Structural correspondence between uranyl chloride complexes in solution and their stability constants

Pair-distribution functions (PDF)s were obtained from high-energy X-ray scattering (HEXS) data on a series of uranyl solutions as a function of chloride ion concentration. Analyses reveal that chloride forms only inner-sphere complexes with the uranyl, replacing inner-sphere waters such that the total uranyl coordination number decreases from 4.7 waters at [Cl(-)] = 0 m to 4.4 (1.7 water and 2.7 Cl(-)) at [Cl(-)] = 6.8 m. Some of the second-coordination sphere waters reorient upon uranyl inner-sphere chloride complexation in order to hydrogen bond with the bound anion. Similar data obtained on a series of solutions maintained at constant ionic strength are used to confirm structural assignments through determining stability constants for the addition of chloride to uranyl and comparison with published values. The stability constants, β(1) = 1.5(10) m(-1), β(2) = 0.8(4) m(-2), and β(3) = 0.4(1) m(-3), obtained in a series of solutions with constant ionic strength of 5.3 m, are in reasonable agreement with previously published results determined by solvent extraction. The agreement of stability constants supports our peak assignments for the PDF and thus our structural model for uranyl chloride complexes in solution. Using coordination numbers and speciation determined here as a function of chloride ion concentration, the monochloro species is found to have four coordinating waters in the uranyl equatorial plane, the dichoro species is found to be an equilibrium of three and two coordinating waters, and the trichloro species has only a single water in the equatorial plane. These values correspond to total average coordination numbers of 5, 4.3, and 4 for the mono-, di-, and trichlorouranyl complexes. From the equilibrium value of the dichloro species, it can be further estimated that ΔG = -0.5 kcal/mol for the conversion of five to four coordinate species. Overall, the HEXS data support the assertion that uranyl chloride correlations do exist and the results are not simply the result of solvent-ion effects.     

The stability constants of PdeDTA and its chloride complexes

From the position of the equilibrium Th + PdEDTA <--> Pd + ThEDTA, the stability constant of PdEDTA can be related to that for ThEDTA. If log k(ThEDTA) = 25.3 is taken as the most reliable value currently available, log k(pdEDTA) = 25.6 +/- 0.2 is found (NaClO(4) medium, 21 +/- 1 degrees ). Repetition of the experiments at different chloride concentrations gives an estimated log K = 5.3 +/- 0.1 for the equilibrium PdEDTA+Cl(-) <--> PdEDTACl(-). The stability constants of ThEDTA and PdEDTA are not very dependent on ionic strength in the range 0.1-1.0.     

Determination of individual stability constants of coexisting molecular complexes formed by unresolvable isomers

Some biogenic substances undergo steric isomerism or tautomerism in which the isomers are unresolvable. Naturally, the isomers are expected to form molecular complexes with distinct stabilities. This paper proposes the method of determining individually the stability constants of complexes formed under isomerisation and complexation equilibria: the NMR titration curves are modelled and formulated for fast and slow isomeric equilibria, the process of least-squares fittings is explained, and the application to supramolecular complexation of unresolvable isomers is discussed as compared with NMR titration data reported for α- and β-D-glucosamine anomers.     

209Bi NQR study of bismuth(III) complexes

Potassium pentafluorobismuthate(III), nitrate-chloride Bi^III complexes MBiCl₃NO₃ (M=K, (NH₂)₂CNH₂), sulfate-chloride Bi^III complexes MBiCl₂SO₄ (M=K, Rb, NH₄, (NH₂(₂CNH₂), and Bi^III complexonates with the anions of ethylenediaminetetraacetic acid M[Bi(edta)]₂·nH₂O (M=Mg, Ca, Ni, Cd) and nitrilotriacetic acid Bi(nta)·2H₂O, and Bi(nta)·3thio·H₂O (thio is thiourea) were studied by²⁰⁹Bi NQR spectroscopy. A second-order phase transition was observed in K₂BiF₅ at 100 K. The compounds Bi(nta)·2H₂O, (NH₂)₂CNH₂BiCl₃NO₃, and MBiCl₂SO₄ (M=K, NH₄) are piezoelectrics. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2237–2240, November, 1998.     

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: \(\log \beta [Cr_p^{3 + } (L_i )_{q_i } ] = 0.84\log \beta [Fe_p^{3 + } (L_i )_{q_i } ]\) .     

Effect of temperature on the stability constants of chloro complexes of actinyl ions

Stability constants of chloride complexes of U(VI), Np(VI) and Pu(VI) have been determined by the method of extraction chromatography at an ionic strength of 2.0 and [H⁺]=2.0M. Dilute HDEHP has been used as the stationary phase.     

The catenation and isomerisation effects on stability constants of complexes formed by some diprotic acids

Stability constants (K(ijk)) of complexes Na(i)K(j)H(k)L(+i+j+k-2) (0相似文献   

Effects of chloride ions on electrochemical reactions of manganese(III) complexes

Electrochemical reactions of manganese(III) complexes, Mn^III(L)X (L; salen, salpn, 5-NO₂–salen or 5-NO₂–salpn, X; Cl, Br or NO₂) and Mn^III(L’)₂X (L’; N-Bu-sal, N-Oct–sal, N-Oct–5-Br–sal or N-Oct–5-NO₂–sal, X; Cl or Br), were investigated by voltammetry at a glassy carbon electrode in the absence/presence of Cl⁻ in acetonitrile solution. By the addition of Cl⁻, oxidation processes of Mn^III(L)X and Mn^III(L’)₂X have been found to be improved from quasi-reversible to reversible, and their oxidation products, [Mn^IV(L)X]⁺ and [Mn^IV(L’)₂X]⁺, were stabilized by the combination with Cl⁻ resulting in [Mn^IV(L)Cl₂] and [Mn^IV(L’)₂Cl₂], respectively. On the other hand, the reduction processes of Mn^III(L)X and Mn^III(L’)₂Cl were not so significantly affected by Cl⁻ as those observed for their oxidation. Other types of manganese(III) complexes and iron(III) complex were also investigated. The present study may clarify the role of Cl⁻ being involved in OEC (oxygen-evolving center) in photosystem II.     

A polarographic study of the pyridine-copper-chloride complexes in methanol and determination of the stability constants

Copper(I) chloride has been shown to form two complexes with pyridine in anhydrous methanol, CuCiPy and CuClPy(2). Formation constants have been determined and found to be log K(1) = 7.8 +/- 0.3 and log K(2) = 9.45 +/- 0.3. The role of the complexes in the catalytic oxidation of xylenol is discussed.     

A spectrophotometric determination of the stability constants of the complexes of titanium(III) with acetylacetone

The stability constants of the consecutive complexes of titanium(III) with acetylacetone were determined by means of spectrophotometric methods. The values are log /gb₁ = 10.4, log β₂ = 18.8, and log β₃ = 24.9. Because of the fact that K₁K_a = 10^1.5 a high concentration of acetylacetone results in a considerable formation of TiL even at pH 0.     

A study of the stability of alkaline-earth metal complexes with fluoride and chloride ions at various temperatures by potentiometry with ion-selective electrodes

The complexes of the alkaline earth metals with fluoride and chloride were studied over the temperature range 15-85 degrees . The stability constants of the MX(+) complexes were determined by potentiometry with fluoride and chloride ion-selective electrodes and the appropriate thermodynamic functions (DeltaH(0)(298), DeltaS(0)(298) and DeltaG(0)(298)) were calculated.     

Magnetic interaction between iron/III/ ions in its complexes of some sugar type ligands

Mössbauer and temperature dependent EPR spectra of three iron/III/ complexes, formed with sugar type ligands /galactose, sorbitol and 1,2-propylene glycol/ were investigated. Measurements showed antiferromagnetic interaction between the iron/III/ central atoms in the specimens. On the basis of the EPR data the temperature dependence of partial susceptibilities of isolated and interacting iron/III/ centres could be determined.     

The stability constants of TAR and PAR complexes

A discussion is given of the problem of ascribing dissociation constants in the hypothetical situation in which the protons of the hydroxy groups of TAR and PAR dissociate in the reverse of the normal order, and it is suggested that the o-hydroxy group should be regarded as intrinsically as acidic as the p-hydroxy group, and that the change in pK due to the internal hydrogen 'bonding is probably less than one unit.     

Stability constants of complexes of uranium/VI/ and plutonium/VI/ with succinate ions

The stability constants of the complexes formed by U/VI/ and Pu/VI/ with succinate ions were determined in 0.5M NaClO₄ medium at 30°C following the Bjerrum-Calvin pH titration technique. The stability constants obtained agreed with values reported in literature following the same technique. The values for the second complexes were reported for the first time. U/VI/ complexes were found to have stabilities higher than the corresponding Pu/VI/ complexes in accordance with the acidities of the cations.     

Determination of stability constants of valinomycin complexes with ammonium and alkali metal ions by capillary affinity electrophoresis

Capillary affinity electrophoresis (CAE) has been employed to investigate quantitatively the interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with univalent cations, ammonium and alkali metal ions, K(+), Cs(+), Na(+), and Li(+), in methanol. The study involved measuring the change in effective electrophoretic mobility of valinomycin while the cation concentrations in the BGE were increased. The corresponding apparent stability (binding) constants of the valinomycin-univalent cation complexes were obtained from the dependence of valinomycin effective mobility on the cation concentration in BGE using a nonlinear regression analysis. The calculated apparent stability constants of the above-mentioned complexes show the substantially higher selectivity of valinomycin for K(+) and Cs(+) ions over Li(+), Na(+), and NH(4)(+) ions. CAE proved to be a suitable method for the investigation of both weak and strong interactions of valinomycin with small ions.     

Formation of bismuth(III) N-methylthiourea complexes in aqueous solutions

The formation constants of bismuth(III) methylthiourea complexes in aqueous solution were determined at 298 K and an acidity of 2 M HClO₄ using the “ligand-oxidized ligand species” potentiometric method and the methylthiourea (mtu)-symmetric dimethylformamidine disulfide (mFDS) redox pair. The formation function was obtained, and the conditional (β _n ^*) and true (β _n ) formation constants of Bi(mtu) _n ³⁺ (1 ≤ n ≤ 8) were calculated. The value of β₁ and the formation of complexes with coordination numbers higher than six was confirmed by spectrophotometry.     

A study on the fluoride complexes of plutonium(III), samarium(III) and bismuth(III) using fluoride ion-selective potentiometry

Stability constants of the fluoride complexes of Pu(III), Sm(III) and Bi(III) in 1.0M NaClO₄/HClO₄ medium at 23±1°C have been determined by potentiometry using a fluoride ion-selective electrode. Plutonium was reduced to the trivalent state using quinhydrone with an excess to serve as holding reductant. The log values of concentration stability constants log ₁, log ₂, and log ₃ are 3.58, 6.40 and 12.61 for Pu(III), 3.23, 5.81 and 10.54 for Sm(III) and 3.69, 6.13 and 11.04 for Bi(III), respectively. The log ₂ values in all these cases have very large deviation and may be taken only as rough estimates.