Spectrofluorimetric determination of iridium(IV) traces using 4-pyridone derivatives

A new spectrofluorimetric determination of iridium(IV) with 3-hydroxy-2-methyl-1-phenyl-4-pyridone (HX) or 3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone (HY) is reported. Iridium(IV) react with HX or HY and chelates were extracted into chloroform or dichloromethane. The organic phase showed fluorescence. The fluorescence measurements to quantify iridium were carried out in its fluorescent band centred at λ_ex=373 nm and λ_em=480 nm. Under optimal conditions, the calibration graphs were linear over the concentration range of 0.1-7.6 μg ml⁻¹ of iridium for Ir(IV)-HX and 0.1-5.8 μg ml⁻¹ for Ir(IV)-HY with a correlation coefficients of 0.999 and 0.992 and relative standard deviation of ±1.1%.The method is free from interference by Rh(III) and Pt(IV), which normally interfere with other methods. Iridium can be determined in the presence of 300-fold excess of rhodium(III) and 10-fold excess of platinum(IV).The method was applied successfully to the determination of iridium in some synthetic mixtures and mineral sample gave satisfactory results.     

Extraction of Iridium(IV) by 1-(2-(2,4-Dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl)-1H-1,2,4-triazole from Hydrochloric Solutions

Extraction of iridium(IV) by 1-(2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl)-¹H-1,2,4-triazole from hydrochloric solutions was studied. Optimal extraction parameters were determined. The mechanism of iridium(IV) extraction in this system is ion exchange (3.0 mol/L HCl and τ_cont = 5 min). Electronic, ¹H NMR, ¹³C NMR, and IR spectroscopy and elemental analysis were used to determine the composition of the extracted compound.     

The formation of flouride complexes of titanium(IV)

The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F^?, the free HF concentration in acid Ti(IV) solutions. The [H⁺] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)²⁺₂. The potentiometric data have been explained by assuming Ti(OH)₂F⁺, TiF₄ and HTiF^?₆, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F^? was found.From a special series of measurements, carried out by replacing a large part of the Cl^? with ClO^?₄, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium.     

Halide and complex halogeno anions as salts of oxinato bis(η5-indenyl)titanium(IV)/zirconium(IV) chelates

Bis(η⁵-indenyl)titanium(IV) dichloride and bis(η⁵-indenyl)zirconium(IV) dichloride, when treated with 8-hydroxyquinoline (oxine) in aqueous medium form ionic derivatives of the type [(η⁵-C₉H₇)₂ML]⁺Cl^? (M = Ti(IV), Zr(IV), L is the conjugate base of oxine). A number of halide and complex halogeno anions present in aqueous solution were isolated as salts of these ionic complexes giving derivatives of the type, [(η⁵-C₉H₇)₂ML]⁺X^? (X = Br^?, I^?, ZnCl₃(H₂O)^?, CdCl₄^2?, HgCl₃^?). Conductivity measurements in nitrobenzene indicate that these complexes are electrolytes. Both the IR and ¹H NMR spectral studies demonstrate that the ligand L is chelating. Consequently there is tetrahedral coordination about the titanium(IV) or zirconium(IV) ion.     

Complexes of Pt(II) and Pt(IV) with disubstituted purines

Mixed-ligand complexes of Pt(II) and Pt(IV) with 2,6-diaminopurine and 6-thioguanine were synthesized and characterised. The complexes were prepared in acidic and basic media. The binding of the ligands to the metal ion varies according to the pH of the medium. Thus, in the complexes of 6-thioguanine, the ligand acts as a monodentate ligand coordinating through the neutral C₆-SH group in the acidic medium and in the basic medium as a bidentate ligand binding to the metal ion through C₆S^? and N₇, forming a five-membered chelate ring. In an acidic medium 2,6-diaminopurine forms mononuclear complexes with Pt(II) and Pt(IV) binding through N₇. In a basic medium binuclear hydroxobridged complexes are formed with Pt(IV) and the ligand is monodentate, coordinating through N₇.     

Kinetic studies on the reduction of a nickel (III) oxime-imine complex by sulphur(IV) and selenium(IV)

The kinetics of the reduction of [Ni^III(L¹)]²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02 and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC₂·H₂O and HSO ₃ ⁻ is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO ₃ ²⁻ seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of HSeO _l3 ⁻ is ≈ 10³ times slower than that of H₂SeO₃. The kinetic data indicate that the oxidation of sulphur(IV) by [Ni^IIIL¹)]²⁺ is much more favourable as compared to the corresponding oxidation of selenium(IV).     

Tin(IV), titanium(IV) and hafnium(IV) complexes of some aromatic Schiff bases derived from 4-aminoantipyrine

Summary Tin(IV), titanium(IV) and hafnium(IV) chloride complexes of ligands such as salicylidene-4-aminoantipyrine (HL¹), 5-chlorosalicylidene-4-aminoantipyrine (HL²), 2,4-dihydroxybenzylidene-4-aminoantipyrine (HL³), 2-hydroxy-1-naphthylidene-4-aminoantipyrine (HL⁴) and 2-hydroxyacetophenonylidene-4-aminoantipyrine (HL⁵) have been prepared and characterized. The analytical data show that tin(IV) forms only 1:1 metal complexes when reacted with HL¹, HL³ and HL⁴, whereas it forms 1:1 and 1:2 metal complexes when reacted with HL², depending on the molar ratio. HL⁵ produces only the binuclear complex SnHL⁵Cl₄(H₂O)SnCl₄. Titanium(IV) gives only one type of complex of the general formula [Ti(HL)₂Cl₂]Cl₂-2H₂O, whilst hafnium(IV) gives HfHL³Cl₄-4H₂O and Hf(L⁵)₂Cl₂.     

Extraction of U(VI), Zr(IV) and Th(IV) from perchlorate media, by PC-88A

Extraction of U(VI), Zr(IV) and Th(IV) has been investigated from perchlorate media using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) dissolved in toluene. The extraction of U(VI), Zr(IV) and Th(IV) was found to be quantitative in the pH range 1.6 to 3.2, 2.0 to 4.7 and 2.3 to 3.8, respectively, with 3.0^.10^-3, 5.6^.10^-4 and 1.0^.10^-2M PC-88A dissolved in toluene. U(VI) was stripped with 4.0M HCl, Zr(IV) with 2.5M NaF and Th(IV) with 8.0M HCl from the metal loaded organic phase containing PC-88A dissolved in toluene. The probable extracted species have been ascertained by plotting log D vs. log [HR] as UO₂R₂ ^.2HR, ZrR₄ ^.2HR and ThR₄ ^.4HR, respectively. U(VI) was separated from Zr(IV) and Th(IV) and from other associated metals. This method was proved by the determination of U(VI) in some real samples.     

Kinetics of iridium(III) catalyzed oxidation of benzaldehyde and <Emphasis Type="Italic">p</Emphasis>-nitrobenzaldehyde by cerium(IV) in aqueous acidic medium

Oxidation of benzaldehyde and p-nitro-benzaldehyde by cerium(IV) sulphate in aqueous sulphuric acid is strongly catalyzed by iridium(III) chloride. The complex formed between cerium(IV) and the organic substrate in the first equilibrium step gives another complex in the presence of iridium(III), which ultimately gives the corresponding aromatic acids as the product of oxidation. The order of the reaction follows first-order kinetics at low concentrations to zero order at higher concentrations of both the oxidant and organic substrate. The rate is directly proportional to the concentration of catalyst, but decreases sharply with increasing H⁺ ions and cerium(III) concentrations, while change in ionic strength of the medium or the concentration of acetic acid and Cl⁻ ions has no effect on the rate.     

Controlled-Potential Coulometric Determination of Iridium in Hexanitroiridate(III) with Microwave Sample Preparation

A procedure is proposed for determining 0.40 to 7.00 mg of iridium (RSD = 1–4%) in Ir(NO₂)^3- ₆. The procedure involved the fast conversion of Ir(NO₂)^3- ₆ into IrCl^2- ₆ by heating it with an HCl solution in a microwave oven and the controlled-potential coulometric determination of iridium using the Ir(IV)/Ir(III) redox system.     

Studies in nickel(IV) chemistry. Kinetics of the Cu(II) ion-mediated acid decomposition of tris(dimethylglyoximato) nickelate(IV) in aqueous acidic medium

Kinetics of the Cu(II) ion-mediated acid decomposition of tris (dimethylglyoximato)nickelate(IV), Ni(dmg)₃^2? (dmg^2? = dimethylglyoximate dianion), are reported in aqueous medium in the range of 3.6 ? pH ? 6.6 at 35°C and μ = 0.57 M. The pseudo-first-order rate constants of the disappearance of Ni(IV) k_obs(M) satisfy the equation where k_ad refers to the pseudo-first-order rate constants for the proton-assisted decomposition of the Ni(IV) complex determined independently and is a function of [H⁺], and k_dec(M) to that for the Cu(II) ion-mediated route and is a function of [H⁺] and [Cu²⁺]. Both k_obs(M) and k_dec(M) are found to increase with increasing [Cu(II)]₀, tending to attain limiting values at higher relative [Cu(II)]₀. At low [Cu(II)]₀ the k_dec(M) is found to register a decrease with increasing pH in the pH range of 3.6–4.4, then an increase in the range of 4.4–5.76, and again a decrease in the range of 5.76–6.6. Results on the Cu(II) ion-mediated acid decomposition are interpreted in terms of a probable mechanism involving pH-dependent adduct formation equilibria involving the one-protonated and the two-protonated species of Ni(IV) and the various species of Cu(II) ion in the media, followed by rate-determining acid decomposition of the adduct(s) to give Ni(II) aq. and Cu(dmgH)₂. While the two-protonated Ni(IV) complex apparently reacts about five orders of magnitude faster than the one-protonated species, the aquacopper(II) reacts about two orders of magnitude slower than the hydroxoaquacopper(II).     

Diorganotin(IV) and triorganotin(IV) derivatives of diphenic acid

The diorganotin(IV) and triorganotin(IV) derivatives R₂SnA (R = Me, n-Pr, n-Bu, n-Oct) and (R₃Sn)₂A [R = Me, Ph, cyclohexyl (Cyh); A = an anion of diphenic acid] have been prepared and characterized by elemental analysis, IR, ¹H and ¹³C NMR spectroscopies. Tetrahedral tin forms a part of a diphenate cyclic ring in the diorganotin complexes with unidentate carboxylates, which have further been used for the synthesis of cyclic acid anhydrides. The soluble dinuclear triorganotin complexes (Me, Ph) possess symmetrically bonded carboxylates while the less soluble compound (Cyh₃Sn)₂A has two asymmetrically bonded carboxylates. All have a trigonal bipyramidal structure with R₃Sn units remote from each other.     

Selective extraction-photometric redox determination of low concentrations of sulfur(IV), selenium(IV), tellurium(IV), and arsenic(III)

A procedure is proposed for the selective extraction-photometric determination of the acid-forming elements S(IV), Se(IV), Te(IV), and As(III) in their mixtures containing molecular forms or anions with different electron densities on donor atoms. The procedure is based on the difference in the oxidizability of analytes with the [SbCl₆]^? complex. The analytical ranges are found at different pHs of the medium, affecting the potential of the two-phase redox systems. The detection limits for sulfite, selenite, tellurite, and arsenite are 1 × 10^?3, 5 × 10^?5, 7 × 10^?5, and 1 μg/mL, respectively. The procedure is applied to the determination of selenium in H₂SO₄ of high-purity grade, which is used in the production of microelectronics items and in some agricultural samples. The error of analysis is no worse than 20%.     

Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium

The kinetics of electron transfer from hexacyanoferrate(II) to tris(dimethylglyoximato)-nickelate(IV), Ni(dmg)₃^2?, to produce Fe(CN)₆^3? and Ni(dmgH)₂, follows a pseudo-first-order disappearance in the Ni(IV). The pseudo-first-order rate constants k_obs are linearly dependent on [Fe(CN)₆^4?]₀ in a fiftyfold range of 2 × 10^?4?1 × 10^?2M, and the average values of k_obs/[Fe(CN)₆^4?]₀ range from 194M^?1·s^?1 at pH = 5.20 to 0.2M^?1·s^?1 at pH = 9.07 in aqueous medium at 35°C and μ = 0.57M. Results are interpreted in terms of a probable mechanism involving rate-determining outer sphere one-electron transfer steps from the reductant and one-protonated reductant species to the unprotonated and one-protonated Ni(IV) species present in solution. The more electrophilic one-protonated reductant species apparently reacts several orders of magnitude faster than the unprotonated one.     

Diorganotin(IV) bis(O,O-alkylenedithiophosphates)

O,O-Alkylenedithiophosphates of diorganotin(IV) of the type R₂Sn[SP(S)O₂G]₂ (R = Me, Et, n-Bu, Ph; G = CH₂CMe₂CH₂, CMe₂CMe₂, CMe₂CH₂CHMe) have been synthesized by the reactions of diorganotin(IV) dichlorides with ammonium O,O-alkylenedithiophosphates or that of diorganotin(IV) oxides with O,O-alkylenedithiophosphoric acids in 1:2 molar ratio in benzene. These new complexes are white solids which are soluble in common organic solvents and are monomeric in refluxing benzene; and they have been characterized by elemental analysis and by different spectroscopic (IR, ¹H, ¹³C, ³¹P and ¹¹⁹Sn NMR) studies, on the basis of which a six coordinated octahedral structure has been suggested in solution.     

Extractive separation and photometric determination of neptunium(IV) and plutonium(IV) from their mixtures

A rapid and sensitive method for the photometric determination of trace amounts of neptunium and plutonium from their mixtures is described. Np(IV) is selectively extracted from about 1 M HNO₃ medium with TTA in xylene retaining Pu in the nonextractable trivalent state in the aq. phase with ferrous sulfamate. Plutonium in the aqueous phase is subsequently oxidized with NaNO₂ to the highly extractable tetravalent state and extracted with TTA. Np(IV) as well as Pu(IV) thus extracted are finally estimated in the organic phase itself spectrophotometrically employing xylenol orange as the chromogenic reagent. Their molar absorptivities are in the 5 × 10⁴ range. Beer's law is valid up to 2.4 ppm Np and 3.5 ppm Pu. The color of the solutions is stable for at least 48 hr. The method tolerates large excess of several common contaminants encountered during spent fuel reprocessing. Cerium(IV) and phosphoric acid, however, interfere with the final estimation.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Spectrophotometric Determination of Iridium (IV) with 3-Nitroso-4-Hydroxy-5, 6-Benzocoumarin

Iridium(IV) gives a deep red complex with 3-nitroso-4-hydroxy-5,6-benzo-coumarin when heated on a boiling water-bath for about 10 minutes. The complex is soluble in 50% aqueous acetone medium and exhibits maximum absorption at 520nm. Beer's law is obeyed up to 10.5 ppm of iridium at 520 nm. Molar absorptivity is 1.28×10⁴ litre mole^-1 cm^-t and the sensitivity of the colour reaction is 0.015 μg Ir(IV)/cm². The composition of the complex is 1:3 as determined by Job's and logarithmic methods. Common anions and cations do not interfere in the determination.     

New mixed heteropolytungstates containing Ge(IV) or Sn(IV)

New mixed heteropolyanions with formulae XZW₁₁O₃₉(OH)^m?[X = Si, Ge, B, As(V), Ga, Co(II), Zn; Z = Ge(IV), Sn(IV)] and X₂′ZW₁₇O₆₁(OH)^7?[X′= As(V), P(V);Z = Ge(IV), Sn(IV)] were prepared. Crystal systems of the potassium salts were determined. The stability range of the anions is given in terms of the pH. The acids corresponding to the salts were obtained and their neutralization studied. Spectroscopic and polarographic reduction studies are reported.     

Iridium Anodic Oxidation to Ir(III) and Ir(IV) Hydrous Oxides

Iridium oxide films (IROFs) are known to have an enhanced or the so‐called super‐Nernstian (<59 mV/pH) pH‐sensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 μm thickness, deposited thermally on titanium or gold‐plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen‐containing solutions of 0.5 M H₂SO₄, 0.1 M KOH and 0.5 M H₃PO₄+KOH. Linear pH‐dependences of the stationary open‐circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V–0.8 V (RHE) in deaerated and at 0.8 V–1.2 V (RHE) in O₂‐containing solutions. They were attributed to reversible Ir/Ir(OH)₃ and Ir/ IrO₂?nH₂O metal‐oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super‐Nernstian pH‐sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH)₃ electrode and the solubility product of Ir(OH)₃ have been evaluated: =0.78±0.02 V and K_sp=3.3×10^?64.