A. I. Karelin

2-Hydroxy-4-methylbenzenesulfonic acid dihydrate: Crystal structure, vibrational spectra, proton conductivity, and thermal stability

The crystal and molecular structure of 2-hydroxy4-methylbenzenesulfonic acid dihydrate C6H3(CH3)(OHSO−3 H5O2+ (I) was studied by X-ray diffraction and vibrational spectroscopy. The compound crystallized in the monoclinic crystal system; crystal data: a=10.853(2) Å, b=7.937(2) Å, c=12.732(3) Å, β=112.13(3)°, V=1015.9(4)Å3,Z=4,dcalc=1.466g/cm3,spacegroupP21/c,Rf=0.0486,GOOF=1.161.The S-O distances in the sulfonate group differed substantially (S1-O2 1.439(2) Å, S1-O3 1.455(2) Å, and S1-O4 1.464(2) Å. The symmetry of the H5O2 cation decreased due to proton displacement toward one of the two water molecules. XRD data on the asymmetry of H5O2 were confirmed by IR and Raman spectral data. The strong triplet at 2900, 3166, 3377 cm−1 in the IR spectrum of I corresponds to different types of H-bond and shifted to 2185, 2363, 2553 cm−1 after deuteration. The proton conductivity of the compound was measured by impedance spectroscopy: 6 × 10−7 S/cm at 298 K (32 rel %), Eact=0.4±0.01 eV. The conductivity increased to 10-3 S/cm, Eact=0.1 eV when ambient humidity increased to 60 rel %.

Protonic conductivity of neutral and acidic silicotungstates

Abstract The salts of composition Me 4− x H x SiW 12 O 40 · n H 2 O (Me=Na, K, Rb, Cs, NH 4 ) are synthesized; their thermal stability, temperature dependence of proton conductivity and structure of protonhydrate shell are studied. The proton conductivity is shown to depend on both the number of acidic protons and polarizability of salt-forming cation of alkaline metal. The presence of differently hydrated protons is discovered in both acidic and neutral salts of 12-silicotungstic acid.

Proton conductivity of calix[n]arene-para-sulfonic acids (n = 4, 8)

High proton conductivity in calix[n]arene-para-sulfonic acid hydrates (n = 4, 8) reaching a value of 10−1 Ohm−1 cm−1 at a relative humidity of 80% was revealed for the first time. This value is close to the record conductivity of solid proton conductors and acid water solutions. The dependence of proton transfer parameters and water quantity in the title compounds dependent on the relative humidity of air was investigated.

The Structure and Properties of Phenol-2,4-disulfonic Acid Dihydrate

The crystal and molecular structure of phenol-2,4-disulfonic acid dihydrate was determined by X-ray structure analysis. All hydrogen positions in the crystal structure were found using difference Fourier syntheses. Oxonium cations and acid anions were linked in the crystal structure by short H-bonds, and the phenol OH group participated in two weak H-bonds with sulfo group oxygens simultaneously. The IR frequency corresponding to νs, as (H3O+) vibrations decreased to 2700 cm−1 under the influence of short H-bonds between oxonium cations and anions. The contour of the corresponding absorption band became anomalously broad. A discrete maximum was observed at 3412 cm−1 on the high-frequency wing of this band; this maximum was assigned to OH stretching vibrations of the phenol group. The protonic conductivity of the compound measured by impedance spectroscopy was 2.5 × 10−6 Ω−1 cm−1 at 298 K in a vacuum, Ea = 0.37 ± 0.01 eV. An increase in the humidity of the environment to 15% at room temperature increased conductivity from 10−6 to 10−5 Ω−1 cm−1, Ea = 0.27 ± 0.02 eV.

Vibrational spectra, structure, and proton conduction in hydrous tin dioxide

SnO2 · nH2O (hydrous tin dioxide, HTD, n = 1.5) and SnO2 · nD2O (deuterated hydrous tin dioxide, DHTD) samples were studied by IR and Raman spectroscopy. The using of these spectroscopic methods elucidated some structural features of the hydrogen-bond network in HTD, where two types of water molecules and two types of hydroxide groups are present. Type 1 water molecules and hydroxide groups are found to be linked to one another by weak hydrogen bonds, as in liquid water. Type 2 water molecules and hydroxide groups are linked to type 1 water molecules and hydroxide groups by rather strong hydrogen bonds. The existence of these strong hydrogen bonds is interpreted as arising from the effect of tin ions on some water molecules and hydroxide groups. Proton conductivity in HTD was found by the impedance method to be a nearly linear function of n. The break of the line at n = 1.3 corresponds to the percolation threshold. The roles of type 1 and type 2 water molecules and hydroxide groups in the generation of proton conduction in HTD are discussed.

Proton conductivity of benzoic and 2-sulfobenzoic acids

The dependence of proton conductivity of 2-sulfobenzoic acid trihydrate on the environmental humidity and temperature is studied. It is shown that trihydrate remains solid when exposed to atmosphere with humidity of up to 65 rel. %. The comparison of 2-sulfobenzoic acid trihydrate with bezoic acid shows that the absence of sulfo group in the benzene ring sharply lowers down the hydrophilic properties of the compound and, correspondingly, its hydration and conductivity.

Water adsorption on tin hydrodioxide and its effect on the contour of the infrared absorption band ν(OH)

Tin hydrodioxide SnO2 · nH2O (THO, n = 1.5) pellets in potassium bromide were studied by IR absorption spectroscopy. Water adsorption by tin hydrodioxide was shown to give rise to a prominent strong and broad band of stretching vibrations ν(OH) with a peak at 3430 cm−1. Absorption intensity of this band decreases with distance from the peak rapidly toward higher frequencies and very slowly toward lower frequencies; therefore, the contour is distinguished by very high asymmetry. Analysis of the reasons for this asymmetry taking into account the computer decomposition of the contour into components implies that the unresolved bands from two types of water molecules in THO are superimposed onto the weak bands from two types of hydroxide groups. First type molecules are involved in physisorption to form, with one another, hydrogen bonds that are similar to weak bonds in zeolite and liquid water. Second type molecules are involved in chemisorption and are coordinated to tin ions. Coordination enhances the strengthening of acidic properties and promotes the appearance of strong H-bonds. The peak intensity of the THO ν(OH) band depends primarily on the contribution of vibrational transitions of first type molecules and to a lesser extent on the contribution of vibrational transitions of the first type hydroxide groups. The vibrational transitions in second type molecules and second type groups influence the curvature of the contour on the low-frequency side of the peak.

FTIR spectroscopic study of the complex formation between H+ and DMSO in Nafion

Nafion membranes plasticized with dimethyl sulfoxide (DMSO) have been examined at room temperature using the vacuum ATR - FTIR spectroscopic technique in the range 50-4000cm-1. The amount of the plasticizer corresponds to the molecular ratio n=DMSO/H+=1.2, 2.3, 4.8, 7.0, 9.7 and 13.3. The medium intensity band with two maxima at 780 and 853cm-1 have been assigned to the ν(SO) stretching vibrations of the H+(DMSO)2 complex. The possible reason of ν(SO) splitting is symmetry decrease of hydrogen bond under the influence of the anion group SO3- electric field. Whereas the mutual association of free DMSO molecules in Nafion leads to appearance of weak band at 86cm-1 assigned to the dipole-dipole interactions.

Structure of lithium ion-conducting polymer membranes based on Nafion plasticized with dimethylsulfoxide

The products of solvation of lithiated Nafion with dimethylsulfoxide (DMSO) have been studied by ATR IR spectroscopy in the frequency range of 50–4000 cm–1 in a vacuum at room temperature. Degree of solvation n = DMSO/Li has been varied in a range of 1.5–18.4. Based on analysis of the dependence of the spectral parameters on the n value, it has been concluded that the test samples contain DMSO molecules of two types. The first type includes molecules coordinated to the lithium ion through the formation of the metal–oxygen bond, and the second is DMSO molecules associated by intermolecular bonds similar to those in the liquid DMSO phase. The structure of the salt depends on n: the changes are attributed to the reorientation of polymer chain units. The coordination number of lithium has been estimated at four. It has been shown that the IR data are consistent with the data on the conductivity of lithiated Nafion membranes as a function of DMSO content, according to which the simplest transport unit is the tetrasolvate [Li(DMSO)4]+. At temperatures below 0°C, all the samples exhibit an abrupt change in conductivity, which is attributed to the freezing of DMSO in the membrane matrix.

Raman spectroscopy data on the phase transition of KO2 mixed with KOH on a glass fiber matrix

The composition of solid products of vacuum decomposition of K2O2 · 2H2O2 (I) on a glass fiber matrix was determined by Raman spectroscopy. The products were mainly mechanical mixtures of potassium superoxide KO2 (II) with KOH · nH2O (III) and, in some cases, with KOH (IV). The n value in III varies from sample to sample (most often, from 0.2 to 1). Component II is represented by the typical tetragonal phase (the ν(O-O) stretching maximum at 1146 ± 1 cm−1). The transformation of the tetragonal phase of II into cubic phase upon sample irradiation with a focused laser beam was studied. The phase transition was initiated by increasing the power of monochromatic radiation (λ = 514.5 nm). The formation of the cubic phase was indicated by a sharp increase in the width of the ν(O-O) stretching mode. Reaching the threshold power facilitates warming up of the sample in the focusing point to ∼120°C. In pure II, the phase transition is enantiotropic; when the laser radiation power drops to the initial minimal level, the tetragonal phase is formed again. When III or IV is present in the sample, this does not take place. Stabilization of the cubic phase of II is attributable to the chemical reaction with IV taking place at phase transition temperature to give a binary compound or a solid solution of the KO2 · KOH type (V). The crystals of V correspond to the cubic system.