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Implications of the unusual redox behavior exhibited by the teteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-}

Description: We report on the novel electrochemical behavior of the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup -12}, with emphasis on the Eu valence in both the oxidized and reduced forms. In aqueous electrolytes, the P-W-O framework is electroactive and can reversibly accept up to 10 electrons before the potential becomes reducing enough for H{sub 2} evolution. Eu L{sub 3}-edge x-ray absorption near edge structure (XANES) results demonstrate that Eu is also electroactive under the same conditions. Implications of this work are discussed re long-standing questions about intermediate- valent materials.
Date: December 1996
Creator: Antonio, M. R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Synthesis and properties of lanthanide-exchanged Preyssler`s heteropolyanions

Description: Na{sup +} in the Preyssler heteropolytungstate anion [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14{minus}} can be exchanged for a trivalent lanthanide ion. The potential significance of this new class of lanthanide heteropolyanions relates to their applications in catalysis science. This view follows from the fact that Keggin heteropolyanions and their free acids are used as heterogeneous solid catalysts and homogeneous solution catalysts. The authors describe synthetic conditions that lead to the incorporation of Ce{sup 3+} and Pr{sup 3+} within the Preyssler anion, and the coprecipitation of Ce{sup 3+} and the Preyssler anion. Initial studies indicate that the latter, coprecipitated, material deserves study for bifunctional catalytic activity.
Date: December 1994
Creator: Antonio, M. R.; Malinsky, J. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Oxidation states of the ``unusual`` rare earths (R=Ce, Pr and Tb) in double layer high-T{sub c} superconductors

Description: X-ray absorption and magnetization experiments are used to describe the oxidation states of the rare earths R= Ce, Pr, and Tb in the double layer high-Tc superconducting series RBa{sub 2}Cu{sub 3}O{sub 7} and Pb{sub 2}Sr{sub 2}R{sub 1-x}Ca{sub x}Cu{sub 3}O{sub 8}. We obtained the same oxidation states for the rare earths in these two classes of compounds, namely, R=Ce tetravalent and R=Pr and Tb trivalent.
Date: July 1, 1996
Creator: Staub, U.; Soderholm, L.; Skanthakumar, S. & Antonio, M.R.
Partner: UNT Libraries Government Documents Department

Implications of the unusual redox behavior exhibited by the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12{minus}}

Description: Materials containing more than one electroactive species may exhibit a variety of unusual properties, including mixed or intermediate valence, and their related phenomena. Intermediate valence arises when localized orbitals, notably valence f-states, interact in a bonding fashion with delocalized, molecular orbitals in the same material. Electrons are viewed to be rapidly hopping between these two very different kinds of orbitals, and it is their relative residence times that are interpreted as a non-integral valence. Whereas there has been considerable efforts expended to understand this unusual behavior, these efforts have not proven successful, largely because the problem is many-bodied and is usually studied on infinite band states, often in chemically complex systems. The authors report here on the novel electrochemical behavior of the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12}, and examine the valence of Eu in both the oxidized and reduced form of the anion, as determined from Eu L{sub 3}-edge X-ray absorption near edge structure (XANES). The results demonstrate that, with careful electrochemical control, Eu in this ion may become intermediate valent. Such a result would provide an entirely new and unique approach to longstanding questions related to the phenomenon of intermediate valence.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Extracellular iron-sulfur precipitates from growth of Desulfovibrio desulfuricans

Description: The authors have examined extracellular iron-bearing precipitates resulting from the growth of Desulfovibrio desulfuricans in a basal medium with lactate as the carbon source and ferrous sulfate. Black precipitates were obtained when D. desulfuricans was grown with an excess of FeSO{sub 4}. When D. desulfuricans was grown under conditions with low amounts of FeSO{sub 4}, brown precipitates were obtained. The precipitates were characterized by iron K-edge XAFS (X-ray absorption fine structure), {sup 57}Fe Moessbauer-effect spectroscopy, and powder X-ray diffraction. Both were noncrystalline and nonmagnetic (at room temperature) solids containing high-spin Fe(III). The spectroscopic data for the black precipitates indicate the formation of an iron-sulfur phase with 6 nearest S neighbors about Fe at an average distance of 2.24(1) {angstrom}, whereas the brown precipitates are an iron-oxygen-sulfur phase with 6 nearest O neighbors about Fe at an average distance of 1.95(1) {angstrom}.
Date: December 20, 1999
Creator: Antonio, M. R.; Tischler, M. L. & Witzcak, D.
Partner: UNT Libraries Government Documents Department

Solution spectroelectrochemical cell for in situ X-ray absorption fine structure

Description: A purpose-built spectroelectrochemical cell for in situ fluorescence XAFS (X-ray Absorption Fine Structure) measurements of bulk solution species during constant-potential electrolysis is described. The cell performance was demonstrated by the collection of europium L{sub 3}-edge XANES (X-ray Absorption Near Edge Structure) throughout the course of electrolysis of an aqueous solution of EuCl{sub 3}{center_dot}6H{sub 2}O in 1 M H{sub 2}SO{sub 4}. The europium L{sub 3}-edge resonances reported here for the Eu{sup III} and Eu{sup II} ions demonstrate that their 2p{sub 3/2} {yields} 5d electronic transition probabilities are not the same.
Date: June 12, 1995
Creator: Antonio, M.R.; Soderholm, L. & Song, I.
Partner: UNT Libraries Government Documents Department

Redox behavior of europium in the Preyssler heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-}

Description: In aqueous, mineral-acid electrolytes, the cyclic voltammetry of the europium- exchanged Preyssler heteropolyanion, [Eu{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-}, is unique among all the other trivalent-lanthanide-exchanged anions, [Ln{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-} for Ln {triple_bond} Ce-Lu. All [LnP{sub 5}W{sub 30}O{sub 110}]{sup 12-}, including Eu, form heteropoly blues upon reduction. In order to obtain insights about this issue, we conducted in situ Eu L{sub 3}-edge XANES (X-ray absorption near edge structure) spectroelectrochemical experiments on an aqueous solution of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} (5.5 mM) in a supporting electrolyte of 1 M H{sub 2}SO{sub 4} at two extreme potentials. The results demonstrate that the Eu{sup III} ion in the colorless Preyssler anion solution at open circuit potential (+0.21 V vs Ag/AgCl) is electroactive and is reduced to Eu{sup II} in the resulting dark blue solution from constant-potential bulk electrolysis at -0.55 V vs Ag/AgCl. This unusual redox behavior of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} may be of technological importance in the area of oxidation catalysis.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Complexants for actinide element coordination and immobilization

Description: The goal of this project is to develop inorganic metal oxide clusters known as polyoxoanions (POAs) as complexants for the immobilization of actinide (An) ions from high-level waste (HLW). A diverse array of rugged isopolyoxoanions, [M{sub x}O{sub y}]{sup z{minus}}, and heteropolyoxoanions, [X{sub a}M{sub b}O{sub c}]{sup d{minus}}, comprised of M = V, Mo, W and X = Si, P polyhedra will be investigated for their ability to incarcerate An ions. The research combines two objectives--An-POA coordination and An-POA containment. The first involves the synthesis, isolation, and characterization of POAs that can selectively bind An ions to form stable An-POA complexes in alkaline and acidic solutions. The second involves investigations of the thermochemistry of the An-POA complexes under vitrification conditions germane to the formation of proposed HLW forms, such as borosilicate glass. The approach is envisioned to provide two levels of An encapsulation for maximum stability and durability as well as the potential to incorporate higher levels of An ions (particularly Pu) in waste forms than now possible. Such versatility bodes well for the potential application of POAs as An complexants in technology of significance to the environmental management of HLW. This report summarizes work performed since the commencement of the project on 1 October 1998. As an overview of the research progress-to-date (15 June 1999), the strategic point is that selective binding of An ions by POAs depends upon the An valence. Actinide reduction-oxidation (redox) chemistry is a pivotal property in the proposed, rational use of POAs as coordinating ligands for An ions. Because POAs are oxidants and the transuranium elements are multivalent, the combined redox chemistry is rich and, oftentimes, confusing. The evidence of contrasting and conflicting valence behavior makes it difficult, if not impossible, to make broad generalizations about the collective properties of An-POA systems without appropriate experimentation. To ...
Date: March 14, 2000
Creator: Antonio, M.R.; Soderholm, L.; Williams, C.W. & Francesconi, L.C.
Partner: UNT Libraries Government Documents Department

The influence of desulfovibrio desulfuricans on neptunium chemistry.

Description: The role of biotic Np(V) reduction is studied in light of its potential role in the environmental immobilization of this hazardous radionuclide. The speciation of Np in Desulfovibrio desulfuricans cultures is compared with Np speciation in the spent medium and in the uninoculated medium. Precipitates formed in all three samples. Optical spectroscopy and X-ray absorption near edge structure (XANES) were used to determine that Np(V) is almost quantitatively reduced in all three samples and that the precipitate is an amorphous Np(IV) species. These results demonstrate that the reduction of Np is independent of Desulfovibrio desulfuricans. The underlying chemistry associated with these results is discussed.
Date: December 20, 1999
Creator: Soderholm, L.; Williams, C.; Antonio, M. R.; Tischler, M. L. & Markos, M.
Partner: UNT Libraries Government Documents Department

In situ Fe K-edge X-ray absorption fine structure of a pyrite electrode in a Li/polyethylene oxide (LiClO{sub 4})/FeS{sub 2} battery environment

Description: Electronic and structural properties of materials generated by the reduction and subsequent oxidation of pyrite in a lithium-based solid polymer electrolyte have been examined by in situ fluorescence Fe K-edge X-ray absorption fine structure (XAFS) in a FeS{sub 2}/Li battery environment. The XAFS results obtained are consistent with the formation of metallic iron as one of the products of the full (4-electron) discharge, in agreement with information reported in other laboratories. Extended X-ray absorption fine structure (EXAFS) data reveal that a subsequent 2-electron or 4-electron recharge generates a species with a Fe-S bond distance identical to that of pyrite, d(Fe-S) = 2.259 {angstrom}, with no other clearly detectable interactions due to more distant atoms. Based on the similarities between the metrical parameters and other features in the X-ray absorption near edge structure (XANES), the ferrous sites in these species appear to be tetrahedrally coordinated, as in chalcopyrite (CuFeS{sub 2}), for which d(Fe-S) is 2.257 {angstrom}, and, thus, different than in Li{sub 2} FeS{sub 2}, a material that exhibits longer Fe-S distances.
Date: December 31, 1996
Creator: Totir, D.; Bae, I.T.; Hu, Y.; Scherson, D.A. & Antonio, M.R.
Partner: UNT Libraries Government Documents Department

TETRAALKYLPHOSPHONIUM POLYOXOMETALATES AS NOVEL IONIC LIQUIDS.

Description: The pairing of a Lindqvist or Keggin polyoxometalate (POM) anion with an appropriate tetraalkylphosphonium cation, [R{sub 3}R{prime}P]{sup +}, has been shown to yield an original family of ionic liquids (POM-ILs), among them salts liquid at or near ambient temperature. The physicochemical properties of several such 'inorganic liquids', in particular their thermal properties, suggests the possible application of these compounds as robust, thermally-stable solvents for liquid-liquid extraction. A preliminary evaluation of the potential of POM-ILs in this application is presented.
Date: November 30, 2007
Creator: DIETZ,M.L.; RICKERT, P.G.; ANTONIO, M.R.; FIRESTONE, M.A.; WISHART, J.F. & SZREDER, T.
Partner: UNT Libraries Government Documents Department

In situ X-ray absorption fine structure studies of a manganese dioxide electrode in a rechargeable MnO{sub 2}/Zn alkaline battery environment

Description: Electronic and structural aspects of a MnO{sub 2} electrode in a rechargeable MnO{sub 2}/Zn battery environment have been investigated by in situ Mn K-edge X-ray absorption fine structure (XAFS). The relative amplitudes of the three major Fourier transform shells of the EXAFS (extended XAFS) function of the rechargeable MnO{sub 2} electrode in the undischarged state were found to be similar to those found for ramsdellite, a MnO{sub 2} polymorph with substantial corner-sharing linkages among the basic MnO{sub 6} octahedral units. The analyses of the background-subtracted pre-edge peaks and absorption edge regions for the nominally 1-e{sup {minus}} discharged electrode were consistent with Mn{sup 3+} as being the predominant constituent species, rather than a mixture of Mn{sup 4+} and Mn{sup 2+} sites. Furthermore, careful inspection of both the XANES (X-ray absorption near edge structure) and EXAFS indicated that the full recharge of MnO, which had been previously discharged either by a 1- or 2-equivalent corner-sharing linkages compared to the original undischarged MnO{sub 2}.
Date: December 31, 1996
Creator: Mo, Y.; Hu, Y.; Bae, I.T.; Miller, B.; Scherson, D.A. & Antonio, M.R.
Partner: UNT Libraries Government Documents Department

Coordination and valence of europium in [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(W{sub 5}O{sub 18}){sub 2}]{sup 9{minus}}

Description: Europium L{sub 3}-edge X-ray absorption fine structure (XAFS) spectroelectrochemistry was used to determine the valence of europium in [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(w{sub 5}O{sub 18}){sub 2}]{sup 9{minus}}. Dilute solutions of these anions in aqueous supporting electrolytes were examined at ambient temperature and at extreme potentials. In situ XANES (X-ray absorption near edge structure) data revealed that Eu is trivalent in both [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(W{sub 5}O{sub 18}){sub 2}]{sup 9{minus}} at rest potential. Furthermore, it was not reduced to Eu{sup 2+} by constant-potential bulk electrolysis at significantly reducing potentials under the electrochemical conditions used herein. These results stand in obvious contrast to the redox behavior of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12{minus}}, in which Eu{sup 3+} is reduced to Eu{sup 2+} under similar electrochemical conditions.
Date: September 1, 1997
Creator: Antonio, M.R.; Soderholm, L.; Jennings, G.; Francesconi, L.C.; Dankova, M. & Bartis, J.
Partner: UNT Libraries Government Documents Department