Spectrophotometric Studies on the Chelate Formation between Zirconium(IV) and Chromotrope 2R

The composition and stability of the chelate formed between Zr(IV) and chromotrope 2R has been investigated using spectrophotometric methods. The chelate is violet in color and has λmax at 530 nm. The composition, determined by different methods is 1 : 1. The chelate is stable between pH 1.0-3.0. The value of log K as determined by two different methods are 4.48±0.2 and 4.21±0.1 and the values of free energy of formation are —6.21±0.2 and —5.83±0.1 respectively at 30°C. The system obeys Beer's Law over a concentration range of 2.50 to 20.0 ppm of zirconium. The effective range of photometric determination is 3.50 to 19.05 ppm of zirconium.     

Spectrophotometric Studies of Cerium(III) and Thorium(IV) Chelates of Diethylenetriaminepentaacetic Acid (DTPA)

The interaction between diethylenetriaminepentaacetic acid (DTPA or H_sZ) and Ce(III) and Th(IV) ions has been investigated spectrophotometrically in aqueous solution at an ionic strength of 0.1 and for various temperatures. It has been found that the Ce(III)-DTPA chelate (1:1) exhibited a characteristic absorption maximum at 297 nm, and the optimum pH range is between 3.4 to 4.4. The absorption of Ce(III)-DTPA chelate is considerably diminished by adding small amounts of Th(IV) ions. This phenomenon was used to evaluate the formation constant of Th(IV)-DTPA chelate (1:1). The formation constants and the thermodynamic properties characterizing the formation of the chelates have been calculated at 25°. The results are as follows:      

Spectrophotometric Studies of Nickel(II) Chelate of 2-Picolylamine

Nickel(II) chelate of 2–picolylamine has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.3 M. The formation of pink color chelate was pH dependent, and the optimum pH range was between 7.0 to 8.5. Its mole ratio of ligand to nickel(II) ion was found to be 3 to 1 stoichiometry and the formation constant, logK, was determined as 13.31 ± 0.10. By using the wavelength 535 run, determination of trace amount of nickel(II) ion with the sensitivity of 5.28 τ/Cm² was possible. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG°=–8.15Kcal mole^-1, ΔH°=–9.65 Kcal mole^-1, ΔS°=28.5eu mole^-1.     

Potentiometric and UV-Visible Spectrophotometric Studies of the Stability of Thorium(IV) Complexes with (o-Hydroxyphenyl) Mono- and Di-Methylenephosphonic Acids

Protometric studies were performed in aqueous solutions at 25^C and 0.1 ,mol.dm⁻³ ionic strength (NaClO₄) to determine the complexing abilities of eight (o-hydroxy-phenyl) mono- and di-methylenephosphonic acids (differently substituted by chromophoric or auxochromic groups) towards thorium(IV). The number, the nature of the species present in solution, their overall stability constants over a broad acidity range and their individual electronic spectra, as resolved by computation, have been determined by potentiometry and UV-visible spectrophotometry.The formation of 1:1 species, partially protonated MLH_x and totally deprotonated [ML], as well as hydroxo species -- mononuclear ML(OH)_x and dinuclear M₂L(OH) _x is reported with thorium(IV). The results show that the complexing power, which is not very different in the lanthanide series, is much higher for thorium(IV). The ratio Th⁴⁺/Eu³⁺ reaches eight log₁₀ units with some of the ligands.     

Physicochemical Studies on Cu(II)-Ferron Complexes

Experiments were carried out at 25°C and μ of 0.1 M. Spectrophotometric and potentiometric methods gave the ionization constants of ferron, pK₁=2.50±0.02 and pK₂=7.12±0.02. Cu(II) and ferron form a sparingly soluble 1:1 complex, [Cu(H₂O)₂L]⁰ (L: ferronate ion) which in higher acidity media, protonates to give [Cu(H₂O)₂HL]⁺and in lower acidity media, ionizes to give [Cu(H₂O)(OH)L]^?. At pH 2.3, the 1:1 complex gives a minimum solubility and the intrinsic solubility was found to be 1.1×10^-4. The Job's continuous variation method and the molar ratio method gave a formation constant (–pK) for Cu²⁺+L^z??CuL, 10.8±0.1 in the pH range of 0.64 to 1.18 and in the pH range of 5.0 to 5.5 (optimum pH condition for formation of complex), the stoichiometry of the Cu(II)-ferron chelate is essentially 1:2 (Cu:L) but with slight tendency to form 1:1 chelate if [L]/[Cu] is less than 2. The overall formation constant (–pK) was determined to be 20.0±0.3.     

Metal Chelates of Cerium (III), Thorium(IV) and Dioxouranium(VI) with Some Heterocyclic AZO Dyes; Potentiometric and Spectrophotometric Studies

ABSTRACT

The stepwise formation constants of Ce³⁺, Th⁴⁺ and UO₂ ²⁺ complexes with four azo compounds based on I-phenyl-2, 3-dimethylpyrazoline-5-one nucleus namely; 4-phenylazo- (2-hydroxy, 5-x) 1-pheny1-2, 3-dimethy1-pyrazoline-5-one, where x= H (1), OH (II), COOH (III) and NH₂ (IV) have been determined potentiometrically at different temperatures and ionic strengths in 30% (v/v) ethanol-water solutions, then the thermodynamic parameters are calculated.

Negatives values of both ∠H and ∠G are obtained indicating the exothermic and spontaneous nature of complexation reactions, whereas positive values of ∠S show that entropy consideration favour complex formation. The study at different ionic strengths shows that an increase in the latter causes a decrese in the pK values. The azo compounds are also tested as new reagents for the spectrophotometric determination of Ce³⁺, Th4⁺ and UO₂ ²⁺ ions in synthetic and natural solutions by extensive investigation of the optimum conditions favoring the formation of colored complexes.     

Spectrophotometric Studies of Cobalt (II) Chelate of P-(2-Hydroxy-1-Naphthylazo) Benzenesulphonate

Cobalt(II) chelate of p-(2-hydroxy-1-naphthylazo)benzenesulphonate (orange II) has been studied spectrophotometrically in aqueous solution at 25° and at an ionic strength of 0.10 M. The formation of this chelate is pH dependent, the optimum pH range is between 9.5 to 10.8. Its mole ratio of ligand to cobalt(II) is 3 to 1 stoichiometry and the formation constant, logK, is determined as 19.17±0.13. By using the wave-length of 357 mμ, determination of trace amount of cobalt(II) with the sensitivity of 0.077 y/cm² is possible.     

Die spektralphotometrische Bestimmung von Vanadium(IV) mit Ferron

Ohne Zusammenfassung     

Spectrophotometric Studies of Uranyl(VI) Chelate of β-Isopropyltropolone

The acid dissociation constant (K_a) of β-isopropyltropolone (IPT or HL) together with the stability constant (K) of its chelate complex with UO₂²⁺ ion have been determined in water-ethanol medium containing 50% ethanol by volume and 0.1 M NaClO, over the temperature range 15-45°C. From these results, values of the free energy, enthalpy and entropy of the chelation have been calculated at 25°C The results are collected as follows:      

Spectrophotometric and Paper Electrophoretic Studies of Uranium(IV) Polyoxotungstogermanate Complexes

The starting point of this study is the monolacunar structure of the Keggin polytungstate anion [GeW₁₁O₃₉]^8–having the capacity of functioning as the coordinating ligand for the uranium U⁴⁺ cation, and the formation of the complex polytungstate anions of the [U(GeW₁₁O₃₉)₂]^12– type. The pH range of the complex formation was established and the stability constants were calculated by the electrophoresis method. By applying the molar ratio method to spectrophotometry, the molar ratio of polyoxometalate ligands and U⁴⁺ cations have been found to have the values of 1:1 and 2:1, respectively.     

Thorium(IV) complexes of bidentate hydroxypyridinonates

The coordination chemistry of actinide(IV) ions with hydroxypyridinone ligands has been initially explored by examining the complexation of Th(IV) ion with bidentate PR-1,2-HOPO (HL(1)()), PR-Me-3,2-HOPO (HL(2)()), and PR-3,4-HOPO-N (HL(3)()) ligands. The complexes Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) were prepared in methanol solution from Th(acac)(4) and the corresponding ligand. Single-crystal X-ray diffraction analyses are reported for the free ligand PR-Me-3,2-HOPO (HL(2)()) [Ponemacr;, Z = 8, a = 8.1492(7) A, b = 11.1260(9) A, c = 23.402(2) A, alpha = 87.569(1) degrees, beta = 86.592(1) degrees, gamma = 87.480(1) degrees ], and the complex Th(L(2)())(4).H(2)O [Pna2(1) (No. 33), Z = 4, a = 17.1250(5) A, b = 12.3036(7) A, c = 23.880 (1) A]. A comparison of the structure of the metal complex Th-PR-Me-3,2-HOPO with that of free ligand PR-Me-3,2-HOPO reveals that the ligand geometry is the same in the free ligand and in the metal complex. Amide hydrogen bonds enhance the rigidity and stability of the complex and demonstrate that the Me-3,2-HOPO ligands are predisposed for metal chelation. Solution thermodynamic studies determined overall formation constants (log beta(140)) for Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) of 36.0(3), 38.3(3), and 41.8(5), respectively. Species distribution calculations show that the 4:1 metal complex Th(L)(4) is the dominant species in the acidic range (pH < 6) for PR-1,2-HOPO, in weakly acidic to physiological pH range for PR-Me-3,2-HOPO and in the high-pH range (>8) for PR-3,4-HOPO-N. This finding parallels the relative acidity of these structurally related ligands. In the crystal of [Th(L(2)())(4)].H(2)O, the chiral complex forms an unusual linear coordination polymer composed of linked, alternating enantiomers.     

Zirconium(IV) Thorium(IV) and Dioxouranium(VI) Complexes of Salicylidene o-Aminobenzothiol

Salicylidene-o-aminobenzothiol and its 5-chloro and 5-bromo derivatives, dibasic tridentate Schiff bases, dervied from the condensation of o-aminothiol and Salicylaldehyde, 5-chloro salicylaldehyde and 5-bromo salicylaldehyde, were used for coordination with Zr(IV), Th(IV) and UO₂(VI) metal inos. The I:I (metal-ligand) stoichiometry of these complexes is shown by elemental analysis and conductometric titrations. Molecular structure of these complexes are proved by Infra-red spectroscopy and thermogravimetric analysis. Magnetic susceptibility measurements of Zr(IV), Th(IV) and UO₂(VI) complexes show their diamagnetic and octahedral geometry. Results show that all the complexes have solvent molecules in coordination with metal ion.     

Uranium(VI) and Thorium(IV) Adsorption Studies on Chelating Resin Containing Pentaethylenehexamine as a Functional Group

A new chelating resin (glycidyl methacrylate/divinylbenzene/pentaethylenehexamine (GMA/DVB/PEHA)) for uranium(VI) and thorium(IV) has been developed by functionalizing GMA/DVB with PEHA. The adsorption of U(VI) and Th(IV) ions onto the functionalized GMA/DVB/PEHA were investigated as a function of pH value, contact time, and temperature using batch adsorption technique. The results showed that U(VI) and Th(IV) adsorption onto GMA/DVB/PEHA was strongly dependent on pH. Kinetic studies revealed that the adsorption process achieved equilibrium within 15 and 90 minutes for Th(IV) and U(VI), respectively, and followed a pseudo-second-order rate equation. The isothermal data correlated with the Langmuir model better than the Freundlich model. Thermodynamic data indicated the spontaneous and endothermic nature of the process. The maximum adsorption capacity of U(VI) and Th(IV) were found to be 114 and 78 mg/g, respectively. Quantitative recovery of uranium and thorium were achieved by desorbing the loaded GMA/DVB/PEHA with 0.5 M HNO₃      

Spectrophotometric Studies of Cerium(III) Chelate of 7-Iodo-8-Hydroxyquinoline-5-Sulphonic Acid

Cerium(III) chelate of 7-iodo-8-hydroxyquinoline-5-sulphonic acid(ferron) has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.1M. The formation of this chelate was pH dependent, and the optimum pH range was between 5.5 to 6.0. Its mole ratio of ligand to cerium(III) ion was found to be 2 to 1 stoichiometry and the formation constant, logK, was determined as 10.15. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG° =-13.85kcal mole^-1, ΔH°= ?5.03 kcal mole^-1, ΔS°=29.56 eu mole^-1. By using the wavelength of 370 nm, determination of trace amount of cerium(III) ion with the sensitivity of 0.056 was possible.     

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

The coordination of tBuNC and CO with the diarsenido complexes (C₅Me₅)₂An(η²-As₂Mes₂), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th^IV and U^IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th^IV and U^IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An^IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C−O) orbitals relative to the An−As bond.     

The crystal structure of Thorium(IV)tetrakis(trifluoroacetylacetonate)

The crystal structure of the compound thorium(IV)tetrakis(trifluoro-acetylacetonate) was determined by means of a threedimensional X-ray analysis. The space group is C2/c and the cell dimensions are a = 25,05 Å, b = 6.43 Å, c = 21.3 Å, β = 125.4°, with Z = 4. The thorium atom is coordinated by 8 oxygen atoms in the form of an 1111 (D₄–422) antiprism. The mean of the Th–O distances is 2.39 Å with a standard deviation ± 0.04 Å. The trifluoroacetylacetonate rings are approximately planar, except for the CH₃ and CF₃ groups which show significant deviations. The Th–O bonds form angles of approximately 72° and 50° with the theoretical 8 -axis of the antiprism. The structure is stabilized by VAN DER WAALS contacts between neighbouring molecules. The refinement of the atomic positions, the anisotropic temperature parameter of thorium and isotropic temperature parameters of all the other atoms by the least squares method, has given a reliability index of 0.148.     

Thorium(IV) and zirconium(IV) complexes of oxygen donor ligands,part 12. Thorium(IV) complexes of monoN-oxides of 2,2′-bipyridine and 1,10-phenanthroline

Summary Crystalline thorium(IV) chelates with monoN-oxides of 2,2-bipyridine (bipyNO) and 1,10-phenanthroline (phenNO), ThX₄ · 2L (X = Cl, Br, NO₃ or NCS) and ThX₄ · 3L (X = I or ClO₄, and I = bipyNO or phenNO) have been synthesised and characterized on the basis of i.r. spectra, molar conductance, molecular weights, t.g.a. and d.t.a. data. All the complexes are weakly diamagnetic and contain bipyNO and phenNO bonded to thorium(IV) through nitrogen and oxygen. The coordination number of thorium(IV) varies from six to twelve depending on the nature of the anions.Author on leave from L. R. Postgraduate College, Sahibabad (Ghaziabad) and to whom all correspondence should be directed.     

Studies on the Complexation Behavior of Thorium(IV). 1. Hydrolysis Equilibria

The stability constants of thorium(IV) hydrolysis species have been measured at15, 25, and 35°C (in 1.0 mol dm^–3 NaClO₄) using both potentiometry and solventextraction. The results indicate the presence of the monomeric speciesTh(OH)³⁺, Th(OH)²⁺ ₂, Th(OH)⁺ ₃, and Th(OH)₄, in addition to the polymericspecies Th₄(OH)^{8+ 8} and Th₆(OH)⁹⁺ ₁₅. The polymeric species were found to beimportant, although the total thorium concentration was limited to 0.01–0.1mmol-dm^–3. The solvent extraction measurements required the use of acetylacetone.As such, the stability constants of thorium(IV) with acetylacetone were alsomeasured using both potentiometry and solvent extraction. All logarithms of thestability constants were found to be linear functions of the reciprocal absolutetemperature indicating that H ^o and S^o of reaction are both independent oftemperature (over the temperature range examined in the study).     

Thorium(IV) complexes with tetradentate Schiff base ligands

Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N₂O₂ donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H₂salen) or acetylacetone (H₂ acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL₂Xa (L = H₂ salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO₄) or ThLX₄ (L = H₂ salen; X = NO₃, ClO₄ and L = H₂ acacen; X = Br, NO₃). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively.