Full Quantitative Multiple-Scattering Analysis of X-ray Absorption Spectra:  Application to Potassium Hexacyanoferrat(II) and -(III) Complexes

Abstract

A recently developed method to the full quantitative analysis of the XAS spectra extending from the absorption edge to the high-energy region is presented. This method is based on the use of two independent approaches to the analysis of the EXAFS and XANES data, the well-known GNXAS and the newly developed MXAN procedures. Herein, we report the application of this technique to two iron complexes of known structure where multiple-scattering effects are prominent, the potassium hexacyanoferrat(II) and -(III) crystals and aqueous solutions. The structural parameters obtained from refinements using the two methods are equal and compare quite well with crystallographic values. Small discrepancies between the experimental and calculated XANES spectra have been observed, and their origin has been investigated in the framework of non-muffin-tin correction. The ligand dependence of the theoretical spectra has been also examined. Analysis of the whole energy range of the XAS spectra has been found to be useful in elucidating both the type of ligands and the geometry of iron sites. These results are of particular use in studying the geometrical environment of metallic sites in proteins and complexes of chemical interest.

Interaction between Fe-cyanide complex and humic acids

“…In case of the second sample, where HA S was added in the ratio of 1:10 to the water solution of ferricyanide, we found again six carbon atoms in the first Fe coordination shell at a distance of 1.95 ± 0.01Å with σ 2 = 0.005 ± 0.001Å 2 , and six nitrogen atoms at a distance of 3.14 ± 0.04Å with σ 2 = 0.003 ± 0.001Å 2 . The best-fit values were obtained in both cases with the EXAFS amplitude reduction factor (S 2 0 = 0.95 ± 0.06) and the E o shift (1.0 ± 0.5 eV) which is, within the experimental errors, in agreement with previous findings (Hayakawa et al 2004 ).…”

“…The structural parameters of the ferricyanide complex before and after the addition of HA S are unchanged, and fully agree with previously reported values for ferricyanide complex in water (Hayakawa et al 2004). The Fe K-edge EXAFS results therefore clearly showed that there are no structural modifications of the ferricyanide complex induced by the interaction with HA S .…”

“…MS contribution was strong because Fe-C-N atoms were almost aligned, which produced strong focusing effects in photoelectron scattering (Hayakawa et al 2004). We constructed the EXAFS model which included all single and significant multiple-scattering paths up to 3.3Å from the central Fe atom.…”

“…EXAFS analysis was performed with IFEFFIT based programs (Ravel and Newville 2005) using the FEFF6 code (Rehr et al 1992), in which the photoelectron scattering paths were calculated "ab initio" from the presumed distribution of neighboring atoms around Fe, from the proposed structure of water solution of K 3 [Fe(CN) 6 ] (Hayakawa et al 2004).…”

Is the Hexacyanoferrate(II) Anion Stable in Aqueous Solution? A Combined Theoretical and Experimental Study

“…This can also be seen from the numerous reported experimental investigations of hexacyanoferrates in the past. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] According to the literature hexacyanoferrate(II) ions, [Fe(CN) 6 ] 4− , are octahedral coordination complexes, which, depending on pH and cyanide concentration, tend to dissociate upon heat or light exposure 14,15,19,31 or in presence of mercury(II), 28 silver(I), 24,28 palladium(II) 28 and gold(III) 28 as they form even stronger complexes with cyanide than iron(II) and iron(III). A degradation of hexacyanoferrates by microorganisms has also been reported.…”