Hydration of the bisulfate ion: atmospheric implications

Using molecular dynamics configurational sampling combined with ab initio energy calculations, we determined the low energy isomers of the bisulfate hydrates. We calculated the CCSD(T) complete basis set (CBS) binding electronic and Gibbs free energies for 53 low energy isomers of HSO(4)(-)(H(2)O)(n=1-6) and derived the thermodynamics of adding waters sequentially to the bisulfate ion and its hydrates. Comparing the HSO(4)(-)/H(2)O system to the neutral H(2)SO(4)/H(2)O cluster, water binds more strongly to the anion than it does to the neutral molecules. The difference in the binding thermodynamics of HSO(4)(-)/H(2)O and H(2)SO(4)/H(2)O systems decreases with increasing number of waters. The thermodynamics for the formation of HSO(4)(-)(H(2)O)(n=1-5) is favorable at 298.15 K, and that of HSO(4)(-)(H(2)O)(n=1-6) is favorable for T < 273.15 K. The HSO(4)(-) ion is almost always hydrated at temperatures and relative humidity values encountered in the troposphere. Because the bisulfate ion binds more strongly to sulfuric acid than it does to water, it is expected to play a role in ion-induced nucleation by forming a strong complex with sulfuric acid and water, thus facilitating the formation of a critical nucleus.     

Sequential hydration energies of the sulfate ion, from determinations of the equilibrium constants for the gas-phase reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O

Sequential hydration energies of SO4(H2O)(n)2- were obtained from determinations of the equilibrium constants of the following reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O. The SO4(2-) ions were produced by electrospray and the equilibrium constants Kn,n-1 were determined with a reaction chamber attached to a mass spectrometer. Determinations of Kn,n-1 at different temperatures were used to obtain DeltaG0n,n-1, DeltaH0 n,n-1, and DeltaS0n,n-1 for n = 7 to 19. Interference of the charge separation reaction SO4(H2O)(n)2- = HSO4(H2O)(n-k)- + OH(H2O)(k-1)- at higher temperatures prevented determinations for n < 7. The DeltaS0n,n-1 values obtained are unusually low and this indicates very loose, disordered structures for the n > or = 7 hydrates. The DeltaH0n,n-1 values are compared with theoretical values DeltaEn,n-1, obtained by Wang, Nicholas, and Wang. Rate constant determinations of the dissociation reactions n,n - 1, obtained with the BIRD method by Wong and Williams, showed relatively lower rates for n = 6 and 12, which indicate that these hydrates are more stable. No discontinuities of the DeltaG0n,n-1 values indicating an unusually stable n = 12 hydrate were observed in the present work. Rate constants evaluated from the DeltaG0n,n-1 results also fail to indicate a lower rate for n = 12. An analysis of the conditions used in the two types of experiments indicates that the different results reflect the different energy distributions expected at the dissociation threshold. Higher internal energies prevail in the equilibrium measurements and allow the participation of more disordered transition states in the reaction.     

Surface Complexation Modeling of K(+), NO(3)(-), SO(4)(2-), Ca(2+), F(-), Co(2+), and Cr(3+) Ion Adsorption on Silica Gel

Surface complex formation of K(+), NO(3)(-), SO(4)(2-), Ca(2+), F(-), Co(2+), and Cr(3+) ions was determined on the surface of silica gel. Experimental data obtained by acid-base titration of suspensions were interpreted in terms of the triple-layer model. The value of the deprotonation constant of surface OH could be determined precisely but the protonation constant was rather uncertain. The logarithms of ion pair formation constants for K(+), NO(3)(-), Ca(2+), and SO(4)(2-) adsorbed in the beta-plane are log K(ipM,X) approximately 0, therefore these species can be considered inert ions in the investigated pH range. F(-), Co(2+), and Cr(3+) ions were found to be strongly sorbed in the o-plane. In order to provide a good fit and to obtain parameters independent of their initial values, all possible equilibrium must be accounted for in the models. Copyright 2001 Academic Press.     

Ab initio investigation on ion-associated species and association process in aqueous Na2SO4 and Na2SO4/MgSO4 solutions

In the present paper, the possible ion associated species in pure Na(2)SO(4) and mixed Na(2)SO(4)/MgSO(4) aqueous solutions are investigated via the ab initio method at the HF/6-31+G? level. The vibrational v(1)-SO(4)(2-) band is analyzed. For the unhydrated species, when the number of metal ions around the SO(4)(2-) ion is less than 3, the dominating effect to the v(1)-SO(4)(2-) band is the polarization of the cations, while the M-O bonding will be dominating as the number is equal to or more than 3. For the hydrated species, the coordinated structures of the Na(+) ion in all ion pairs are not stable due to the strong effect of the SO(4)(2-) ion but relatively stable in the triple ion (TI) clusters since there are fewer vacant hydration sites around the SO(4)(2-). The v(1)-SO(4)(2-) frequencies are close to that of the hydrated SO(4)(2-) ion in the ion pairs and larger in both Na(2)SO(4) and Na(2)SO(4)/MgSO(4) TI clusters. On the basis of our calculated results, the evolvement of Raman spectra in the Na(2)SO(4)/MgSO(4) droplet with the molar ratio of 1:1 is explained.     

Density functional theory analysis of the reaction pathway for methane oxidation to acetic acid catalyzed by Pd2+ in sulfuric acid

Density functional theory has been used to investigate the thermodynamics and activation barriers associated with the direct oxidation of methane to acetic acid catalyzed by Pd2+ cation in concentrated sulfuric acid. Pd2+ cations in such solutions are ligated by two bisulfate anions and by one or two molecules of sulfuric acid. Methane oxidation is initiated by the addition of CH4 across one of the Pd-O bonds of a bisulfate ligand to form Pd(HSO4)(CH3)(H2SO4)2. The latter species will react with CO to produce Pd(HSO4)(CH3CO)(H2SO4)2. The most likely path to the final products is found to be via oxidation of Pd(HSO4)(CH3)(H2SO4)2 and Pd(HSO4)(CH3CO)(H2SO4)2 to form Pd(eta2-HSO4)(HSO4)2(CH3)(H2SO4) and Pd(eta2-HSO4)(HSO4)2(CH3CO)(H2SO4), respectively. CH3HSO4 or CH3COHSO4 is then produced by reductive elimination from the latter two species, and CH(3)COOH is then formed by hydrolysis of CH3COHSO4. The loss of Pd2+ from solution to form Pd(0) or Pd-black is predicted to occur via reduction with CO. This process is offset, though, by reoxidation of palladium by either H2SO4 or O2.     

Size-dependent charge-separation reaction for hydrated sulfate dianion cluster, SO(2-)(H2O)n, with n=3-7

The decrease in the reaction rate for the charge separation in SO(4) (2-)(H(2)O)(n) with increasing cluster size is examined by first-principles calculations of the energetics, activation barriers, and thermal stability for n=3-7. The key factor governing the charge separation is the difference in the strength of solvation interaction: while interaction with water is strong for the reactant SO(4) (2-) and the product OH(-), it is relatively weak for HSO(4) (-). It gives rise to a barrier for charge separation as SO(4) (2-) is transformed into HSO(4) (-) and OH(-), although the overall reaction energy is exothermic. The barrier is high when more than two H(2)O are left to solvate HSO(4) (-), as in the case of symmetric solvation structure and in the case of large clusters. The entropy is another important factor since the potential surface is floppy and the thermal motion facilitates the symmetric distribution of H(2)O around SO(4) (2-), which leads to the gradual reduction in reaction rate and the eventual switch-off of charge separation as cluster size increases. The experimentally observed products for n=3-5 are explained by the thermally most favorable isomer at each size, obtained by ab initio molecular-dynamics simulations rather than by the isomer with the lowest energy.     

Kinetics of oxygen exchange between the two isomers of bisulfite ion,disulfite Ion (S(2)O(5)(2-)), and water as studied by oxygen-17 nuclear magnetic resonance spectroscopy

The nuclear magnetic transverse relaxation time of oxygen-17 in aqueous sodium bisulfite solutions in the pH range from 2.5 to 5 was measured over a range of temperatures, pH, and S(IV) concentrations at an ionic strength of 1.0 m. From these data the rate law for oxygen exchange between bisulfite ion and water was determined and found to be consistent with oxygen exchange occurring via the reactions SHO(3)(-) + H(+) SO(2) + H(2)O, SO(3)H(-) + SHO(3-) SO(3)(2-) + SO(2) + H(2)O, and SO(3)H(-) + SHO(3-) S(2)O(5)(2-) + H(2)O, where the symbol SHO(3-) refers to both isomeric forms of bisulfite ion, one in which the hydrogen is bonded to the sulfur (denoted HSO(3-)) and another in which the hydrogen is bonded to an oxygen atom (denoted SO(3)H(-)). The SO(3)H(-) isomer exchanges oxygen atoms with water much more rapidly than does the HSO(3-) isomer. The value of k(-1) was determined and is in essential agreement with the results of a previous determination by relaxation measurements. The value of k(16a) + k(16b) was also found, and k(16b) is at least as large as k(16a). The rate and mechanism of oxygen exchange between the two bisulfite ion environments were studied by analyzing the broadening of the HSO(3-) resonance. Oxygen exchange occurs through isomerization caused by proton transfers.     

Densities and apparent molar volumes of atmospherically important electrolyte solutions. 1. The solutes H2SO4, HNO3, HCl, Na2SO4, NaNO3, NaCl, (NH4)2SO4, NH4NO3, and NH4Cl from 0 to 50 °C, including extrapolations to very low temperature and to the pure liquid state, and NaHSO4, NaOH, and NH3 at 25 °C

Calculations of the size and density of atmospheric aerosols are complicated by the fact that they can exist at concentrations highly supersaturated with respect to dissolved salts and supercooled with respect to ice. Densities and apparent molar volumes of solutes in aqueous solutions containing the solutes H(2)SO(4), HNO(3), HCl, Na(2)SO(4), NaNO(3), NaCl, (NH(4))(2)SO(4), NH(4)NO(3), and NH(4)Cl have been critically evaluated and represented using fitted equations from 0 to 50 °C or greater and from infinite dilution to concentrations saturated or supersaturated with respect to the dissolved salts. Using extrapolated densities of high-temperature solutions and melts, the relationship between density and concentration is extended to the hypothetical pure liquid solutes. Above a given reference concentration of a few mol kg(-1), it is observed that density increases almost linearly with decreasing temperature, and comparisons with available data below 0 °C suggest that the fitted equations for density can be extrapolated to very low temperatures. As concentration is decreased below the reference concentration, the variation of density with temperature tends to that of water (which decreases as temperature is reduced below 3.98 °C). In this region below the reference concentration, and below 0 °C, densities are calculated using extrapolated apparent molar volumes which are constrained to agree at the reference concentrations with an equation for the directly fitted density. Calculated volume properties agree well with available data at low temperatures, for both concentrated and dilute solutions. Comparisons are made with literature data for temperatures of maximum density. Apparent molar volumes at infinite dilution are consistent, on a single ion basis, to better than ±0.1 cm(3) mol(-1) from 0 to 50 °C. Volume properties of aqueous NaHSO(4), NaOH, and NH(3) have also been evaluated, at 25 °C only. In part 2 of this work (ref 1 ) an ion interaction (Pitzer) model has been used to calculate apparent molar volumes of H(2)SO(4) in 0-3 mol kg(-1) aqueous solutions of the pure acid and to represent directly the effect of the HSO(4)(-) ? H(+) + SO(4)(2-) reaction. The results are incorporated into the treatment of aqueous H(2)SO(4) density described here. Densities and apparent molar volumes from -20 to 50 °C, and from 0 to 100 wt % of solute, are tabulated for the electrolytes listed in the title and have also been incorporated into the extended aerosol inorganics model (E-AIM, http://www.aim.env.uea.ac.uk/aim/aim.php) together with densities of the solid salts and hydrates.     

Novel cation [N(SO2NMe3)2]+ and its synthesis and crystal structure. Dichloride of imido-bis(sulfuric) acid HN(SO2Cl)2. Part 1. Crystal structures of KN(SO2Cl)2.(1/2)CH3CN, KN(SO2Cl)2.(1/6)CH2Cl2, and [PCl4][N(SO2Cl)2

Several salts of bis(chlorosulfonyl)imide HN(SO2Cl)2 (1), namely, two solvates of its potassium salt, KN(SO2Cl)2.(1/2)CH3CN (1K1), KN(SO2Cl)2.(1/6)CH2Cl2 (1K2), and its tetrachlorophosphonium salt, [PCl4][N(SO2Cl)2] (2), were prepared and structurally characterized. The reaction of HN(SO2Cl)2 with Me3N gives the [N(SO2Cl)2]- salt of a novel cation, [N(SO2NMe3)2]+. This cation is analogous to the [HC(SO2NMe3)2]+ cation, but in contrast to the latter, it is fairly stable to hydrolysis. The salt [N(SO2NMe3)2]+[N(SO2Cl)2]- (3) can be converted into salts of other anions by being treated with diluted aqueous solutions of the respective acids, and thus NO3-, Cl-.H2O, SeO3(2-), CH3COO-, HSO4-, (COO)2(2-) salts were prepared. Treatment of 3 with concentrated HNO3 gave the [N(SO2NMe3)2]+ [O2NO-H-ONO2]- salt, and the addition of an HCl-acidified FeCl3 aqueous solution yielded the FeCl4- salt. Methanolysis resulted in the formation of MeOSO3- and [MeOSO2NSO2OMe]- salts. All salts have been characterized by chemical analysis, vibrational spectroscopy, and X-ray structure determinations.     

Theoretical study of the first acid dissociation of H2SO4 at a model aqueous surface

Electronic structure calculations on the H2SO4.(H2O)(4,6) model system embedded at the surface of an aqueous layer have been performed to examine the feasibility of the first acid dissociation of H2SO4 to an H2SO4-.H3O+ contact ion pair over a wide temperature range, with a special focus on the 190-250 K range relevant for atmospheric sulfate aerosols. The results indicate that the acid dissociation can be either thermodynamically favored or disfavored depending on the degree of solvation of the acid and the produced ions, as well as on the temperature.     

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria,ionic conductivities,and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.     

镉离子在H2SO4溶液中极谱行为的研究

本文研究了在没有动物胶的0.5M H_2SO_4溶液中镉离子的极谱行为,得到了如下的结果:(1)在0.050～20.0mM CdSO_4 0.5M H_2SO_4的十种溶液中测得的电流-电位曲线都有良好的波形、恒定的极限扩散电流和易于确定的半波电位.这些曲线上都没有极谱极大出现;其极限扩散电流(波高)与镉离子的浓度成正比.在镉离子低浓度(0.050～0.20mM)时,半波电位保持不变,在镉离子高浓度(1.00～20.0mM)时,也仅有很小的变化.故镉离子在0.5MH_2SO_4,溶液中的电流-电位曲线可供定量和定性测定之用.(2)镉离子在低浓度时的极谱波是一种可逆波.(3)前人在H_2SO_4溶液中研究镉离子时之所以没有能得到令人满意的极谱行为的原因是他们在H_2SO4溶液中添加了动物胶的缘故.(4)作者从得到的波形良好的电流-电位曲线上,测定了25±0.2℃时镉离子在0.5M H_2SO_4溶液中的扩散电流常数、半波电位和电极反应中得失的电子数.结果如下: i_d/cm~(2/3)t~(1/6)=3.97μA/mM·mg~(2/3)·s~(-1/2) E_(1/2)=-1.011V(0.5M硫酸亚汞电极)=-0.559V(饱和甘汞电极) n=2 这些数据比Lingane的数据,扩散电流常数2.6μA/mM·mg~(2/3)·s~(-1/2)和半波电位-0.59V(饱和甘汞电极)],要合理些.     

Spectroscopic and computational evidence for SO2 ionization on 128 K ice surface

The experimental part of this study focuses on FTIR spectroscopy of SO(2) adsorbate on the surface of ice nanoparticles at 128 K, in the 0.5-1 monolayer coverage range. In addition to the infrared spectroscopic features due to molecular SO(2), a structured band is observed at approximately 1030 cm(-1). A similar band was observed in past spectroscopic studies of SO(2) aqueous solutions, and assigned to anionic products of SO(2) ionization. Ab initio normal mode analysis of HSO(3)(-) yielded intense SO stretch bands in the vicinity of the observed "ionic" feature. The relative intensities of the molecular and the anionic bands indicate that 0.3 approximately 0.5 of the adsorbate is ionized. These results are consistent with the previously published data on isotopic exchange in SO(2)-covered ice nanoparticles (Devlin and Buch, J. Chem. Phys., 2007, 127, 091101) which pointed towards substantial SO(2) ionization at low temperatures. Density functional theory modeling of molecular and ionized adsorbate on a crystal ice slab suggests that anion solvation by molecular SO(2) adsorbate facilitates the SO(2) ionization process at the ice surface.     

Infrared spectroscopy of SO2 aqueous solutions

The chemistry of SO2 solutions was studied with infrared transmission and total internal reflection (ATR) spectroscopy. The cross-sections of the SO2 stretching vibrations v1, v3 and the combination band of v1 + v3 were obtained and found to be slightly different from their gas phase values. Six features we associate with sulfur-containing ions were observed. We present the first infrared evidence for the bisulfite ion HOSO2- through detection of its OH stretching vibration. Other features may be associated with HSO3-, another isomer of the bisulfite ion, and a new compound we propose to be H2S2O6(2-). We found no evidence for sulfurous acid H2SO3.     

Proton mobility and stability of water clusters containing the bisulfate anion, HSO4(-)(H2O)n

Bisulfate water clusters, HSO(4)(-)(H(2)O)(n), have been studied both experimentally by a quadrupole time-of-flight mass spectrometer and by quantum chemical calculations. For the cluster distributions studied, there are some possible "magic number" peaks, although the increase in abundance compared to their neighbours is small. Experiments with size-selected clusters with n = 0-25, reacting with D(2)O at a center-of-mass energy of 0.1 eV, were performed, and it was observed that the rate of hydrogen/deuterium exchange is lower for the smallest clusters (n < 8) than for the larger (n > 11), with a transition taking place in the range n = 8-11. We propose that the protonic defect of the bisulfate ion remains rather stationary unless the degree of hydration reaches a given level. In addition, it was observed that H/D scrambling becomes close to statistically randomized for the larger clusters. Insight into this size dependency was obtained by B3LYP/6-311++G(2d,2p) calculations for HSO(4)(-)(H(2)O)(n) with n = 0-10. In agreement with experimental observations, these calculations suggest pronounced effectiveness of a 'see-saw mechanism' for pendular proton transfer with increasing HSO(4)(-)(H(2)O)(n) cluster size.     

Neutron scattering studies of K(3)H(SO(4))(2) and K(3)D(SO(4))(2): The particle-in-a-box model for the quantum phase transition

In the crystal of K(3)H(SO(4))(2) or K(3)D(SO(4))(2), dimers SO(4)???H???SO(4) or SO(4)???D???SO(4) are linked by strong centrosymmetric hydrogen or deuterium bonds whose O???O length is ≈2.50 A?. We address two open questions. (i) Are H or D sites split or not? (ii) Is there any structural counterpart to the phase transition observed for K(3)D(SO(4))(2) at T(c) ≈ 85.5 K, which does not exist for K(3)H(SO(4))(2)? Neutron diffraction by single-crystals at cryogenic or room temperature reveals no structural transition and no resolvable splitting of H or D sites. However, the width of the probability densities suggest unresolved splitting of the wavefunctions suggesting rigid entities H(L1∕2) -H(R1∕2) or D(L1∕2) -D(R1∕2) whose separation lengths are l(H) ≈ 0.16 A? or l(D) ≈ 0.25 A?. The vibrational eigenstates for the center of mass of H(L1∕2) -H(R1∕2) revealed by inelastic neutron scattering are amenable to a square-well and we suppose the same potential holds for D(L1∕2) -D(R1∕2). In order to explain dielectric and calorimetric measurements of mixed crystals K(3)D((1 - ρ))H(ρ)(SO(4))(2) (0 ≤ ρ ≤ 1), we replace the classical notion of order-disorder by the quantum notion of discernible (e.g., D(L1∕2) -D(R1∕2)) or indiscernible (e.g., H(L1∕2) -H(R1∕2)) components depending on the separation length of the split wavefunction. The discernible-indiscernible isostructural transition at finite temperatures is induced by a thermal pure quantum state or at 0 K by ρ.     

Vibrational spectroscopic study of the mineral pitticite Fe, AsO4, SO4, H2O

Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the determination of the structure of these minerals. Among this group of minerals is pitticite, simply described as (Fe, AsO(4), SO(4), H(2)O). In this work, the analogue of the mineral pitticite has been synthesised. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman and infrared bands are attributed to the AsO(4)(3-), SO(4)(2-) and water stretching and bending vibrations. The Raman spectrum of the pitticite analogue shows intense peaks at 845 and 837cm(-1) assigned to the AsO(4)(3-) stretching vibrations. Raman bands at 1096 and 1182cm(-1) are attributed to the SO(4)(2-) antisymmetric stretching bands. Raman spectroscopy offers a useful method for the analysis of such colloidal minerals.     

Kinetics and mechanism of the oxidation of sulfite by chlorine dioxide in a slightly acidic medium

The sulfite-chlorine dioxide reaction was studied by stopped-flow method at I = 0.5 M and at 25.0 +/- 0.1 degrees C in a slightly acidic medium. The stoichiometry was found to be 2 SO(3)(2-) + 2.ClO(2) + H(2)O --> 2SO(4)(2) (-) + Cl(-) + ClO(3)(-) + 2H(+) in *ClO(2) excess and 6SO(3)(2-) + 2*ClO(2) --> S(2)O(6)(2-) + 4SO(4)(2-) + 2Cl(-) in total sulfite excess ([S(IV)] = [H(2)SO(3)] + [HSO(3)(-)] + [SO(3)(2-)]). A nine-step model with four fitted kinetic parameters is suggested in which the proposed adduct *SO(3)ClO(2)(2-) plays a significant role. The pH-dependence of the kinetic traces indicates that SO(3)(2-) reacts much faster with *ClO(2) than HSO(3)(-) does.     

Raman spectroscopic study of crystallization from solutions containing MgSO4 and Na2SO4: Raman spectra of double salts

Mg(2+), Na(+), and SO(4)(2-) are common ions in natural systems, and they are usually found in water bodies. Precipitation processes have great importance in environmental studies because they may be part of complex natural cycles; natural formation of atmospheric particulate matter is just one case. In this work, Na(2)Mg(SO(4))(2)·5H(2)O (konyaite), Na(6)Mg(SO(4))(4) (vanthoffite), and Na(12)Mg(7)(SO(4))(13)·15H(2)O (loeweite) were synthesized and their Raman spectra reported. By slow vaporization (at 20 °C and relative humidity of 60-70%), crystallization experiments were performed within small droplets (diameter ≤ 1-2 mm) of solutions containing MgSO(4) and Na(2)SO(4), and crystal formations were studied by Raman spectroscopy. Crystallization of Na(2)Mg(SO(4))(2)·4H(2)O (bloedite) was observed, and the formation of salt mixtures was confirmed by Raman spectra. Bloedite, konyaite, and loeweite, as well as Na(2)SO(4) and MgSO(4)·6H(2)O, were the components found to occur in different proportions. No crystallization of Na(6)Mg(SO(4))(4) (vanthoffite) was observed under the crystallization condition used in this study.     

H-bonding dependent structures of (NH4+)3H+(SO4 2-)2. Mechanisms of phase transitions

The role of different H-bonds in phases II, III, IV, and V of triammonium hydrogen disulfate, (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), has been studied by X-ray diffraction and (1)H solid-state MAS NMR. The proper space group for phase II is C2/c, for phases III and IV is P2/n, and for phase V is P onemacr;. The structures of phases III and IV seem to be the same. The hydrogen atom participating in the O(-)-H(+).O(-) H-bond in phase II of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) at room temperature is split at two positions around the center of the crucial O(-)-H(+).O(-) H-bonding, joining two SO(4)(2)(-) tetrahedra. With decreasing temperature, it becomes localized at one of the oxygen atoms. Further cooling causes additional differentiation of possibly equivalent sulfate dimers. The NH(4)(+) ions participate mainly in bifurcated H-bonds with two oxygen atoms from sulfate anions. On cooling, the major contribution of the bifurcated H-bond becomes stronger, whereas the minor one becomes weaker. This is coupled with rotation of sulfate ions. In all the phases of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), some additional, weak but significant, reflections are observed. They are located between the layers of the reciprocal lattice, suggesting possible modulation of the host (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) structure(s). According to (1)H MAS NMR obtained for phases II and III, the nature of the acidic proton disorder is dynamic, and localization of the proton takes place in a broader range of temperatures, as can be expected from the X-ray diffraction data.