Copper K-edge Research Articles

X-ray K-absorption spectroscopic studies of copper complexes

The X-ray absorption spectra at the K-edge of copper have been recorded in five mixed ligand copper complexes having orthophenylenediamine as one of the ligand. Various X-ray absorption near edge structure (XANES) parameters, such as chemical shift, i.e., shift of K-edge of copper in complexes with respect to K-edge of copper metal, energy position of principal absorption maximum and edge-width have been determined. Copper has been found to be in oxidation state +2 in all the complexes. From these XANES data the effective nuclear charge on copper and percentage covalency in these complexes has been estimated.

X-ray absorption fine structure (XAFS) studies of copper (II) mixed ligand complexes having tetramethylethylenediamine as one of the ligands

X-ray absorption fine structure (XAFS) has been studied at the K-edge of copper in copper(II) mixed ligand complexes, having tetramethylethylenediamine (tmen) as one of the ligands, viz., Cu(tmen)(gly)ClO4, Cu(tmen)(bipy)(ClO4)2 and Cu(tmen)(phen)(ClO4)2. The spectra have been recorded at the dispersive XAFS beamline (BL-8) at the 2.5 GeV INDUS-2 synchrotron, RRCAT, Indore, India. The data obtained has been processed and analyzed using the computer program Athena. It has been observed that K-edge has been found to split in two edges, K and K', in each of the complex. The chemical shift has been utilized to determine the oxidation state of copper in the complexes and also the effective nuclear charge (ENC). The EXAFS data has been analyzed to obtain the bond lengths in the complexes using Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The first peak in the Fourier transform of the spectra gives the value of first shell phase uncorrected bond length. The results obtained from the Fourier transformation and LSS methods are in good agreement.

X-ray absorption spectral studies of copper(II) mixed ligand complexes having ethylenediamine as one of the ligands

X-ray absorption spectra of copper(II) mixed ligand complexes, having ethylenediamine (en) as one of the ligands, have been recorded at the K-edge of copper at the dispersive extended X- ray absorption fine structure (EXAFS) beamline (BL-8) at the 2.5 GeV INDUS-2 Synchrotron, RRCAT, Indore, India. The samples studied are: Cu(en)2(ClO4)2, Cu(en)2Br2.H2O and Cu(en)2SO4. The data obtained has been processed using EXAFS data analysis program Athena. The K-edge has been found to split in two edges K and K' in each of the complex. The energies of the edges K(EK) and K'(EK') and the principal absorption maximum A(EA) have been determined from the derivative spectra. The chemical shift has been utilized to determine the oxidation state of copper in the complexes and to estimate effective nuclear charge (ENC) on the absorbing atom. The EXAFS data has been used to determine the bond lengths in the complexes using three different graphical methods. The bond lengths, obtained from one of these methods and the Fourier transformation method, are comparable with each other, showing that both of these methods give phase uncorrected bond lengths.

Theoretical calculations of X-ray absorption spectra of a copper mixed ligand complex using computer code FEFF9

The terms X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) refer, respectively, to the structure in the X-ray absorption spectrum at low and high energies relative to the absorption edge. Routine analysis of EXAFS experiments generally makes use of simplified models and several many-body parameters, e.g. mean free paths, many-body amplitude factors, and Debye-Waller factors, as incorporated in EXAFS analysis software packages like IFEFFIT which includes Artemis. Similar considerations apply to XANES, where the agreement between theory and experiment is often less satisfactory. The recently available computer code FEFF9 uses the real-space Green's function (RSGF) approach to calculate dielectric response over a broad spectrum including the dominant low-energy region. This code includes improved treatments of many-body effects such as inelastic losses, core-hole effects, vibrational amplitudes, and the extension to full spectrum calculations of optical constants including solid state effects. In the present work, using FEFF9, we have calculated the X-ray absorption spectrum at the K-edge of copper in a complex, viz., aqua (diethylenetriamine) (isonicotinato) copper(II), the crystal structure of which is unknown. The theoretical spectrum has been compared with the experimental spectrum, recorded by us at the XAFS beamline 11.1 at ELETTRA synchrotron source, Italy, in both XANES and EXAFS regions.

Extended X-ray absorption fine structure data analysis of copper (II) hydroxamic acid mixed ligand complexes

The X-ray absorption spectra of copper mixed ligand complexes, having hydroxamic acid as one of the ligands, have been recorded at the K-edge of copper at BL-8 Dispersive EXAFS beamline at the 2.5 GeV INDUS-2 Synchrotron, RRCAT, Indore, India. For the analysis of EXAFS data, crystallographic data of the complex or of its analog is required, which is not available. Hence, for the analysis of EXAFS data, theoretical EXAFS data of the studied complexes have been generated using the EXAFS equation employing computer software program Mathcad. Firstly, the experimental data has been processed using the computer program Athena to obtain the normalized absorption versus energy data. From the experimental EXAFS data, the phase shift parameter (an energy independent constant 5) has been computed using Lytle, Sayers and Stern's (LSS) method. The backscattering amplitude has been taken from the available theoretical tabulations and other parameters have been taken from crystallographic data of the copper metal. Fourier transforms of both the experimental and theoretical data have been computed, and the two Fourier transforms are found to agree with each other for all the complexes. The position of the first peak in the Fourier transform gives the value of the first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factor (5(k)) in the sine function of the EXAFS equation. Since, the Fourier transform method and LSS method both are uncorrected for phase and other parameters of the EXAFS equation, the present method gives phase uncorrected bond length of the first coordination shell.

X-ray absorption spectral studies of copper (II) mixed ligand complexes

X-ray absorption spectra at the K-edge of copper have been studied in two copper mixed ligand complexes, one having tetramethyethylenediamine (tmen) and the other having tetraethyethylenediamine (teen) as one of the ligands. The spectra have been recorded at BL-8 dispersive extended X-ray absorption fine structure (EXAFS) beamline at the 2.5 GeV INDUS- 2 synchrotron, RRCAT, Indore, India. The data obtained has been processed using the data analysis program Athena. The energy of the K-absorption edge, chemical shift, edge-width and shift of the principal absorption maximum in the complexes have been determined and discussed. The values of these parameters have been found to be approximately the same in both the complexes indicating that the two complexes possess similar chemical environment around the copper metal atom. The chemical shift has been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length because of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase- uncorrected bond length. Bond length has also been determined by Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The results obtained from LSS and the Fourier transformation methods are comparable with each other, since both are phase uncorrected bond lengths.

Extended X-ray absorption fine structure data analysis of copper (II) hydroxamic acid mixed ligand complexes

The X-ray absorption spectra of copper mixed ligand complexes, having hydroxamic acid as one of the ligands, have been recorded at the K-edge of copper at BL-8 Dispersive EXAFS beamline at the 2.5 GeV INDUS-2 Synchrotron, RRCAT, Indore, India. For the analysis of EXAFS data, crystallographic data of the complex or of its analog is required, which is not available. Hence, for the analysis of EXAFS data, theoretical EXAFS data of the studied complexes have been generated using the EXAFS equation employing computer software program Mathcad. Firstly, the experimental data has been processed using the computer program Athena to obtain the normalized absorption versus energy data. From the experimental EXAFS data, the phase shift parameter (an energy independent constant 5) has been computed using Lytle, Sayers and Stern's (LSS) method. The backscattering amplitude has been taken from the available theoretical tabulations and other parameters have been taken from crystallographic data of the copper metal. Fourier transforms of both the experimental and theoretical data have been computed, and the two Fourier transforms are found to agree with each other for all the complexes. The position of the first peak in the Fourier transform gives the value of the first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factor (δ(k)) in the sine function of the EXAFS equation. Since, the Fourier transform method and LSS method both are uncorrected for phase and other parameters of the EXAFS equation, the present method gives phase uncorrected bond length of the first coordination shell.

X-rayKabsorption spectral studies of copper (II) hydroxamic acid mixed ligand complexes

X-ray absorption spectra at the K-edge of copper have been studied in copper mixed ligand complexes having hydroxamic acid as one of the ligands. The X-ray absorption spectra have been recorded at BL-8 Dispersive Extended X-ray Absorption Fine Structure (EXAFS) beamline at the 2.5-GeV INDUS-2 Synchrotron Source, RRCAT, Indore, India. The data obtained has been processed using EXAFS data analysis program Athena. The energies of the K absorption edge, chemical shifts, edge-widths and shifts of the principal absorption maximum in the complexes have been determined and discussed. The chemical shift data have been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase-uncorrected bond length and has also been determined by Lytle, Sayers and Stern's (LSS) graphical method. The results obtained from LSS and the Fourier transformation methods are comparable with each other. The first shell bond length has also been estimated by Lytle's and Levy's methods from the EXAFS data. Copyright © 2014 John Wiley & Sons, Ltd.

Speciation of Mixtures of Copper (I) and Copper (II) Mixed Ligand Complexes by X-Ray Absorption Fine Structure Spectroscopy

ABSTRACT Studies on speciation have been done in the mixtures of mixed ligand copper complexes. Three heterogeneous mixtures have been studied, each having one Cu(I) complex and one Cu(II) complex. The Cu(I) complex is [Cu(thu)Cl 0.5H2O] (1) and the Cu(II) complexes are [Cu(L-phen)(bpy) H2O] (2), [Cu(L-tyr)(phn) 2.5H2O] (3), and [Cu(dien)(ina) 4H2O.1/2SO4] (4) (where thu = thiourea, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, tyr = tyrosine, dien = diethylenetriamine, and ina = isonicotinate anion). The mixtures have been prepared by mixing the Cu(I) complex with each of the Cu(II) complexes in the ratio of 1:1 by mole percentage. The X-ray absorption fine structure (XAFS) spectra have been recorded at the K-edge of copper in the mixtures as well as in the complexes, separately. The aim of the present work is to make a study of the different methods of speciation using XAFS, viz., principal component analysis (PCA) and the target transformation (TT) method, the linear combination fitting (LCF) method, derivative spectra methods, and normalized difference absorption edge spectra (NDAES) analysis. It has been shown that these methods can be used to determine the relative quantity of the mixed ligand complexes in their mixtures.

X-ray absorption studies of copper(II) mixed ligand complexes with tetramethylethylenediamine as primary ligands

X-ray absorption near edge structure (XANES) measurements have been made on the K-edge of copper in some of its biologically important complexes involving tetramethylethylenediamine (tmen) as primary ligand. Other inorganic anionic ligands are oxalate anion (ox), acetylacetonate anion(acac), glycinate(gly) anion and ethylenediamine(en). Various X-ray absorption parameters in the near edge region, e.g., chemical shift, i.e., shift of K-edge of copper in complex with respect to K-edge of copper metal, energy position of the principal absorption maximum and edge-width have been determined. The K-edge has been found to split into two components, i.e., K1 and K2 in the complexes. This feature suggests square planar geometry for the complexes. The chemical shift data suggests that in the complexes copper is in oxidation state +2 and that the relative ionic character of the complexes is in the following sequence: Cu(tmen)(ox).4H2O < Cu(tmen)(acac)(ClO4) < Cu(tmen)(gly)ClO4 < Cu(tmen)(en)SO4.4H2O. For these four complexes, we observe that the sequence of variation of chemical shifts follows the same trend as obtained in the available spectrochemical series, i.e., oxalate < glycinate < ethylenediamine. The effective nuclear charge has been estimated from the chemical shift data.

EXAFS study of mixed ligand copper complexes having nicotinic acid as one of the ligands

Copper K-edge EXAFS spectra of the copper (II) complexes [Cu3(NA)4(dca)2(H2O)8].2H2O (1) and [Cu2(2,2'-bipy)(NA)2](ClO4)2.H2O (2) (where NA = Nicotinic acid; dca = dicyanamide anion; 2,2'-bipy = 2-2' bipyridine) having different coordination environments and geometries have been investigated. The complex 1 is supposed to have six coordinated geometry and complex 2 five coordinated geometry. EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. Theoretical models have been generated for both the complexes separately using their reported crystal structures. These theoretical models have been fitted to the respective experimental EXAFS data and the structural parameters, which include bond lengths, coordination numbers and thermal disorders, have been determined. The results obtained have been found to be comparable with those reported using crystallography. The coordination geometry about the copper (II) ion has been depicted for both the complexes. Further, copper has been found to be in +2 oxidation state in both the complexes. The study shows that the dispersive EXAFS beamline can be used to obtain information about the coordination geometry of a sample, though the beamline provides limited range of EXAFS data.

EXAFS study of tetramethylethylenediamine copper(II) complexes with Cl and Br as secondary ligands

Extended X-ray absorption fine structure (EXAFS) have been recorded at the K-edge of copper in binuclear copper(II) complex [Cu(tmen)Cl2] (1) and its analogous complex [Cu(tmen)Br2] (2) (where tmen = tetramethylethylenediamine), using the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. Theoretical model has been generated for 1 using its available crystallographic data [1] and then fitted to the experimental EXAFS data of 1 to obtain its structural parameters, which include bond-lengths, coordination numbers and thermal disorders. The results obtained have been found to be comparable with the crystallographic results. As complex 2 is analogous to complex 1, the same theoretical model, which was generated for 1, has been fitted to the experimental EXAFS data of 2. The structural parameters, thus determined for 2 have been reported. The coordination geometry around the copper center in both the complexes has been depicted showing the bond-lengths obtained in the present study. It has been demonstrated that if crystal structure is available for a complex from X-ray crystallographic studies, the structural parameters can be determined for an analogous complex from EXAFS studies. Further, the values of the chemical shifts suggest that copper is in +2 oxidation state in these complexes.

Study of XAFS spectroscopic methods of speciation using mixtures of Cu(I) and Cu(II) chlorides

Speciation concerns determination of the chemical forms along with the relative quantities of the different species in a given sample. The aim of the present work is to make a comparative study of the different methods of speciation using X-ray absorption fine structure (XAFS) spectroscopy. For this purpose, mixtures have been prepared by mixing CuCl2 and CuCl in different proportions. The X-ray absorption spectra have been recorded at the copper K-edge in the mixtures and the two chlorides separately. The different characteristic features of the XANES spectra of the two chlorides, useful for speciation, have been identified. Firstly, Principal component analysis (PCA) and target transformation (TT) methods have been used to check the number and identity of components in the mixtures. After the identification of the components, the percentages of the species in the mixtures have been quantitatively determined by linear combination fitting (LCF) of XANES, derivative XANES, and EXAFS (k3chi and k2chi) spectra. The other methods of speciation which have been employed are normalized difference absorption edge spectra analysis (NDAES), methods based on derivative XANES spectra of species and the method based on the relative position of the absorption edge. Results obtained from these methods have been compared and their relative merits discussed. It is probably for the first time that such a study has been done. The first section in your paper

Cluster-Seeded Synthesis of Doped CdSe:Cu4 Quantum Dots

We report here a method for synthesizing CdSe quantum dots (QDs) containing copper such that each QD is doped with four copper ions. The synthesis is a derivative of the cluster-seed method, whereby organometallic clusters act as nucleation centers for quantum dots. The method is tolerant of the chemical identity of the seed; as such, we have doped four copper ions into CdSe QDs using [Na(H2O)3]2[Cu4(SPh)6] as a cluster seed. The controlled doping allows us to monitor the photophysical properties of guest ions with X-ray spectroscopy, specifically XANES and EXAFS at the copper K-edge. These data reveal that copper can capture both electrons and holes from photoexcited CdSe QDs. When the dopant is oxidized, photoluminescence is quenched and the copper ions translocate within the CdSe matrix, which slows the return to an emissive state.

A copper and iron K-edge XANES study on chalcopyrite leached by mesophiles and moderate thermophiles

To reveal the mechanism of chalcopyrite biooxidation at different temperatures, pure chalcopyrite leached by mesophiles (30°C) and moderate thermophiles (48°C) was characterized by synchrotron X-ray absorption near-edge structure (XANES). Solution studies show that elevated temperatures promoted chalcopyrite dissolution. A final copper recovery of 41% was achieved at 48°C, while only 15% at 30°C. Cu K-edge XANES analyses indicated more iron than copper dissolved, leaving on the particle surface CuSn-like species in the early stages of leaching. In the late stages of leaching, copper in CuSn-like species was leached, leaving behind Sn-like species. The slowness of leaching of Sn-like species may be the reason why no CuSn-like species were formed in the late stages, and thus why chalcopyrite passivated. In addition, Fe K-edge XANES indicates no significant amount of jarosite formed at 30°C; however, at 48°C, jarosite precipitation was profoundly accelerated, which accounted for 51% of the iron species in the residue at day 35.

X-ray diffraction and absorption spectroscopic studies of copper mixed ligand complexes with aminophenol as one of the ligands

X-ray diffraction (XRD) and X-ray absorption spectroscopic (XAS) studies have been conducted on two copper complexes, i.e., copper macrocyclic complex of succinic acid and ortho aminophenol (complex-1) and copper macrocyclic complex of pthalic acid and ortho aminophenol (complex-2). The diffraction pattern of the complexes have been recorded using Rigaku RINT-2000 X-ray diffractometer equipped with rotating anode X-ray tube operated at 40 kV and 100 mA. The X-ray absorption spectra of the complexes have been recorded at the K-edge of copper on Cauchois type bent crystal spectrograph having radius 0.4 m employing a mica crystal, oriented to reflect from (100) planes, for dispersion. The X-ray absorption near edge structure (XANES) parameters, viz., chemical shift, energy position of the principal absorption maximum and edge-width have been determined and discussed. From the extended X-ray absorption fine structure (EXAFS) data, the bond lengths have been calculated using three methods, namely, Levy's method, Lytle, Sayers and Stern's (LSS) method and Fourier transformation method. The results obtained have been compared with each other and discussed.

Coordination geometry around copper in a Schiff-base trinuclear copper complex using EXAFS spectroscopy

In the present investigation, we have studied extended X-ray absorption fine structure (EXAFS) spectra of a trinuclear Schiff-base copper complex tetraaqua-di-μ3-(N-salicylidene-DL-glutamato)-tricopper(II)heptahydrate, [Cu3(C12H10NO5)2 (H2O)4]. 7H2O, in which three metal sites are present. One metal site is square-pyramidal (4+1) and other two similar metal sites are tetragonally distorted octahedral (4+2). EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The analysis of EXAFS spectra of multinuclear metal complexes pose some problems due to the presence of many absorbing atoms, even when the absorbing atoms may be of the same element. Hence, using the available crystal structure of the complex, theoretical models have been generated for the different copper sites separately, which are then fitted to the experimental EXAFS data. The two coordination geometries around the copper sites have been determined. The contributions of the different copper sites to the experimental spectrum have been estimated. The structural parameters, which include bond-lengths, coordination numbers and thermal disorders, for the two types of copper sites have been reported. Further, copper has been found to be in +2 oxidation state at these metal sites.

EXAFS study of tetrakis(imidazole) dinitratocopper (II) complex

The extended X-ray absorption fine structure (EXAFS) spectra at the K-edge of copper in tetrakis(imidazole)dinitratocopper(II) complex [Cu(im)4(NO3)2] (im= imidazole), has been recorded using the dispersive EXAFS beamline at the 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The EXAFS data analysis has been done using the computer programs Athena and Artemis. Theoretical model has been generated using the available crystal structure of the complex and fitted to its experimental EXAFS data. The structural parameters thus obtained, which include bond-lengths, coordination numbers and thermal disorders, have been reported. The results obtained have been found to be in good agreement with crystallographic results. The coordination geometry around the copper site has been determined and depicted. Further, copper has been found to be in +2 oxidation state in this complex.

Time-gated measurements of electron beam generated Kα emission lines from brass planar wire array implosions

The relative amount of Kα radiation emitted by partially ionized copper and zinc from planar wire arrays on the 1 MA Zebra generator at the University of Nevada, Reno, does not correspond to the composition (70% copper, 30% zinc) of the array's brass wires. For example, the copper Kα line at 8 keV was observed to be much stronger than would be expected from zinc's Kα radiation at 8.6 keV, but this ratio also reversed, more emission from zinc than from copper, during the X-ray pulse. An excess of Kα photons from copper is consistent with a beam of electrons with energies above copper's K-edge but below that of zinc, but the opposite case is perplexing. Preferential ablation of Zn over Cu early in the current pulse could be a contributing factor, but opacity effects are not. Synthetic spectra for brass computed by a non-LTE collisional-radiative model that includes an electron beam component compare well with observed K-shell spectra, and suggest the parent ions of the Kα emission. These ionization stages are consistent with L-shell spectra. This comparison also indicates that the total energy in the electron beam increases towards the end of the radiation pulse while the electron temperature decreases. The crucial diagnostic in this measurement is a time-resolved X-ray spectrometer based on a LiF crystal.

A Comparative Study of the Methods of Speciation Using X-ray Absorption Fine Structure

Determination of the chemical forms along with the relative quantity of the di erent species in a given sample, termed as speciation, can be done by analyzing X-ray absorption ne structure spectra. The di erent methods that can be used for speciation are: principal component analysis, target transformation, methods based on derivative spectra, method based on the relative position of the absorption edge, residual phase analysis, normalized di erence absorption edge spectra analysis and linear combination tting. An attempt has been made to make a comparative study of these di erent methods of speciation by recording the X-ray absorption ne structure at the copper K-edge in a mixture having cuprous oxide and cupric oxide in a speci c ratio. The X-ray absorption ne structure spectra of the two oxides have also been recorded separately and the di erent characteristic X-ray absorption near edge structure features have been identi ed and their origins have been discussed. Speciation of the mixture has been done using these di erent methods and the results obtained have been compared and discussed.