Hydrolytic precipitation reaction of titanium(IV) from (Na,H)Cl aqueous solution

The hydrolytic precipitation of titanium(IV) in 2.0 mol dm⁻³ (Na, H)Cl aqueous solution at 25.0°C has been studied by measuring the free hydrogen ion concentration by a potentiometric method and the aqueous concentration of titanium(IV) by a spectrophotometric method. Under conditions where the solution is saturated with regard to precipitated titanyl(IV) hydroxide, monomeric and polycationic species, such as, TiO²⁺, TiO(OH)₂, and [(TiO)₈(OH)₁₂]⁴⁺, were deduced as being present in the solution. A scheme for the hydrolytic precipitation equilibria has been deduced.     

Sol-Gel Synthesis of Transparent Alumina Gel and Pure Gamma Alumina by Urea Hydrolysis of Aluminum Nitrate

-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al³⁺/urea solution presented urea coordinated with the aluminum ion, as shown in the ¹³C NMR and ²⁷Al NMR spectra and longitudinal relaxation times, T ₁, from the latter. The substitution of water molecules in the Al³⁺ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90°C. The resulting sol, composed of Al(OH)₃ nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. The freshly prepared gel was transformed, under heating at 300°C, directly to -alumina, characterized by FTIR, ²⁷Al-MAS-NMR and S_BET techniques, without - or -phases, as a consequence of the high degree of homogeneity of the -alumina precursor.     

Formation of variable-composition iron(III) hydrosilicates with the сhrysotile structure

The process of formation of iron hydrosilicates (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was studied. It was shown that the stage of coprecipitation of magnesium and iron hydroxides in the presence of silica nanoparticles forms poorly crystallized layered Mg–Fe double hydroxides having Fe³⁺ ions in the octahedral sites. Hydrothermal treatment of the mixtures of coprecipitated hydroxides and silica nanoparticles gives rise to layered hydrosilicates, where Fe³⁺ ions occupy both the octahedral (preferentially) and tetrahedral sires. The possibility of the formation and a fairly stable existence of the variable-composition layered hydrosilicate (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was shown to correlate with the stability range of its precursor brucite-like Mg–Fe layered double hydroxide.     

Enthalpies de formation des hydroxynitrates de zinc

The standard enthalpies of reaction of four zinc hydroxide nitrates Zn(OH)(NO₃)-H₂O, Zn₃(OH)₄(NO₃)₂, Zn₅(OH)₈(NO₃)₂·2H₂O et Zn₅(OH)₈(NO₃)₂ and zinc oxide with a solution of nitric acid (2N) were measured in a solution calorimeter. These results, combined with auxiliary thermochemical values from the literature, yielded values of ?429.34, ?442.41, ?897.41 and ?750.70 kcal mol^?1 respectively, for the molar enthalpies of formation of these zinc hydroxide nitrates.     

Influence of the morphology and impurities of Ni(OH)2 on the synthesis of neutral Ni(II)–amino acid complexes

Synthesis of neutral complexes of Ni²⁺ with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH)₂ toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate)₂(H₂O)₂]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH)₂ sheets arrangements, assigned to the substitution of Cl⁻ ions to OH⁻ ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 °C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate)₂(H₂O)₂], but with a different crystal structure, is also formed. Spectroscopic results may suggest a structure involving bridging ligands.     

The synthesis and thermochemical study of (Mg,Fe)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Nanotubular (Mg,Fe²⁺,Fe³⁺)₃Si₂O₅(OH)₄ hydrosilicates with a chrysotile structure were synthesized under hydrothermal conditions. The phases prepared were studied thermochemically on a high-temperature Tian-Calvet microcalorimeter by solution calorimetry. The standard enthalpies of formation of magnesium-iron nanotubular hydrosilicates were determined. The formation of iron-containing nanotubes was shown to be lass favorable energetically than the formation of magnesium nanotubes.     

Thermodynamics of the association of aqueous calcium and hexacyanoferrate ions

Thermodynamic quantities have been obtained for the formation of the ion pairs Ca²⁺Fe(CN)₆ ^4- and Ca²⁺Fe(CN)₆ ^3- in dilute aqueous solution by a potentiometric method employing an ion-exchange (Orion) calcium electrode. The reversibility of the electrode was examined against calomel and silver chloride references and was further tested in a determination of the formation constant for CaSO₄ (aq). The mean enthalpies of ion association of calcium with both hexacyanoferrates were obtained from the temperature variation of equilibrium constants within the range 15 to 35°C. The enthalpies were also independently determined calorimetrically. The results, discussed in terms of the electrostatic model, suggest that there is little penetration, if any, of hydration shells in the ion pairs.     

Hydrothermal Synthesis and Characterization of Nb3O7(OH)

Triniobium hydroxide heptaoxide, Nb₃O₇(OH), was prepared hydrothermally by treating niobic acid or triniobium chloride heptaoxide with 3.0 mol/dm³ sulfuric acid at 250–350°C and 15 MPa. The hydroxide oxide was isomorphous with the low-pressure form of triniobium fluoride heptaoxide which is built up of 3 X ∞ blocks of the ReO₃ structure with crystallographic shear in one dimension. When heated in air, Nb₃O₇(OH) dehydrated up to 460°C to give poorly crystallized Nb₂O₅, which, on further heating, changed slowly into a less ordered precursor of M? Nb₂O₅(¹). Hydrothermal treatment of Nb₃O₇(OH) with pure water at 400–500°C afforded P? and R? Nb₂O₅; the conversion of Nb₃O₇(OH) is explained in terms of the close structural relation among these three forms.     

The solution thermochemistry of antimony pentafluoride and some fluoroantimonates

From hydrolysis and solution measurements the enthalpies of formation of SbF₅(?), LiSbF₆(s), NaSbF₆(s), KSbF₆(s), CsSbF₆(s), AgSbF₆(s), and SbF₆^?aq. are estimated to be ?1324 ± 12, ?2062 ± 5, ?2060 ± 6, ?2080 ± 3, ?2082 ± 15, ?1653 ± 3, and ?1789 ± 4 kJ mol^?1 respectively. Less precise estimates of the enthalpies of formation of O₂SbF₆ and of CsSb₃F₁₆ are also given. From the results the fluoride ion affinity of SbF₅, the single ion hydration enthalpy of SbF₆^? (g), and the charge distribution within the SbF₆^? ion have been calculated.     

Tailoring Transition‐Metal Hydroxides and Oxides by Photon‐Induced Reactions

Controlled synthesis of transition‐metal hydroxides and oxides with earth‐abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition‐metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺, Mn²⁺, and Co²⁺ ion‐containing aqueous solution undergoes photo‐induced reactions and produces hollow metal‐oxide nanospheres (Ni_0.18Mn_0.45Co_0.37O_x) or core–shell metal hydroxide nanoflowers ([Ni_0.15Mn_0.15Co_0.7(OH)₂](NO₃)_0.2?H₂O), depending on the laser wavelengths. We propose two reaction pathways, either by photo‐induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon‐induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.     

Thermodynamics of the Interaction of the Ni<Superscript>2+</Superscript> Ion with the L-β-Phenyl-α-Alanine Anion in Aqueous Solution

The enthalpies of the interaction of the L-β-phenyl-α-alanine anion with the Ni²⁺ ion in aqueous solution were measured by calorimetry for the ionic strength I = 0.5, 1.0, and 1.5 (KNO₃ as a supporting electrolyte) at 298.15 K. The thermodynamic parameters of the formation of Ni(II) complexes with phenylalanine in aqueous solution were calculated. The effect of the ligand structure on the thermodynamic parameters of complexation reactions in solution was discussed.     

Enthalpie de formation de la whitlockite Ca18Mg2H2(PO4)14

Pure and well crystallised whitlockite Ca₁₈Mg₂H₂(PO₄)₁₄ has been synthesized by precipitation from the magnesium and calcium nitrates and the diammonic phosphate. The product of the reaction has been characterized by X-ray diffraction, IR spectroscopy and chemical analysis. Using differential conduction calorimeters the enthalpies of solution of the whitlockite and of a mixture of the solid reactants - the tricalcium, the trimagnesium and the dicalcium phosphates - have been measured at 25°C for various concentrations of solid in a 46 wt% nitric acid solution. A combination of the enthalpies of solution with the enthalpies of formation of the reactants allows us to determine the standard enthalpy of formation of the whitlockite. The value deduced, -27,93·10³kJ mol^-1, is compared to the standard enthalpies of formation of the trimagnesium and the tricalcium phosphates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reactions of trivacant lone-pair-containing tungstobismutate and electrochemical behaviors of its sandwich-type products

We report the crystal structure of dimeric precursor Na₁₂[(Na(H₂O)₂)₆(α-BiW₉O₃₃)₂] (1), and the interaction of this precursor with transition metal ions. Interaction of 1 with Cu²⁺ in neutral medium leads to the formation of a Hervé-type sandwich polyoxoanion [(Cu(H₂O))₃(α-BiW₉O₃₃)₂]^12? (2) in high yield. Interaction of 1 with M²⁺ (M?=?Zn, Ni, Co, Mn) in acidic aqueous medium leads to formation of Krebs-type sandwich polyoxoanions [(M(H₂O)₃)₂(WO)₂(β-BiW₉O₃₃)₂]^10? (3–6). Coordination geometry of the M²⁺ ions, counterions and precursors can affect the structure of products. In our experiments, only the interaction of 1 with Cu²⁺ forms a trisubstituted sandwich-type product. The method using [α-Bi^IIIW₉O₃₃]^9? as starting material is a convenient and effective route for the synthesis of sandwich-type tungstobismutates in high purity and yield. The electrochemical properties of these sandwich-type tungstobismutates in aqueous solution are described.     

Thermodynamics of Ni(II) Complexation with L-Asparagine in Aqueous Solution

Complexation of the Ni²⁺ ion with L-asparagine (HAsn^±) is studied by potentiometric titration at 298.15 K and at the 0.3, 0.5 and 1.0 ionic strength of the solution (KNO₃). The formation of the NiAsn⁺ and NiAsn₂ complexes was established and their stability constants were determined. The thermodynamic stability constants of the mono- and bis(L-asparagine)nickel(II) complexes were obtained by extrapolation to zero ionic strength. The direct calorimetry method was used to measure the heat effect of the L-asparagine reaction with the Ni(II) nitrate solution in different pH intervals at 298.15 K and at the 0.5, 1.0, and 1.5 ionic strength (KNO₃). The standard enthalpies of the NiAsn⁺ and NiAsn₂ formation were found using extrapolation and the equation with one individual parameter. The enthalpies of the formation of the Ni(II) complexes with L-asparagine in aqueous solution were calculated in the standard hypothetically undissociated state.     

Equilibria in complexes ofN-Heterocyclic molecules,part XXIII. Reaction of hydroxide ion with bis-[2,4,6-tri-(2-pyridyl)-1,3,5-triazine] cobalt(II) and nickel(II)

Summary The reactions of [Ni(TPT)₂]²⁺ and [Co(TPT)₂]²⁺ with aqueous hydroxide ion involve the formation of pseudo-base species prior to the dissociation of a ligand molecule. The [M(TPT)(H₂O)₃]²⁺ or [M(TPT)(OH)₃]^– species thus formed react further with hydroxide ion to yield compounds previously described. The kinetics of pseudo-base formation have been followed in each case and the results are compared with a number of other reactions of analogous compounds with hydroxide ion and with water.Part XXII, ref. 3.     

Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potential

DyI₂ and Dy_3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be Δ_fH°(DyI₂, s, 298 K) = ?(394 ± 16) kJ· mol^?1 and Δ_fH°(DyI₃, s, 298 K) = ?(616 ± 10) kJ· mol^?1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy³⁺/Dy²⁺, aq) was calculated to be ?(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI₃ to DyI₂ and of DyCl₃ to DyCl₂.     

Synthesis and crystal structures of supramolecular compounds of polynuclear aluminum(III) aqua hydroxo complexes with cucurbit[6]uril

Supramolecular compounds of the di-, trideca-, and triacontanuclear aluminum aqua hydroxo complexes, viz., [Al₂(OH)₂(H₂O)₈]⁴⁺, [Al₁₂(AlO₄)(OH)₂₄(H₂O)₁₂]⁷⁺, and [Al₃₀O₈(OH)₅₆(H₂O)₂₆]¹⁸⁺, respectively, with the organic macrocyclic cavitand cucurbit[6]uril (C₃₆H₃₆N₂₄O₁₂) were prepared by evaporation of aqueous solutions of aluminum nitrate and cucurbit[6]uril after the addition of pyridine, ammonia, KOH, or NaOH at pH 3.1–3.8. X-ray diffraction study demonstrated that the aqua hydroxo complexes are linked to the macrocycle through hydrogen bonds between the hydroxo and aqua ligands of the polycations and the portal oxygen atoms of cucurbit[6]uril. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 261—268, February, 2006.     

白硼钙石的合成新方法及其热化学研究(英)

0IntroductionTherearemanykindsofhydratedcalciumbo-rates,bothnaturalandsynthetic.Someofthemarematerialsusedinglass,potteryandporcelainenamelindustry,especiallyinunalkaliglassindustry.4CaO·5B2O3·7H2O,calledpriceite,isacalciumboratemin-eral,notfoundinCaO-B…     

The hydrolytic precipitation reaction of Mg(II) from aqueous NaNO3 solution

An equilibrium study has been made of the hydrolytic precipitation reaction of Mg(II) in 1.0 mol dm⁻³ aqueous NaNO₃ solution at 25.0°C by measurements of the free hydrogen ion concentration by a potentiometric method and of the dissolved Mg(II) by a complexometric method. Under the condition that the solution is saturated with precipitated Mg(II) hydroxide, such species as Mg²⁺, Mg₂(OH)₂²⁺, Mg₃(OH)₄²⁺ and Mg(OH)₂ may be present; their stability constants and solubility products were determined. A scheme for the hydrolytic precipitation equilibria of Mg(II) is presented.     

Standard enthalpy of the formation of Ba[AuF6]2(cr.)

The enthalpies of the interaction of Ba[AuF₆]₂(cr.) with water and an aqueous potassium hydroxide solution have been measured in a calorimeter with an isothermal shell at 298.15 K. The standard enthalpy of the formation of the studied compound Δ_f H° Ba[AuF₆]₂(cr.) = −2341 ± 10 kJ/mol has been found by two independent methods based on these results and literature data.