The composition, charge and architecture of hydronium ions as observed in the crystalline state

The structures of hydronium ions present in single crystals have, by and large, been thought as being relatively simple and characterized by the classical formulae H₃O⁺, , and . All of them are thought to be quasi-planar, acyclic entities of charge +1, exclusively. In this review, we show that such is not the case in view of the fact that there exist documented examples of cyclic hydronium ions, that their charge can be larger than +1 and that they exist in aggregates containing more than four oxygens. Moreover, it is documented that hydronium ions exist in the form of geometrical isomers or conformers. To cite this article: I. Bernal, C. R. Chimie 9 (2006).     

Proton segregation on a growing ice interface

Hydronium segregates to the surface of H₂O (D₂O) ice films grown on Pt(1 1 1) above 151 K (158 K). This is observed via the voltage that develops across the films, utilizing work function measurements. The dependence of this voltage on the film’s thickness is explained by a simple equilibrium model: as the film grows, most of the surface ions migrate so as to remain at the ice–vacuum interface, while a fixed percentage (0.05%) take the thermodynamically–unfavored route, to become incorporated into the growing bulk ice. This model implies a ΔG of about +0.1 eV for the movement of ions from the ice surface into the bulk ice.     

Enhanced field ionization of water adsorbed on a carbon monoxide-covered, platinum field emitter tip

The influence of carbon monoxide, adsorbed on a platinum field emitter tip, on field ionization of adsorbed water was examined. Ramped field desorption (RFD) measurements of water ionization were performed at 108 K for water layer thicknesses up to 80 ML on a clean or CO-saturated tip surface. In RFD the applied field is ramped linearly in time until water ionization is detected, giving the onset field of ionization. Water ionization yields hydrated hydroxide ions and protons; the hydroxide ions remain within the water layer on the tip, while the hydrated protons are emitted into vacuum. At a low water coverage of 1.5 ML, the CO adlayer substantially reduced the onset field of ionization (that is, facilitated ionization) of water by 40%, from a value of 0.43 V/Å for water on clean Pt to 0.26 V/Å for water on CO-covered Pt. The extent of the reduction gradually diminished with thicker coverages of water and was absent at coverages of 20 ML or greater. The characteristic decay length of the field enhancement was 4.7 ± 1 ML. The results were analyzed with the charge exchange model of ionization kinetics and changes in dipole moments of water adsorbed without and with CO. The analysis reveals that a change in water structure (dipole moment) caused by CO is an important contributor in field enhancement and that the dipole moment for hydrated hydroxide ion in an ice-like layer must be greater than that for bulk ice-like water. The significance of these results with respect to electrochemical oxidation of CO is discussed.     

The electrolyte NRTL model and speciation approach as applied to multicomponent aqueous solutions of H2SO4, Fe2(SO4)3, MgSO4 and Al2(SO4)3 at 230–270 °C

This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe₂O₃) in aqueous ternary and quaternary systems of H₂SO₄, MgSO₄ and Al₂(SO₄)₃ at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H₂SO₄–MgSO₄–H₂O, H₂SO₄–Al₂(SO₄)₃–H₂O at 235–270 °C and H₂SO₄–Fe₂(SO₄)₃–H₂O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al³⁺, Mg²⁺ Fe³⁺ and SO₄²⁻, HSO₄⁻, OH⁻, H₃O⁺, respectively, as well as molecular species. The solid phases were hydronium alunite (H₃O)Al₃(SO₄)₂(OH)₆, hematite Fe₂O₃ and magnesium sulfate monohydrate (MgSO₄)·H₂O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H₂SO₄–Fe₂(SO₄)₃–MgSO₄–H₂O, H₂SO₄–Fe₂(SO₄)₃–Al₂(SO₄)₃–H₂O at 250 °C and H₂SO₄–Al₂(SO₄)₃–MgSO₄–H₂O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.     

The composition and architecture of hydrated hydroxy anions as observed in the crystalline state – A review

Search of the Cambridge Structural Database reveals that hydrated hydroxide anions can be quite complex in their stereochemistry. As in the case of hydronium cations [I. Bernal. C.R. Chim. 9 (2006) 1454], they can be acyclic as well as cyclic. Moreover, it is documented here that hydrated hydroxide anions exist in the form of geometrical isomers or conformers. A simple example occurs in species of composition H₅O₃⁻ which exist in isomeric forms in which their stereochemistry depends on whether the OH⁻ is the hydrogen donor to waters or vice versa. All illustrations in this survey were generated with DIAMOND.     

A thermogravimetric and infrared emission spectroscopic study of alunite

Thermogravimetric and differential thermogravimetric analysis has been used to characterize alunite of formula [K₂(Al³⁺)₆(SO₄)₄(OH)₁₂]. Thermal decomposition occurs in a series of steps (a) dehydration up to 225°C, (b) well defined dehydroxylation at 520°C and desulphation which takes place as a series of steps at 649, 685 and 744°C.The alunite minerals were further characterized by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3463 and 3449 cm^?1 are observed. At 550°C all intensity in these bands is lost in harmony with the thermal analysis results. OH stretching bands give calculated hydrogen bond distances of 2.90 and 2.84–7 Å. These hydrogen bond distances increase with increasing temperature. Characteristic (SO₄)^2? stretching modes are observed at 1029.5, 1086 and 1170 cm^?1. These bands shift to lower wavenumbers on thermal treatment. The intensity in these bands is lost by 550°C.     

Neue Kronenether‐stabilisierte Oxoniumhalogenochalkogenate: [H3O(Dibromo‐benzo‐18‐Krone‐6)]2[Se3Br10] und [H5O2(Bis‐dibromo‐dibenzo‐24‐Krone‐8]2[Se3Br8]

Novel Oxonium Halogenochalcogenates Stabilized by Crown Ethers: [H₃O(Dibromo‐benzo‐18‐crown‐6)]₂[Se₃Br₁₀] and [H₅O₂(Bis‐dibromo‐dibenzo‐24‐crown‐8]₂[Se₃Br₈] Two novel complex oxonium bromoselenates(II,IV) and –(II) are reported containing [H₃O]⁺ and [H₅O₂]⁺ cations coordinated by crown ether ligands. [H₃O(dibromo‐benzo‐18‐crown‐6)]₂[Se₃Br₁₀] ( 1 ) and [H₅O₂(bis‐dibromo‐dibenzo‐24‐crown‐8]₂[Se₃Br₈] ( 2 ) were prepared as dark red crystals from dichloromethane or acetonitrile solutions of selenium tetrabromide, the corresponding unsubstituted crown ethers, and aqueous hydrogen bromide. The products were characterized by their crystal structures and by vibrational spectra. 1 is triclinic, space group (Nr. 2) with a = 8.609(2) Å, b = 13.391(3) Å, c = 13.928(3) Å, α = 64.60(2)°, β = 76.18(2)°, γ = 87.78(2)°, V = 1404.7(5) ų, Z = 1. 2 is also triclinic, space group with a = 10.499(2) Å, b = 13.033(3) Å, c = 14.756(3) Å, α = 113.77(3)°, β = 98.17(3)°, γ = 93.55(3)°. V = 1813.2(7) ų, Z = 1. In the reaction mixture complex redox reactions take place, resulting in (partial) reduction of selenium and bromination of the crown ether molecules. In 1 the centrosymmetric trinuclear [Se₃Br₁₀]^2? consists of a central Se^IVBr₆ octahedron sharing trans edges with two square planar Se^IIBr₄ groups. The novel [Se₃Br₈]^2? in 2 is composed of three planar trans‐edge sharing Se^IIBr₄ squares in a linear arrangement. The internal structure of the oxonium‐crown ether complexes is largely determined by the steric restrictions imposed by the aromatic rings in the crown ether molecules, as compared to complexes with more flexible unsubstituted crown ether ligands.     

Adsorption of Acid Dyes from Aqueous Solutions by Calcined Alunite and Granular Activated Carbon

Dyestuff production units and dyeing units have always had a pressing need for techniques that allow economical pretreatment for color in the effluent. The effectiveness of adsorption for dye removal from wastewaters had made it an ideal alternative to other expensive treatment options. This paper deals with an investigation on alunite, existing wide reserves in Türkiye and in the world, for dye removal. Calcined alunite was utilized for this study and its performance evaluated against that of granular activated carbon (GAC). The use of calcined alunite for the removal of Acid Blue 40 and Acid Yellow 17 (AB 40 and AY 17) from aqueous solution at different calcination temperature and time, particle size, pH, agitation time and dye concentration has been investigated. The adsorption followed by Langmuir and Freundlich isotherms. The process follows first order adsorption rate expression and the rate constant was found to be 7.65 × 10^–2 and 5.74 × 10^–2 min^–1 for adsorption of AB 40 and AY 17 on calcined alunite, and 8.41 × 10^–2 and 10.04 × 10^–2 min^–1 for adsorption of AB 40 and AY 17 on GAC, respectively. The equilibrium saturation adsorption capacities were 212.8 mg dye/g calcined alunite and 151.5 mg dye/g calcined alunite for AB 40 and AY 17, respectively. The adsorption capacities were found to be 57.47 mg and 133.3 mg dye per g of GAC for AB 40 and AY 17, respectively. The results indicate that, for the removal of acid dye, calcined alunite was most effective adsorbent, although comparable dye removals were exhibited by GAC.     

Simulations of quantum computation with a molecular ion

The capabilities of a new system for coherent control—intense terahertz light pulses acting on trapped, gas phase D₃O⁺ molecules—are investigated using realistic molecular and pulse parameters. Computer simulations show that a set of three shaped pulses can be used to perform four level (two qubit) quantum computational gates on the inversion–rotation energy levels and read-out the result using degenerate four-wave mixing. Two pulse shaping techniques are employed, one directly shaping a terahertz pulse, and another shaping a visible laser pulse that is rectified by a terahertz antenna. Both are found to be effective for control. Methods for initializing the inversion–rotation wavepacket, making the pulse robust against power variations, maximizing its fidelity to a unitary gate transformation and addressing limitations of energy level connectivity are discussed.