightfastness, good solvent resistance and thermal stability, although they exhibited rather dull colors. However, several products provide brilliant effects when used in combination with metallic and pearlescent pigments in automotive paints. Many of the pigments introduced have since been withdrawn by the original manufacturers, but a few remain on the market. The synthesis of metal complex pigments generally involves the preparation of the colored ligand, which is then complexed with the transition metal ion

Iron(II) Complexes Featuring a Redox-Active Dihydrazonopyrrole Ligand.

Nature uses control of the secondary coordination sphere to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that more typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious when complexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox-chemistry in this set is still primarily ligand based. Finally, these complexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.

First row transition metals on the ethanol Guerbet reaction: Products distribution and structural behavior of mixed metal oxides as catalysts

Described is the transformation of ethanol into 1-butanol, acetaldehyde and other products by the Guerbet reaction (GR) over mixed metal oxides (MMOs) as catalysts. The MMOs, in which Mg2+ was partially (20 mol%) substituted by Fe2+, Co2+, Ni2+, Cu2+, and Zn2+, were obtained from hydrotalcite precursors and the reactions conducted in a fixed bed flow reactor. EPR was used to observe oxygen vacancies after the catalytic reactions, which may be related to the ethanol reactivity due to the basicity enhancement of the catalyst. Carbon deposition, mostly filamentous, was observed in all catalysts and a trend between the metal-carbon bond energy and the percentage of deposited carbon was established. This correlation and the catalyst product distribution can be useful to tailor new catalysts. Using four parameters, ethanol conversion, 1-butanol and side-product selectivities and percentage of carbon deposition, Zn20MMO proved to be the best choice for GR.

Structural, photophysical, electrochemical and spintronic study of first-row metal Tetrakis(meso-triphenylamine)-porphyrin complexes: A combined experimental and theoretical study

Different metal ions in the center of 3d-metalloporphyrins have subtle influences on their structural, photophysical, electrochemical, and spintronic properties. A new series of symmetrically meso-substituted porphyrins with six first row transition metals, namely TPA-MPs (M = 2H, Mn, Fe, Co, Ni, Cu, and Zn) have been synthesized and characterized by various spectroscopic techniques. The electrostatic potential energy surface (ESP) calculated by density functional theory (DFT) exhibits the concentrated positive electrostatic potential on the substituted triphenylamine group, while the negative electrostatic potential localized on the porphyrin ring varies depending on metal ions. All compounds were crystallographically characterized and showed a coplanar porphyrin macrocyclic ring except for TPA-MnP and TPA-ZnP, which are distorted due to their occupied axial sites by Cl− and H2O, respectively. Furthermore, the X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) confirmed the valence states of the metal ions in the TPA-MPs. Electronic spectra revealed a gradual bathochromic shift following the order of TPA-CoP < TPA-CuP < TPA-P = TPA-NiP < TPA-FeP < TPA-ZnP < TPA-MnP by appending different metal ions in the porphyrin skeleton. TPA-MnP exhibited the most significant bathochromic shift (Δλmax = 49 nm) in the Soret band compared to TPA-P. The electrochemical redox potentials of the TPA-MPs decrease with the stepwise filling of d orbitals of the central metal ions from 0.86 to 0.81 V and the completely filled 3d orbital of Zn endows TPA-ZnP with the lowest oxidation onset. Meanwhile, TPA-MnP and TPA-FeP exhibited dramatically reduced HOMO-LUMO gaps of 1.78 eV and 1.58 eV, respectively, compared to other TPA-MPs. The excellent thermal stability, panchromatic absorption in the whole visible range, and suitable energy levels of TPA-MPs indicate huge potential in the application as dyes.

Tandem photoelectrochemical and photoredox catalysis for efficient and selective aryl halides functionalization by solar energy

Tandem photoelectrochemical and photoredox catalysis for efficient and selective aryl halides functionalization by solar energy

The First Row Transition Metals on Stabilization of Biliverdin Complexes: Theoretical Study

Biliverdin is a product of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises. Biliverdin has been found in excess in the blood of humans suffering from hepatic diseases. Structure of biliverdin from catabolism process of heme is one of the cases that has been less discussed. In this research characterization of biliverdin analogues in the presence of hydroxide as a nucleophile and imidazole as axial ligands was investigated using the B3LYP method and the 6-31G basis set both in gas and solvent phases. By changing the central metal in the structure of billiverdin, some features such as gap energy, hardness and softness, electrophilicicity index and exact polarizability were studied and compared with iron.