Dimeric Copper Research Articles

Simulation of the Interaction of Graphene with a Copper Surface Using a Modified Morse Potential

A new carbon–copper interaction potential is proposed to simulate the moire structure of graphene on the copper surface. It is shown that the resulting moire structure is in qualitative agreement with scanning tunneling microscopy images. The thickness of the moire structure and the binding energy of graphene with the surface agree within the error with the existing experimental data. The proposed potential can also be used to simulate the diffusion of copper atoms over the graphene surface. The diffusion of an atom and a copper dimer in a wide temperature range is studied. It is found that the contribution of the vibrational free energy of copper atoms should be taken into account when simulating diffusion.

Synthesis, X-Ray Characterization, Spectroscopic (Ft-Ir, Uv-Vis, EPR ) and Hirshfeld Surface Analysis of Dimer Copper(Ii)-Benzoate Complex

The copper(II) complex with benzoic acid, [Cu2 (BA) 4 (BAH) 2]) (BAH: Benzoic acid) was synthesized and the original dimer complex formed by complexing copper ions with benzoic acid was investigated. The dimer complex has been characterized by spectroscopic (FT-IR, EPR, UV-Vis), structural (XRD), thermogravimetric analysis and have displayed satisfactory elemental analysis. The copper(II) compound crystallizes in the monoclinic space group P21/c, Z=4, with the unit-cell dimensions: a=10.775(5) A, b=11.730 (5) A, c=15.271 (4) A, β=91.393 (4)˚. The coordination polyhedron around each copper central is described as an elongated (4+1) square pyramidal sphere. The trigonality factor (τ=(β-α)/60) value of the copper complex is 0.01 and this value expresses having slightly distorted square pyramidal environment of the Cu(II) ions coordination. Hydrogen bonds and π⋯π weak interactions form a three-dimensional supramolecular structure. The FT-IR studies of the complex were commented, focusing on the shifts in the vibrational peaks between the complex form and free benzoic acid. The powder EPR spectra of complex was investigated at liquid nitrogen temperature. As a result of EPR analysis, spin Hamiltonian parameters were obtained. In addition, zero field splitting parameters of the dimer-complex was obtained as Dobs= 0.60 cm-1 and E≈0. Thermal properties were carried out by thermogravimetric Analysis (TGA). Moreover, the intermolecular interactions have been also analyzed using Hirshfeld surface analysis.

Vibrational autodetachment from hot copper dimer anions: breakdown of the Born-Oppenheimer approximation

SynopsisThe decay of hot copper dimer anions is studied in a cryogenic storage ring. We detect atomic anion and neutral products and determine the fragmentation and vibrational autodetachment (VAD) rates separately. For short storage times the dimer anions predominantly decay by fragmentation of highly rotationally excited ions by tunneling through the rotational barrier. For storage times exceeding 100 ms, however, VAD is dominating. This process is driven by the very weak direct coupling between nuclear and electronic degrees of freedom.

Insight into the influence of terminal ligands on magnetic exchange coupling in a series of dimeric copper(II) acetate adducts

AbstractA combination of experimental (SQUID magnetometry) and quantum‐chemical (BS‐DFT, CASSCF(n,m)/NEVPT2, DDCI3) methods is used to probe the influence of terminal ligands on magnetic exchange coupling in the series of [Cu2(μ2‐OAc)4L2] complexes with O‐donor terminal ligands extended by two novel complexes containing phosphine oxide ligands. The possibilities and limitations of these approaches are discussed. The influence of terminal ligands on magnetic superexchange interaction was quantified by two contributions—the first contribution is associated with structural changes within the {Cu(μ2‐OAc)4Cu} core, while the second contribution is due to the difference in the electronic influence of different terminal ligands at a given core geometry. Both contributions were found to be approximately of the same order of magnitude. These results indicate that magnetic exchange coupling, known to be highly sensitive to the distortions in core geometry, is not solely determined by the core structure. Our findings are consistent with the fact that various one‐ and multiparameter magnetostructural correlations reported in the literature have only a qualitative predictive capability.

DNA and RNA binding studies on a novel bromo-bridged dimeric copper(II) complex stabilized from a Schiff base ligand

A novel red copper(II) compound, bis(μ-bromo)bis(2-(benzothiazol-2-yl-hydrazono)-1,2-diphenyl-ethanone)-dicopper(II) (1), has been fostered by equimolar reaction of a Schiff-base ligand, 2-(benzothiazol-2-yl-hydrazono)-1,2-diphenyl-ethanone (LH), with copper(II) bromide in satisfactory yield. 1 has thoroughly been characterized by C, H and N elemental analyses, FT-IR and UV-vis (both in solid state and in solution) spectroscopies, and room-temperature magnetic susceptibility and conductivity measurements. Dimeric 1 bears symmetric rare bromo-bridges in its crystal structure. 1 retains its solid-state identity even in a protic solvent like methanol. 1 in methanol displays two-step one-electron redox response. Theoretical calculations based on DFT were executed to probe the electronic structure of 1 and to augment its color. DNA- and RNA-binding aspects of both LH and 1 have been explored. Thermodynamic binding parameters have been determined. LH is a major-groove binder to DNA, while 1 manifests itself as a minor-groove binder. This binding has been corroborated through molecular docking. Nucleic acid binding aspect of such type of rare bromo-bridged red copper(II) dimer is unprecedented.

Syntheses, spectral aspects and biological studies of bromide and azide bridged box dimer copper(II) complexes of an NNO donor aroylhydrazone

A new NNO donor aroylhydrazone, di-2-pyridyl ketone-3-methoxybenzhydrazone (Hdkm) and three copper(II) complexes of Hdkm have been synthesized and characterized by different physicochemical techniques including single crystal X-ray diffraction technique. The structural analysis of copper(II) complexes revealed that a mononuclear bis coordinated complex [Cu(dkm)2] (1) and two monocoordinated Hdkm with dinuclear metal center [Cu(dkm)Br]2(2) and [Cu(dkm)N3]2(3) are formed. The coordination geometry of complex 1 is distorted octahedral with an N4O2 chromophore while complexes 2 and 3 are bromide and azide bridged box dimers respectively with distorted square pyramidal geometry. These complexes showed a axial spectra with g|| > g⊥ ≥ 2.0023. The antibacterial activity and cytotoxicity studies performed showed that these complexes display good activity.

Synthesis and characterization of a double oximato bridged dimeric copper(II) complex and its use in oxidative dimerisation of o-aminophenol

A dinuclear copper(II) complex, [(CH3CN)Cu(L)2Cu](ClO4)2, has been synthesized by reacting an oxime-based tridentate Schiff base ligand, 3-[2-(dimethylamino)-ethylimino] butan-2-one oxime (HL), with copper(II) perchlorate hexahydrate. The complex has been characterized by elemental and spectral analyses. Structure of the complex has been confirmed by single crystal X-ray diffraction technique. The complex may be used as moderate catalyst for the oxidation of o-aminophenol to 2-aminophenoxazine-3-one.

Hydrogen Bond-Enabled Heterolytic and Homolytic Peroxide Activation within Nonheme Copper(II)-Alkylperoxo Complexes.

To explore the reactivity of copper-alkylperoxo species enabled by the heterolytic peroxide activation, room-temperature stable mononuclear nonheme copper(II)-alkylperoxo complexes bearing a N-(2-ethoxyethanol)-bis(2-picolyl)amine ligand (HN3O2), [CuII(OOR)(HN3O2)]+ (R = cumyl or tBu), were synthesized and spectroscopically characterized. A combined experimental and computational investigation on the reactivity and reaction mechanisms in the phosphorus oxidation, C-H bond activation, and aldehyde deformylation reactions by the copper(II)-alkylperoxo complexes has been conducted. DFT-optimized structures suggested that a hydrogen bonding interaction exists between the ethoxyethanol backbone of the HN3O2 ligand and either the proximal or distal oxygen atom of the alkylperoxide moiety, and this interaction consequently results in the enhanced stability of the copper(II)-alkylperoxo species. In the phosphorus oxidation reaction, both experimental and computational results indicated that a phosphine-triggered heterolytic O-O bond cleavage occurred to yield phosphine oxide and alcohol products. DFT calculations suggested that (i) the H-bonding between the ethoxyethanol backbone and distal oxygen of the alkylperoxide moiety and (ii) the phosphine binding to the proximal oxygen of the alkylperoxide moiety engendered the heterolytic peroxide activation. In the C-H bond activation reactions, temperature-dependent reactivity of the copper(II)-alkylperoxo complexes was observed, and a relatively strong activation energy of 95 kcal mol-1 was required to promote the homolytic peroxide activation. A rate-limiting hydrogen atom abstraction reaction of xanthene by the putative copper(II)-oxyl radical resulted in the formation of the dimeric copper product and the substrate radical that further underwent autocatalytic oxidation reactions to form an oxygen incorporated product. Finally, amphoteric reactivity of copper(II)-alkylperoxo complexes has been assessed by conducting kinetic studies and product analysis of the aldehyde deformylation reaction.

A linear chain of carbazolyl-bis(tetrazole) supported copper(II) dimers held together by bridging tribromide anions

Reaction of NaCzTiPr with CuBr, followed by exposure to air, results in formation of {[Cu(κ3-N3-μ-N’-CzTiPr)(μ-OH)]2[μ-Br3]}x, 2. The structure of 2 in the solid state consists of hydroxo-bridged Cu(II) dimers connected into a linear chain polymer by bridging Br3– units. The Cu(II) centers have axially elongated coordination with a Br3– terminus and a bridging N from a tetrazole on the adjacent Cu forming the ligands on the long axis. The Br3– unit is linear with short Br–Br distances while the Cu–Br–Br angle is close to 90°. The reaction involves oxidation of both the Cu(I) and Br– of CuBr in air.

Spectroscopic disentanglement of the quantum states of highly excited Cu2

Transition metals, characterised by their partially filled d orbitals, provide the basis for many of the most relevant processes in chemistry, biology, and physics. Embedded as single atoms or in small clusters, they give rise to exceptional optical, chemical, and magnetic properties. So far, it has proven impossible to disentangle the complex network of excited quantum states, which greatly hinders prediction and control of material properties. Here, we apply two-colour resonant four-wave mixing to quantitatively resolve the quantum states of the neutral copper dimer. This allows us to unwind the individual spectral lines by isotopic composition and rotational quantum number and reveals a rich network of bright and perturbing dark states. While this work presents a road map for the experimental study of the bonding between and with transition metal atoms, it also provides experimental reference data for prospective quantum chemical approaches on handling systems with a high density of states.

Activation of the Cyano Group at Imidazole via Copper Stimulated Alcoholysis

Reactions of 4,5-dicyano-1-methylimidazole with CuX2 (X = Cl, Br) in alcohol solvents (ethanol and methanol) resulted in the formation of Cu(II) carboximidate complexes [CuCl2(5- cyano-4-C(OEt)N-1-methylimidazole)(EtOH)] (1), [Cu2(µ-Cl)2Cl2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (2), [Cu2(µ-Br)2Br2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (3), and [Cu2(µ-Br)2Br2(5-cyano-4-C(OEt)N-1-methylimidazole)2] (4). The structures were determined by the X-ray crystallographic method, and further spectroscopic and computational methods were employed to explain the structural features. The solvent contributed to the alcoholysis reaction of the cyano group, as the result of which the ligand coordinated to the metal center in bidentate mode forming a five-membered chelating ring. In 1, the solvent also acts as an additional ligand, which coordinates to the metal center of a monomeric complex. In compounds 2–4, two halogen ligands link the metal atoms forming dihalo-bridged copper dimers. The infrared absorption characteristics were verified by simulation of the infrared spectra at the density functional theory level. In addition, the electronic absorption characteristics were explained by simulation of the UV–Vis spectra using the TD-DFT method. Molecular modelling at the DFT level was performed to study the effects of halogen type and steric hindrance of the alkoxy groups in forming the copper(II) complexes.

Continuous Partial Oxidation of Methane to Methanol Catalyzed by Diffusion-Paired Copper Dimers in Copper-Exchanged Zeolites.

Copper-exchanged zeolites can continuously and selectively catalyze the partial oxidation of methane to methanol using only oxygen and water at low temperatures, but the genesis and nature of the active sites are currently unknown. Herein, we demonstrate that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites. While various Cu configurations may be present and active for methane oxidation, a dimeric Cu motif is the primary active site for selective partial methane oxidation. Mechanistically, CH4 activation proceeds via rate-determining C-H scission to form a surface-bound C1 intermediate that can either be desorbed as methanol in the presence of H2O/H+ or completely oxidized to CO2 by gas-phase O2. High partial oxidation selectivity can be obtained with (i) high methane and water partial pressures and (ii) maximizing Cu dimer formation by using zeolites with high Al content and low Cu loadings.

Development of novel Cu(I) compounds with vitamin B1 derivative and their potential application as anticancer drugs

The synthesis and crystal structure of two new copper(I) compounds with molecular formula of {Cu4[(µ3-thiocrome)2Cl4]∙2(H2O)}n1, and Cu2[(µ2-thiocrome)2Cl2] 2 are reported. The crystal structure of compounds 1 and 2 are solved by single crystal X-ray diffraction. The reaction of Cu(II) with thiamine chloride in water at room temperature produces Cu(I) thiochrome compounds 1 and 2. Compound 1 shows a 1D chain structure based on the linkage of two crystallographic different copper centers and thiochrome ligand through the N(1), N(2) and N(3) nitrogen atoms. Compound 2 is a 0D dimeric copper structure assembled by two thiochrome ligands. For both compounds, the copper(I) centers exhibits a distorted trigonal pyramidal geometry. The antitumor capacity of both compounds was tested in vitro against a human cancer cell line, the colorectal adenocarcinoma (Caco-2) cell line, by determining their effect on cell viability. The two compounds showed similar IC50 values, and were slightly more potent than cisplatin, against the same cell line.

Dimeric copper(II) tetracarboxylates as catalysts in the selective epoxidation of styrene

Dicopper(II) tetracarboxylate complexes of the type [Cu2(µ-O2CR)4L2] have received a great deal of attention from inorganic chemists in the past. However, these well-known species have been rarely studied as catalysts. Herein we describe the synthesis, UV–Vis spectral behavior and catalytic properties of six species of this type, viz. [Cu2(µ-O2CC6H5)4(py)2] (I), [Cu2(µ-O2CC6H5)4(4-CNpy)2] (II), [Cu2(µ-O2CC6H5)4(3-CNpy)2] (III), [Cu2(µ-O2CCH3)4(py)2] (IV), [Cu2(µ-O2CC7H15)4(4-CNpy)2] (V) and [Cu2(µ-O2CC7H15)4(3-CNpy)2] (VI). As evidenced by their solid state and solution UV–Vis spectra, these complexes retain their dinuclear integrity in solution and therefore they have been investigated as homogenous catalysts for styrene epoxidation. They exhibit very good to excellent catalytic activities towards the oxidation of styrene with aqueous tert-butylhydroperoxide (TBHP) as the terminal oxidant. The reactions give styrene oxide (SO) and benzaldehyde (Bzal) as products in varying proportions, but with good selectivity for SO. Under optimized conditions, a maximum of 82% selectivity towards SO is obtained at 78% styrene conversion catalyzed by I at room temperature.

Synthesis, crystal structures and antimicrobial activity of dimeric copper(II) complexes with 2-hydroxyphenyl-ethylidene-dithiocarbazates

The current work reports the synthesis and crystals structure of two copper(II) complexes [(CuL1)2] (1) and [(CuL2)2] (2), with S-allyl-2-(2-hydroxyphenyl-ethylidene)dithiocarbazato and S-benzyl-2-(2-hydroxyphenyl-ethylidene) dithiocarbazato (H2L1 and H2L2, respectively). The single-crystal X-ray analyses reveal dimeric structures of the complexes with a distorted square planar coordination geometry. The phenoxo bridging mode observed in these complexes is located between the two copper atoms with ONS-donor ligands. The crystal packings are stabilized by hydrogen bonds involving the adjacent molecules. The compounds were also characterized by physicochemical and spectroscopic methods. The antibacterial and antifungal properties of the free dithiocarbazates and its Cu(II) complexes have been evaluated against several multiresistant bacteria and fungi. In all experiments, a superior antimicrobial activity of the complexes was observed compared to the free ligands.

Selective Synthesis of Tetrasubstituted Olefins by Copper-Mediated Acetoxythiolation of Internal Alkynes: Scope and Mechanistic Studies.

The Cu-mediated synthesis of tetrasubstituted olefins by the addition of an acetate group and a thiolate to an unactivated internal alkyne is described. The reaction is fully stereoselective, because only the E alkene is obtained. If the alkyne is asymmetric, the reaction also shows a very high degree of regioselectivity. The mechanism of the reaction is elucidated by DFT methods, which show that it takes place through Cu-stabilized radical species. Calculations highlight the crucial role of the dimeric copper(II) diacetate in the process, as it generates the active species in which the sulfur center has an incipient thiyl radical character and accepting, through a series of changes in the oxidation states of the two copper centers, the two electrons released in the addition of two nucleophiles to the alkyne.

Copper Dimer Supported on a C2N Layer as an Efficient Electrocatalyst for CO2 Reduction Reaction: A Computational Study

The carbon dioxide electrochemical reduction (CO2RR) to useful fuels and chemicals with renewable electricity offers a promising strategy for resolving energy security and environmental issues. Sea...

Development and Validation of a Two-Site Kinetic Model for NH3-SCR over Cu-SSZ-13. Part 1. Detailed Global Kinetics Development Based on Mechanistic Considerations

In this study, we present the first of two parts in the development and validation of a two-site detailed global kinetic model for NH3 Selective Catalytic Reduction (SCR) over a well-characterized Cu-SSZ-13 catalyst. Based on fundamental literature studies and experimental data for two distinct hydrothermal aging conditions, it was observed that at least two distinct sites were necessary to describe the storage, oxidation, and SCR behavior for this catalyst. The site definitions were allocated based on analysis of simulated net desorption rates during the NH3-TPD experiment. The S1 sites were associated with extra framework copper ions stabilized by -OH ligands (ZCuOH), likely located near the eight-membered ring CHA cages, along with Bronsted acid sites, while S2 sites were associated with copper ions attached directly to the repeating units (Z2Cu) near the six-membered rings, along with physisorbed NH3 sites and low temperature transient copper dimers. The selective NH3 oxidation and NO oxidation reactions were only modeled over S1, in line with the expected catalytic sites for these reactions. Standard, fast, and NO2 SCR reactions were modeled on both sites, with different activation energies. Finally, noticeable nitrate-based hysteresis effects were observed, in both N2O concentrations and fast SCR NO conversions. These were accounted for by explicitly modeling nitrate formation, titration by NO, and thermal decomposition to N2O. The developed SCR model was validated with additional reactor data at nominal inlet NH3-to-NOx ratios (ANRs) of 0.8 and 1.2. In general, the model showed good predictability in the temperature range of 150–550 °C for both hydrothermal ageing conditions and space velocities. Further full-scale engine dynamometer validation and development of a downstream NH3 slip catalyst (ASC) reaction-diffusion model will be reported in the second part of the paper.

ONIOM studies on thermally activated delayed fluorescence of copper(I) dimers in crystal

Herein we have employed M06 and TD-M06 methods with the ONIOM approach to study the thermally activated delayed fluorescence (TADF) phenomenon of three halide-bridged Cu(I) dimers bearing amino-phosphane ligands in crystal (Cl-, Br-, and I-coordinated ones). On the basis of spectroscopic properties, ground- and excited-state geometric and electronic structures, and photophysical properties, we have found that the S1 and T1 states have a very small energy gap ▵ES1-T1, less than 4.0 kcal/mol, which makes the forward and reverse intersystem crossing ISC and rISC processes between S1 to T1 very efficient and a population equilibrium can be established. The rISC rates are visibly sensitive to temperature and increasing temperature clearly enhances the rISC rates thus rationalizing experimentally observed TADF phenomenon. Moreover, we have also found that the low-frequency vibrational modes related to the torsional motion of the coordinated ligands have large Huang-Rhys factors, which increase from Cl via Br to I-coordinated Cu(I) dimers. In this varying process, the ISC rates increase visibly whereas the rISC rates change slightly. Our work provides useful microscopic knowledge to understand the TADF emission of the Cu(I) dimers, which could be helpful for the rational design of TADF materials with excellent performance.

Photoswitching of Copper(I) Chromophores with Dithienylethene-Based Ligands.

Metal-containing dithienylethenes offer new opportunities for variations in photochromic behavior. This work reports a series of copper(I) complexes containing dithienylethene-based bidentate phosphine ligands displaying varying photochromic properties. A copper dimer is used as a common precursor, allowing diverse photochromic functionality to be achieved. Calculations show that ring closing of the peripheral dithienyl moiety leads to a slight expansion of the five-membered metallacycle. The photochromic properties and photoreaction quantum yields of these complexes are tunable by variation of the ancillary ligands. Photoswitchable catalysis of a hydroboration reaction with one of the copper complexes is demonstrated.