B. D. Shrivastava

Copper K-edge XANES of Cu(I) and Cu(II) oxide mixtures

XAFS at the copper K-edge has been recorded for cuprous oxide and cupric oxide separately and also for a mixture of the two in a specific ratio, at the XAFS beam line at SSRL. The normalized μ(E) data obtained for the two oxides, i.e., Cu(I) and Cu(II) oxides separately was linearly combined to fit the normalized μ(E) data of the mixture using the Linear Combination Fitting (LCF) method. The values obtained for the statistical goodness-of-fit parameters, R-factor and chi-square, show that the fit is reasonably good. This procedure yielded the percentage of the oxides in the mixture which was found to be nearly the same as the actual percentage which was used to prepare the mixture. Another method based on the analysis of normalized difference absorption edge spectra has also been used to quantitatively determine the percentage of the two copper species in the mixture. The LCF method is, however, found to be better than the normalized difference absorption edge analysis.

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.

Extended X-ray absorption fine structure study of mixed-ligand copper(II) complexes having analogous structures

X-ray absorption fine structure spectra have been studied at the Cu K-edge in five mixed-ligand copper(II) complexes, viz., [Cu(L-glu)(bipy)] 1, [Cu(L-glu)(phen) (H2O)]·3H2O 2, [Cu(L-tyro)(bipy)(ClO4)]·2H2O 3, [Cu(L-phen)(bipy)(H2O)] (ClO4) 4, and [Cu(L-tyro)(phen)(H2O)] (ClO4)·1·5H2O 5 (where L-glu = L-glutamate dianion, L-tyro = L-tyrosinate anion, bipy = 2,2′-bipyridine, and phen =1,10-phenanthroline), having essentially the same structure. The crystallographic data are available for all the complexes using which five theoretical models have been generated. Firstly, extended X-ray absorption fine structure (EXAFS) data of each complex has been analyzed using its own theoretical model and the results obtained are found to be comparable with the crystallographic results. Then, the EXAFS data of each complex has been analyzed using the theoretical models of the remaining four of these complexes. For each complex, the structural parameters obtained by fitting EXAFS data with theoretical models of the four ...

X-ray absorption fine structure study of multinuclear copper(I) thiourea mixed ligand complexes

X-ray absorption fine structure spectra of five copper(I) thiourea complexes [Cu4(thu)6 (NO3)4 (H2O)4] (1), [Cu4(thu)9 (NO3)4 (H2O)4] (2), [Cu2(thu)6 (SO4) H2O] (3), [Cu2(thu)5 (SO4) (H2O)3] (4), and [Cu(thu)Cl 0.5H2O] (5) have been investigated. Complexes 1 and 3 are supposed to have one type of copper centers in trigonal planar and tetrahedral environment, respectively. Complexes 2 and 4 are supposed to have two types of copper centers, one center having trigonal planar geometry and another center having tetrahedral geometry. The aim of the present work is to show how extended X-ray absorption fine structure (EXAFS) spectra of these complexes, having different types of coordination environment, can be analyzed to yield the coordination geometry around one type of copper centers present in complexes 1 and 3, and two types of copper centers present in complexes 2 and 4. The crystal structure of complex 5 is unavailable due to inability of growing its single crystals, and hence the coordination geometry of this complex has been determined from EXAFS. The structural parameters determined from the EXAFS spectra have been reported and the coordination geometry has been depicted for the metal centers present in all the five complexes. Also, the chemical shifts have been used to determine the oxidation state of copper in these complexes. The X-ray absorption near edge spectra features have also been correlated with the coordination geometry. Also, the presence of both three and four coordinated Cu(I) centers in complexes 2 and 4 has been suggested from a comparison of the intensity of the feature at 8984 eV with those of 1 and 3. Further, in case of complex 5, the high intensity of peak A at 8986.5 eV is found to correspond to the presence of Cl coordinated to the copper center.

K-Absorption spectral studies of some copper(II) mixed-ligand complexes

Edge shifts (ΔE), effective nuclear charge (Zeff) and % covalency for some copper(II) mixed-ligand complexes were determined by investigating the copper K-absorption edge using a Seifert x-ray generator and a 0.4 m Cauchois-type bent crystal transmission spectrograph. The shift values are suggestive of a parabolic dependence on Zeff of copper. Using the method of least squares, an expression ΔE = a + b(Zeff) + c(Zeff)2 was found to hold good for the dependence of ΔE on Zeff in the case of the complexes studied. Copyright

X-ray absorption near edge studies of some binuclear copper(II) complexes.

X-ray K-absorption near edge studies have been carried out on the binuclear copper (II) dithiocarbamate (dtc) complexes having the following general structure: [structure in text] where R = me (methyl); et (ethyl); npr (normal propyl); chx (cyclohexane) It has been found that the chemical shift values are higher in the chlorine adducts as compared to the values of chemical shift reported by us in an earlier work for the parent complexes, showing that the chlorine adducts are more ionic. The observed splitting of the principal absorption maximum (1s-4p) in the chlorine adducts has been explained in terms of the splitting of the metal 4p orbital degeneracy.

A Comparative XANES Study of Some Copper(II) Complexes in Solid State and Solution Form

X-ray K-absorption spectra of some structurally important copper(II) mixed ligand complexes with alpha amino butyric acid as primary ligand have been studied using a Cauchois type bent crystal X-ray spectrograph of 0.4 m radius. The spectra have been recorded using both the solid complexes as well as their aqueous solutions. The observed X-ray absorption parameters e.g., edge-shift, edge-width, shift of the principal absorption maximum and structure of the K-edge have been used to interpret the proposed structure of the complexes. The changes in the structure of the complexes as they form aqueous solutions have also been studied.

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-?3-(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.

Laboratory EXAFS using photographic method

Laboratory EXAFS facilities have been used since long. However, EXAFS data analysis has not been reported as yet for the spectra recorded photographically. Though from our laboratory we have been reporting various studies employing X-ray spectrographs using the photographic method of registration of EXAFS spectra, but the data has never been analyzed using the Fourier transformation method and fitting with standards. This paper reports the study of copper metal EXAFS spectra at the K-edge recorded photographically employing a 400 mm curved mica crystal Cauchois type spectrograph with 0.5 kW tungsten target X-ray tube. The data obtained in digital form with the help of a microphotometer has been processed using EXAFS data analysis programs Athena and Artemis. The experimental data for copper metal foil have been fitted with the theoretical standards. The results have been compared with those obtained from another laboratory EXAFS set up employing 12 kW Rigaku rotating anode, Johansson-type spectrometer with Si(311) monochromator crystal and scintillation counter. The results have also been compared with those obtained from SSRL. The parameters obtained for the first two shells from the photographic method are comparable with those obtained from the other two methods. The present work shows that the photographic method of registering EXAFS spectra in laboratory set up using fixed target X-ray tubes can also be used for getting structural information at least for the first two coordination shells.

EXAFS Studies of Some Copper(II) Mixed‐Ligand Complexes

X‐ray K‐absorption spectroscopic studies have been carried out on copper (II) mixed‐ligand complexes with glutamic acid and aspartic acid as the primary ligands, where as water, pyridine, imidazole and benz‐imidazole have been used as secondary ligands. Chemical shifts obtained from the X‐ray absorption data have indicated that the glutamic acid complexes are more ionic as compared to their corresponding aspartic acid complexes having similar secondary ligands. Further, we have estimated the average metal‐ligand bond distances from the from structure data. For the different complexes studied under the present investigation, the studies reveal that the bonding parameter α1 decreases with the increase in the percentage covalency of the metal‐ligand bond. Thus, the bonding parameter α1 may be used for the estimation of percentage covalency of the metal‐ligand bond in other similar complexes.