Sequential potentiometric complexometric redox determination of iron(III) and cobalt(II) with application to alloys

A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys.     

Solid-liquid equilibrium diagrams of common ion binary salt hydrate mixtures involving nitrates and chlorides of magnesium, cobalt, nickel, manganese, and iron(III)

The solid-liquid equilibrium diagrams of binary mixtures involving magnesium nitrate hexahydrate with cobalt nitrate hexahydrate, nickel nitrate hexahydrate (partly), manganese nitrate tetrahydrate, and iron(III) nitrate nonahydrate and of magnesium chloride hexahydrate with cobalt and nickel chlorides hexahydrates and manganese chloride tetrahydrate, and the of two manganese salts were determined. Those diagrams that showed a simple eutectic were fitted by the Ott equation and where the required BET parameters were available, the magnesium salt rich parts of the liquidus were modeled by means of this method.     

Iron(II), cobalt(III), nickel(II) and copper(II) chelates of furan and thiophene azo-oximes

Summary Complexes of furan and thiophene azo-oximes with iron(II), cobalt(III), nickel(II) and copper(II) have been prepared and characterised. Iron(II), cobalt(III) and copper(II) complexes are diamagnetic in the solid state. The diamagnetism of the copper(II) chelates is suggestive of antiferromagnetic interaction between two copper centres.¹H n.m.r. spectral data suggest atrans-octahedral geometry for the tris-chelates of cobalt(III). Nickel(II) complexes are paramagnetic, in contrast to the diamagnetism of the analogous complexes of arylazooximes. The electronic spectra are suggestive of octahedral geometry for the iron(II), cobalt(III) and nickel(II) complexes, andD _4h -symmetry for copper(II). Infrared data indicate N-bonding of the oximino-group to the metal ions.     

Synthesis and spectral properties of cobalt(II) and cobalt(III) tetraarylporphyrinates

Reactions of 5,10,15,20-tetraphenylporphin, 5,10,15,20-tetra(4′-methoxyphenyl)porphyrin, and 5,10,15,20-tetra(4′-chlorophenyl)porphyrin with cobalt(II) acetate in dimethylformamide were studied by spectrophotometry. The corresponding cobalt(II) porphyrinates were synthesized and identified. The corresponding cobalt porphyrinates in +3 oxidation state were obtained by reaction of cobalt(II) 5,10,15,20-tetraphenylporphyrinate and cobalt(II) 5,10,15,20-tetra(4′-methoxyphenyl)porphyrinate with 2,3-dichloro-5,6-dicyano-p-benzoquinone in chloroform. The oxidation of cobalt(II) 5,10,15,20-tetra(4′-chlorophenyl)porphyrinate with hydrochloric acid in dimethylformamide leads to cobalt(III) porphyrinate.     

Studies on extraction of iron(III) and cobalt(II) chlorides by quaternary ammonium halides

Summary The extraction of iron(III) and cobalt(II) from hydrochloric acid solutions by Hyamine 1622, a quaternary ammonium halide, in dichloroethane is described. The effect of acidity, salting-out agent, metal and extradant concentrations and temperature, has been investigated. The extraction mechanism is discussed in the light of results obtained. Separation of iron(III) and cobalt(II) is also outlined.     

Reactions of diiron(III) tris[(1-hydroxyethylidene)diphosphonate] tetrahydrate and iron(III) tris[(1-hydroxyethylidene)diphosphonate] tetrahydrate with <Emphasis Type="Italic">p</Emphasis>-aminobenzoic acid. Molecular structure of bis(4-carboxyphenylaminium) (1-hydroxyethylidene)diphosphonate

Diiron(III) tris[(1-hydroxyethylidene)diphosphonate] tetrahydrate and iron(III) tris[(1-hydroxyethylidene) diphosphonate] tetrahydrate react with p-aminobenzoic acid in water to form diiron(III) pentakis(4-carboxyphenylaminium) tris(1-hydroxyethylidene)diphosphonate dihydrate and iron(III) hexakis(4-carboxyphenylaminium) tris(1-hydroxyethylidene)diphosphonate dihydrate. The crystal structure of bis(4-carboxyphenylaminium) (1-hydroxyethylidene)diphosphonate obtained by the reaction of (1-hydroxyethylidene)diphosphonic acid with p-aminobenzoic acid in methanol was established.     

Model Compounds for Iron Proteins. Structures and Magnetic, Spectroscopic, and Redox Properties of Fe(III)M(II) and [Co(III)Fe(III)](2)O Complexes with (&mgr;-Carboxylato)bis(&mgr;-phenoxo)dimetalate and (&mgr;-Oxo)diiron(III) Cores

A series of heterobimetallic complexes of the type [Fe(III)M(II)L(&mgr;-OAc)(OAc)(H(2)O)](ClO(4)).nH(2)O (2-5) and [{Fe(III)Co(III)L(&mgr;-OAc)(OAc)}(2)(&mgr;-O)](ClO(4))(2).3H(2)O (6) where H(2)L is a tetraaminodiphenol macrocyclic ligand and M(II) = Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The (1)H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV-vis spectra of 2-5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (&mgr;-acetate)bis(&mgr;-phenoxide)-Ni(II)Fe(III) core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear Co(III)Fe(III) units are bound by an Fe-O-Fe linkage. 6 crystallizes in the orthorhombic space group Ibca with a = 17.577(4) ?, b = 27.282(7) ?, c = 28.647(6) ?, and Z = 8. The two iron(III) centers in 6 are strongly antiferromagnetically coupled, J = -100 cm(-1) (H = -2JS(1).S(2)), whereas the other two S(1) = S(2) = (5)/(2) systems, viz. [Fe(2)(III)(HL)(2)(&mgr;-OH)(2)](ClO(4))(2) (1) and the Fe(III)Mn(II) complex (5), exhibit weak antiferromagnetic exchange coupling with J = -4.5 cm(-1) (1) and -1.8 cm(-1) (5). The Fe(III)Ni(II) (3) and Fe(III)Co(II) (4) systems, however, exhibit weak ferromagnetic behavior with J = 1.7 cm(-1) (3) and 4.2 cm(-1) (4). The iron(III) center in 2-5 exhibits quasi-reversible redox behavior between -0.44 and -0.48 V vs Ag/AgCl associated with reduction to iron(II). The oxidation of cobalt(II) in 4 occurs quasi-reversibly at 0.74 V, while both nickel(II) and manganese(II) in 3 and 5 undergo irreversible oxidation at 0.85 V. The electrochemical reduction of 6 leads to the generation of 4.     

Dosage electrochimique du cobalt: I. Etude des Courbes Intensité— Potentiel du Système cobalt(III)/cobalt(II) en Milieu Picolique

Electrochemical determination of cobalt. Part I. Studies of current—voltage curves of the cobalt(III)/cobalt(II) system in picolinic acid mediaAs a preliminary to the development of electrochemical determinations of cobalt in steels, current—voltage curves at a platinum electrode were studied for the systems coblt(III)/cobalt(II) and iron(III)/iron(II) in media containing picolinic acid as complexing agent. Iron(III) oxidizes cobalt(II) in this complexmg medium, and the iron-(II) formed can be determined by an oxidant such as cerium(IV).     

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.     

Cobalt(III) tetrabenzoporphyrin: Synthesis,spectral and coordination properties

Comparison of tetrabenzoporphyrin complexation reactions and transmetalation of cadmium(II) tetrabenzoporphyrinate with cobalt(II) acetate and chloride in dimethylformamide (DMF) has been carried out Cobalt(III) tetrabenzoporphyrinate has been prepared and identified. Acido ligands displacement in Co(III) tetrabenzoporphyrinate by pyridine, imidazole, and quinuclidine molecules has been studied.     

Coordination compounds of hydrazine derivatives with transition metals,part XVIII. Cobalt(II) and cobalt(III) chelates with schiff bases derived from hydrazine-S-methyldithiocarboxylate and thiosemicarbazide

Summary The reactions of aldehydic and ketonic Schiff bases derived from hydrazine-S-methyl dithiocarboxylate and thiosemicar-bazide with cobalt(II) acetate were investigated. Octahedral tris ligand cobalt(III) chelates were formed with aldehydic Schiff bases whereas tetrahedral bis ligand cobalt (II) chelates were isolated with ketonic Schiff bases.N-isopropylidene hydrazine-S-methyldithiocarboxylate, however, gave both octahedral tris cobalt(III) and tetrahedral bis cobalt(II) chelates. These results are interpreted in terms of the steric requirements of the Schiff base used.     

Spectrophotometry Determination of Iron(III) and Cobalt(II) with Salicylaldehyde Hydrazone (SH)

Iron and cobalt complexation with salicylaldehyde hydrazone (SH) has been studied spectrophotometrically employing solvent extraction technique. The Fe(III)-SH (1:3) and Co-SH (1:2) complex absorb at 510nm and 450 nm respectively. The sensitivity of the colour reactions are 0.014 and 0.005 in terms of Sandell's definition for iron and cobalt systems. Both the complexes show maximum and constant absorbance in the pH ranges 3.5 to 5.0 and 6.2 to 7.0 for Fe(III)-SH and Co(II)-SH respectively. The complexation has been used in the spectrophotometric determination of iron and cobalt in coexistence with several ions.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Synthesis, structure and spectroscopic behaviors of a five- and six-coordinated tri-cobalt(II) cluster: [(CoL)2(OAc)2Co].2C2H5OH

A tri-nuclear cobalt(II) cluster, [(CoL)2(OAc)2Co].2C2H5OH, has been synthesized by the reaction of cobalt(II) acetate tetrahydrate with a novel Salen-type bisoxime chelating ligand, 3,3'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L), and characterized by elemental analyses, IR spectra, TG-DTA and molar conductances. UV-vis spectroscopic titration in methanol solution clearly indicated the exclusive formation of the 3:2 [Co3L2]2+ cluster. The single-crystal X-ray diffraction determination of the Co(II) cluster shows that there are two acetate ions coordinate to three cobalt(II) ions through Co-O-C-O-Co bridges, and quadruple mu-phenoxo oxygen atoms from two [CoL] chelates also coordinate to cobalt(II) ions. Interestingly, different conformational central ions: five- and six-coordinated geometries were found in the cluster.     

Amperometric titrations of cobalt(II) with hexacyanoferrate(III) in ammonium citrate and glycine media

An amperometric titration of cobalt(II) with hexacyanoferrate(III) in aqueous ammonium citrate or aqueous glycine solution at pH 9.8 or pH 8.0 respectively, is reported. Cobalt concentrations of 2-30 mg/l were successfully determined. In citrate solutions cerium(III) and iron(III) interfered, and in glycine solutions, copper(II) and vanadium(V).     

Synthesis,magnetic and spectral studies of iron(III) and cobalt(II,III) complexes of 4-formylantipyrine N(4)-substituted thiosemicarbazones

The synthesis and characterization of complexes of iron(III), cobalt(II) and cobalt(III) with 4-formylantipyrine N(4)-methyl-, N(4)-dimethyl-, and 3-piperidylthiosemicarbazones are reported. Elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., electronic and e.s.r.) studies have been used to elucidate the nature of the metal complexes. The i.r. spectra show that the thiosemicarbazones behave as bidentate or tridentate ligands, either in the thione or thiolato form. Different stereochemistries are proposed for the various cobalt(II) complexes on the basis of spectral and magnetic studies. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.     

Ion Exchange Treatment of Cobalt Acetate Solutions to Remove Iron(III) Impurity

Russian Journal of Applied Chemistry - The possibility of removing an iron(III) impurity from cobalt acetate solutions by sorption was examined. Among a number of tested ion exchange resins with...     

Sorption of small amounts of cobalt(II) on iron(III) oxide

Summary The sorption of small amounts of cobalt(II) on iron (III) oxide has been studied as a function of pH. The mechanism of sorption is discussed. Iron (III) oxide carrier can be used for the preconcentration of small or trace amounts of cobalt(II). The influence of EDTA, glycine,L(+)-arginine andL(+)-cysteine on the sorption yields of cobalt(II) has also been studied.

---

Zusammenfassung Die Abhängigkeit der Adsorption geringer Mengen Co (II) an Eisen (III)-hydroxid vom pH wurde untersucht und der Mechanismus der Adsorption erörtert. Eisen (III) oxidträger kann für die Anreicherung kleiner Mengen oder Spuren Co(II) verwendet werden. Der Einfluß von ÄDTA, Glycin, L(+)-Arginin und L(+)-Cystein auf die sorbierte Menge Co(II) wurde gleichfalls geprüft.

     

Simultaneous determination of iron(II) and iron(III) in aqueous solution by kinetic spectrophotometry with tiron

A kinetic spectrophotometric method that requires no prior measurement of rate constants is developed for the simultaneous determination of iron(II) and iron(III). The method is based on the aerial oxidation of iron(II) in the presence of tiron and acetate ions. The iron(III) formed is subsequently complexed with tiron and the absorbance/time relation is evaluated. The concentrations of iron(III) and iron(II) are obtained from the absorbance values at the start and at equilibrium, respectively, calculated by non-linear least-squares fitting. A linear calibration graph is obtained up to 12 μg ml^?1 iron(II)/iron(III). The method is applied to iron-rich ground water.