Some reactions of iron (III) and chromium (III) fluorides with oxides

Reactions of FeF₃ with several oxides at elevated temperatures are described. Reaction products were usually Fe₂O₃ and the fluoride of the other element. With higher valency elements complete fluorine exchange did not always occur and oxyfluorides were formed. Intermediates in the reactions include oxyfluorides and mixed oxides, again only found with higher valency elements. Some shorter studies on the reaction of CrF₃ with oxides are included for comparisons, the reactions observed being generally similar.     

Solid-state mechanochemical synthesis of cobalt(III), iron(III), and chromium(III) bisdicarbollyl complexes

Thallous dicarbollide reacts with cobalt(II), iron(III) and chromium(III) chlorides without a solvent under conditions of mechanical activation to form the corresponding carborane complexes of tervalent metals. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1715–1717, October, 1993.     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex (lambda(max) = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.     

Triamidoamine complexes of chromium(III) and chromium(IV)

Treatment of [CrCl3(THF)3] with slightly more than 1 equiv of Li3(N3N) [(N3N)(3-) = ((Me3SiNCH2CH2)3N)(3-)] affords the triamidoamine complex [Cr(N3N)] (1) in 75% yield. 1 is oxidized by PhICl2, CuCl2, or AgCl to give the chromium(IV) complex [Cr(N3N)Cl] (2) in moderate yields. Alternatively, complex 2 is obtained directly from [CrCl3(THF)3] in 50% yield after treatment with 0.5 equiv of Li3(N3N). Both compounds are high-spin complexes bearing three and two unpaired electrons, respectively. Their molecular structures are described revealing a trigonal monopyramidal and trigonal bipyramidal coordination geometry of the chromium center, respectively.     

Prediction and correlations between the stability constants of mono- and polynuclear chromium(III) and iron(III) complexes

Correlations between the experimentally determined stability constants of mono- and polynuclear chromium(III) and iron(III) complexes are discussed. An equation to evaluate the stability constants of mono- and polynuclear chromium(III) complexes is obtained: \(\log \beta [Cr_p^{3 + } (L_i )_{q_i } ] = 0.84\log \beta [Fe_p^{3 + } (L_i )_{q_i } ]\) .     

Porosity of some iron(III), chromium(III), and zirconium(IV) hydroxide oxide xerogels

Porosity and density in water are studied for xerogels prepared by drying iron(III), chromium(III), and zirconium(IV) hydroxide oxide (HO) hydrogels. The hydrogels are either freshly precipitated at pH 7–11 or aged in sodium chloride or sodium sulfate solutions. The space distribution in the xerogels between the volume occupied by the constituent ions and the interstitial volume (spaces between metal-oxygen chains, mesopores, micropores, and macropores) is determined. The meso-and micropore volumes of the chromium(III) HO xerogels are two to four times the volumes of iron(III) and zirconium(IV) HO xerogels. We suggest that the microstructure of the chromium(III) HO hydrogels is almost fully inherited by their xerogels.     

Cyclopentadienyl mesityl complexes of chromium(II) and chromium(III)

Chromium(III) mesityl complexes were synthesized by protonolysis of chromocene with 1,3-diisopropylimidazolium chloride or DBU hydrochloride, salt metathesis with MesMgBr, and single electron oxidation with iodine.     

The reaction of neodymium(III) oxide with chromium(III) oxide

The reaction of Nd₂O₃ and Cr₂O₃ in air has been studied in the temperature range 350–950°C. The nature and quantity of products formed was investigated primarily by an analytical scheme developed to permit the determination of the amounts of unreacted Nd₂O₃ and Cr₂O₃ and the amounts of possible products. From 350–600°C the sole product was Nd₂(CrO₄)₃, from 630–840°C the products were Nd₂(CrO₄)₃ and NdCrO₃, and from 880 to 950°C the sole product was NdCrO₃. The variation with temperature of the amounts of products formed at constant reaction time was investigated. The kinetics of the reaction were investigated at the following temperatures, 630, 650, 680, 700, 720 and 760°C. At each temperature, with increasing time the amount of Nd₂(CrO₄)₃ formed increased to a maximum and then decreased whereas the amount of NdCrO₃ formed increased continually. The results together with experiments on the effect of oxygen and argon atmospheres are interpreted as follows. NdCrO₃ is not formed by direct combination of Nd₂O₃ with Cr₂O₃. Instead the reaction of the two oxides produces Nd₂(CrO₄)₃, the thermal decomposition of which then leads to the formation of NdCrO₃. The absence of NdCrO₄ as a reaction product is investigated and discussed as is the absence of NdCrO₃ as a reaction product below 630°C.     

Sorption of hydrolytic products of iron(III), aluminium(III) and chromium(III) on the silica column and its analytical use

Summary The influence of pH upon the sorption of hydrolytic products of Fe³⁺, Al³⁺, and Cr³⁺ on silica was studied under kinetic conditions. The capacity of the silica column and the influence of ionic strength upon the sorption were investigated. The results obtained are utilized for the pre-concentration of trace amounts of Al³⁺, and Fe³⁺ and their separation from an excess of several other metals (e.g. Cr, Cu, Zn, Co) at pH 4.5. The separation of Al³⁺ traces from an excess of Fe³⁺ was achieved by reduction and masking of Fe with thioglycollic acid.

---

Zusammenfassung Es wurde eine Untersuchung durchgeführt über die Sorption von Hydrolyseprodukten von Fe(III), Al(III) und Cr(III) an Silicasäulen und die Abhängigkeit vom pH-Wert, von der Kapazität der Säule und der Konzentration an Fremdsalzen (KCl, KNO₃) wurde geprüft. Analytische Anwendungsmöglichkeiten ergaben sich in der Anreicherung von Al³⁺- und Fe³⁺-Spuren und ihrer Trennung von anderen Elementen (z.B. Cr, Cu, Zn, Co) sowie in der Trennung von Al³⁺-Spuren von überschüssigem Fe³⁺, wobei letzteres mit Hilfe von Thioglykolsäure reduziert und maskiert wurde.

     

Surface speciation of As(III) and As(V) in relation to charge distribution

The adsorption of As(III) and As(V) on goethite has been studied as a function of pH and loading. The data can be successfully described with the charge distribution (CD) model (extended Stern layer option) using realistic species observed by EXAFS. The CD values have been derived theoretically. Therefore, the Brown bond valence approach has been applied to MO/DFT optimized geometries of a series of hydrated complexes of As(III) and As(V) with Fe(III) (hydr)oxide. The calculated ionic CD values have been corrected for the effect of dipole orientation of interfacial water, resulting in overall interfacial CD coefficients that can be used to describe the surface speciation as a function of pH and loading. For As(III), the main surface species is a bidentate complex and a minor contribution of a monodentate species is found, which is in agreement with EXAFS. The CD values have also been fitted. Such an analysis of the adsorption data resulted in the same surface species. The fitted CD values for the bidentate complex points to the presence of strong AsO bonds with the surface and a weaker AsOH bond with the free OH ligand. This agrees quantitatively with the MO/DFT optimized geometry. Interpretation of free fitted CD values for As(V) binding suggests that the main surface species is a non-protonated bidentate complex (B) with a contribution of a singly protonated surface complex (MH) at sub-neutral pH and high loading. In addition, a protonated bidentate surface complex (BH) may be present. The same species are found if the theoretical CD values are used in the data analysis. The pH dependency of surface speciation is strongly influenced by the charge attribution of adsorbed species to the electrostatic surface plane while the effect of loading is primarily controlled by the amount of charge attributed to the 1-plane, illustrating the different action of the CD value. The MO/DFT geometry optimizations furthermore suggest that for As(V) the B, MH and BH surface complexes may have very similar AsFe distances which may complicate the interpretation of EXAFS data.     

Microscopic detection of chromium as chromium(III)

Summary Trisodium phosphate is recommended as a reagent for the microscopic detection of chromium (III). Sensitivity of the test is 6 of chromium (III) in a volume of 0.01 ml. Of particular importance is the fact that aluminum and iron (III) do not react with the reagent to form crystalline precipitates.

---

Zusammenfassung Tertiäres Natriumphosphat gibt mit Chrom(III)-Lösungen eine charakteristische Fällung, in der unter dem Mikroskop rechteckige Kristalle zu erkennen sind. Weder Aluminium noch Eisen(III) gibt mit diesem Reagens einen kristallinen Niederschlag. Die Reaktion gestattet den Nachweis von 6 Chrom in 0,01 ml Lösung. Auch Quecksilber(II) gibt charakteristische Kristalle.

---

Résumé On recommande le phosphate trisodique comme réactif pour la recherche microscopique du chrome-III. La sensibilité de l'essai est 6 de chrome-III dans un volume de 0,01 ml. Le fait que l'alumine et le fer-III ne se combinent pas avec le réactif pour former des précipités cristallins présente une importance particulière.

---

---

With 2 figures.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Sorption of chromium(III) and chromium(VI) on lead sulfide

The sorption of chromium(III) and chromium(VI) on lead sulfide has been investigated in dependence on pH, time of sorption and the concentrations of sorbate and sorbent. The mechanisms of the sorption of Cr³⁺ and CrO ₄ ^2– traces on lead sulfide are discussed; a difference between CrO ₄ ^2– sorption on PbS and -Fe₂O₃ has been found. Sulfates and molybdates affect the removal of chromates from aqueous solutions. Lead sulfide carrier prepared in this work was also used for the preconcentration of chromium(III) and chromium(VI) from tap water.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

The reaction of phenylarsenazo with chromium(III)

The conditions for the reaction between phenylarsenazo (PAA) (2-[(2-arsonophenyl)azoj-7-(phenylazo)-1, 8-dihydroxynaphthalene-3,6-disulphonic acid) and chromium(III) have been studied. A blue 1:1 complex is formed at pH 2.2 on heating the reactants at 100 degrees for 15 min. It has maximum absorption at 635 nm and is stable for at least 24 hr. The molar absorptivity is 3.3 x 10(4) 1.mole(-1).cm(-1). Beer's law is obeyed in the chromium concentration range 0-1.4 mug ml . The reaction has been successfully applied to determination of chromium in alloy steel.