Raman spectroscopic study of aqueous (NH4)2SO4 and ZnSO4 solutions

The Raman spectra of the v₁-SO ₄ ^2– band in 0.5–2.5 molar aqueous (NH₄)₂SO₄ and ZnSO₄ solutions in the temperature range 25–85°C were studied. The molar scattering coefficient of the v₁ band is the same for all forms of sulfate in (NH₄)₂SO₄ and ZnSO₄ solutions and is independent of temperature up to 85°C. The v₁ band profile is symmetrical in (NH₄)₂SO₄ solutions. In ZnSO₄ solutions, a shoulder appears on the high frequency side which increases slightly in intensity with increasing concentration and temperature. This high frequency component is attributed to the formation of the contact ion pair (Zn²⁺·SO ₄ ^2– ). The enthalpy of formation for the contact ion pair is estimated from the Raman data to be approximately 3 kJ-mol^–1 which is in reasonable agreement with measurements by other methods.     

Raman spectroscopic investigation of aqueous FeSO4 in neutral and acidic solutions from 25‡C to 303‡C: inner- and outer-sphere complexes

Raman spectra of aqueous FeSO₄ and (NH₄)₂SO₄ solutions have been recorded over broad concentration and temperature ranges. Whereas the v₁-SO ₄ ^2- band profile is symmetrical in noncomplexing (NH₄)₂SO₄ solutions, in FeSO₄ solutions a shoulder appears on the high-frequency side, which increases in intensity with increasing concentration and temperature. The molar scattering coefficient of the v_1-SO ₄ ^2- band is the same for all forms of sulfate in (NH₄)₂SO₄ and FeSO₄ solutions and is independent of temperature up to 150‡C, the highest temperature studied. The high-frequency shoulder is attributed to the formation of a contact ion pair, Fe²⁺OSO^3/2-, as is the splitting of the v_3-SO ₄ ^2- antisymmetric stretching mode which is observed in the FeSO₄ solution. The bending modes v_2-SO ₄ ^2- and v_4-SO ₄ ^2- , normally forbidden in the isotropic spectrum, show a gain in intensity with increasing ion-pair formation. A polarized band has been assigned to the Fe²⁺-O ligand vibration. No higher associates or anionic complexes are required to interpret the spectroscopic data. No evidence of contact ion pairing between Fe²⁺ and HSO4 ₄ ^- could be detected at temperatures up to 303‡C in 1 molal solutions of FeSO₄ with an excess of 2 molal H₂SO₄.     

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N₂O₄ solutions in organic solvents have been recorded. The frequencies ofv ₁,v ₂, andv ₃ bands of N₂O₄ increase with increasing solvent electron-donor properties. Especially large changes ofv ₃ N-N stretching band have been observed (254.5 cm^–1 in n-hexane, 276.5 cm^–1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N₂O₄ and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N₂O₄ in agreement with the results of Raman study.     

Spectroscopic properties of guanidinium zinc sulphate [C(NH2)3]2Zn(SO4)2 and ab initio calculations of [C(NH2)3]2 and HC(NH2)3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH₂)₃]₂Zn(SO₄)₂ are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO₄²⁻ tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN₃ group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH₂)₃]₂ and HC(NH₂)₃ are computed using Gaussian 03 with HF/6-31G* as basis set.     

14N NMR studies of thallium nitrate solutions in liquid ammonia

¹⁴N chemical shifts and linewidths were determined for NO ₃ ^– and NH₃ in liquid ammonia solutions of thallium nitrate at concentrations between 0.07 and 10 M. The concentration dependences of the¹⁴NO ₃ ^– shift and linewidth are consistent with the presence of C_2v ion pairs at a 2:1 mole ratio of NH₃ to TINO₃ and C_3v ion pairs at mole ratios of 3:1 or higher. Previous studies had indicated the formation of ion pairs at low concentrations. The small value of the¹⁴NO ₃ ^– linewidth below 1 M suggests that these are contact ion pairs. Studies of the¹⁴NH₃ linewidth as a function of thallium salt concentration indicate slow solvent exchange at very high concentrations.¹⁴NH₃ exhibits a downfield shift upon incorporation into the solvation sphere of the Tl⁺NO ₃ ^– ion pair, in constrast to upfield shifts reported for complexation with transition metal cations.     

Breakdown of the Rule of “Linearity of Water Isoactivity Lines” in a System Containing Solid Solutions

Osmotic coefficients of water have been measured isopiestically for the entire region of homogeneous ternary solutions for the Rb₂SO₄- (NH₄)₂SO₄-H₂O system at 25°C. One might expect that water isoactivity lines should be straight since this system involves a continuous series of solid solutions. The related systems (K₂SO₄-Rb₂SO₄-H₂O and (K₂SO₄- (NH₄)₂ SO₄-H₂O) obey the linearity of water isoactivity lines rule. Contrary to expectations, the (Rb₂SO₄-(NH₄)₂-SO₄-H₂O appears to be the first water–salt system containing continuous solid solutions in which the mentioned rule is not obeyed.     

The speed of sound in mixtures of the major sea salts. A test of Young's rule for adiabatic PVT properties

The relative sound speed of mixtures of aqueous solutions of NaCl–MgSO₄ and MgCl₂–Na₂SO₄ at I=0.1 and 0.5m have been determined at 5, 15, and 25°C and pressures to 1000 bars. The resulting sound speeds, adiabatic and apparent molal compressibilities have been compared to results estimated from binary solutions using an additivity principle — Young's rule. The estimated sound speeds agree with the measured values for the NaCl–MgSO₄ system to ±0.15 m-sec^–1 and for the Na₂SO₄–MgCL₂ system to ±0.20 m-sec^–1. The deviations increase with increasing ionic strength (±0.08 m-sec^–1 at I=0.1 and ±0.25 m-sec^–1 at I=0.5 m).The sound speed of seawater have also been estimated from 0 to 40°C, 0.1 to 0.7 ionic strength and 0 to 1000 bars. The estimates were found to be in good agreement (±0.4 m-sec^–1) with the measured values.These results indicate that reasonable estimates of the adiabatic PVT properties of dilute mixtures of electrolyte solutions can be made using the additivity principle, without excess mixing terms.     

The PVT properties of concentrated aqueous electrolytes. IV. Changes in the compressibilities of mixing the major sea salts at 25°C

The speed of sound of mixtures of the six possible combinations of the major sea salt ions (Na⁺, Mg²⁺, Cl^–, and SO ₄ ^2– ) have been determined at I=3.0 and at 25°C. The results have been used to determine the changes in the adiabatic compressibility of mixing K_m the major sea salts. The values of K_m have been fit to the equation K_m=y₂y₃I²[k₀+k₁(1-2y₃)] where y_i is the ionic strength fraction of solute i, k₀ and k₁ are parameters related to the interactions of like-charged ions. The Young cross-square rule is obeyed to within ±0.04×10^–6 cm³-kg^–1-bar^–1. A linear correlation was found between the compressibility k₀ and volume v₀ interaction parameters (10⁴k₀=–0.24+3.999 v₀, s=0.15) in agreement with out earlier findings. Estimates of the sound speeds for the cross square mixtures (NaCl+MgSO₄ and MgCl₂+Na₂SO₄) were made using the equations of Reilly and Wood. The estimated sound speeds were found to agree on the average with the measured values to ±0.36 m-sec^–1.     

Negative ion formation in compounds relevant to SF6 decomposition in electrical discharges

Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF₂ SOF₄, SO₂F₂, SF₄, SO₂, and SiF₄ compounds which can be formed by electrical discharges in SF₆. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F^– and SOF ₂ ^–* from SOF₂; SOF ₃ ^– and F^– from SOF₄; SO₂F ₂ ^–* , SO₂F^–, F ₂ ^– , and F^– from SO₂F₂; SF ₄ ^–* and F^– from SF₄; O^–, SO^–, and S^– from SO₂; and SiF ₃ ^– and F^– from SiF₄. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF ₂ ^–* , SO₂F ₂ ^–* , and SF ₄ ^–* are also reported.     

Ion sites in deuterated dimethylsulfoxide solutions of NaNO3 and cryptand complexed NaNO3 by digital infrared spectroscopy

Infrared spectra in digitized form were measured for NaNO₃ and [Na·C221]⁺NO ₃ ^– solutions in DMSO-d₆ between 1150 and 1500 cm^–1 using a technique and instrumentation that obtains each point of the average absorbance spectrum at the same (reduced) noise level. Similar spectra were also obtained for the solvent and the Na⁺ complexed cryptand C221 and used to remove the contribution of these entities from the above spectra. By taking appropriate differences of spectra, it was possible to reveal both bands of the contact ion pair in the NaNO₃/DMSO-d₆ solution-removing one from under the strong band of the D_3h site—and to show the presence of three ion sites in this solution. The third site is tentatively identified as a close ion pair. Two ion sites are also identified in the [Na·C221]⁺NO ₃ ^– /DMSO-d₆ solution.Paper X in the series, Studies of Solution Character, by Molecular Spectroscopy.     

Zinc(II) Hydration in Aqueous Solution: A Raman Spectroscopic Investigation and An ab initio Molecular Orbital Study of Zinc(II) Water Clusters

Raman spectra of aqueous Zn(II)–perchlorate solutions were measured over broad concentration (0.50–3.54 mol-L^–1) and temperature (25–120°C) ranges. The weak polarized band at 390 cm^–1 and two depolarized modes at 270 and 214 cm^–1 have been assigned to ₁(a _1g), ₂(e _g), and ₅(f _2g) of the zinc–hexaaqua ion. The infrared-active mode at 365 cm^–1 has been assigned to ₃(f _1u). The vibrational analysis of the species [Zn(OH₂) ₂ ⁺ ] was done on the basis of O _h symmetry (OH₂ as point mass). The polarized mode ₁(a _1g)-ZnO₆ has been followed over the full temperature range and band parameters (band maximum, full width at half height, and intensity) have been examined. The position of the ₁(a _1g)-ZnO₆ mode shifts only about 4 cm^–1 to lower frequencies and broadens by about 32 cm^–1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaqua–Zn(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. These findings are in contrast to ZnSO₄ solutions, recently measured by one of us, where sulfate replaces a water molecule of the first hydration sphere. Ab initio geometry optimizations and frequency calculations of [Zn(OH₂) ₂ ⁺ ] were carried out at the Hartree–Fock and second-order Møller–Plesset levels of theory, using various basis sets up to 6-31 + G*. The global minimum structure of the hexaaqua–Zn(II) species corresponds with symmetry T _h. The unscaled vibrational frequencies of the [Zn(OH₂) ₂ ⁺ ] are reported. The unscaled vibrational frequencies of the ZnO₆, unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH₂) ₂ ⁺ ] was calculated and accounts for ca. 66% of the experimental single-ion hydration enthalpy for Zn(II).Ab initio geometry optimizations and frequency calculations are also reported for a [Zn(OH₂) ₂ ¹⁸ ] (Zn[6 + 12]) cluster with 6 water molecules in the first sphere and 12 in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6 + 12] cluster correspond well with the observed frequencies in solution. The ₁-ZnO₆ (unscaled) mode occurs at 388 cm^–1 almost in perfect correspondence to the experimental value. The theoretical binding enthalpy for [Zn(OH₂) ₂ ¹⁸ ] was calculated and is very close to the experimental single ion-hydration enthalpy for Zn(II). The water molecules of the first sphere form strong hydrogen bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.     

Volume changes for mixing the major sea salts: Equations valid to ionic strength 3.0 and temperature 95°C

Equations in the ion-interaction (Pitzer) system are derived for the volume change on mixing any combination of the sea salts NaCl, Na₂SO₄, MgSO₄, MgCl₂ at constant ionic strenth. For these mixings of different charge types, the equations include complex differences of pure electrolyte terms. Recently measured data for each of the pure electrolytes provide these pure electrolyte terms. Other recent measurements on the volume change on mixing are compared with values calculated from the equations. At 25°C there is no need to introduce the mixing terms based on differences in the interactions of ions of the same sign. At other temperatures, the agreement without the mixing terms is good, but significant improvement is obtained by inclusion of the binary mixing terms Cl,SO ₄ ^v and _Na,Mg ^v . The equations and parameters can then predict the volumetric properties of any mixed solution of these salts over the range 0–100°C and to at least 3 mol-kg^–1 ionic strength.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.     

An NMR study of thallium nitrate ion association in liquid ammonia

²⁰⁵Tl and¹H magnetic resonance frequencies have been determined for liquid ammonia solutions of TlClO₄ and TlNO₃ as a function of electrolyte concentration (5×10^–4 to 9.8 M) and temperature. The dependence of the resonance frequency on concentration suggests the presence of free, fully solvated thallium ions, ion pairs, and higher-order ion aggregates. Analysis of lowconcentration²⁰⁵Tl data between 0 and 30°C allowed the determination of TlNO₃ ion-pair association constants and thermodynamic parameters (H_A=+6.5 kcal-mole^–1, S_A=+36 e.u.). A preciptous decrease in²⁰⁵Tl resonance frequency was observed for NH₃ to TlNO₃ mole ratios below 3:1, suggesting the formula (NH₃)₃Tl⁺ NO ₃ ^– for the fully solvated, contact ion pair.     

Effect of ionic interactions on the oxidation of Fe(II) with H2O2 in aqueous solutions

The oxidation of Fe(II) with H₂O₂ has been measured in NaCl and NaClO₄ solutions as a function of pH, temperature T (K) and ionic strength (M, mol-L^–1). The rate constants, k (M^–1-sec^–1), d[Fe(II)]/DT=-k[Fe(II)][₂O₂]at pH=6.5 have been fitted to equations of the formlog k = log k₀+ AI ^1/2+BI+CI ^1/2/T Where log k₀=15.53-3425/T in water; A=–2.3, –1.35; B=0.334, 0.180; and C=391, 235, respectively, for NaCl (=0.09) and NaClO₄ ( =0.08). Measurements made in NaCl solutions with added anions yield rates in the order B(OH) ₄ ^– >HCO ₃ ^– >ClO ₄ ^– >Cl^–>NO ₃ ^– >SO ₄ ^2– and are attributed to the relative strength of the interactions of Fe²⁺ or FeOH⁺ with these anions. The FeB(OH) ₄ ⁺ species is more reactive while the FeCO ₃ ⁰ , FeCl⁺, FeNO ₃ ⁺ and FeSO ₄ ⁰ species are less reactive than the FeOH⁺ ion pair. The general trend is similar to our earlier studies of the oxidation of Fe(II) with O₂ except for B(OH) ₄ ^– . The effect of pH on the logk was found to be a quadratic function of the concentration of H⁺ or OH^– from pH=4 to 8. These results have been attributed to the different rate constants for Fe²⁺ (k₀) and FeOH⁺ (k₁) which are related to the measured k by, k=k_0Fe + k_1FeOH, where _i is the molar fraction of species i. The rates increase due to the greater reactivity of FeOH⁺ compared to Fe²⁺. k₀ is independent of composition and ionic strength but k₁ is a function of ionic strength and composition due to the interactions of FeOH⁺ with various anions.     

Clathrate and inclusion compounds. Part 11 [1]. A pre-resonance Raman study of the β-quinol/SO2 clathrate

A pre-resonance Raman study of the yellow -quinol/SO₂ clathrate has been carried out using 609.8, 586.8, 514.5, 488.0 and 457.9 run excitation. Pre-resonance enhancement is observed for the guest v_l (Al) band at 1147 cm^–1 and the host band at 1257 cm^–1. These observations are consistent with a charge transfer interaction arising from the LUMO of S0₂ (S 3pz) and the HOMO of quinol, which consists mainly of the ring electrons.     

Thermodynamics of aqueous mixtures of sodium chloride,potassium chloride,sodium sulfate,and potassium sulfate at 25°C

Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate can be mixed in six ways to give ternary mixtures. Two of these have already been studied and results are now presented for the remaining four systems: H₂O–NaCl–K₂SO₄, H₂O–Na₂SO₄–K₂SO₄, H₂O–KCl–Na₂SO₄, and H₂O–KCl–K₂SO₄.     

Effect of the structure of frozen solutions of H2SO4 on radiothermoluminescence

A pronounced effect of structural heterogeneity (cracks) of glass-like solutions of 4.9M H₂SO₄ on their radiothermoluminescence (RTL) was found. In perfect glasses one RTL peak was observed at 115 K. Additional luminescence peaks appeared at 165, 195, and 240 K in glasses having cracks. The effect observed was explained by elevated thermal stability of the SO₄ ^– radical stabilized on the surface of sulfuric acid crystal hydrates: H₂SO₄ · 4H₂O and H₂SO₄· 6.5H₂O.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1566–1568, June, 1996.     

Structures of Concentrated Sulfuric Acid Determined from Density, Conductivity, Viscosity, and Raman Spectroscopic Data

Addition of water to stoichiometric 100% sulfuric acid increases the density untila maximum results near 87 mole% H₂SO₄. The density and conductivity maximaand viscosity minimum, the latter two near 75 mole%, are direct macroscopicresponses to microscopic quantum mechanical properties of H₃O⁺ and of nearlysymmetric H-bond double-well potentials, as follows: (1) lack of H bonding tothe O atom of H₃O⁺; (2) short, 2.4–2.6 A, O—O distances of nearly symmetricH bonds; and, (3) increased mobility of protons in such short H bonds, give riseto the density maximum via (1) and (2); (1) produces the viscosity minimum;and the conductivity maximum results from (2) and (3). A pronounced minimumnear 1030 cm^–1 in the symmetric SO₃ stretching Raman frequency of HSO₄ ^–,observed near 45 mole% also results from double-well effects involving the shortH bonds of direct hydronium ion—bisulfate ion pair interactions. Estimates of theconcentrations of the (H₃O⁺)(HSO₄ ^–) and (H₂SO₄)(HSO₄ ^–) pair interactions weredetermined from Raman intensity data and are given for compositions between42–100 mole%     

An aqueous thermodynamic model for Ca2+−SO 3 2− ion interactions and the solubility product of crystalline CaSO3·1/2H2O

The solubility of CaSO₃·1/2H₂O(c) was studied under alkaline conditions (pH>8.2), in deaerated and deoxygenated Na₂SO₃ solutions ranging in concentration from 0.0002 to 0.4M and in CaCl₂ solutions ranging in concentration from 0.0002 to 0.01M, for equilibration periods ranging from 1 to 7 days. Equilibrium was approached from both the over- and the under-saturation directions. In all cases, equilibrium was reached in <1 days. The aqueous Ca²⁺–SO ₃ ^2– ion interactions can be satisfactorily modeled using either ion-association or ion-interaction aqueous thermodynamic models. In the ion-association model, the log K°=2.62±0.07 for Ca²⁺+SO ₃ ^2– CaSO ₃ ⁰ . In the Pitzer ion-interaction model, the binary parameters (⁰) and (¹) for Ca²⁺–SO ₄ ^2– were used, and the value of (²) was determined from the experimental data. As expected given the strong association constant, the value of (⁰) was quite small (about –134). We feel a combination of the two models is most useful. The logarithm of the thermodynamic equilibrium constant (K°) of the CaSO₃·1/2H₂O(c) solubility reaction (CaSO₃·1/2H₂O(c)Ca²⁺+SO ₃ ²⁺ +0.5H₂O) was found to be –6.64±0.07.