One- and two-electron reduction of chromium(VI) by polyaminocarboxylatocobaltate(II) complexes and the formation of chromium(V) and chromium(IV)

The kinetics of the oxidation of Co^IILⁿ complexes {where L = ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), or N-(2-hydroxyethyl)ethylenediaminetriacetate (HEDTA)} by Cr^VI were studied under pseudo-first-order conditions with [Co^IILⁿ] ? [Cr^VI]. The kinetics showed first-order dependence on [Cr^VI]. The rate constant, k _obs, decreases with increasing concentration of [Cr^VI]. At constant [H⁺], ionic strength, and temperature, the rate law is described by Eq. (i)

$$ - {\text{d}}\left[ {{\text{Cr}}^{\text{VI}} } \right] / {\text{dt}} = \left\{ {{\text{k}}_{ 2} \left[ {{\text{Co}}^{\text{II}} {\text{L}}^{\text{n}} } \right]{\text{ + k}}_{ 3} \left[ {{\text{Co}}^{\text{II}} {\text{L}}^{\text{n}} } \right]^{ 2} } \right\}\left[ {{\text{HCrO}}_{4}^{ - } } \right] $$

(i)

Both k ₂ and k ₃ showed acid-dependent and acid-independent pathways. The direct conversion Co^IILⁿ to Co^IIIL^m is ruled out by spectrophotometric and ESR spectroscopic measurements that showed the formation of initial reaction intermediate(s). The rate law is consistent with one-electron and concurrent two-electron transfers leading to the formation of Cr^V and Cr^IV, respectively. An inner-sphere process, at least for the first term, leading to the formation of a relatively stable Cr^V species is almost certain. The kinetic term showing second-order dependence on [Co^IILⁿ], most likely, involves concurrent two-electron transfer leading to the formation of Cr^IV. The type of rate law and the proposed mechanism, reported here, depart from the well-established rate laws observed and mechanisms proposed for the oxidation of one-electron reductants by Cr^VI.

     

Micro-determination of As(V), V(V), Mo(VI), W(VI) in the presence of Cu(II), Ni(II) and Zn(II)

A rapid procedure is described for the separation and determination of 0.025 mg to 1.0 mg quantities of As(V), V(V), Mo(VI) and W(VI) from small quantities of Cu(II), Ni(II), and Zn(II) using silica gel as the selective sorbent for the cations. The individual anionic components, which remain in the supernatant solution after separation from the cations, are determined by colorimetric methods. The complete recovery of As(V) in supernatant solution has also been tested radiometrically using⁷⁶As as the radioactive indicator. The sorbed cations after extraction with dilute hydrochloric acid are determined by EDTA titrations.     

Vanadium(V), Cer(IV) und Chrom(VI)

Ohne Zusammenfassung     

Modeling Speciation and Solubility in Aqueous Systems Containing U(IV,VI), Np(IV,V, VI), Pu(III,IV, V,VI), Am(III), and Cm(III)

A comprehensive thermodynamic model, referred to as the Mixed-Solvent Electrolyte model, has been applied to calculate phase equilibria and chemical speciation in selected aqueous actinide systems. The solution chemistry of U(IV, VI), Np(IV, V, VI), Pu(III, IV, V, VI), Am(III), and Cm(III) has been analyzed to develop the parameters of the model. These parameters include the standard-state thermochemical properties of aqueous and solid actinide species as well as the ion interaction parameters that reflect the solution’s nonideality. The model reproduces the solubility behavior and accurately predicts the formation of competing solid phases as a function of pH (from 0 to 14 and higher), temperature (up to 573 K), partial pressure of CO₂ (up to \( p_{{{\text{CO}}_{2} }} \)  = 1 bar), and concentrations of acids (to 127 mol·kg^?1), bases (to 18 mol·kg^?1), carbonates (to 6 mol·kg^?1) and other ionic components (i.e., Na⁺, Ca²⁺, Mg²⁺, OH^?, Cl^?, \( {\text{ClO}}_{4}^{ - } \), and \( {\text{NO}}_{3}^{ - } \)). Redox effects on solubility and speciation have been incorporated into the model, as exemplified by the reductive and oxidative dissolution of Np(VI) and Pu(IV) solids, respectively. Thus, the model can be used to elucidate the phase and chemical equilibria for radionuclides in natural aquatic systems or in nuclear waste repository environments as a function of environmental conditions. Additionally, the model has been applied to systems relevant to nuclear fuel processing, in which nitric acid and nitrate salts of plutonium and uranium are present at high concentrations. The model reproduces speciation and solubility in the U(VI) + HNO₃ + H₂O and Pu(IV, VI) + HNO₃ + H₂O systems up to very high nitric acid concentrations (\( x_{{{\text{HNO}}_{3} }} \approx 0.70 \)). Furthermore, the similarities and differences in the solubility behavior of the actinides have been analyzed in terms of aqueous speciation.     

Photoelectron spectra of uranium(IV), (V) and (VI) complexes

Satellites were observed on 4f photoelectron spectra of uranium (IV) complexes, while none was seen for diamagnetic uranyl complexes. Photoelectron lines of oxygen 1s coordinated to the uranium ion were broad for NaUO₃ and uranyl complexes.     

Electrometric titrations of Cr(VI), Mn(IV), V(V), Co(III) and U(VI) with a standard iron(II) solution in alkaline media containing hexitols

Direct and indirect potentiometric, bipotentiometric and biamperometric titrations with a standard iron(II) solution are described for some inorganic compounds in alkaline media containing hexitols (mannitol, dulcitol and sorbitol). The optimal conditions for titrations based on the Cr(VI) → Cr(III), Mn(IV) → Mn(III) → Mn(II), V(V) → V(IV), Co(III) → Co(II) and U(VI) → U(IV) systems are discussed. Of the hexitols studied, sorbitol has the greatest effect on the value of the redox potential of the Fe(III)/Fe(II) system; the E_f° value is about —1.10 V vs. SCE.     

Investigation of removal of Cr(VI), Mo(VI), W(VI), V(IV), and V(V) oxy-ions from industrial waste-waters by adsorption and electrosorption at high-area carbon cloth

Adsorption and electrosorption of Cr(VI), Mo(VI), W(VI), V(IV), and V(V) ions from water samples at low concentration were studied at high-area C-cloth electrodes. The concentrations of ions in the solution were monitored using in situ UV spectroscopy. All the investigated ions, except V(IV), showed better adsorption in acidic media. Positive polarization of the C-cloth caused increased adsorption of Cr(VI), Mo(VI), and V(V) ions. When previously adsorbed, Mo(VI) and V(V) ions were shown to be largely desorbable by negative polarization of the C-cloth. Since V(IV) does not become adsorbed significantly at the C-cloth in acidic media, the method provides an interesting means for separation of V(V) and V(IV) species in solution.     

Kinetic studies on the bromate ion oxidation of 12-tungstocobaltate(II) in aqueous acid

The oxidation of Co^IIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [Co^IIW] and [Br^v], and exhibits a complex dependence on [H⁺]. These observations were successfully explained by considering HBrO₂, one of the intermediates formed in the direct but slow reaction between Co^IIW and bromine(V), as the reacting species. The first-order limiting dependence in [H⁺] was due to the involvement of a protic equilibrium of HBrO₂. The induction period appears due to the scavenging effect of Br^– inadvertently present in the medium. It appears to be the first report where HBrO₂ was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO^– ₃.     

Molybdenum(VI), (V) and (IV) complexes with chiral benzoin thiosemicarbazone

The chiral (ONS) dianionic Schiff base ligand benzoin thiosemicarbazone (H₂L) reacts with MoO₂(acac)₂ to give the polymeric complex [(MoO₂L) _n ] (1) (Type 1). The reaction of MoO₂L with pyridine (py), 3-picoline (3-pic) or 4-picoline (4-pic) gives [Mo^VIO₂LD] (D = py, 3-pic or 4-pic) (Type 1). Further, the reaction of [MoO₂L] or [MoO₂LD] with PPh₃ or reaction of [MoO₂L] with PPh₃ (plus bpy or phen, D) in the presence of donor reagents D gives [Mo^IVOL] or [Mo^IVOLD] (Type 2). On the other hand, the reaction of [MoO₂L] with hydrazides (zdhH₃) such as benzoylhydrazine (bhH₃), isonicotinoylhydrazine (inhH₃), nicotinoylhydrazine (nhH₃), salicyloylhydrazine (slhH₃) and thiosemicarbazide (tscH₃) produced non-oxo–diazenido complexes [MoL(zdh)] (Type 3). The complexes have been characterized by elemental analyses, molar conductance, magnetic moment, electronic, i.r. and e.s.r. spectroscopic measurements.     

Biphasic oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) by N-bromosuccinimide and the formation of chromium(IV) and chromium(V)

The kinetics of oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) complex, [Cr^III(phen)(H₂O)₂Cl₂]⁺, by N-bromosuccinimide (NBS) is biphasic. The first faster step involves the oxidation of Cr(III) to Cr(IV). The second slower step is due to the oxidation of Cr(IV) to Cr(V). The reaction product is isolated and characterized by electron spin resonance (ESR), IR, and elemental analysis. The chromium(V) product is consistent with the formula [Cr^V(phen)Cl₂(O)]Br. The rate constants k_f and k_s, for the faster and the slower steps respectively, were obtained using an Origin 9.0 software program. Values of both k_f and k_s, varied linearly with [NBS] at constant reaction conditions. The effect of pH on the reaction rate is investigated over the pH (4.11–6.01) range at 25.0°C. The rate constants k_f and k_s increased with increasing pH. This is consistent with hydroxo forms of the chromium species being more reactive than the aqua forms. Chromium(III) complexes, more often than not, are inert. The oxidation of the Cr(III) complex to Cr(IV), most likely, proceeds by an outer sphere mechanism. Since chromium(IV) is labile the mechanism of its oxidation to chromium(V) is not certain.     

Acridone — A new reagent for the detection of cerium(IV), chromium(VI), and vanadium(V) in binary or ternary mixtures

Summary A new scheme for the detection of Ce(IV), Cr(VI) and V(V) in binary or ternary mixtures is reported. The procedure is based on the reaction of these species with acridone to give a rose-red oxidation product, combined with methods of selective reduction of Ce(IV) and Cr(VI) in the mixtures. The method is free from a number of interferences that are encountered in the diphenylcarbazide, diphenylamine and benzidine tests and does not require prior separation of the constituents.

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Zusammenfassung Ein neues Nachweis-Schema für Ce(IV), Cr(VI) und V(V) in binären oder ternären Gemischen wurde beschrieben. Es beruht auf der Reaktion dieser Elemente mit Acridon, wobei ein rosarotes Oxydationsprodukt entsteht, in Kombination mit der selektiven Reduktion von Ce(IV) und Cr(VI) in diesen Mischungen. Die angegebene Arbeitsweise ist frei von einigen Störungen der Nachweise mit Diphenylcarbazid, Diphenylamin bzw. Benzidin und erfordert nicht die vorhergehende Trennung der einzelnen Bestandteile der erwähnten Gemische.

     

Die quantitative Oxydation von Methanol (I), ?thyl- (II), Propyl- (III), Isopropyl (IV), Butyl- (V) und Isobutylalkohol (VI)

Ohne Zusammenfassung     

Monomeric dioxouranium(VI), chromium(III), cobalt(II), nickel(II) and copper(II) complexes with primary cellulose acetate (PCA)

Monomeric UO ₂ ²⁺ , Cr^III, CO^II, Ni^II and Cu^II complexes with primary cellulose acetate (PCA) have been prepared and characterized. Infrared,¹H NMR, UV/visible spectroscopy, elemental analysis, therniogravimetry, conductance and magnetic measurements were used to assign the mode of coordination in the isolated species. The investigation revealed that PCA exhibits octahedral coordination with Cr^III, Co^II, Ni^II and a square planar form with Cu^II whereas the UO₂ moiety is virtually linear. PCA acts as a neutral bidentate chelating agent via the two oxygen atoms of the vicinal ester groups in the secondary positions forming a five-membered chelate ring. A comparative study between chelates of PCA and those previously prepared with secondary cellulose acetate (SCA) has been undertaken.     

Heterobinuclear and Heterotrinuclear complexes of Oxorhenium(V) with Cu(II), Ni(II), Fe(III), UO2(VI) and Th(IV) in the solid state

New heteronuclear complexes containing oxorhenium(V), Cu(II), Ni(II), Fe(III), UO₂(VI) and Th(IV) ions were prepared by the reaction of the complex ligand, [ReO(H₄L)Cl]Cl₂, where H₄L = 8,17-dimethyl-6,15-dioxo-5,7,14,16-tetrahydrodibenzo[a,h][14]annulene-2,11-dicarboxylic acid, with the previous transition and actinide salts. Three heteronuclear Cu(II) complexes were isolated depending on the ratio of [ReO(H₄L)Cl]Cl₂?:?Cu(II) ion. When the ratios were 1?:?0.5, 1?:?1 and 1?:?2, the heteronuclear complexes {[ReO(H₃L)Cl]₂CuCl₂(OH₂)₂}SO₄ · H₂O (I), [ReO(H₃L)Cl₂Cu(OH₂)₂(SO₄)] (II) and {ReO(H₂L)Cl[Cu(OH₂)₃ SO₄]₂} (III) were obtained, respectively. Heteronuclear complexes of the other metal cations were obtained by mixing [ReO(H₄L)Cl]Cl₂ with the metal salt in the ratio 1?:?1 to obtain the heteronuclear complexes [ReO(H₃L)Cl₂Ni(OH₂)₂](NO₃)₂ (IV), [ReO(H₃L)Cl₃Fe(OH₂)₃](NO₃)₂ (V), [ReO(H₃L)ClUO₂(NO₃)₂ (OH₂)]Cl (VI) and [ReO(H₃L)Cl₃Th(NO₃)₂(OH₂)]NO₃ · 2H₂O (VII). The complex ligand coordinates with the heterometal ion via the carboxylate group, and the infrared bands ν_as COO and ν_s COO indicate that the carboxylate acts as a unidentate ligand to the heterometal cations. Cu(II) and Fe(III) cations in the heteronuclear complexes have octahedral geometry, while Ni(II) is square planar. Thermal studies explored the possibility of obtaining new heteronuclear complexes pyrolytically in the solid state from the corresponding mother complexes. The structures of the complexes were elucidated by conductance, IR and electronic spectra, magnetic moments, ¹H NMR and TG-DSC measurements as well as by mass spectroscopy.     

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O_{2 3}]·3H₂O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O₂)₂(H₂O)] and VOSO₄ were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO₄. In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)₃, on being reacted with a hydrogen peroxide adduct, KF·H₂O₂, and bpy and phen afforded crystalline [Mn(acac)₂(bpy)] and [Mn(acac)₂(phen)], respectively. The X-ray structural analysis of [Mn(acac)₂(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac⁻(C₅H₅O ₂ ⁻ ) and a phen ligand with the molecule lying on two-fold axis. Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C₅H₅NH[CrO₃F] (PFC), and quinolinium fluorochromate C₉H₇NH [CrO₃F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ₁. The structure consists of discrete pyridinium cations and CrO₃ F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO₃ F]⁻ ion lies on a crystallographic mirror plane.