Bond Distances Of Cu Research Articles

Observation of Cu Spin Fluctuations in High-Tc Cuprate Superconductor Nanoparticles Investigated by Muon Spin Relaxation.

The nano-size effects of high-Tc cuprate superconductor La2−xSrxCuO4 with x = 0.20 are investigated using X-ray diffractometry, Transmission electron microscopy, and muon-spin relaxation (μSR). It is investigated whether an increase in the bond distance of Cu and O atoms in the conducting layer compared to those of the bulk state might affect its physical and magnetic properties. The μSR measurements revealed the slowing down of Cu spin fluctuations in La2−xSrxCuO4 nanoparticles, indicating the development of a magnetic correlation at low temperatures. The magnetic correlation strengthens as the particle size reduces. This significantly differs from those observed in the bulk form, which show a superconducting state below Tc. It is indicated that reducing the particle size of La2−xSrxCuO4 down to nanometer size causes the appearance of magnetism. The magnetism enhances with decreasing particle size.

Desulfurization of Gasoline and Diesel by Adsorption with Cu(I)-Y Zeolite

The objectivesof thiswork wereto fabricate Cu(I)–Y zeolite nanoparticlesforthe delsulfurizationof commercial gasoline and diesel using fixed-bed adsorption processes at room temperature. The Cu(I)–Y zeolite prepared in the present study showed that the breakthrough capacities of 21 and 9 mg/g of adsorbents of diesel and gasoline, respectively at 298 K for sulfur removal. Under the same experimental conditions, the saturation loadings were 36 and 23 mg/g for diesel and gasoline, respectively. Moreover, the structural morphology, crystallinity, fine structure and characteristics of the adsorbents were also systematically investigated. TPR profile of Cu(II)–Y zeolite indicated that the two reduction steps at 462 and 509 K, respectively were observed. A reduction temperature of about 462 K is sufficient to obtain the cuprous species required for π-complexation. EXAFS spectra showed that the bond distances of Cu–S in Cu2S and CuS were 2.35 and 2.47 A, respectively in the sulfur-adsorbed Cu–Y adsorbent.

Speciation and distribution of copper and zinc in MCM-41

Speciation and distribution of copper and zinc in the channels of the surface modified MCM-41 (MCM-41-SH) (pore opening = 2.6 nm) has been studied by X-ray absorption near edge structural (XANES) and X-ray absorption fine structural (EXAFS) spectroscopies in the present work. By least-square fitted XANES spectroscopy, mainly CuO and ZnO are observed in the channels of MCM-41-SH after calcination at 298–1173 K. Interestingly, a small amount of Cu–Zn alloys is also found in the MCM-41-SH at the calcination temperature of 573 K. At T > 573 K, nanosize CuO and Zn 2SiO 4 are the copper and zinc compounds in the MCM-41-SH. Due to aggregation of nanosize CuO at 1173 K, the bond distance of Cu–O is increased to 1.97 Å with the coordination number (CN) of 3.3. A decrease of the Zn–O bond distance (1.94 Å) at 1173 K is also observed. This work is also an example of the usefulness of the XANES and EXAFS spectroscopies for revealing the chemical structure of copper and zinc and possible reaction paths in the channels of MCM-41-SH during calcination at elevated temperatures.

Speciation of copper in plasma-melted slag

Speciation of copper in the laboratory waste incineration ashes and plasma-melted slag has been studied by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXFAS) spectroscopies. The component-fitted XANES spectra show that main copper species in the bottom and fly ashes are CuO (9–45%), Cu(OH) 2 (25–40%) and nanosize CuO (30–35%). During the plasma melting process at 1773 K, about 97% of Cu 2S in the slag is observed possibly due to sulfurization and self-reduction of CuO at high temperatures. By EXAFS, we also found that copper in the bottom and fly ashes possessed Cu O bond distances of 1.97 and 1.99 Å with coordination numbers (CNs) of 2.1 and 2.3, respectively. In the slag, the bond distance of Cu–S is 2.3 Å with a CN of 3.8.

Speciation of CuO in MCM-41 during oxidation of naphthalene

By extended X-ray absorption fine structural (EXAFS) spectroscopy, copper oxide clusters with a square-plane structure are found in the channels of mesoporous molecular sieve MCM-41. Bond distances of Cu–O and Cu–Cu are 1.90 and 2.80 Å, respectively. Oxidation of naphthalene at 723 K for 4 h in MCM-41 leads to structural perturbation of the clusters (e.g., Cu–O: −0.02 Å and Cu–Cu: +0.02 Å) with little change in their coordination numbers.

In situ X-ray absorption spectroscopic studies of CCl 4 mineralization with CuO

Mineralization of CCl 4 with CuO has been studied by in situ X-ray absorption spectroscopy (XAS) in the present work. The least-square fitted X-ray absorption near-edge structural (XANES) spectra showed that 18.9–20.1% of CuCl 2 was yielded in the mineralization of CCl 4 with CuO at 513–603 K for 20 min. By in situ extended X-ray absorption fine structural (EXAFS) spectroscopy, the structural perturbation of CuO during mineralization was observed. The perturbation may be due to an insertion of Cl species into the matrix of CuO and formation of CuCl 2. Bond distances of Cu O (first shell) and Cu (O) Cu (2nd shell) were increased by 0.01–0.04 Å with slight decreases of their coordination numbers (CNs) in the mineralization process. CuCl 2 in the CCl 4-mineralized product solids possessed Cu Cl bond distances of 2.10–2.12 Å, which were greater than that of the CuCl 2 model compound (2.05 Å). The in situ XAS technique exemplifies a direct observation of perturbation of CuO by Cl species during the mineralization at elevated temperatures.

In situ speciation studies of copper in the electroplating sludge under an electric field

Speciation of copper in the electrokinetic treatments of an industrial sludge was studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near-edge structural (XANES) spectroscopies in the present work. The least-square fits (LSF) of the XANES spectra indicated that the main copper species in the sludge were Cu(NO) 3 (82%) and adsorbed copper (Cu/SiO 2) (17%). Copper in the sludge possessed a CuO bond distance of 1.97 Å with a coordination number (CN) of 3.8. In the second shells, the bond distance of Cu(O)Si was 3.03 Å with a CN of 1.5. Most of Cu/SiO 2 was dissolved in the aqueous phase since little Cu(O)Si species in the sludge was found after 180 min of the electrokinetic treatments. About 69% of total Cu(II) was dissolved into the aqueous phase and 51% of which was migrated to the cathode under the electric field (5 V cm −1) for 180 min.

Preparation, properties and crystal structure of two isomers of R, R, S, S- and R, S, R, S-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1 12,16,0 4,9]tetracosane)copper(II)] +

Two isomers ( R, S, R, S- and R, R, S, S-) of five coordinate complex [Cu(L)Cl] + have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of R, S, R, S-[Cu(L)Cl] + shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of R, R, S, S-[Cu(L)Cl] +. R, S, R, S-[Cu(L)Cl] + is significantly distorted to trigonal-bipyramidal structure, whereas R, R, S, S-[Cu(L)Cl] + retains almost square-planar geometry. The average bond distance of Cu–N in basal plane of R, S, R, S-[Cu(L)Cl] + is longer by 0.024 Å than that of R, R, S, S-[Cu(L)Cl] +, whereas the bond distance of Cu–Cl in former is shorter by 0.200 Å than that in latter. The isolated square-planar complexes of R, R, S, S- and R, S, R, S-[Cu(L)](ClO 4) 2 are converted to the R, R, S, S- and R, S, R, S-[Cu(L)Cl] + by the addition of Cl − in nitromethane solution with the rate constants, k=1.70 (±0.02) and 8.31 (±0.07) M −1 s −1, respectively.

Structure, magnetic properties and catecholase activity study of oxo-bridged dinuclear copper(II) complexes

Six alkoxy-bridged dinuclear copper(II) complexes with catecholase-like sites, [Cu(L 1)(NCS)] 2 ( 1), [Cu(L 2)(CH 3CO 2)] 2·2H 2O ( 2), [Cu(L 3)(NCO)] 2 ( 3), [Cu(L 4)(NCS)] 2 ( 4), [Cu(L 5)(NCS)] 2 ( 5), and [Cu(L 4)(Cl)] 2 ( 6), where HL 1=2-(hydroxymethyl)-pyridine, HL 2=6-methyl-2-pyridine-methanol, HL 3=2-(2-hydroxyethyl)-pyridine, HL 4=1-dimethylamino-2-methyl-1-propanol, and HL 5=1-dimethylamino-2-propanol, respectively), have been prepared and characterized. The single crystal X-ray analysis show that the structures of complexes 1– 6 are dimeric with two adjacent copper(II) atoms bridged by pairs of μ-oxy atoms from the alkoxyl group of the ligands. Magnetic susceptibility measurements in the temperature range 2–300 K for complexes 1– 6 indicate significant antiferromagnetic coupling between the copper(II) atoms. The kinetic studies on catecholase activity of complexes for the oxidation of 3,5-di- tert-butylcatechol by O 2 was studied and it found that the complexes with the bond distance of Cu(II)⋯Cu(II) located near 2.98 to ∼2.99 Å show high catecholase activity. The reaction rate constant for the catecholase activity was obtained by Michaelis–Menten model.

Speciation of copper in the incineration fly ash of a municipal solid waste

The speciation of copper and zinc in the incineration fly ash of a municipal solid waste in Taiwan was investigated in the present work. By the least-squares fitted X-ray absorption near edge structural (XANES) spectroscopy, we found that CuCO 3, Cu(OH) 2, and CuO (fractions of 0.09, 0.39 and 0.51, respectively) were the main copper species in the fly ash. Quantitative analysis of the extended X-ray absorption fine structural (EXAFS) spectra indicated that the bond distance of CuO in the fly ash was 1.96 Å with a coordination number (CN) of 3.9 in the first shell of copper. In the second shell, the bond distance and CN of Cu(O)Cu were 2.91 Å and 2.7, respectively. In addition, speciation of Zn was also examined in the same X-ray absorption energy (8780–9970 eV). The bond distance of ZnO and ZnOZn were 1.97 and 2.94 Å, respectively. However, the ZnOCu structure was not found because of the physically unreasonable σ 2 (Debye–Waller factor) values in the EXAFS data fitting process.

Mineralization of CCl4 with Copper Oxide

Experimentally, CCl4 was effectively mineralized by CuO to yield stable inorganic species of CO2 and CuCl2 (CCl4 + 2CuO --> 2CuCl2 + CO2). High CCl4 conversions (63-83%) were found in the mineralization process performed at 513-603 K for 10-30 min. Using X-ray-absorption near edge structure (XANES) and X-ray photoelectron spectroscopies, we found that most CuCl2 was encapsulated in the CCl4-mineralized product solid (mineralization at 513 K for 30 min). At higher mineralization temperatures (563-603 K), CuCl2 was found to be predominant on the surfaces of the mineralization product. Speciation of copper in the mineralization product solid was also studied by extended X-ray absorption fine structure (EXAFS) spectroscopy. Bond distances of Cu-O and Cu-Cl in the CCl4-mineralized product solid were 1.93-1.94 and 2.10-2.12 , respectively, which were greater than those of normal CuO and CuCl2 by 0.03-0.07 A. The increase of the bond distances for Cu-O and Cu-Cl might be due to Cl insertion and concomitant structural perturbation of unreacted CuO in the mineralization process. Forthe second shell around copper atom, bond distances of Cu-(O)-Cu also increased by 0.03-0.05 A, and the coordination numbers of Cu-O and Cu-(O)-Cu decreased, as expected, in the mineralization process. In addition, stoichiometrically excess oxygen atoms were found on the solid surfaces, and they might play an important role in the mineralization of CCl4, leading to the formation of CO2 and Cl. Chloride atoms might be further captured by CuO, yielding CuCl2 in the mineralization process. This work exemplifies the utilization of X-ray spectroscopies (XANES, EXAFS, and XPS) to reveal the speciation and possible reaction pathway in a very complex mineralization process in detail.

EXAFS and XANES studies of copper in a solidified fly ash.

Speciation of copper in the fly ash solidification process has been studied by X-ray based spectroscopies inthe present work. Fourier transformed EXAFS (extended X-ray absorption fine structural) spectra of the solidified fly ashes showed that the bond distance of Cu-O (first shell) was 1.96 A with a coordination number (CN) of about 3.0. However, in the second shell of copper atoms, the bond distance of Cu-(O)-Cu was decreased by 0.12-0.22 A during solidification, which might cause the stabilization of the CuO species in the solidified fly ash matrix. By the least-squares fits of the XANES (X-ray absorption near edge structural) spectra, fractions of the main copper species in the solidified fly ashes such as CuCl2 (0.08-0.11), Cu2O (0.07-0.09), Cu(OH)2 (0.31-0.33), and CuO (0.49-0.52) were observed. Combined EXAFS and XANES observations suggested that chemical reactions such as hydroxylation of CuCl2 and oxidation of Cu2O and/or metallic Cu might involve in the solidification process, which also led to a significant reduction of the leachability of copper from the solidified fly ashes.

Structural correlation of catecholase-like activities of oxy-bridged dinuclear copper(II) complexes.

Eight oxy-bridged dinuclear copper(II) complexes with catecholase-like sites, [Cu(L1)X]2 (HL1 = 1-diethylaminopropan-2-ol, X=N3- 1, NCO- 2, and NO2- 3), [Cu(L2)X]2 (HL2=N-ethylsalicylaldimine, X=NO3- 4, Cl- 5, N3- 6, NCS- 7), and [Cu(L3)]2(ClO4)2, 8 (HL3=N-(salicylidene)-N'-(2-pyridylaldene)propanediamine) have been prepared and characterized. The single crystal X-ray analysis show that the structures of complexes 6 and 8 are dimeric with two adjacent copper(II) atoms bridged by pairs of micro-oxy atoms from the L2 and L3 ligands. Magnetic susceptibility measurements in the temperature range 4-300 K indicate significant antiferromagnetic coupling for 4, 5 and 7 and ferromagnetic coupling for 6 between the copper(II) atoms. The catecholase activity of complexes for the oxidation of 3,5-di-tert-butylcatechol by O2 was studied and it was found that the complexes with the bond distance of Cu(II)...Cu(II) located at 2.9-3.0 A show higher catecholase activity.

In-situ EXAFS study of copper in the electrokinetic remediation process.

The speciation of copper in the early stage of the electrokinetic remediation (EKR) process has been studied by extended X-ray absorption fine structure (EXAFS) spectroscopy in the present work. By in-situ EXAFS, we found that copper in a contaminated soil possessed a Cu-O bond distance of 1.98 A with a coordination number (CN) of 5.8. In the second shell, the bond distance of Cu-(O)-Cu was 2.87 A with a CN of 6.4. However, possibly due to the fact that incompact copper atoms in the outer shells were distorted by EKR, the Cu-(O)-Cu (2nd shell) bond distance and the CN of copper in the contaminated soil decreased by 0.08 A and 5.4, respectively in the early stage of the EKR process. Interestingly, after prolonging the contact time to about 80 minutes, the 1st-shell copper atoms were also perturbed by EKR. This work is an example of usefulness of the in-situ EXAFS spectroscopy for detailed studies of the speciation of copper in the contaminated soil during EKR process.

Oxidation of printed circuit board wastes in supercritical water

A feasibility study for oxidation of printed circuit board wastes with NaOH in supercritical water has been investigated. Experimentally, Br species in the printed circuit board resin was abstracted by sodium cations and the destruction efficiency of the waste was enhanced in the supercritical water oxidation (SCWO) process. By X-ray diffraction (XRD) spectroscopy, Cu 2O, CuO, and Cu(OH) 2 were found in the SWCO solid residue of the printed circuit board wastes. The extended X-ray absorption fine structural (EXAFS) spectra indicated that the bond distance of Cu–O in the residue was 1.87 Å with a coordination number of 2.61. Since the Cu–Br species was not observed by XRD and EXAFS spectroscopies, one may eliminate the possibility that the copper was involved in the abstraction of bromine species from the resin matrix in the SCWO process.

Oxygen-content dependence of crystal structure and Tc of (Nd 0.675Ce 0.325) 2(Ba 0.664Nd 0.336) 2Cu 3.00O y

The crystal structure of (Nd 0.675Ce 0.325) 2(Ba 0.664Nd 0.336) 2Cu 3.00O y is described as a modified YBa 2Cu 3O y structure, in which the Y layer is replaced by a (Nd,Ce) 2–O 2 block. While the dependence of T c on oxygen content differs among the rare-earth copper oxide superconductors, superconductivity appears in a range of y=9.12–9.14 in the present system. One of the reasons for this difference is related to the nature of defects associated with oxygen in the plane contained Cu. We studied the crystal structure of single-phase (Nd 0.675Ce 0.325) 2(Ba 0.664Nd 0.336) 2Cu 3.00O y samples of different oxygen contents by neutron powder diffraction and the superconducting properties by T c measurements and chemical analysis. Over the y range where superconductivity is realized, the Cu valence changes from 2.32–2.33 but the Ce valence remains ca. +4. From Rietveld refinements of the neutron data, we found a direct correspondence between the oxygen content and the occupation of oxygen sites in the CuO δ plane. The average bond distances of Cu–O in CuO δ and CuO 2 plane, (Nd,Ba)–O(16l) and (Nd,Ba)–O(16 m) decrease with increasing oxygen content. Moreover, since the average Ce valence does not vary with respect to oxygen content, the average bond distances connecting the (Nd,Ce) site to its oxygen neighbors are almost constant. The calculated bond valence sum for the Cu(1) atoms in the CuO δ plane and the average Cu valence increase markedly with oxygen content.

Tetranuclear copper complexes with new β-diketone and β-iminoketone-containing ligands

Novel tetranuclear copper complexes, Cu4(OH)2(ClO4)3 (HA)·H2O (1) and Cu4(ClO4)5(H3B)·3H2O (2), were synthesized by reacting 1,5-bis(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1 ,5-pentanedione with 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine in the presence of a template reagent copper ion. New [2+2] type open cyclic multidentate ligands are also obtained from the reaction (H4A and H6B stand for new compounds from 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine, respectively). They each contain five C = O, three C = N and one NH2 groups. The complexes were characterized by elemental analyses, conductivity, FT-i.r. (micro-i.r., deconvolution technique), FAB-MS, e.s.r., electronic spectra and extended X-ray absorption fine structure (EXAFS). Copper ions in (1) are basically four coordinate with tetragonal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.91 A and 2.05 A. In (2), copper ions are primarily five coordinate with square-based pyramidal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.93A and 2.08A. Four copper atoms in molecules may be arranged tetragonally. Both the ligand field and the coordination bonds in complex (1) are stronger than those in (2). Investigations on variable temperature susceptibilities show that some antiferromagnetic exchange interaction exist in the complexes. The plots of χ−1 versus T obey the Curie-Weiss law only at low temperature. Preliminary results of a bioassay indicate that the two complexes have some antitumour activity in vitro.

Syntheses and structural studies on copper(II) complexes derived from ethyl(2-benzothiazolyl)aminoformate

The reaction of copper(II) acetate with ethyl(2-benzothiazolyl)aminoformate (HL) gave red crystals of [Cu 2L 4] 2 ( 1). When complex 1 was treated with pyridine (Py) in chloroform/toluene, red crystals of CuL 2(Py) 2 ( 2), were deposited. Both complexes have been characterized by single-crystal X-ray diffraction methods, showing that the binuclear complex 1 has the copper atoms each located in a four-coordinate square-planar geometry of N 4, with two independent molecules in an asymmetric unit. The average bond distances of CuN(amine) and CuN(bta) (bta = benzothiazoyl) are 1.98 and 2.07 Å, respectively. Complex 2 is mononuclear with the Cu atom also in a square plane. The bond distances of CuN(py) and CuN(amine) are 2.011(4) and 1.997(4) Å, respectively.

A two-dimensional copper(I) polymer containing both molecular rod and anionic bridges: synthesis and crystal structure of (µ-chloro)-(µ-pyrazine)copper(I)

The crystal structure of bright-red crystals of the bidimensional polynuclear diamagnetic (µ-chloro)(µ-pyrazine)copper(I) complex has been analyzed from X-ray diffraction data. The structure was solved by the heavy-atom method. Full-matrix least-squares refinement based on 673 reflections with F > 4σ(F) converged to a final R = 0.043 and Rw = 0.048. Crystals of this complex are monoclinic, space group P2/c, a = 3.814(1), b = 6.356(1) and c = 11.497(5) Å; β = 96.04(2)°, Z = 2. The structure consists of planes of copper(I) atoms linked by pyrazine and Cl− bridges, each Cu(I) being in a distorted tetrahedral environment formed by two chloride ions and two nitrogen atoms belonging to two pyrazine molecules, with bond distances of Cu—Cl = 2.349(1) and Cu—N = 2.038(4) Å. Vibrational and electronic spectroscopy of the title compound is also reported. Keywords: two-dimensional copper(I)–pyrazine complexes.

Synthesis and structure of cytosine dichloride cuprate: direct bonding of copper to cytosine

Dichlorobis(cytosine)copper(II), [CuCl2-(C4H5N3O)2], Mr = 356.65, monoclinic, P2(1)/n, a = 8.399 (2), b = 13.773 (2), c = 10.775 (2) A, beta = 90.8 (2) degrees, V = 1246.3 (9) A3, Z = 4, Dx = 1.901 Mg m-3, lambda (Mo K alpha) = 0.7107 A, mu = 2.195 mm-1, F(000) = 716, T = 298 K, R = 0.032, wR = 0.037 for 2313 reflections greater than 2 sigma(F). The crystal structure of the title compound consists of two crystallographically independent cytosine molecules attached together through the direct bonding of a Cu2+ ion with two N atoms of the pyrimidine rings. In addition to the N atoms, the Cu ions are coordinated to two Cl atoms forming approximately a square-planar environment. The bond distances of Cu to Cl(1), Cl(2), N(3) and N(3') atoms are 2.299 (1), 2.267 (1), 1.985 (4) and 1.996 (3) A, respectively. Packing of the Cyt(I)-CuCl2-Cyt(II) complex in the crystal is ensured by an extensive extramolecular N--H...Cl and N--H...O network. Hydrogen bonds involving Cl, O and H atoms of the neighboring Cyt(I) and Cyt(II) induce a slight distortion in Cu--Cl, C = O distances but do not significantly affect intramolecular bond lengths and angles in the cytosine rings and their flatness.