Regularities of complexation in the series of sorbents on the polystyrene matrix and their complexes with chromium(III) and manganese(II)

The physicochemical properties of polymeric complexing sorbents with the o,o′-dihydroxy-(1-azo-1′)-functional complexing group were studied. Optimal sorption parameters for chromium(III) and manganese(II) (medium acidity, temperature, time), the sorption capacity of the sorbents, and the stability constants (pK _a′)of the complexes were determined. Correlation relations were established between the dissociation constants (pK _a′) of the sorbent functional group and pH₅₀ of the complexation of the considered elements; between and the stability of the formed complexes (logβ); and between pK _a′ and the deprotonation energy (E _depr) of the sorbent hydroxy group located in the para-position to the introduced substituent. The established correlation relations are useful for targeted prediction of the physicochemical parameters of the sorbents, their complexes, and the sorption of manganese(II) and chromium(III) aimed at recovery and pre-concentration of these ions from objects with various chemical composition.     

A physicochemical study of the sorption of lead: Correlations in a series of chelating polymer sorbents

The sorption properties of chelating polymer sorbents (CPSs), the derivatives of poly(styrene-2-oxy-azo-2′-oxybenzene), with respect to the lead ion are studied. The parameters of the sorption processes—optimum conditions of sorption (acidity, temperature, and time), the sorption capacities of sorbents, the possibility of desorption, and the stability constants of the chelated polymers—are determined. Quantitative correlations between p K′_OH of the functional analytical group (FAG) of the sorbent and σ _{o + p(p)} for ortho-and para-substituents, between p K′_OH and pH₅₀ for the formation of chelate complexes of lead, between p K′_OH and the stability of lead complexes (logβ), and between σ _{o + p(p)} and pH₅₀ for the formation of chelate complexes of lead are established with the aim of studying regularities of the influence of the structure and acid-base properties of FAGs on parameters of chemisorption of Pb²⁺. It is shown that the established correlations provide a means for quantitatively predicting physicochemical parameters of sorbents and the process of sorption of lead with the aim of targeted synthesis of CPSs and their use in the chemistry of polymer compounds and in the process of concentrating.     

Zirconium sorption by chelating polymer sorbents with an <Emphasis Type="Italic">o</Emphasis>,<Emphasis Type="Italic">o</Emphasis>′-dihydroxyazo analytical functional group

The complexing properties of new chelating polymer sorbents (CPSs) with an o, o′-dihydroxyazo functionality and zirconium sorption on these sorbents were studied. Quantitative correlations were found between pK′_OH of the analytical functional groups (AFGs) of sorbents and the stability of chelates (logβ) in order to understand the lows governing the effect of the structural features and acid-base properties of the AFGs on zirconium chemisorption parameters. These correlations make it possible to quantitatively predict the physicochemical parameters of sorbents and their chelates, synthesize them, and use CPSs for zirconium preconcentration in analyses of natural and industrial objects.     

Laws of complex formation in a series of azo-substituted pyrocatechol derivatives and their tin(II) complexes

Physicochemical properties of new reagents, azo-substituted pyrocatechol derivatives and their tin(II) complexes, are studied. The acid-base properties of the hydroxy groups (pK′_i, pK″_i), parameters of complex formation reactions (pH, temperature, time), and instability constants of the complexes formed (pK _i) are determined. Quantitative correlations between the dissociation constants (pK′_a) of the functional analytical group, and the electronic Hammett constant σ for a substituent (pK′_a-pH₅₀ of the complex formation reaction), as well as between pK′_a and instability constants of the complexes (pK _a), are established. The quantitative correlations established allow the prediction of the physicochemical properties of the reagents and tin(II) complexes with new reagents of this class with the same functional analytical group (FAG) but other substituents.     

Estimation of stability constants of copper(II) and nickel(II) chelates with dipeptides by using topological indices

The estimation of the overall stability constants β₁ of copper(II) and nickel(II) chelates with dipeptides was performed by using the model with the valence connectivity index of the 3rd order (³χ^v). It was done by dividing β₁ to its constituting constants K₁ and K_a, and subsequently by dividing the basic set into subsets or treating the chelate rings as separate units. Altogether 15 copper(II) and eight nickel(II) chelates with dipeptides were investigated. Six models for the estimation of log K₁ and pK_a were checked, most of them by usage of indicator variables (for differentiation of copper(II) and nickel(II) complexes or subclasses of ligands). Estimates of log β₁ gave the range of rms values from 0.19 to 0.27. For the best model, errors of estimates were less than 0.34.     

Beryllium(II) sorption from aqueous solutions by polystyrene-based chelating polymer sorbents

Optimal parameters of beryllium(II) sorption from aqueous solutions by polystyrene-based sorbents have been studied, namely: optimal sorption acidity (pH_opt), pH providing 50% sorption (pH₅₀), optimal time (τ, min) and temperature of quantitative sorption. The sorption capacities of the sorbents under study (SCSs) for beryllium(II) have also been determined; sorption isotherms have been constructed. The parameters determined for beryllium(II) sorption by chelating polymer sorbents (CPSs) make it possible to select the most efficient sorbent for practical use.     

Potentiometric studies on the complexation of copper(II) by phenolic acids as discrete ligand models of humic substances

Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK_a1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK_a2 and pK_a3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.     

Solvent extraction and spectrophotometric determination of iron(II) with 2,2′-dipyridyl-2-furancarbothiohydrazone

2,2′-Dipyridyl-2-furancarbothiohydrazone (DPFTH) was used for the spectrophotometric determination of trace amount of iron(II) after the extraction process. Iron(II) can be quantitatively extracted with DPFTH in benzene from aqueous solution buffered to 3.0–8.0. The extracted species has absorption maxima at 440, 477, and 738 nm and obeyed Beer's law over the range 0–40 μg of iron in 10 ml at 738 nm. The molar absorptivity at this wave length is 1.17 × 10⁴ liters mole^?1 cm^?1. The proposed method is relatively selective for iron(II) and is satisfactorily applied to the determination of the total iron in natural waters. The proton dissociation constants of the ligand determined spectrophotometrically were pK_a1 = 2.88 and pK_a1 = 6.70 at 25 °C and μ = 0.1.     

Quantitative relations holding in coordination of (Tetraphenylporphyrinato)zinc(II) and nucleophilic substitution with anilines

Thermodynamic parameters (??G°, ??S°) of quasi-isoenthalpic coordination of (tetraphenylporphyrinato) zinc(II) with anilines (except for 4-halo derivatives) in chloroform at 273?C313 K in the absence of steric factors are linearly related to shifts of their absorption bands in the electronic spectra in reactions with anilines, as well as with logarithms of the stability constants of the complexes, pK _a values of the ligands in water, and Hammett substituent constants ??⁺. Linear relations were also found between thermodynamic and kinetic parameters of some nucleophilic substitution reactions and complex formation of (tetraphenylporphyrinato) zinc(II) with anilines.     

Sorption of Copper(II) Ions with Nanosized Magnesium Phosphate

A new approach to the preparation of a nanosized sorbent based on magnesium phosphate has been developed. The patterns of copper(II) ions sorption with nanosized magnesium phosphate from aqueous solutions have been investigated. The sorption parameters have been determined, and the kinetics and mechanism of the processes have been elucidated. The high sorption ability of the nanoscale sorbent has been shown in comparison with existing sorbents based on magnesium phosphate.     

The titrimetric determination of beryllium(II) with 1,2-phenylenediamine-N,N,N′,N′-tetraacetic acid

Beryllium (ca. 10^?2?10^?4 M) is determined by adding excess of 1,2-phenylenediamine-N,N,N′, N′-tetraacetic acid (PhDTA, H₄L) and back-titrating with copper(II); arsenazo-I serves as indicator. Formation constants of BeL and BeHL were determined by potentiometry: log K_BeL=6.48±0.02 and log K^H_BeHL=3.48±0.03 (25°C, I=1 M in NaClO₄). Expressions for the titration curve are given together with theoretical errors.     

Complexation of copper(II) with azo derivatives of benzoylacetone

1-Phenyl-2-[2-hydroxy-3-sulfo-5-nitrophenylazo]butadione-1,3 (H₂L) was synthesized from benzoylacetone. The dissociation constants of the reagent were determined (pK ₁ = 4.98 ± 0.03 and pK ₂ = 8.53 ± 0.01). Stability constants of some metal complexes with this reagent were determined by potentiometric and conductometric titrations. The stability of these complexes decreased in the following order: Fe > Cu > UO₂ > Ni > Co > Zn > Cd > Mn > Mg > Ca. The copper(II) H₂L complex with a stoichiometry of 1: 2 was studied by photometry. ε = 1.4 × 10⁴, Beer is law was obeyed in the copper concentration range from 0.25 to 3.07 μg/mL. The effect of foreign ions and masking agents on complexation was studied. A procedure for the photometric determination of copper(II) in seawater was developed.     

Chromatographic properties of mesoporous silica gel modified with acetylacetonates of europium and copper

New mesoporous materials prepared from tetraethoxysilane, i.e., sorbents obtained with the use of surfactants, are synthesized. Their chromatographic polarity is assessed quantitatively. Their Kovats retention indices and Rohrschneider polarity coefficients are calculated. Based on physicohemical data, it is demonstrated that modifying supports with metal chelates changes the structure and properties of the initial sorbents: the differential molar Gibbs free energies rise considerably for sorbent modified with copper acetylacetonate with respect to ethanol (?ΔG′ _i = 7.09 kJ/mol) and nitromethane (?ΔG′ _i = 6.75 kJ/mol), relative to the initial silica gel (5.43 and 4.15 kJ/mol, respectively).     

Strontium(II) sorption by complexing polymeric sorbents with various structures

Optimal conditions for strontium(II) sorption by new complexing polymeric sorbents (CPSs) from aqueous solutions were studied, namely, optimal solution acidity (pH_opt), pH of 50% sorption (pH₅₀), and optimal time and temperature of quantitative sorption. The strontium(II) sorption capacities of the test sorbents (SCSs) were determined, and sorption isotherms were plotted. The strontium(II) sorption parameters determined were used to recognize the most efficient CPSs.     

Regularities of the sorption behavior of actinide ions on mineral colloid particles

It is shown that an alternative to K _d in describing sorption at low degrees of surface saturation of colloid particles is pH₅₀ which takes into account both the properties of the sorbent and sorbate. The correlations of pH₅₀ with cation charge density for the An(III)-An(IV)-An(V)-An(VI) series and with hydrolysis constants are presented. The redox reactions with plutonium that accompany its sorption onto Fe(III) oxides are discussed.     

Photometric determination of copper(II) in nickel alloys using azoderivatives of ethyl acetoacetate

1-Ethoxy-2-(2-hydroxy-3-sulfo-5-chlorophenylazo)butane-1,3-dion (L₁), 1-ethoxy-2-(2-hydroxy-3,5-disulfophenylazo)butane-1,3-dion (L₂), 1-ethoxy-2-(2-hydroxy-4-nitrophenylazo)butane-1,3-dion (L₃), and 1-ethoxy-2-(2-hydroxyphenylazo)butane-1,3-dion (L₄) were synthesized on the basis of ethyl acetoacetate, and their analytical characteristics were studied. The following dissociation constants of the reagents were determined by potentiometric titration: pK ₁ = 5.94 ± 0.04 and pK ₂ = 9.75 ± 0.04 (L₁), pK ₁ = 5.78 ± 0.02 and pK ₂ = 9.55 ± 0.03 (L₂), pK ₁ = 6.03 ± 0.03 and pK ₂ = 9.86 ± 0.05 (L₃), and pK ₁ = 6.19 ± 0.05 and pK ₂ = 9.98 ± 0.06 (L₄). The chemical analytical characteristics of copper(II) complexes of L₁–L₄ were determined by spectrophotometry. It was found that, with an increase in the elecrophilic properties of the substituents introduced into the aromatic ring of the molecule, the sensitivity of the reaction increased; the substituents had no effect on the ratio of Cu : L = 1 : 2. A photometric procedure was developed for determining copper in nickel-based alloys.     

Synthesis and physicochemical properties of chelating sorbents containing functional groups of N-aryl-3-aminopropionic acids

Two types of chelating sorbents with different types of addition of iminodipropionate groups to a polymeric matrix were synthesized: carboxyethylated aminopolystyrene (sorbent 1) based on linear polystyrene and carboxyethylaminomethylpolystyrene (sorbent 2) based on the copolymer of styrene and divinylbenzene. The ionization constants and concentrations of functional groups of the sorbents (exchange capacity for hydrogen ions) were determined. The sorbents exhibit high selectivity for copper(II) ions with the maximum of sorption from ammonia—acetate buffer solutions lying in a range of pH 5.0–7.5. The time needed for a solution of copper(II)—sorbent system with continuous stirring to reach exchange equilibrium is 3.5 and 2 h for sorbents 1 and 2, respectively. The exchange capacity for copper(II) ions is 2.54 and 0.10 mmol g⁻¹, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 800–806, May, 2006.     

NMR, potentiometric and ESI-MS combined studies on the zinc(II) magnesium(II) and calcium(II) complexation by (morpholin-1-yl)methane-1,1-diphosphonic acid and its thio-analog

The crystal structures of the two derivatives of aminomethane-1,1-diphosphonic acid with morpholinyl- (1) and thiomorpholinyl- (2) side chains were determined by single crystal X-ray diffraction and discussed with respect to molecular geometry and solid state organization. The protonation equilibria, solution behavior and complex-formation equilibria in solutions of 1 and 2 with the Zn(II), Mg(II) and Ca(II) ions were studied by means of NMR, pH-potentiometry and ESI-MS methods.As the pK_(NH⁺) protonation constants of 1 and 2 are high (11.65 and 11.91, respectively) two different approaches were used to evaluate the pH-potentiometric data. The first approach disregarded the proton-dissociation from the NH⁺ group. In the second one, all the pK_a values were considered in the M(II):ligand formation equilibria. For 1, the accuracy of the pK_(NH⁺) determination was shown to be sufficient to calculate reliable stability constants of metal complexes with the use of both approaches. For 2, only approach neglecting the pK_(NH⁺) protonation constant was shown to be correct.The studied acids form dinuclear, [M₂L₃H_x], [M₂L₂H_x] and mononuclear MLH_x and ML₂H_x complexes with different degree of ligand protonation. Tendency to undergo some oligomerization with the increase in the metal and ligand concentration was demonstrated for the [CaLH] complex of 1 and 2. As far as 1 and 2 remain protonated, the Zn(II), Mg(II) and Ca(II) ions are coordinated exclusively through oxygen atoms of the phosphonate groups. The metal promoted proton dissociation from the NH⁺ ring atom takes place in alkaline pH.     

Über Kaliumtetracyanoplatinat(II), Kaliumtetracyanopalladat(II) und deren Monohydrate

We have determined the crystal structures of the potassium tetracyanoplatinates(II) and ‐palladates(II), and of their monohydrates, by X‐ray powder diffraction techniques and single crystal structure analysis. K₂[Pt(CN)₄]: orthorhombic; Pccn; a = 1370.11(2); b = 907.09(1); c = 703.91(2) pm; Z = 4; R_F² = 0.0903 (N(hkl) = 415). K₂[Pt(CN)₄] · H₂O: orthorhombic; Pnna; a = 715.79(4); b = 977.91(6); c = 1322.46(8) pm; Z = 4; R(F)_N′ = 0.027 (N′(hkl) = 1066). K₂[Pd(CN)₄]: monoclinic; P2₁/c; a = 433.03(2); b = 782.90(3); c = 1328.17(6) pm; ß = 93.069(3)°; Z = 2; R_p = 0.0583 (N(hkl) = 352). K₂[Pd(CN)₄] · H₂O: orthorhombic; Pnna; a = 721.48(6); b = 976.77(8); c = 1326.4(1) pm; Z = 4; R(F)_N′ = 0.048 (N′(hkl) = 1137). In all examined representatives the anions are stacked one upon the other, even though they are tilted in part. The results are completed by spectroscopic and thermo analytical investigations.