Calorimetric and spectroscopic studies of solutions of copper(II) and nickel(II) nitrates in water-carbamide mixtures at 298.15 K

The heat effects of mixing aqueous solutions of copper(II) and nickel(II) nitrates with water-carbamide mixtures were measured on an isothermic-shell calorimeter in the amide concentration region. An increase in the concentration of carbamide strengthened solvation in copper(II) salt solutions to a greater extent. The electronic absorption spectra were recorded at fixed concentrations of the electrolytes to find that the solvation of copper(II) and nickel(II) nitrates in water-carbamide mixtures involved intrasphere and predominantly outer-sphere cation-solvent interactions, respectively.     

Thermochemical parameters of Ni(NO3)2 solutions in water + formamide + α-alanine mixtures at 298 K

The enthalpies of mixing of aqueous solutions of nickel(II) nitrate in water + formamide + α-alanine mixtures in the range of existing amide concentrations have been measured calorimetrically. From these data the standard enthalpies of electrolyte transfer from water into ternary mixtures have been calculated. The type and character of electrolyte transfer isotherms are discussed on the basis of the heats of transfer of individual ions that were studied earlier, as well as the contributions into these values that characterize structural changes in the solution and chemical ion-solvent interactions.     

Thermochemical characteristics of transfer of copper(II) and nickel(II) nitrates from water to water-formamide mixtures

The enthalpies of mixing of aqueous solutions of copper(II) and nickel(II) nitrates with water-formamide mixtures were measured calorimetrically at 298.15 K in the entire composition range. The standard enthalpies of transfer of the electrolytes from water to water-formamide mixtures were calculated from these data. The shape of the isotherms of transfer of the electrolytes is discussed on the basis of the calculated enthalpies of transfer of individual ions and contributions to these quantities made by universal, chemical, and electrostatic interactions of ions with the solvents.     

The thermochemical characteristics of solutions of Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> in water-formamide-α-L-alanine mixtures at 298 K

The enthalpies of mixing of aqueous solutions of copper(II) nitrate with aqueous solutions of formamide and α-L-alanine were measured calorimetrically over the whole composition range with respect to amide. The results were used to calculate the standard enthalpies of electrolyte transfer from water into ternary mixtures. The shape and character of electrolyte transfer isotherms are discussed on the basis of the enthalpies of transfer of individual ions studied earlier in a binary solvent and the contributions of universal and chemical interactions between the ion and solvents to these values characterizing structural changes in solution.     

Thermochemistry of formation of copper(II)-ethylenediamine complexes and solvation of reagents in aqueous organic solvents

The heat effects of the reactions of formation of ethylenediamine-copper(II) complexes were determined calorimetrically in mixtures of water with ethanol, acetone and dimethylsulfoxide. The results were interpreted in terms of the enthalpies of transfer (Δ_t H ⁰) of the complex former, the ligand and the complex ion from water to binary solvents. In water—DMSO mixtures, the Δ_t H ⁰ values for copper(II) and complex ions were found to change in similar ways, and their contributions to the reaction heat effects compensate each other to a large extent. Thus, the reaction enthalpy change due to solvent composition variation is caused mainly by the changes in ligand solvation enthalpies. In aqueous ethanol and acetone solutions, the changes in Δ_t H ⁰ for all reagents influence the heat effect equally.     

Nanocomposites of Metallic Silver with Octamolybdate Amine Complexes of Nickel(II) and Copper(II)

Theoretical and Experimental Chemistry - It was shown that interaction of photoreduced octamolybdate amine complexes of nickel(II) and copper(II) with silver(I) nitrate in aqueous solutions leads...     

Thermodynamic parameters of complexation reactions between nickel(II) ion and L-serine in aqueous solutions

A thermochemical study of coordination equilibria in the nickel(II) ions-L-serine system was carried out. The heats of reaction between solutions of an amino acid and nickel(II) nitrate at 288.15, 298.15, and 308.15 K and ionic strength of 0.25, 0.50, and 0.75 (KNO₃) were measured. The heats of dilution of nickel nitrate solution in background electrolyte solutions were determined under identical conditions to make proper corrections. The results were processed with allowance for stepwise equilibria. The standard thermodynamic parameters of the complexation processes were calculated. The effect of temperature on heats of complexation reactions in the L-serine-nickel(II) ions was studied. The standard enthalpies of formation of NiSer⁺, NiSer₂, and NiSer ₃ ^? complexes in aqueous solutions were determined.     

Preparation and characterization of potassium copper nickel hexacyanoferrate(II) as an ion exchanger for cesium

Potassium copper nickel hexacyanoferrate(II) [KCNF] was prepared by treating potassium nickel hexacyanoferrate(II) with copper nitrate solution in 0.1M HNO₃. The resulting material was dried at various temperatures. Chemical analysis, i.r., thermal decomposition and surface property measurements were used to characterize the material. The adsorption of cesium from aqueous solutions on KCNF was investigated and optimized as a function of equilibration time and pH. The material dried at 110°C was found to be fairly stable in dilute acids, salt solutions, high doses of gamma-radiation and at high temperature. It also showed better surface properties and a high value of ion exchange capacity (2.25 mmol·g^–1) for cesium.     

Nickel(II) complexing with glycylglycine and acid-base equilibria of the ligand in aqueous ethanol solvents

The protonation and dissociation constants of glycylglycine and the stability constants of its complexes with nickel(II) in aqueous ethanol of a variable composition with the ethanol mole fraction ranging from 0.00 to 0.55 are determined potentiometrically at a 0.1 M (NaClO₄) ionic strength and temperature of 298 K. The stability of nickel(II) complexes of glycylglycine is found to grow with an increase in ethanol concentration in a solution. The solvation contributions of reagents into the displacement of complexing equilibria are analyzed. The change in the stability of nickel(II) glycylglycinate complexes is explained by the weakening of ligand solvation in aqueous ethanol.     

Selective extraction of iron(III) from aqueous nitrate solution in the presence of cobalt(II), copper(II) and nickel(II) ions using bis(delta2-2-imidazolinyl)-5,5'-dioxime.

The feasibility of using bis(delta2-2-imidazolinyl)-5,5'-dioxime (H2L) for the selective extraction of iron(III) from aqueous solutions was investigated by employing an solvent-extraction technique. The extraction of iron(III) from an aqueous nitrate solution in the presence of metal ions, such as cobalt(II), copper(II) and nickel(II), was carried out using H2L in binary and multicomponent mixtures. Iron(III) extraction has been studied as a function of the pH, equilibrium time and extractant concentration. From the extracted complex species in the organic phase, iron(III) was stripped with 2 M HNO3, and later determined using atomic-absorption spectrometry. The extraction was found to significantly depend on the aqueous solution pH. The extraction of iron(III) with H2L increases with the pH value, reaching a maximum in the zone of pH 2.0, remaining constant between 2 and 3.5 and subsequently decreasing. The quantitative extraction of iron(III) with 5 x 10(-30 M H2L in toluene is observed at pH 2.0. H2L was found to react with iron(III) to form ligand complex having a composition of 1:2 (Fe:H2L).     

Initial state versus transition state solvation effects on the kinetics of oxidation of nickel(II) dioxocyclam by peroxodisulfate

The kinetics of oxidation of 1,4,8,11-tetraazacyclotetradecane-5,7-diamidonickel(II) (nickel dioxocyclam) by peroxodisulfate have been measured in a range of binary aqueous solvent mixtures. Reaction rates are retarded by the presence of organic co-solvents, indicative of destabilization of the transition state (TS) relative to the initial state (IS) in the binary aqueous mixtures. Thus the TS is more hydrophilic than the IS. From solubility measurements of the nickel(II) macrocycle, the transfer chemical potential of the IS of the reaction has been estimated and compared with that of the TS. The transfer potential of the IS is dominated by the solvation of the peroxodisulfate ion.     

Thermochemistry of solvation and complexation in the Cu(NO3)2-water-ethanol-L-α-alanine system at 298.15 K

The heats of mixing of aqueous solutions of copper(II) nitrate and sodium alaninate and the heats of dilution of an aqueous solution of sodium alaninate in water-ethanol mixtures were calorimetrically measured at 298.15 K. The enthalpies of transfer of α-alaninate from water into water-alcohol mixtures and the standard molar enthalpies of the reaction of copper(II) complexation with α-alaninate ion in the mixtures under study are calculated. The resulting enthalpy parameters are compared with those of the similar system containing synthetic β-alanine, which was studied earlier.     

Synthesis and characterisation of copper(II) hydroxide gels

The formation of copper(II) hydroxide gels from aqueous precursors requires very critical conditions. Gels have been obtained by adding ammonia to aqueous solutions of copper(II) acetate, in the presence of a small amount of sulphate ions. Other salts (chloride, nitrate, sulphate) or bases (NaOH, KOH) lead to precipitation rather than gelation. These gels are actually made of an intimate mixture of acetate-based organic/inorganic polymers and nanometric posjnakite crystals Cu₄(OH)₆(SO₄) · H₂O. Acetate ions and ammonia can be partially removed upon washing, which after drying leads to crystalline copper(II) hydroxide needles deposited on a strongly oriented layer of posjnakite crystals. A theoretical model based on the electronegativity equalisation principle is used to describe these experimental results. It provides a better understanding of the role of complexing anions during the formation of condensed phases.     

Studies on the electrode reaction of Cr(III)CyDTA/Cr(II)CyDTA by the coulostatic method in various alcohol + water mixtures

Standard rate constants (k_s)_ms and cathodic transfer coefficients (α_c)_ms of the electrode reaction of Cr(III)CyDTA/Cr(II)CyDTA have been obtained by the coulostatic method in methanol + water, ethanol + water, n-propanol + water and n-butanol + water mixtures, where CyDTA means trans-1,2-cyclohexanediaminetetraacetate. The values of (k_s)_ms obtained at low concentrations of the alcohols are nearly equal to that obtained in aqueous solutions. With increasing concentrations of alcohols, they decrease, in the cases of methanol and n-butanol, in the concentration ranges in which the measurements were made, while, in the cases of ethanol and n-propanol, they decrease to reach minima at certain concentrations and then increase again. The values of (α_c)_ms obtained at high concentrations of n-propanol and n-butanol are much larger than those obtained in aqueous solutions.     

Solvatochromism and piezochromism of pentacyanoferrate(II) complexes in binary aqueous solvent media

Summary The solvatochromic behaviour of a number of pentacyano-ferrates (II), [Fe^II(CN)₅L] ^n-, is described, for solutions in H₂O-alcohol, -Me₂CO and -DMSO mixtures. The strong dependence of solvent sensitivity on the nature of the ligand L is particularly fully documented for H₂OMeOH mixtures (0–100% MeOH). The piezochromic behaviour of seven pentacyanoferrates(II) has been established, in aqueous solution. The connection between piezochromism and solvatochromism is detailed, and the solvatochromic results discussed in terms of (preferential) solvation.     

Electrodialytic separation of cobalt(II) and nickel(II) using liquid membranes based on tri-n-octylamine and trialkylbenzylammonium chloride

Electrodialytic separation of Co(II) and Ni(II) in the course of their transfer from 3–4 M HCl solutions into dilute solutions of various acids using liquid membranes that contain anion-exchange carriers was studied. The influence exerted on the metal transport rate and separation efficiency by the compositions of the feed and receiving aqueous solutions and of liquid membranes and by the electrodialysis current density was examined. Under optimal conditions, in metal recovery from a solution containing an equimolar mixture of 0.01 M CoCl₂ and NiCl₂, the separation factor β_Co/Ni is 147; when nickel in the feed solution is in excess, it reaches 330, and when cobalt(II) is in excess, it exceeds 400.     

Studies on systems of salts and mixed solvents. XXXIII. On the solvation of cations (Li+, Mg2+, Al3+) in dimethylsulphoxide-water mixtures (Raman spectroscopic investigations into concentrated electrolyte solutions)

Starting from pure DMSO (DMSO-d₆) the solvent-solvent interactions detectable in the aqueous systems were investigated by means of v_SO and v_CS. On the basis of the results obtained the solvation behaviour of cations (Li⁺, Mg²⁺, Al³⁺) in DMSO (DMSO-d₆)? H₂O mixtures is discussed. In spite of the prevailing solvent-solvent interactions direct cation-DMSO (DMSO-d₆) interactions can still be proved in solutions rich in water, which suggest preferred cation solvation by the organic molecule.     

Thermochemical study of complexation and solvation in the β-alanine-Cu(NO3)2-water-ethanol system: 2. Enthalpies of solvation of sodium alaninate and copper(II) nitrate in mixed solvents

The heats of mixing of aqueous copper(II) nitrate and sodium β-alaninate with water-ethanol solvents were measured thermochemically at 298.15 K. The enthalpies of transfer of the Ala⁻ alaninate anion and Cu²⁺ ion in binary water-ethanol mixtures were calculated. The effect of the composition of the binary solvent on the enthalpy of formation of [CuAla]⁺ and the enthalpies of solvation of the ligand, central ion, and complex ion was studied.     

Physicochemical Properties of Solutions of Amides in H2O and in D2O

Excess volume, partial molar volumes, viscosity, and ultrasound velocity in H₂O and D₂O solutions of formamide (FM), acetamide (AM), dimethylformamide (DMF), and dimethylacetamide (DMA) were studied at 20°C. The change in the excess volume of the various amide solutions on substitution of D₂O for H₂O varies both in magnitude and direction. On the other hand, the isotope effect on the ultrasound velocity behaves similarly in all cases. Its magnitude is greatest for pure water and then decreases monotonically with increasing amide concentration. Although the behavior of the concentration dependence of viscosity is similar to that for ultrasound velocity, the isotope effect on the viscosity behaves in a different way. For methyl-substitued amides, a maximum isotope effect is observed at amide mole fraction 0.2, but the isotope effect for FM and AM increases monotonically with increasing amide concentration. The differences in the behavior of amides in aqueous solution are discussed in terms of their interactions with water.     

Copper(II) Complexes of N,N′-Bis-βCarbamoylethyl) Ethylenediamine in Aqueous Solution

The interactions of the ligand N, N -bis-(β-carbamoylethyl)-ethylenediamine (BCEN) with copper (II) in aqueous solution have been investigated by potentiometric and spectrophotometric techniques. The two protonation constants of the ligand at 25° in 0.2 M NaNO₃are 10^5-51and 10^5-44 The quantitative equilibrium studies of the stepwise reactions which precede the formation of CuBCEN²⁺ and the Cu-O to Cu-N bond rearrangements at the two amide sites are described in detail. Electronic spectra of the copper (II) chelates formed are measured and discussed.