R. V. Pisarev

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 %.

Quantum chemical modeling of the structure formation and proton transfer in 2-hydroxybenzenesulfonic, 4-hydroxy-1,3-benzenedisulfonic, and 1,3-benzenedisulfonic acids

Hydrate clusters of 2-hydroxybenzenesulfonic and 1,3-benzenedisulfonic acids were calculated in terms of the density functional theory (DFT) by the B3LYP/6-31G** method. The process of water adsorption on the crystal surface of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate was simulated using the generalized gradient approximation (DFT/PBE) and periodic boundary conditions. For the model system (OHC6H4SO3−)·H5O2+, the activation barriers for the proton transfer were calculated depending on the distance between the O atoms and the deviation of the proton from the O...O bond line. The presence of one H2O molecule per SO3H group is energetically most favorable for the formation of clusters of 1,3-benzenedisulfonic acid containing a stoichiometric amount of water. The simulation of the hydration of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate (OHC6H3(SO3H)2·2 H2O + n H2O, n = 1–3) showed that the superstoichiometric H2O molecule is adsorbed on the crystal surface of this dihydrate with energy release of 0.75–0.95 eV. The position of this water molecule is less favorable in the bulk than on the surface.

Quantum chemical modeling of the structure and proton conductivity of mesitylenesulfonic acid dihydrate 2,4,6-Me3C6H2SO3−·H5O2+

The process of water adsorption on the surface of a 2,4,6-Me3C6H2SO3−·H5O2+ crystal was simulated in terms of the density functional theory using the generalized gradient approximation (DFT/PBE) and taking into account periodic boundary conditions. The most energetically favorable clusters are those, which contain two water molecules per SO3H group, whereas the superstoichiometric water molecule is adsorbed on the crystal surface with the adsorption energy of 0.3–0.6 eV. The barriers for the proton conductivity are 0.2–0.3 eV.

Calix[4]arene-p-sulfonic acid hydrates [CH2(OH)C6H2SO3H]4•nH2O (n = 6, 8, 9, 10, 12): a quantum chemical study

The cluster structures of calix[4]arene-p-sulfonic acid hydrates [CH2(OH)C6H2SO3H]4•nH2O (n = 6, 8, 9, 10, 12) and the activation barriers to proton migration in them were studied as functions of the number of water molecules (n) within the framework of the density functional theory using the gradient-corrected methods PBE/PAW and B3LYP/6-31G** in the cluster approximation. The average attachment energy of a water molecule calculated for calix[4]arenep-sulfonic acid polyhydrates is 0.5—0.7 eV, while the calculated activation barriers to proton transfer are close to experimental values (0.2—0.4 eV) and depend on the number of water molecules per SO3H group.

IR Study of a Polymer Proton-Conducting Electrolyte Based on Poly(vinyl alcohol) and Phenol-2,4-Disulfonic Acid

The structure and hydration of phenol-2,4-disulfonic acid in the individual state and in the system with poly(vinyl alcohol) at low and high humidity levels are studied by IR spectroscopy. It is shown that all characteristic features of the electrolytic dissociation of phenol-2,4-disulfonic acid via proton transfer from acid molecules to the molecules of water in the liquid phase of the binary system phenol-2,4-disulfonic acid–water are also observed for the viscous solutions of the triple system poly(vinyl alcohol)–phenol-2,4-disulfonic acid–water, although differences make themselves evident if water molecules are in deficiency. It is found that evacuation of the phenol-2,4-disulfonic acid film for several hours at room temperature leads to its dehydration and eventually causes formation of molecular dimers [C6H3OH(SO2OH)2]2. A similar operation with the poly(vinyl alcohol)–phenol-2,4-disulfonic acid film is completed by the transfer of a proton from the acid molecule to the–ОН group of poly(vinyl alcohol) according to the following scheme: nC6H3OH(SO2OH)2 + (–CH2OH) n → nC6H3OH(SO3)(SO2OH)– + (–CH2OH2) + .

Synthesis, structure and proton conductivity of 2,4,5-trimethylbenzenesulfonic acid dihydrate

2,4,5-Trimethylbenzenesulfonic acid dihydrate was isolated in the monocrystalline state. Crystal and molecular structures of the compound were determined by X-ray diffraction analysis and vibrational spectroscopy. The compound crystal system is monoclinic: a =7.7445(3) A, b = 7.5360(3) A, c = 9.9477(4) A, α = γ = 90°, β = 92.123(4)°, V = 580.17(4) A3, P21, Z = 2, R1 = 0.0323, dcalc. = 1.353 g cm−3, T = 150 K. A 2D hydrogen bond network formed of a dioxonium ion and oxygen atom of a sulfogroup was identified in the crystal structure. IR absorption spectra, Raman spectra and ATR IR spectra of 2,4,5-trimethylbenzenesulfonic acid dihydrate and deuterodihydrate have been obtained in the region 50–4000 cm−1. It was found that the proton and deuterium in the H5O2+ and D5O2+ cations shifted from the midpoint of the strong hydrogen bond toward one of two water molecules according to the scheme O⋯H+⋯O → O⋯H+–O and O⋯D+⋯O → O⋯D+–O. Spectroscopic data concerning dioxonium ion formation show satisfactory agreement with X-ray diffraction analysis. The effect of environment humidity on the state of 2,4,5-trimethylbenzenesulfonic acid dihydrate aggregation was investigated. It was shown that the number of water molecules increases up to 2.5 per sulfogroup in the 7–84 rel.% air humidity interval through additional water molecules adsorption. A further humidity increase led to compound deliquescence. The proton conductivity as measured by impedance spectroscopy is 10−9–10−5 S cm−1 in the 7–58 rel.% humidity interval at 298 K with a [H2O]/[SO3−] = 2.2 ratio at maximum conductivity.

Photophysical properties of the extract of endometallofullerenes La@C2n inortho-dichlorobenzene. Picosecond laser photolysis

The kinetics of relaxation of optical anisotropy induced by polarized light in endometallofullerenes La@C2n inortho-dichlorobenzene was studied by picosecond laser photolysis. Decay of the optical absorption signal due to the excited states of La@C2n follows the biexponential law with two values of relaxation time:t1=35±3 ps andt2=1100±200 ps. The lifetimet or decay of the optical anisotropy is 19±5 ps and determined by the orientational diffusion of La@C2n. The experimentally determined lifetime of optical anisotropy agrees satisfactorily with the value yielded by the theoretical model of orientational diffusion under slip boundary conditions at the interface of the La@C2n molecule with the solvent.