Coordination Number Of Cu Research Articles

Selective Formation of Cu Active Sites with Different Coordination States on Pseudospinel CuAl2O4 and Their NO Reduction Catalysis.

In the spinel framework, copper (Cu) in two distinct coordination states exhibits catalytic activity for NO reduction through different mechanisms. However, detailed exploration of their respective catalytic properties, such as the redox behavior of Cu and substrate molecule adsorption, has been challenging due to difficulties in their separate formation. In this study, we present the controlled formation of pseudospinel CuAl2O4, containing exclusively tetrahedrally or octahedrally coordinated Cu, achieved by manipulating aging temperature and O2 concentration. Through these materials, we observed that in the CO-NO reaction, the step primarily determining the rate differs: NO reduction dominates with octahedrally coordinated Cu, whereas carbon monoxide (CO) oxidation is prominent with tetrahedrally coordinated Cu. The lower coordination number of Cu significantly benefits NO reduction but negatively impacts the CO-NO reaction, albeit positively influencing NO reduction in three-way catalytic reactions.

(Digital Presentation) Investigations on the Ethanol/Ethylene Bifurcation and Restructure of Cu/Ag Catalysts for Electrochemical CO2 Reduction

Electrochemical CO2 reduction (ECO2R) converts greenhouse gas CO2 into valuable fuels and chemicals, and thus helps with closing the anthropogenic carbon cycle. Currently, Cu is the only known material being capable of producing a variety of hydrocarbons and alcohols, while the poor selectivity limits its further use. Ethanol and ethylene have been proved to go through similar pathways but their bifurcation is yet to be fully understood.It has been found that introducing Ag atoms into Cu lattice could shift the product distribution toward ethanol compared to ethylene. However, previous studies have proposed contradictory speculations: DFT calculations predict the introduced Ag atoms prefer to dope on the undercoordinated sites on Cu surface [1], while experiments have proved that C-C coupling occurs at these sites and is promoted when they are occupied by Ag [1]–[3]. Literature also interpreted various mechanisms of the interaction between Cu and, such as the constrained effect [1], [4], “spillover” [5], and different C-C coupling pathways between *CO and *CHx (x=1,2) at the boundaries [6]. The oxidation state [7] and faceting [1] as well as the composition of CuAg catalysts over time have been observed during the reaction course, but explicitly real-time information remains scarce.To provide more mechanistic information on the above controversies, we prepared both bimetallic (with miscible Cu and Ag phases s) and surface alloy (with separated Cu and Ag phases) CuAg thin films by physical vapor deposition (PVD) and galvanic exchange, respectively. Ex situ X-ray Photoelectron Spectroscopy (XPS) and O perando X-ray Absorption Spectroscopy (XAS), including X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) on surface alloy CuAg are performed under ECOR/ECO2R conditions to investigate the oxidation state and coordination numbers of Cu and Ag. By this means, electron transfer and the interface miscibility between Cu and Ag are identified. Combined with DFT calculations, we speculated possible doping sites of Ag atoms in the Cu lattice and potential adsorption sites of the produced intermediates for ethanol/ethylene formation. Besides, variations of the oxidation state, electric and geometric local structure, as well as the transformation in crystallinity of the CuAg catalysts over time are monitored by correlating XAS with operando Grazing Incidence X-ray Diffraction (GIXRD). The produced CO intermediates are substantiated to be the reason for Cu-enrichment occurring on the CuAg electrodes as speculated.

Copper(II) complexes based on N-(bis(diethylamino)phosphoryl)-2,2,2-trichloroacetamide with pyridine and 4,4′-bipyridine

Two new Cu(II) complexes, {CuL2⋅(4,4′-bipy)}n (1) and CuL2(Py)2 (2), where bipy = bipyridine; HL = N-(bis(diethylamino)phosphoryl)-2,2,2-trichloroacetamide, representative of carbacylamidophosphate (CAPh) type ligands), have been synthesized and characterized by FTIR and single-crystal X-ray analysis. In both complexes CAPh ligands are coordinated to the copper ions in a bidentate chelate manner through oxygens of the carbonyl and phosphoryl groups. Nitrogen atoms of bipyridine, 1, or pyridine molecules, 2, complete the coordination number of Cu(II) to six. The Cu ions are located in special positions on inversion centers. In the structure of 1, the bipyridine molecules display a bridging function between adjacent copper complexes forming a polymer chain. Phosphoryl and 4,4′-bipy (Py) ligands in both structures are located in trans positions relative to each other.

Synthesis, crystal structure, DNA interaction, DFT analysis and molecular docking studies of copper(ii) complexes with 1-methyl-l-tryptophan and phenanthroline units

Three new mixed-ligand copper(II) complexes [CuL(neocup)H2O]NO3·2·5H2O (1), [CuL(bathoph)H2O]NO3·2·5H2O (2) and [CuL(bathocup)H2O]NO3·2·5H2O (3) (L = 1-methyl-l-tryptophan, neocup = Neocuproine, bathoph = bathophenanthroline and bathocup = bathocuproine) have been synthesized and structurally characterized by elemental analysis, IR, EPR, UV–Vis and single crystal XRD techniques. The XRD analysis shows the complex (2) crystallized in a Triclinic system with space group P1, a = 12.5630 (5) Å, b = 8.0433 (3) Å, c = 19.7816 (7) Å, α= 68.817 (2)°, β = 79.664 (2)°, and γ = 72.016 (2)°. Crystal structure study have revealed that the coordination number of Cu(II) is five with square pyramidal geometry in complex (2). The structure of the present complex (2) has been optimized using the DFT/UB3LYP/6–31G(d,p)/LANL2DZ level of theory. The interactions of the complex with calf thymus DNA (CT-DNA) have been investigated by UV–Vis absorption titration, ethidium bromide displacement assay, viscometric titration experiment and cyclic voltametric studies. Complex (2) was shown to bind DNA by intercalative mode and cleave pBR322 DNA. Molecular docking analysis was carried out.

Effect of the coordination environment of Cu in Cu2O on the electroreduction of CO2 to ethylene

The coordination number (CN) of Cu–Cu and Cu–O in Cu2O play crucial role on the catalytic performance of CO2 electrocatalytic reduction to C2H4. And the CN of Cu–Cu and Cu–O could be tuned by changing the crystal surface and size of Cu2O.

A Cuprous [4 × 4] Grid: Single-Crystal to Single-Crystal Transformation and Fading of Luminescence by Solvent Inclusion.

The subtle balance of the metrics of the highly supple 5,5'-pyridyl-3,3'-bis-1 H-pyrazolate and the variable coordination numbers of Cu(I) favor the stabilization of a [4 × 4] grid complex with all Cu(I). It has numerous cuprophilic bonds (Cu···Cu = 2.56-3.02 Å), and consequently, exhibits strong orange luminescence that fades upon insertion of solvents without loss of crystallinity.

MgCu metallic glass

We generate an amorphous MgCu model using the rapid solidification of the melt through a first-principles molecular dynamics approach within a generalised gradient approximation and reveal, for the first time, its structural features and mechanical properties in details. The liquid and glassy MgCu are found to acquire slightly distinct local structures. Yet in both forms of MgCu, most Cu atoms have a tendency to form the ideal and defective icosahedrons while Mg atoms are arranged in complex configurations. The mean coordination number of Cu and Mg at 300 K is 11.31 and 13.73, respectively. The short-range order of MgCu glass is projected to be different than the known crystalline MgCu and Mg2Cu phases. The mechanical properties of MgCu glass and the CsCl-type MgCu crystal are computed and compared. On the basis of the enthalpy analyses, a possible pressure-induced crystallisation of the MgCu glass into a CsCl-type structure is proposed to occur at around 11 GPa.

Short range order of As40-xCuxTe60 glasses

Short range order of As40-xCuxTe60 (x=0, 10, 20, 25, 30) glasses was studied by neutron- and X-ray diffraction, combined with extended X-ray absorption fine structure (EXAFS) measurements at the K-edges of all components. Large-scale structural models were generated by fitting the experimental datasets simultaneously in the framework of the reverse Monte Carlo simulation technique. These simulations revealed that As and Te atoms bind to about 3 and 2 As/Te neighbors, respectively, both of which possess Cu neighbors. The CuTe bond length is 2.57±0.02Å while the CuAs distance is as high as 2.86±0.04Å. The results further showed that besides As and Te, Cu atoms also bind to Cu. The total coordination number of Cu is significantly higher than 4 for the compositions x=25 and 30.

Evidence of Mixed Oxide Formation on the Cu/SiO2 Interface

The deposition of Cu onto SiO2 has been carried out by electron beam evaporation in order to study the interface formation by X-ray photoelectron spectroscopy and angle resolved X-ray photoelectron spectroscopy. Shifts in the binding energy of Cu 2p3/2 and Si 2p bands, as well as in the Cu LMM kinetic energy, have been observed during the growth. These changes are indicative of a modification in the coordination number of Cu or the formation of M–O–M′ cross-linking bonds at the interface. Moreover, different coordination states of Cu+ and Cu2+ (tetrahedral and octahedral) have been detected. Apart from different coordination numbers, a new chemical state appears during the Cu/SiO2 interface formation. This new contribution, Cux+, is attributed to the formation of a mixed oxide Cu-O-Si. Additionally, two different stages of growth of the Cu/SiO2 interface have been observed: The first one, where no metallic Cu is detected and a mixture of copper oxides is measured onto the SiO2 substrate, and the second on...

Preparation and characterization of CuO[sbnd]Al2O3 catalyst for dimethyl ether production via methanol dehydration

In the present study, a CuOAl2O3 catalyst with CuAl2O4 spinel structure was prepared by a co-precipitation method and used for dimethyl ether (DME) production via methanol dehydration at 50 bar and different reaction temperatures (150, 250, and 350 °C). Upon XPS analysis of the copper and aluminum species in the fresh and used CuOAl2O3 catalyst, CuAl2O4 was found to be the dominant species with more than 50% of total composition. Three reductive reactions and temperatures for the formation of CuH (102.3 °C), the interaction between Cu2+ and Al atoms (356.6 °C), and the reduction of CuO (520.1 °C) were analyzed by H2-TPR. Furthermore, the copper oxidation state in the fresh and used catalyst was Cu(II), as determined by the XANES spectra. The fine structural parameters revealed that the coordination number of Cu changed from 2.75 to 2.44 during the catalytic reaction, and that the CuO bond distance increased from 1.94 to 1.98 Å due to strengthened Cu2+Al interactions. On-line FTIR spectra revealed that the optimum temperature for the formations of HCOOH (by-product) and DME (product) were 150 and 250 °C, respectively. The catalytic reactions in the duration of DME synthesis were found that included methanol decomposition, methanol/formic acid formations, and methanol dehydration occurring at CuO, Cu, and Al2O3/CuAl2O4 active sites, respectively. The highest methanol conversion (67.3%) and DME yield (40.6%) were obtained at 250 °C and 50 bar, as demonstrated by the catalyst performance. In addition, optimum DME formation (equilibrium constant 1.76 × 10−2 L mol−1 h−1 and activation energy 5.14 kJ mol−1) occurred at 250 °C, as determined from the linear regression of the second order model with a high R2 value (0.98). The exothermal and non-spontaneous nature of DME formation at high temperature was evaluated through thermodynamic calculations of the reaction enthalpy, entropy, and Gibbs energy.

Electrochemical Synthesis of Cu (II) Coordination Polymer Coatings Based on 2,2′-Thiodiacetic Acid and 1,2,4,5-Benzenetetracarboxylate

Electrochemical synthesis of coordination polymers of Cu(II), [Cu(TDA)]n and [Cu2(BTC)(H2O)6‚6H2O]n in which H2TDA is 2,2′-thiodiacetic acid and BTC stands for 1,2,4,5-benzenetetracarboxylate was carried out by the electrochemical oxidation of Cu anode in the presence of H2TDA (a flexible ligand), and 1,2,4,5-benzentetracarboxylic acid (H4BTC) (a rigid ligand) in aqueous solutions. The structure of coordination polymers were characterized by scanning electron microscopy, X-ray powder diffraction, elemental analysis, thermal gravimetric and differential thermal analyses. The crystal structure of the compounds consists of one-dimensional cubical crystal polymeric units of [Cu(TDA)]n and [Cu2(BTC)(H2O)6‚6H2O]n. Furthermore, the coordination number of Cu (II) ions in synthesized coordination polymers to be found five. The main advantages of electrosynthesis are the minor synthesis time, the milder conditions and the facile synthesis of coordination polymer coatings.

Tautomerism of a compartmental Schiff base ligand and characterization of a new heterometallic CuII–DyIII complex — Synthesis, structure and magnetic properties

A crystal structure of a compartmental ligand N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane (H4L=C17H18N2O4) (1) containing N2O2-inner and O4-outer coordination sites and a characterization of its novel diphenoxo-bridged discrete dinuclear complex [CuDy(H2L)(MeOH)(NO3)3]·2MeOH (2) are reported. The Schiff base ligand 1 crystallizes in the orthorhombic P212121 space group with a molecule in a bent conformation. The compound at 100 and 293K displays the keto-enol tautomerism with the equilibrium in both temperatures shifted with a different degree towards the zwitterionic keto-amino form. The quantum chemical calculations showed preferences for enol-imino form in a gas phase and for keto-amine in solutions. The keto-amino tautomer is stabilized by intermolecular interactions. The complex 2 crystallizes in the triclinic P-1 space group as a dinuclear compound with CuIIDyIII core. The Dy(III) ion is nine-coordinated whereas the coordination number of Cu(II) is five. The temperature dependence of the magnetic susceptibility and the field-dependent magnetization indicated that the interaction between Cu(II) and Dy(III) metal centers in 2 is ferromagnetic.

Synthesis, crystal structure determination and antimicrobial studies of copper(II) picrate complexes with N,N,N′,N″-tetrakis(2-hydroxyethyl/propyl) ethylenediamine and tris(2-hydroxyethyl)amine

The present work consist of synthesis, spectroscopic and crystal structure investigations of complexes [Cu(THEEN) (H2O)] (PIC)2 (1), [Cu(THPEN)] (PIC)2·C3H8O (2) and [Cu(TEAH3)(PIC)] (PIC)·(H2O) (3) and their application in antimicrobial activities. In these complexes, THEEN is N,N,N′,N″-tetrakis(2-hydroxyethyl) ethylenediamine and THPEN is N,N,N′,N″-tetrakis(2-hydroxypropyl) ethylenediamine, are tetrapodal ligands and TEAH3 is tris(2-hydroxyethyl)amine, a tripodal ligand. Crystal structure investigations have revealed that the coordination number of Cu(II) is five with square pyramidal geometry in complex (1) and THEEN is interacting with metal ion through both of its amine nitrogens and two of the four hydroxyl oxygens in a tetradentate manner. The metal ion in complex (2) is having a distorted octahedral geometry with coordination number six and THPEN is interacting with it through all ligating sites in a hexadentate way. The picrate anions are present outside the coordination sphere in both of these complexes and are involved in hydrogen bonding interactions resulting in the formation of charge-separated complexes (1) and (2). The coordination number of Cu(II) is five with square pyramidal geometry in complex (3) where the ligand tris(2-hydroxyethyl)amine (TEAH3) is interacting through all of its donor atoms in a tetradentate way. One of the two picrate anions is in coordination with metal ion whereas other is present outside the coordination sphere and is involved in hydrogen bonding interactions resulting in formation of partially charge-separated complex.

Fourfold coordinated Te atoms in amorphous GeCu2Te3 phase change material

Amorphous GeCu2Te3 was investigated by X-ray diffraction and extended X-ray absorption fine structure measurements at the Ge, Cu and Te K-edges. Structural models were obtained by fitting the four experimental datasets simultaneously by reverse Monte Carlo simulation. It was found that Ge–Ge and Cu–Cu bonding are both significant. The average coordination numbers of Cu and Te, as well as Ge, are close to four. The high average coordination number of the network contributes to the enhanced thermal stability of amorphous GeCu2Te3.

Investigation of Carbon Tetrachloride Destruction by Copper Acetate

Halogenated synthetic organic compounds are used in a wide variety of pesticides, solvents, refrigerants, fire retardants, and paints that cause extensive pollution to the air, surface water, groundwater, and soils. Carbon tetrachloride (CCl) is a typical halogenated synthetic organic compound that has been suspected to be toxic and carcinogenic and to cause ozone depletion. In the present work, molecular-level destruction of CCl by copper acetate was investigated by extended X-ray absorption fine structural spectra, X-ray absorption near-edge spectra, X-ray photoelectron spectroscopy, and X-ray diffraction spectroscopy. Experimentally, the Cl species dissociated from CCl were abstracted by copper species and formed CuCl. At 473 to 533 K, reaction products (copper chloride) aggregated on the surfaces of CuO, which might cause the obstruction of further CCl destruction. Due to the insertion of Cl species into the matrix of CuO, the bond distances of Cu-O and Cu-(O)-Cu were increased by 0.3 to 0.4 Å and 0.3 to 0.6 Å, respectively. However, at 603 K, because 79.5% of the Cu was in the CCl destruction solid products, the coordination number of Cu-(O)-Cu increased to 5.6. Molecular level investigations are a key to identifying the mechanisms of the CCl destruction process. In addition, identification of the molecular characteristics of the products may help in safe disposal of the toxic substances. The success of this study paved the way for the destruction of halogenated organic compounds by copper acetate.

The Cu and Te coordination environments in Cu-doped Ge–Te glasses

The structure of Ge 20Te 80, Ge 15Cu 8Te 77 and Ge 15Cu 5Te 80 glasses was investigated by diffraction techniques and extended X-ray absorption fine structure measurements. Large structural models were generated by fitting experimental data by the reverse Monte Carlo simulation technique. In Ge 20Te 80 glass, both Ge and Te obey the 8 − N rule, and the structure is built up of GeTe 4 tetrahedra connected via Te–Te bonding or shared Te atoms connected to two Ge atoms. The coordination number of Te is significantly higher than 2 in Ge 15Cu 8Te 77. The average coordination number of Cu is 3.41 ± 1 in this alloy. In Ge 15Cu 5Te 80 glass, Cu binds mostly to Te, while Cu–Cu bonding is significant in Ge 15Cu 8Te 77.

Ab initiosimulation of solid electrolyte materials in liquid and glassy phases

We use plane-wave density functional methods to model Ge-Se-Ag-Cu liquids and glasses. The models are analyzed for structural and electronic properties and transition metal ion dynamics. Electronic properties are analyzed with the electronic density of states and projected density of states. The optical gap increases with increasing Ag content and decreases with increasing Cu content. We carry out thermal simulation at 300, 700, and 1000 K on these Ge-Se glasses doped with various concentrations of copper and silver. Our study shows that the most diffusive ions sample the widest variation in local density. The study of trap centers for Ag-rich and Cu-rich glasses shows that because of the higher coordination number of Cu, it is more rigidly trapped compared to Ag, with its lower coordination number.

High pressure induced coordination evolution in chain compound Li 2CuO 2

Using diamond anvil cell technique with angle dispersive X-ray diffraction (ADXD) of synchrotron radiation and electrical conductivity measurements, we have observed that CuO 2 chain compound Li 2CuO 2 transforms from ambient orthorhombic symmetry into a new phase at above 5.4 GPa and room temperature. The new phase was found to be of monoclinic structure with an increased oxygen coordination number of Cu 2+ from four at ambient to six at high pressure that provides a structural basis of the evolution of principle physical properties. The high pressure phase of Li 2CuO 2 is discussed in line with the first principle calculations.

On the Nanostructure of Cu in Ti<sub>x</sub>Cu<sub>1-x</sub> and TiN/Cu Films: A XAFS Study

The effect of chemical composition on the bonding environment of Cu, in a series of Ti1-x Cux and TiN/Cu films, is studied using X-Ray Absorption Spectroscopies (XAFS) at the Cu-K-edge. The EXAFS analysis reveals that in all studied samples Cu is amorphous. However, its bonding environment depends on the chemical composition. More specifically, in the Ti1-xCux films, Cu is coordinated with Ti and Cu and belongs both to intermetallic TiCu and to an amorphous Cu matrix. The coordination number of Cu, i.e., the sum of Ti and Cu first neighbours, increases systematically from 6.3 ± 0.7 to 10.6 ± 0.9 when the Cu content increases from 24.1 to 52.7 at%. On the contrary, in the TiN/Cu films, the type of atoms that consists the 1st nearest neighbour shell of Cu varies as a function of the Cu concentration. More specifically, in the TiN/Cu film with the lowest Cu content (27.3 at%), intermetallic TiCu is detected. At intermediate Cu concentration (37.8 at%), Cu is bonded to both Ti and Cu atoms. Finally, in the TiN/Cu film with the highest Cu content (67.7 at%), Cu is metallic.

The Influence of Alkyl Chain Length in 1,2-Dialkylimidazoles on the Extraction Capacity and Structure of Their Copper(II) Complexes

Formation of Cu(II) complexes of 1,2-dialkylmidazoles (where 1-alkyl = ethyl, propyl, butyl, pentyl, and hexyl, and 2-alkyl = propyl, butyl, and pentyl) has been studied using the liquid-liquid partition method, at 25°C and at a fixed ionic strength of the aqueous phase (I = 0.5; (HL)NO3, KNO3). The complexes were extracted with 2-ethyl-1-hexanol, and chloroform. The length of the 1-alkyl, and 2-alkyl groups, and the solvent nature have been shown to influence the extraction process. Extraction curves (log DM vs. pH) are displaced towards lower pH with increasing chain length of the 1-alkyl and 2-alkyl substituents. Stability constants of the complexes in aqueous solution as well as their partition constants between the aqueous and organic phase were determined. The stability of the Cu(II) complexes increased with increasing 1-alkyl chain length. The stability constants were comparable with β n values for the Cu(II) complexes of 1-alkyl-2-ethylimidazoles, but smaller than those of the Cu(II) – 1-alkylimidazole counterparts. The length of the 2-alkyl substituent has been found to affect both the pH1/2 values and the partition constants of the complexes. The partition constants P1 are small for all of the 1,2-dialkylimidazole complexes with Cu(II), whereas P2 and P3 are high and they increase with elongation of the 1-alkyl chain owing to a decrease in the co-ordination number of Cu(II), probably from 6 to 4 at the second and third complexation step. This change is likely to produce square coplanar species, readily extractable with organic solvent. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.