Application of Capillary Electrophoresis to the Study of Equilibria on an Example of Gold(III) Complexes

Three systems of gold(III) complexes in an aqueous solution (I = 0.05 M, 25°C) with slow equilibration were studied by capillary electrophoresis. It was shown on an example of mixed chloride–hydroxide complexes Au(OH) _i Cl _4-i ^- that, despite close sizes and identical charges of the forms, the mixed forms can be separated if they are kinetically inert. For the equilibria AuCl ₄ ^? + am = AuamCl ₂ ⁺ + 2Cl^– and AuamCl ₂ ⁺ + am = + Auam₂³⁺ + 2Cl^–, where am is ethylenediamine (en) and 1,3-diaminopropane (tn), the logarithmic constants were logK₂ = 10.4 for en, and logK₁ = 16.1 and logK₂ = 12.0 for tn, which satisfactorily agrees with the spectrophotometric data. There was a considerable effect of side processes, insignificant under normal conditions.     

Stability of diammine and chloroammine gold(I) complexes in aqueous solution

The substitution equilibria AuCl ₂ ^? + iNH ₄ ⁺ = Au(NH₃)_iCl_{2 ? i} + iCl^? + iH⁺, β _i ^* . were studied pH-metrically at 25°C and I = 1 mol/L (NaCl) in aqueous solution. It was found that logβ ₁ ^* = ?5.10±0.15 and logβ ₂ ^* = ?10.25±0.10. For equilibrium AuNH₃Cl_solid = AuNH₃Cl, log K _s = ?3.1±0.3. Taking into account the protonation constants of ammonia (log K _H = 9.40), the obtained results show that for equilibria AuCl ₂ ^? + iNH₃ = Au(NH₃)_iCl_{2 ? i} + iCl^?, logβ₁ = 4.3±0.2, and logβ₂ = 8.55±0.15. The standard potentials E ₀ ^1/0 of AuNH₃Cl⁰ and Au(NH₃) ₂ ⁺ species are equal to 0.90±0.02 and 0.64±0.01 V, respectively.     

Effect of the salting-out agent anion nature on the phase separation of a potassium salt–potassium bis(alkyl polyoxyethylene)phosphate–water systems

The effect the salting-out agent anion nature has on the temperature and concentration intervals of the existence of the separation area is established by analyzing the phase diagrams of pseudoternary KCl (KBr, KI, KNO₃, K₂SO₄, K₄P₂O₇)–potassium bis(alkyl polyoxyethylene)phosphate (oxyphos B)–water systems. It is concluded that the anionic salting-out capability is reduced in the order P₂O₇^4-> SO₄^2-> Cl^? > Br^?> NO₇^4-> SO₃^-> I^?. The thermodynamic parameters of phase separation used to interpret the results are calculated. The observed pattern of a change in the salting-out ability of the investigated salts relative to aqueous solutions of the surfactants is in good agreement with the lyotropic (Hofmeister) series.     

The mechanism of Pu<Superscript>VI</Superscript> oxidation with ozone and other reagents in alkaline solutions

The analysis of reported data on the interaction of ozone with alkaline solutions of Pu^VI leads to the conclusion that the process of ozonation involves reactions O₃ + OH^– → HO ₂ ^- + O₂, O₃ + + HO ₂ ^- + OH^– → O ₃ ^- + O ₂ ^- + H₂O and O₃ + O ₂ ^- → O ₃ ^- + O₂. The O ₃ ^- radical ion oxidizes Pu^VI, the HO ₂ ^- and O ₂ ^- anions reduce Pu^VII and Pu^VI and react with O ₃ ^- . Using persulfate instead of O₃ in aerated solution at 80—95 °C results in thermal decomposition of the S₂O ₈ ^2- anion into radical ions of SO ₄ ^- , oxidizing OH^– to the O^– ion, which in reaction with O₂ forms O ₃ ^- . The oxidation of PuVI proceeds via the formation of an activated complex with O ₃ ^- . where charge transfer occurs with the simultaneous elimination of two H⁺ ions. A similar mechanism is operating in reactions of Pu^VI with BrO^–, Fe(CN) ₆ ^3– , Am^VI, and Am^VII. Upon the γ-radiolysis of alkaline solutions of Pu^VI saturated with N₂O or containing S₂O ₈ ^2– , e _aq ^– is converted into O^– and then into O ₃ ^- ; F₂ and XeF₂ in alkaline solutions are decomposed with the formation of H₂O₂, which prevents producing Pu^VII.     

Complex formation of thiocyanate ions with iron(III) on the solid phase of fibrous ion exchangers

Characteristics of complex formation of SCN^–-ions with iron(III) on fibrous materials filled with an AV-17 anion exchanger (PANV–AV-17) and a KU-2 cation exchanger (PANV–KU-2) are studied by diffuse reflection spectroscopy. Sorption conditions of thiocyanate ions on PANV–AV-17 in the dynamic mode and the influence of concentrations of Cl^–, SO ₄ ^2- and NO ₃ ^- on the sorption and analytical signals of thiocyanate complexes are studied. Sorption conditions of iron(III) on PANV–KU-2 and the conditions of formation of thiocyanate complexes are studied. Systems for the sorption–spectroscopic determination of 0.1–0.7 μg/mL of SCN^–-ions in aqueous solutions of pH 5 ± 1 on PANV–AV-17 and test-determination of 5–30 μg of SCN^–-ions on PANV–KU-2 are proposed.     

On equilibria with participation of gold(I) complexes in sulfite-thiocarbamide media

The constants of protonation and sulfite ligand substitution by thiocarbamide for Au(SO₃) ₂ ^3? complex were determined. Mixed forms Autu(SO₃)^? and probably binuclear complex [Au₂tu₂SO₃] were shown to occur in noticeable concentrations in sulfite-thiocarbamide media in addition to Autu ₂ ⁺ and Au(SO₃) ₂ ^3? complex forms.     

Estimation of degree of lability of gold(I) sulfite and thiocarbamide complexes

The supposition that gold thiocarbamide complexes can be involved in the reduction of electrochemically inactive sulfite complex gold ions as intermediate species is supported by investigating the kinetics of cathodic process in the solution of the following composition: 10^?3 M Na₃Au(SO₃)₂, 0.1 M Na₂SO₃, 0.1M thiocarbamide (TC), and 0.2 M Na₂SO₄. The study was performed by the potentiodynamic method in the potential scan rate range from 0.05 to 1 V/s using an electrode with mechanically renewed surface. It is found that both Au(SO₃) ₂ ^3? , and Au(TC) ₂ ⁺ are labile complexes. This confirms the hypothesis for the mechanism of the catalytic effect of thiocarbamide on the electrode processes involving gold ions in the sulfate solutions, which was proposed earlier.     

Investigation of Chloride Ion Substitution Equilibria in AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> with Ethylenediamine and 1,3-Diaminopropane Using Capillary Zone Electrophoresis

Substitution of chloride ions in AuCl ₄ ^? with ethylenediamine (en) and propylenediamine (tn) is studied by capillary zone electrophoresis at I = 0.05 M and T = 25°C. The substitution constants are determined: AuenCl ₂ ⁺ + en = Auen ₂ ³⁺ + 2Cl^–, logK₂ = 10.4; AuCl ₄ ^? + tn = AutnCl ₂ ⁺ + 2Cl^–, logK₁ = 16.1; AutnCl ₂ ⁺ + tn = Autn³⁺₂ + 2Cl^–, logK₂ = 12.0.     

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Synthesis and physicochemical properties of <Emphasis Type="Italic">N</Emphasis>-decylpyridinium salts with inorganic anions

Ionic liquids with N-decylpyridinium cation and inorganic anions SO ₄ ^2– , NO ₃ ^– , SCN^–, NO ₂ ^– , BF ₄ ^– were synthesized. The structure and composition of the synthesized compounds was proved by elemental analysis and IR spectroscopy. Electroconductivity of aqueous solutions of new ionic liquids was studied, critical concentrations of micelle formation was determined, and thermal stability in air in the temperature range 25–500°С was investigated.     

Theoretical study of oxoborate complexes with MO<Stack><Subscript>4</Subscript><Superscript><Emphasis Type="Italic">n</Emphasis>−</Superscript></Stack> tetraoxo anions in the inner and outer spheres of the B<Subscript>20</Subscript>O<Subscript>30</Subscript> cluster

The energies and structural and spectroscopic characteristics of endohedral (MO₄©B₂₀O ₃₀ ^n? ) and exohedral (MO₄ · B₂₀O ₃₀ ^n? ) isomers of oxoborate complexes with MO ₄ ^n? tetraoxo anions with 32 valence electrons located in the inner and outer spheres of the B₂₀O₃₀ cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO₄©B₂₀O ₃₀ ^n? clusters with strong multiply charged anions (VO ₄ ^3? , CrO ₄ ^2? , PO ₄ ^3? , SO ₄ ^2? , AsO ₄ ^3? , SeO ₄ ^2? , etc.), the isomer in which a “guest” tetrahedron MO₄ is located at the center of the B₂₀O₃₀ cage and bonded to it through internal oxygen bridges M-O*-B is the most favorable one. Among the exohedral analogues MO₄ · B₂₀O ₃₀ ^n? , two most favorable isomers contain the “capping” MO₄ tetrahedron bonded to the B₂₀O₃₀ cage through two and three external M-O-B bridges. For the complexes with doubly charged SO ₄ ^2? and SeO ₄ ^2? anions, the third exohedral isomer in which the sulfite or selenite group MO₃ is bidentately coordinated to the oxidized B₂₀O₂₉(OO) cage with one peroxide bridge turns out to be close in energy to the above two isomers. For the systems with high negative charge n, the exohedral isomers are much more favorable than the endohedral isomer; however, with decreasing charge, the difference in energy between them decreases to ~10–18 kcal/mol, so that the exo–endo transition between them can require moderate energy inputs. For the endohedral complexes with singly charged ClO ₄ ^? and BrO ₄ ^? anions, two isomers with close energies are preferable in which the central atoms of the guest tetrahedra are reduced to the state of singly charged ions, while the oxoborate cage is oxidized to B₂₀O₂₆(OO)₄ with four peroxide groups B-O-O-B and retains its closed (closo) structure. In the most favorable isomer of the complexes with multicharged ortho-anions BO ₄ ^5? , CO ₄ ^4? , and NO ₄ ^3? , the outersphere anion is reduced to, respectively, borate, carbonate, and nitrate bidentately coordinated to the oxidized B₂₀O₂₉(O)₂ cage with an open structure and two strongly elongated terminal B-O bonds. The results are compared with the data of previous calculations of endohedral and exohedral vanadate complexes MO₄©V₂₀O ₅₀ ^n? and MO₄ · V₂₀O ₅₀ ^n? with the same guest anions MO ₄ ^n? .     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.     

Complexation of Chlorodiethylenetriaminegold(III) with Chloride Ions in Aqueous Solutions

The reaction of Au(Dien)Cl²⁺ (Dien is diethylenetriamine) with the chloride ion was studied spectrophotometrically in an aqueous solution at I = 1.0 mol/l and T = 20°C. The formation constant of pentacoordinated Au(Dien)Cl ₂ ⁺ was determined and its spectrum was calculated.     

Formation of alloys upon the simultaneous electrochemical deposition of gold and tin from ethylene glycol and aqueous electrolytes

An ethylene glycol (EG) solution containing Au(III) and Sn(IV) compounds, and conditions for the electrochemical deposition of Au–Sn alloy based on AuSn and Au₅Sn intermetallics with total tin content of 30–55 at % are proposed. Fundamental difficulties of the deposition of alloys with high tin content, (including eutectic Au–Sn alloy) from aqueous electrolytes are revealed. It is determined via voltammetry that the simultaneous deposition of gold and tin from aqueous and EG electrolytes proceeds with the depolarization effect of both Au(III) and Sn(IV) as a result of the formation of the alloy, the increase in the rate of tin cathodic reduction being more noticeable in case of EG solution. Formation of SnCl₂EG(H₂O)₂⁺ complex upon the dissolution of SnCl₄ · 5H₂O in glycol, the stability of the composition of tetracyanoaurate ions upon the dissolution of K[Au(CN)₄], and the weakening of intermolecular interactions in EG with small amounts of water were revealed via IR spectroscopy. It is suggested that the depolarization effect is due not only to alloy formation, but also to the formation of SnCl₂EG(H₂O)₂⁺ cations, their association with Au(CN)₄^- anions, and a change in the mechanism of Au(III) and Sn(IV) reduction.     

On the oxidation states of metal elements in MO3- (M=V,Nb, Ta,Db, Pr,Gd, Pa) anions

Relativistic quantum chemistry investigations are carried out to tackle the puzzling oxidation state problem in a series of MO_3~- trioxide anions of all d- and f-block elements with five valence electrons. We have shown here that while the oxidation states of V, Nb, Ta, Db, Pa are, as usual, all +V with divalent oxygen O(-II) in MO_3~- anions, the lanthanide elements Pr and Gd cannot adopt such high +V oxidation state in similar trioxide anions. Instead, lanthanide element Gd retains its usual +III oxidation state, while Pr retains a +IV oxidation state, thus forcing oxygen into a non-innocent ligand with an uncommon monovalent radical(O~·) of oxidation state -I. A unique Pr·- ·(O)_3 biradical with highly delocalized unpairing electron density on Pr(IV) and three O atoms is found to be responsible for stabilizing the monovalent-oxygen species in PrO_3~- ion, while GdO_3~- ion is in fact an OGd~+(O_2~(2-)) complex with Gd(III). These results show that a na?ve assignment of oxidation state of a chemical element without electronic structure analysis can lead to erroneous conclusions.     

Influence of the nuclearity of copper(II) chloride complexes on their activity in catalytic C-Cl bond metathesis

Catalytic systems containing mainly mononuclear (CuCl ₄ ^2? ) or dinuclear (Cu₂Cl ₆ ^2? ) tributylbenzylammonium chlorocuprates are prepared by adsorption on silica surfaces of different structures (Aerosil and Silokhrom). Using ESR, XANES, and electronic spectroscopy, the CuCl ₄ ^2? ions are shown to be reduced rapidly under conditions of C-Cl bond metathesis, whereas the dinuclear chlorocuprates are relatively stable. A correlation between the number of copper ions in the chlorocuprate anion and its catalytic activity is established: the mononuclear complexes are several times more active than their dinuclear counterparts.     

The thermodynamic characteristics of vaporization in the NaI-PrI<Subscript>3</Subscript> system

The vaporization of the NaI-PrI₃ quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI) _n and (PrI₃) _n molecules (n = 1, 2) and Na⁺(NaI) _n (n = 0–4) and I^?(PrI₃) _n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI₄, Na₂PrI₅, NaPrI ₃ ⁺ , Na₂PrI ₄ ⁺ , Na₃PrI ₅ ⁺ , Na₄PrI ₆ ⁺ , NaPrI ₅ ^? , and NaPr₂I ₈ ^? ). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.     

Quantum Chemical Study of Niobium and Tantalum M<Subscript>4</Subscript>O<Subscript>10</Subscript> Oxide Clusters and M<Subscript>4</Subscript>O<Stack><Subscript>10</Subscript><Superscript>–</Superscript></Stack> Anions

Structural parameters and vibrational frequencies of the clusters (T_d)–Nb₄O₁₀, (C_3v)-TaNb₃O₁₀, (D_2d)-Nb₄O ₁₀ ^– , and (C_s)-TaNb₃O ₁₀ ^– were calculated. According to the (U)DFT/SDD calculations with BLYP, B3LYP, and PBE0 functionals magnetization of the anion (D_2d)-Nb₄O ₁₀ ^– is distributed equally among four niobium atoms. In the anion (C_s)-TaNb₃O ₁₀ ^– unpaired electron presumably occupies niobium atoms. The distinction in contributions from Nb atoms in the magnetization of the tantalum-containing cluster grows with the exchange component of the DFT functional in the series of functionals BLYP < B3LYP < PBE0 < UHF.     

Thermal properties of dimethylgold(III) 8-hydroxyquinolinate and 8-mercaptoquinolinate

Dimethylgold(III) complexes with 8-hydroxyquinoline Me₂Au(Ox) (I) and 8-mercaptoquinoline Me₂Au(Tox) (II) were synthesized and studied. Complex II obtained for the first time was identified from the elemental analysis, IR, ¹H NMR, and mass spectrometry data. The thermal properties of complexes I, II in condensed state were investigated by thermography. The temperature dependences of the saturated vapor pressure over crystals were measured by the Knudsen effusion method with mass spectrometric recording of the gas phase composition and the thermodynamic characteristics of the sublimation process were determined: for I, log P[Torr] = (14.6 ± 0.3) ? (6.34 ± 0.10) × 10³/(T, K), Δ H _subl ^o = 121.2 ± 1.9 kJ^?1, Δ S _subl ^o = 224.1 ± 4.6 J mol^?1 K^?1 (the temperature interval under study 80–115°C); for II, log P [Torr] = (13.3 ± 0.2) ? (6.30 ± 0.09) × 10³/(T, K), Δ H _subl ^o = 120.5 ± 1.7 kJmol^?1, ΔS _subl ^o = 199.3 ± 3.0 J mol^?1 K^?1 (86–145°C).