Thermodynamic characterization of the amphoterism of hydroxides and oxides of scandium subgroup elements in aqueous media

Effect of the pH value on the molar solubility of solid hydroxides M(OH)₃ and oxides M₂O₃ at 25°C and the constants of acid-base equilibria in aqueous media for crystalline hydroxides and oxides and dissolved hydroxides M(OH)₃ (M = Sc, Y, La) were calculated using the thermodynamic method, with the formation of hydroxo complexes taken into account.     

Solubilities of metal hydroxides

The solubilities of freshly precipitated and aged hydroxides of 21 metals have been calculated. The initial data set used for calculations comprised the stability constants and solubility products of hydroxides. The compositions and pHs of saturated solutions and the solubilities of hydroxides are dictated by the polarizing ability of charged metal atoms. The results of solubility calculations are in satisfactory agreement with experimental values.     

Thermodynamic characterization of the amphotericity of oxides and hydroxides of group-IIIA elements in aqueous media

Dependences of the molar solubility of M₂O₃ solid oxides on the pH of aqueous media at 25°C and also the constants of acid-base equilibria in aqueous media for stable crystalline M₂O₃ oxides and for crystalline and dissolved M(OH)₃ hydroxides (M = In, Al, Ga, In, and Tl) were calculated by the thermodynamic method with account of the formation of hydroxo complexes.     

Thermodynamic characterization of the amphoterism of oxides M<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = As,Sb, Bi) and Their hydrates in aqueous media

Thermodynamic method was used to calculate, taking into account the formation of hydroxo complexes, the effect of the pH value on the molar solubility of M₂O₃ solid oxides and their hydrates at 25°C and the constants of acid-base equilibria in aqueous media for crystalline oxides and dissolved hydroxides M(OH)₃, where M = As, Sb, Bi.     

The thermodynamic properties of hydroxo compounds and the mechanism of ion flotation for cerium,europium, and yttrium

The pH values of formation of hydroxo complexes and hydrates in solutions of cerium(III), europium(III), and yttrium salts were determined by conductometric titration. The instability constants of hydroxo complexes, solubility products of hydroxides, and Gibbs energies of formation of the compounds specified were calculated. Conclusions about the mechanism of extraction and ion flotation of these metal cations from aqueous solutions were drawn.     

Initial stages of the formation of the structure of metal hydroxides

Based on the data for the initial stage of aging of metal hydroxides that exhibit nitrogen fixation properties and the exact solution of the model kinetic problem for the association of aqua and hydroxo complexes, the regularities of the formation of the structure of primary amorphous particles of metal hydroxides have been revealed. The primary particles consist of chain hydroxo polymers that containca. 10 units and are chemically bound to each other by ₃-OH bridging groups in sites at chaotically arranged intersections.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 12, pp. 2852–2857, December, 1996. 1996.     

Thermodynamic calculation of the solubility of solid hydroxides of group IIIA elements in water and aqueous media

The effect of pH on the molar solubility of amorphous and crystalline hydroxides M(OH)₃ and metahydroxides MO(OH), where M is B, Al, Ga, In, or Tl, in aqueous alkaline and acidic media at 25°C was calculated thermodynamically taking into account the formation of hydroxo complexes.     

Thermodynamic characterization of the amphoteric oxides M<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Cr,Fe, Co) and their hydrates in aqueous media

The molar solubilities of solid oxides M₂O₃ and their hydrates at 25°C as functions of pH of aqueous media, as well as the acid-base equilibrium constants were calculated for crystalline oxides and dissolved M(OH)₃ hydroxides, where M = Cr, Fe, Co, by the thermodynamic method, taking into account the formation of mono- and polynuclear hydroxo complexes.     

Effect of Chloride Ions on the Hydrolysis of Trivalent Lanthanum,Praseodymium and Lutetium in Aqueous Solutions of 2 <Emphasis Type="Italic">M</Emphasis> Ionic Strength

The solubility product of the solid hydroxides and the first hydrolysis constants of trivalent ions of lanthanum, praseodymium and lutetium, were determined in 2 M NaClO₄(aq) and 2 M NaCl(aq) at 303 K, where M denotes the concentration in mol-L⁻¹. Solubility diagrams (pLn_(aq)−pC_H) were measured by means of a radiochemical method. The pC_H borderlines of precipitation and the solubility products were determined from these diagrams. The fitting of the solubility equation with the experimental values from the pLn_(aq)−pC_H diagrams also allowed the calculation of the first hydrolysis constants and the solubility products. In separate experiments, the stability constants for the first monohydroxide species were determined by means of potentiometric pH titrations, where the data were treated with both the program SUPERQUAD and by fitting of the results to the mean ligand number equation. Values of the log₁₀ < eqid20 > _1,Cl constants for the LnCl²⁺ species were also calculated at 2 M ionic strength and 303 K, using the hydrolysis constants obtained in both perchlorate and chloride media. The quantitative effects of chloride ions on the hydrolysis reactions and solubilities were determined for these three rare-earths spanning the lanthanide series.     

Aqueous Long-Term Solubility of Titania Nanoparticles and Titanium(IV) Hydrolysis in a Sodium Chloride System Studied by Adsorptive Stripping Voltammetry

The solubility of industrially produced titanium dioxide nanoparticles has been studied in aqueous sodium chloride media in the pH range 1 to 13 at 25 °C by using adsorptive stripping voltammetry (AdSV). Kinetic dissolution curves have been obtained as well as long-term solubilities that provide an approximation of the equilibrium solubilities. The titania nanoparticles used in the dissolution experiments have been characterized by nitrogen sorption measurements, XRD and colloid titration. The equilibrium solubilities and titanium(IV) speciation and their dependences on pH have been modelled by assuming the formation of the mononuclear titanium hydroxo complexes [Ti(OH) _n ]⁽⁴⁻ⁿ⁾⁺ (n=2 to 5) to be the only titanium species present. The solubility product of titanium dioxide and equilibrium constants for titanium(IV) hydrolysis, calculated from the AdSV solubility data, are presented.     

Extraction of microamounts of europium and americium into nitrobenzene by using hydrogen dicarbollylcobaltate in the presence of diphenyl-N-butylcarbamoylmethyl phosphine oxide

Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of diphenyl-N-butylcarbamoylmethyl phosphine oxide (DPBCMPO, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, HL₂⁺, ML₂³⁺, ML₃³⁺ and ML₄³⁺ (M³⁺ = Eu³⁺, Am³⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It has been found that the stability constants of the corresponding complexes EuL _n ³⁺ and AmL _n ³⁺, where n = 2, 3, 4 and L is DPBCMPO, in water saturated nitrobenzene are comparable.     

Potentiometric and Conductometric Studies on the Complexes of Some Rare Earth Metals with Rhodanine Azosulfonamide Derivatives, XII

Stability constants for La³⁺, Ce³⁺, UO₂ ²⁺, and Th⁴⁺ metal ion complexes with rhodanine azosulfonamide derivatives have been determined potentiometrically in 0.1 M KCl in a 30% (v/v) ethanol–water mixture. The order of the stability constants of the complexes found was to La³⁺ < Ce ²⁺ < UO ₂ ²⁺ < Th ⁴⁺. The influence of substituents on the stability of the complexes was examined on the basis of electron-repelling property of the substituent. The effect of temperature on the stability constants was studied and the Gibbs energy, the enthalpy, and entropy of complexation thermodynamic parameters were derived and are discussed. The stoichiometries of these complexes were determined conductometrically and the results indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.     

π-Complexes of transition metal tricarbonyls with cyclopolyenes and their boron analogs

The structures and stability of complexes of transition metal tricarbonyls (M = Co, Fe, Mn, Cr) with hydrocarbon and borane basal rings, (C _n H _n )M(CO)₃ and (B _n H _2n )M(CO) _n , respectively, as well as internal rotation of the metal tricarbonyl fragments in these systems were studied by the DFT B3LYP/6-311+G(df,p) method. Replacement of hydrocarbon basal fragments by isoelectronic borane rings leads to strengthening of the interaction between the apical and basal fragments, but does not change the trend in the heights of barriers to internal rotation. In all cases, the metal tricarbonyl fragment stabilizes the nonclassical planar form of the borane rings, whereas the complexes of metal tricarbonyls based on the classical nonplanar borane conformations are less thermodynamically stable.     

Potentiometric and thermodynamic studies of 3-methyl-1-phenyl-{p-[N-(pyrimidin-2-yl)-sulfamoyl]phenylazo}-2-pyrazolin-5-one and its metal complexes

The dissociation constants of 3-methyl-1-phenyl-{p-[N-(pyrimidin-2-yl)sulfamoyl]phenylazo}-2-pyrazolin-5-one and metal-ligand stability constants of its complexes with some transition metal ions have been determined potentiometrically in 0.1 M-KCl and ethanol—water mixture (30 vol. %). The order of the stability constants of the formed complexes increases in the sequence Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, La³⁺, Hf³⁺, UO ₂ ²⁺ , Zr⁴⁺. The effect of temperature was studied and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were derived and discussed. The dissociation process is nonspontaneous, endothermic, and entropically unfavourable. The formation of the metal complexes was found to be spontaneous, exothermic, and entropically favourable. Abstracted from his M.Sc. Thesis.     

Thermodynamics of complexation in an aqueous solution of Tb(III) nitrate at 298 K

The pH of the formation of hydroxo complexes and hydrates in an aqueous solution of terbium Tb(III) is determined using combined means of potentiometric and conductometric titration. The stability constants of the hydroxo complexes, the products of hydroxide solubility, and the Gibbs energy of terbium hydroxo complex formation are calculated.     

Adduct ion formation by metal complexes under methane negative chemical ionization conditions

Negative chemical ionization mass spectrometry is used as a probe to examine reactions between hydrocarbon radicals and metal complexes in the gas phase. The methane negative chemical ionization mass spectra of 27 complexes of cobalt(II ), nickel(II ) and copper(II ) in the presence of O₄, O₂N₂ and N₄ donor atom sets are characterized by two dominant series of adduct ions of the form [M + C_nH_2n]^? and [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Insertion of the CH radical into the ligand followed by radical/radical recombination and electron capture is proposed as the major mechanism leading to the formation of [M + C_nH_2n]^? adduct ions. A second pathway involves ligand substitution by C_nH_2n+1 radicals concomitant with H elimination and electron capture. Oxidative addition at the metal followed by ionization is suggested as the principal pathway for the formation of [M + C_nH_2n+1]^? adduct ions.     

Transition metal complexes of heterocyclic Schiff base

Metal complexes of Schiff base derived from 2-furancarboxaldehyde and 2-aminobenzoic acid (HL) are reported and characterized based on elemental analyses, IR, ¹H NMR, UV-Vis, solid reflectance, magnetic moment, molar conductance and thermal analysis. The ligand dissociation as well as the metal-ligand stability constants have been calculated pH-metrically at 25°C and ionic strength μ=0.1 (1 M NaCl). The complexes are found to have the formulae [M(HL)₂](X)_n·yH₂O (where M=Fe(III) (X=Cl, n=3, y=4), Co(II) (X=Cl, n=y=2), Ni(II) (X=Cl, n=y=2), Cu(II) (X=Cl, n=y=2) and Zn(II) (X=AcO, n=y=2)) and [UO₂(L)₂]·2H₂O. The thermal behaviour of these chelates is studied and the activation thermodynamic parameters are calculated using Coats-Redfern method. The ligand and its metal complexes show a biological activity against some bacterial species.     

Extraction of calcium and strontium into nitrobenzene by using hydrogen dicarbollylcobaltate in the presence of 1,2-(diphenylphosphino)ethylene dioxide

Extraction of microamounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of 1,2-(diphenylphosphino)ethylene dioxide (DPPEDO, L) has been investigated. The equilibrium data have been explained assuming that the species HL⁺, HL₂ ⁺, CaL₂ ²⁺, CaL₃ ²⁺, CaL₄ ²⁺, SrL₂ ²⁺ and SrL₃ ²⁺ are extracted into the organic phase. The values of extraction and stability constants of the cationic complexes in nitrobenzene saturated with water have been determined. In the considered nitrobenzene medium, it was found that the stability constants of the CaL _n ²⁺ complexes, where n = 2, 3 and L is DPPEDO, are somewhat higher than those of the corresponding complex species SrL _n ²⁺.     

Divalent transition metal complexes of 3,5-pyrazoledicarboxylate

New divalent transition metal 3,5-pyrazoledicarboxylate hydrates of empirical formula Mpz(COO)₂(H₂O)₂, where M=Mn, Co, Ni, Cu, Zn and Cd (pz(COO)₂=3,5-pyrazoledicarboxylate), metal hydrazine complexes of the type Mpz(COO)₂N₂H₄ where M=Co, Zn or Cd and Mpz(COO)₂nN₂H₄·H₂O, where n=1 for M=Ni and n=0.5 for M=Cu have been prepared and characterized by physico-chemical methods. Electronic spectroscopic data suggest that Co and Ni complexes adopt an octahedral geometry. The IR spectra confirm the presence of unidentate carboxylate anion (Δν=ν_asy(COO^–)–ν_sym(COO^–)>215 cm^–1) in all the complexes and bidentate bridging hydrazine (ν_N–N=985–950 cm^–1) in the metal hydrazine complexes. Both metal carboxylate and metal hydrazine carboxylate complexes undergo endothermic dehydration and/or dehydrazination followed by exothermic decomposition of organic moiety to give the respective metal oxides as the end products except manganese pyrazoledicarboxylate hydrate, which leaves manganese carbonate. X-ray powder diffraction patterns reveal that the metal carboxylate hydrates are isomorphous as are those of metal hydrazine complexes of cobalt, zinc and cadmium.     

Potentiometric determination of the formation constants for complexes of 3,2′,2″-triaminopropyldiethylamine with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II)

The tripodal tetraamine ligand N{(CH₂)₃NH₂}{(CH₂)₂NH₂}₂ (pee), has been investigated as an asymmetrical tetraamine chelating agent for Co^II, Ni^II, Cu^II, Zn^II and Cd^II. The protonation constants for this ligand and the formation constants for its complexes have been determined potentiometrically in 0.1 M KCl at 25 °C. The successive protonation constants (log K _n ) are: 10.22, 9.51, 8.78 and 1.60 (n = 1–4). One complex with formula M(pee)²⁺ (M = Co, Ni, Cu, Zn and Cd) is common to all five metal ions and the formation constant (log _ML) is: 12.15, 14.17, 16.55, 13.35 or 9.74, respectively. In addition to the simple complexes, Co^II, Cu^II and Zn^II also give hydroxo complexes, and Cu^II and Ni^II give complexes with monoprotonated pee. [Zn(pee)](ClO₄)₂ and [Cd(pee)Cl](ClO₄) complexes were isolated and are believed to have tetrahedral and trigonal-bipyramidal structures, respectively.