Transition Metal Coordination Research Articles

Enhanced Bactericidal Effect of Chitosan Using Coordinated Transition Metal Ions

Enhanced Bactericidal Effect of Chitosan Using Coordinated Transition Metal Ions

A Voltammetric Investigation of the Electrocatalytic Cycle Mechanism of Fe(I) and Mn(I) Complexes

Earth-abundant, first row, low coordinate transition metal complexes are promising candidates for the electrocatalysis of a variety of organic synthesis reactions. However, transition metal complexes in the M(I) state have the propensity to undergo disproportionation, hindering their ability to carry out the electrocatalytic cycle. In this study, we seek to identify and understand the mechanism by which the M(I) complexes may act as an electrocatalyst for a simple organic coupling reaction, beginning with the radicalization of benzyl bromide as a representative starting material. Initial characterization of the complex and its components by cyclic voltammetry demonstrate general stability of the catalyst, while equivalent additions of benzyl bromide exhibit the execution of the electron transfer and radical generation. Cyclic voltammetry simulations provide supplementary guidance into the relationship between benzyl bromide and the catalyst. Additional experiments conducted using analytical techniques such as mass spectrometry, x-ray spectroscopy, and nuclear magnetic resonance help to further characterize portions of the proposed mechanism and supporting details. Analysis to date suggests that the model electrocatalytic cycle is interrupted to an extent, with contributions from both disproportionation and substituted coordination at the transition metal center. Experimental and simulated voltammograms are qualitatively consistent with this proposed catalytic cycle interruption.

Changing Directions: Influence of Ligand Electronics on the Directionality and Kinetics of Photoinduced Charge Transfer in Cu(I)Diimine Complexes.

A key challenge to the effective utilization of solar energy is to promote efficient photoinduced charge transfer, specifically avoiding unproductive, circuitous electron-transfer pathways and optimizing the kinetics of charge separation and recombination. We hypothesize that one way to address this challenge is to develop a fundamental understanding of how to initiate and control directional photoinduced charge transfer, particularly for earth-abundant first-row transition-metal coordination complexes, which typically suffer from relatively short excited-state lifetimes. Here, we report a series of functionalized heteroleptic copper(I)bis(phenanthroline) complexes, which have allowed us to investigate the directionality of intramolecular photoinduced metal-to-ligand charge transfer (MLCT) as a function of the substituent Hammett parameter. Ultrafast transient absorption suggests a complicated interplay of MLCT localization and solvent interaction with the Cu(II) center of the MLCT state. This work provides a set of design principles for directional charge transfer in earth-abundant complexes and can be used to efficiently design pathways for connecting the molecular modules to catalysts or electrodes and integration into systems for light-driven catalysis.

Characterization of the Ligand Field in Pseudo‐Octahedral Ni(II) Complexes of Pincer‐Type Amido Ligands: Magnetism, Redox Behavior, Electronic Absorption and High‐Frequency and ‐Field EPR Spectroscopy

AbstractThe description of π‐donor amido moieties as ‘weak‐field’ ligands can belie the influence of metal‐ligand covalency on the overall ligand field of coordination complexes, which can in turn influence properties including the magnetic ground state and those of their excited states. In this contribution, the ligand fields of pseudo‐octahedral Ni(II) complexes supported by diarylamido pincer‐type amido ligands – three previously reported examples supported by asymmetric (2‐R‐phenanthridin‐4‐yl)(8‐quinolinyl)amido ligands (R = Cl, CF3,tBu;RL1) along with a new congener bearing a symmetricbis(8‐quinolinyl)amido ligand (BQA;L2) – were investigated in two ways. First, high‐frequency and ‐field electron paramagnetic resonance spectroscopy (HFEPR), SQUID magnetometry, and electronic absorption spectroscopy were used to determine the ligand field parameters. Second, the ability to electrochemically address ligand‐based oxidations despite metal‐centered SOMOs in the parentS=1 paramagnets was investigated, supported by time‐dependent density functional theory (TDDFT) identification of strong intervalence charge‐transfer (IVCT) transitions attributed to electronic communication between two Namidomoieties mediated by a Ni(II) bridge. These findings are discussed in the broader context of 3d transition metal coordination complexes of weak‐field π‐donor ligands.

Statement of Retraction: Two transition metal coordination polymers: inhibitory effect on Staphylococcus aureus biofilms formation and prevention against spine surgery incision infection

Statement of Retraction: Two transition metal coordination polymers: inhibitory effect on Staphylococcus aureus biofilms formation and prevention against spine surgery incision infection

Synthesis route and structural, magnetic, optical, and non-linear optical properties of triboluminescent [Cu(NCS)(py)2(PPh3)] complex

Transition-metal coordination compounds exhibit many unique properties, which can be used in a broad range of state-of-the-art technologies. One of these interesting complexes is copper(I) thiocyanate bipyridine triphenylphosphine [Cu(NCS)(py)2(PPh3)]. Herein, we report detailed structural, magnetic, spectroscopic, and nonlinear optical properties, as well as the optimized synthesis route of the [Cu(NCS)(py)2(PPh3)] complex. Performed Raman, infrared (IR), X-ray photoelectron (XPS), and X-ray diffraction (XRD) spectroscopy provide valuable data about the synthesis time dependence and general structural characteristics. Optical studies describe in detail the photoluminescence properties and emission temperature dependence behavior. For the first time, the magnetic and third-order nonlinear optical measurements of the [Cu(NCS)(py)2(PPh3)] complex were performed. Additionally, thermogravimetric analysis was conducted to detail the thermal stability of the complex. The results constitute a detailed description of the physical properties of the [Cu(NCS)(py)2(PPh3)] complex, which is an essential tool for designing sensing solutions based on the triboluminescent properties of the investigated compound.

Isobutene isomerization via metal-organic coordination polymer catalyst

One-dimensional, two-dimensional and three-dimensional Ni-containing metal-organic coordination polymer (1D-Ni, 2D-Ni and 3D-Ni MOCP) catalysts were solvothermally synthesized and used for isomerization of isobutene. These catalysts showed the same conversion of isobutene and selectivity for 2-butene as homogeneous catalysts. At the same time, 1D-Ni catalyst evacuated at 100 °C revealed the conversion of isobutene and selectivity to 2-butene were up to 89.2% and 100.0%, respectively. Moreover, the results demonstrated that the conversion of isobutene was different depending on metal coordination mode, dimension of coordination polymer, and the reaction pressure. In addition, The MOCP catalysts were relatively environmentally friendly, and easily recovered and recycled. Finally, the mechanism of metal hydride addition elimination was proposed.

Design, DFT and molecular doping studies of metal complexes as a neurotransmitter modulator of autism spectrum disease in preschool children

Coordination of transition metals with pyrazolines has formed complexes of cobalt(II), nickel(II), copper(II) and zinc(II) utilizing new pyrazoline ligand 3-(2-pyrollyl)-5-(4-bromophenyl)-1-carbomathyl-2-pyrazoline (L). The ligand was synthesized by Micheal addition of chalcone (E)-3-(4-bromophenyl)-1-(1H-pyrrol-2-yl)prop-2-en-1-one with excess 4-methylthio-semicarbazide. The metal complexes were isolated using the thin layer chromatography technique and synthesized and characterized based on elemental analyses (C, H, N, and S), IR, UV–visible spectra, thermal analyses,1H-and13C-NMRspectra, molar conductivity and magnetic susceptibility measurements. The results indicated a tetrahedral geometry around the zinc(II) complex and octahedral environments around the copper(II), nickel(II) and cobalt(II) complexes. The density function theory of 2-pyrazoline, L, and its metal complexes showed agreement in the gap energies between HOMO–LUMO levels. The bond lengths (Zn–S) and (Zn–Cl) were less than ones of Ni–S, Co–S and Cu–S. The density functional theory calculations were used to investigate geometry optimization, natural bond orbital analysis, and molecular electrostatic potential maps of the synthesized ligand and its complexes. Additionally, time-dependent density function theory calculations were performed to study their electronic structures. The effect of those complexes on the neurotransmitter GABA offers potential insights into new therapeutic mechanisms. This method relies on coordination to a heterocyclic molecule like pyrazoline to release the excess metal ions.

Synthesis, Characterization, Antimicrobial Properties, and Antioxidant Activities of Silver-N-Heterocyclic Carbene Complexes.

The emergence of antimicrobial resistance has become a major handicap in the fight against bacterial infections, prompting researchers to develop new, more effective, and multimodal alternatives. Silver and its complexes have long been used as antimicrobial agents in medicine because of their lack of resistance to silver, their low potency at low concentrations, and their low toxicity compared to most commonly used antibiotics. N-Heterocyclic carbenes (NHCs) are widely used for coordination of transition metals, mainly in catalytic chemistry. In this study, several N-alkylated benzimidazolium salts 2a-j were synthesized. Then, the N-heterocyclic carbene (NHC) precursor was treated with Ag2O to give silver (I) NHC complexes (3a-j) at room temperature in dichloromethane for 48 h. Ten new silver-NHC complexes were fully characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and LC-MSMS (for complexes) techniques. The antibacterial and antioxidant activities of salt 2 and its silver complex 3 were evaluated. All of these complexes were more effective against bacterial strains than comparable ligands. With MIC values ranging from 6.25 to 100 g/ml, the Ag-NHC complex effectively showed strong antibacterial activity. Antioxidant activity was also tested using conventional techniques, such as 2, 2-diphenyl-1-picrylhydrazine (DPPH) and hydrogen peroxide scavenging assays. In DPPH and ABTS experiments, compounds 3a, 3b, 3c, 3e, 3g, and 3i showed significant clearance.

Two 2D transition metal coordination polymers based on 5-(1H-1,2,4-triazol-1-yl) isophthalic acid: synthesis, structure and magnetic properties

Two coordination polymers {[Co(TIA)(H2O)2]·0.25H2O}n (Co-1), and {[Mn(TIA)(H2O)2]·0.5H2O}n (Mn-2) were obtained solvothermally based on the exquisite combination of multidentate rigid linker 5-(1H-1,2,4-triazol-1-yl) isophthalic acid (H2TIA) and M(NO3)2·6H2O (M = Co(II), Mn(II)). The structures of 1-2 are both as 3,3-linked two-dimensional layers, which assemble into three dimensional supramolecular microporous structures by O−H⋅⋅⋅O hydrogen bonds. In addition, the static and/or dynamic magnetic characteristics of the two polymers were investigated.

Modelling the structural disorder in trigonal-prismatic coordinated transition metal dichalcogenides.

Trigonal-prismatic coordinated transition metal dichalcogenides (TMDCs) are formed from stacked (chalcogen)-(transition metal)-(chalcogen) triple layers, where the chemical bond is covalent within the triple layers and van der Waals (vdW) forces are effective between the layers. Bonding is at the origin of the great interest in these compounds, which are used as 2D materials in applications such as catalysis, electronics, photoelectronics, sensors, batteries and thermoelectricity. This paper addresses the issue of modelling the structural disorder in multilayer TMDCs. The structural model takes into account stacking faults, correlated displacement of atoms and average crystallite size/shape, and is assessed by simulation of the X-ray diffraction pattern and fitting to the experimental data relative to a powdered sample of MoS2 exfoliated and restacked via lithiation. From fitting, an average crystallite size of about 50 Å, nearly spherical crystallites and a definite probability of deviation from the fully eclipsed atomic arrangement present in the ordered structure are determined. The increased interlayer distance and correlated intralayer and interlayer atomic displacement are attributed to the presence of lithium intercalated in the vdW gap between triple layers (Li/Mo molar ratio of about 0.06). The model holds for the whole class of trigonal-prismatic coordinated TMDCs, and is suitably flexible to take into account different preparation routes.

Crystal structure of trimeth-yl({tris-[(phenyl-sulfan-yl)meth-yl]sil-yl}meth-oxy)silane and Hirshfeld surface analysis of 3-bromo-2,2-bis-(bromo-meth-yl)propan-1-ol.

Trimeth-yl({tris-[(phenyl-sulfan-yl)meth-yl]sil-yl}meth-oxy)silane (3), C26H32OS3Si, is a new ligand for transition-metal coordination chemistry derived from 3-bromo-2,2-bis-(bromo-meth-yl)propan-1-ol (1), C5H9Br3O, through silylation and following exchange of bromine groups with NaSPh. Silylated thio-ether ligand 3 crystallizes in the centrosymmetric space group C2/c. Bromo-methyl-alcohol 1 crystallizes in the space group P in the triclinic crystal system with four mol-ecules in the asymmetric unit. Analysis of the Hirshfeld surface shows structure-defining inter-actions for bromo-methyl-alcohol 1, resulting in inter-molecular hydrogen bonds between the hydroxyl groups along the a-axis direction.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

Carbenes have evolved from transient laboratory curiosities to a robust, diverse, and surprisingly impactful ligand class. A variety of different carbenes have significantly contributed to the development of low-oxidation state main group chemistry. This Perspective focuses upon advances in the chemistry of carbene complexes containing main group element cores in the formal oxidation state of zero, including their diverse synthetic strategies, unusual bonding and structural motifs, and utility in transition metal coordination chemistry and activation of small molecules.

Metal Complexes with Naphthalene-Based Acetic Acids as Ligands: Structure and Biological Activity.

Naproxen (6-methoxy-α-methyl-2-naphthaleneacetic acid), 1-naphthylacetic acid, 2-naphthylacetic acid and 1-pyreneacetic acid are derivatives of acetic acid bearing a naphthalene-based ring. In the present review, the coordination compounds of naproxen, 1- or 2-naphthylacetato and 1-pyreneacetato ligands are discussed in regard to their structural features (nature and nuclearity of metal ions and coordination mode of ligands), their spectroscopic and physicochemical properties and their biological activities.

Geometric frustration of Jahn-Teller order in the infinite-layer lattice.

The Jahn-Teller effect, in which electronic configurations with energetically degenerate orbitals induce lattice distortions to lift this degeneracy, has a key role in many symmetry-lowering crystal deformations1. Lattices of Jahn-Teller ions can induce a cooperative distortion, as exemplified by LaMnO3 (refs. 2,3). Although many examples occur in octahedrally4 or tetrahedrally5 coordinated transition metal oxides due to their high orbital degeneracy, this effect has yet to be manifested for square-planar anion coordination, as found in infinite-layer copper6,7, nickel8,9, iron10,11 and manganese oxides12. Here we synthesize single-crystal CaCoO2 thin films by topotactic reduction of the brownmillerite CaCoO2.5 phase. We observe a markedly distorted infinite-layer structure, with ångström-scale displacements of the cations from their high-symmetry positions. This can be understood to originate from the Jahn-Teller degeneracy of the dxz and dyz orbitals in the d7 electronic configuration along with substantial ligand-transition metal mixing. A complex pattern of distortions arises in a [Formula: see text] tetragonal supercell, reflecting the competition between an ordered Jahn-Teller effect on the CoO2 sublattice and the geometric frustration of the associated displacements of the Ca sublattice, which are strongly coupled in the absence of apical oxygen. As a result of this competition, the CaCoO2 structure forms an extended two-in-two-out type of Co distortion following 'ice rules'13.

Nature of NMR Shifts in Paramagnetic Octahedral Ru(III) Complexes with Axial Pyridine-Based Ligands.

In recent decades, transition-metal coordination compounds have been extensively studied for their antitumor and antimetastatic activities. In this work, we synthesized a set of symmetric and asymmetric Ru(III) and Rh(III) coordination compounds of the general structure (Na+/K+/PPh4+/LH+) [trans-MIIIL(eq)nL(ax)2]- (M = RuIII or RhIII; L(eq) = Cl, n = 4; L(eq) = ox, n = 2; L(ax) = 4-R-pyridine, R = CH3, H, C6H5, COOH, CF3, CN; L(ax) = DMSO-S) and systematically investigated their structure, stability, and NMR properties. 1H and 13C NMR spectra measured at various temperatures were used to break down the total NMR shifts into the orbital (temperature-independent) and hyperfine (temperature-dependent) contributions. The hyperfine NMR shifts for paramagnetic Ru(III) compounds were analyzed in detail using relativistic density functional theory (DFT). The effects of (i) the 4-R substituent of pyridine, (ii) the axial trans ligand L(ax), and (iii) the equatorial ligands L(eq) on the distribution of spin density reflected in the "through-bond" (contact) and the "through-space" (pseudocontact) contributions to the hyperfine NMR shifts of the individual atoms of the pyridine ligands are rationalized. Further, we demonstrate the large effects of the solvent on the hyperfine NMR shifts and discuss our observations in the general context of the paramagnetic NMR spectroscopy of transition-metal complexes.

Competition between Li2Se2Sx conversion and Li Ion transport on graphene surface coordination doped with transition metal and N

The shuttling of polyselenide (Li2Se2Sx) was prevented effectively by building a separator in Li-SexSy batteries. Nitrogen atoms are used to coordinate transition metal (TM=Ti, Zr, V) co-doped graphene to restrict the free shuttling of polylithium selenide (Li2Se2Sx, x = 1–6) through physical confinement and chemical adsorption. The nitrogen (N) atom assisted transition metal co-doped graphene surface to build a model of strong adsorption of cations and anions on lithium-sulfur-selenium compounds to inhibit the shuttle phenomenon. Nitrogen atoms are not only coordinately doped with transition metals, but also lithium atoms can easily form bonds to improve the adsorption strength of Li2Se2Sx on the graphene surface. The evolution of the N-type to P-type adsorption model of Li2Se2Sx on the graphene co-doped Ti-N-G surface to the Zr-N-G surface was constructed based on the phenomenon of Fermi level changes strong adsorption capacity and immobilization. The Fermi energy level of the V-N-G weak adsorption catalytic model was located between the valence and conduction bands. The doping of N and TM improves the ionic conductivity of graphene, which adsorbs Li2Se2Sx and causes a high Li diffusion barrier. A coupled physical model of ion transport and polyselenide conversion was built by adjusting the Fermi level of separator.

Pseudomonas aeruginosa and Staphylococcus aureus Display Differential Proteomic Responses to the Silver(I) Compound, SBC3.

The urgent need to combat antibiotic resistance and develop novel antimicrobial therapies has triggered studies on novel metal-based formulations. N-heterocyclic carbene (NHC) complexes coordinate transition metals to generate a broad range of anticancer and/or antimicrobial agents, with ongoing efforts being made to enhance the lipophilicity and drug stability. The lead silver(I) acetate complex, 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*) (SBC3), has previously demonstrated promising growth and biofilm-inhibiting properties. In this work, the responses of two structurally different bacteria to SBC3 using label-free quantitative proteomics were characterised. Multidrug-resistant Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) are associated with cystic fibrosis lung colonisation and chronic wound infections, respectively. SBC3 increased the abundance of alginate biosynthesis, the secretion system and drug detoxification proteins in P. aeruginosa, whilst a variety of pathways, including anaerobic respiration, twitching motility and ABC transport, were decreased in abundance. This contrasted the affected pathways in S. aureus, where increased DNA replication/repair and cell redox homeostasis and decreased protein synthesis, lipoylation and glucose metabolism were observed. Increased abundance of cell wall/membrane proteins was indicative of the structural damage induced by SBC3 in both bacteria. These findings show the potential broad applications of SBC3 in treating Gram-positive and Gram-negative bacteria.

Conductivity in Thin Films of Transition Metal Coordination Complexes.

Two coordination complexes have been made by combining the dithiolene complexes [M(mnt)2]2- (mnt = maleonitriledithiolate; M = Ni2+ or Cu2+) as anion, with the copper(II) coordination complex [Cu(Stetra)] (Stetra = 6,6'-bis(4,5-dihydrothiazol-2-yl)-2,2'-bipyri-dine) as cation. The variation of the metal centers leads to a dramatic change in the conductivity of the materials, with the M = Cu2+ variant (Cu-Cu) displaying semiconductor behavior with a conductivity of approximately 2.5 × 10-8 S cm-1, while the M = Ni2+ variant (Ni-Cu) displayed no observable conductivity. Computational studies found Cu-Cu enables a minimization of reorganization energy losses and, as a result, a lower barrier to the charge transfer process, resulting in the reported higher conductivity.

Cu(II)-Triggered Ion Channel Properties of a 2,2'-Bipyridine-Modified Amphotericin B.

The development of stimuli-responsive synthetic channels that open and close in response to physical and chemical changes in the surrounding environment has attracted attention because of their potential bioapplications such as sensing, drug release, antibiotics, and molecular manipulation tools to control membrane transport in cells. Metal coordination is ideal as a stimulus for stimuli-responsive channels because it allows for reversible gating behavior through the addition and removal of metal ions and fine-tuning of channel structure through coordination geometry defined by the type of the metal ion and ligand. We have previously reported on transition metal-ion dependent ion permeability control of Amphotericin B (AmB) modified with a metal coordination site, 2,2'-bipyridine ligand (bpy-AmB). AmB is one of the polyene macrolide antibiotics, and it is known that the interaction between AmB and ergosterol molecules is required for AmB channel formation. In contrast, the Cu2+ coordination to the bpy moiety of bpy-AmB induces formation of Ca2+ ion-permeable channels in the ergosterol-free POPC membrane. However, the details of bpy-AmB properties such as channel stability, ion selectivity, pore size, and the effect of ergosterol on channel formation remain unclear. Here, we investigate bpy-AmB channels triggered by transition metal coordination in POPC or ergosterol-containing POPC liposomes using an HPTS assay, electrophysiological measurements, and time-resolved UV-vis spectral measurements. These analyses reveal that bpy-AmB channels triggered by Cu2+ ions are more stable and have larger pore sizes than the original AmB channels and enable efficient permeation of various cations. We believe that our channel design will lead to the construction of metal coordination-triggered synthetic ion channels.