Entropies and Heat Capacities of Gaseous Selenium Molecules Sen (n = 5 ... 12)

Thermodynamic functions are calculated for gaseous Se8 molecules from spectroscopic and structural data and listed for temperatures up to 3000 K. Entropy (S°) and heat capacity (Cp0) data for Sen molecules (n = 5, 6, 7, 9, 10, 11, 12) are obtained from linear relationships between both S0 and Cp0 and ring size n which are derived from the corresponding values of Se2 and Se8

Barrier to Rotation about Sulfur-Sulfur Bonds in Homocyclic Sulfur Molecules

It is shown that the distances (d) of the 19 longest bonds in 9 homocyclic sulfur rings of type Sn (n = 6-20) depend on the torsional angles (τ) which vary between 0° and 140°. The function d = f(τ) is smallest for τ = 90-100° and largest for τ = 0°; the corresponding bond distance variation amounts to 13 pm or 6%. The height of the torsional cis-barrier is estimated from the enthalpy of formation of gaseous S7 as equal to or smaller than 24 kJ/mol

Vibrational Spectra and Force Constants of Tetrasulfurtetranitride, S4N4 [1]

Infrared and Raman spectra of solid and dissolved S414N4 and of solid S415N4 have been recorded and assigned in accordance with the molecular point group D2d. 22 of the 28 fundamental vibrations of both molecules have been identified and used to calculate force constants applying a modified Urey-Bradley force field with 9 independent constants. Good agreement between observed and calculated wavenumbers was obtained, and both Urey-Bradley and valence force constants are given. The results indicate that-S4N4 basically contains eight SN single bonds and two extremely weak SS bonds

Low Temperature Raman Spectra of Dichlorosulfane (SC12), Tetrachlorosulfurane (SC14), Dichlorodisulfane (S2C12) and Dichlorodiselane (Se2Cl2) [1]

The Raman spectrum of commercial "sulfur dichloride" shows strong lines due to SCl2 and S2Cl2 and weak Cl2 lines at 25 °C, but strong SCl2 and SCl4 signals at -100 °C (the latter are superimposed on the S2Cl2 lines). Thus, the intense Raman effect of SCl4 can be used to detect small amounts of chlorine in SCl2 . Mixtures of SCl2 and Cl2 (1:15) yield the Raman spectrum of SCl4 at -140 °C, while at 25 °C not trace of this compound can be detected. The spectra of SCl4 and α-SeCl4 are quite different, indicating different molecular and/or crystal structures, although ECl3 + ions (E = S, Se) are present in both cases. While Se2Cl2 dimerizes reversibly below -50 °C, S2Cl2 neither dimerizes nor isomerizes on cooling. The S2Cl2 dimer is characterized by a Raman line at 215 cm-1 the intensity of which was used to calculate an enthalpy of dimerization as of -17 kJ/mol

The role of polysulfide dianions and radical anions in the chemical, physical and biological sciences, including sulfur-based batteries

The well-known tendency of sulfur to catenate is exemplified by an extensive series of polysulfide dianions [Sn]2− (n = 2–9) and related radical monoanions [Sn]˙−. The dianions can be isolated as crystalline salts with appropriate cations and structurally and spectroscopically characterized. Although the smaller radical monoanions may be stabilized in zeolitic matrices, they are usually formed in solution via disproportionation or partial dissociation of the dianions as well as by electrochemical reduction of elemental sulfur. An understanding of the fundamental chemistry of these homoatomic species is key to unravelling their behaviour in a broad variety of chemical environments. This review will critically evaluate the techniques used to characterize polysulfide dianions and radical anions both in solution and in the solid state, i.e. Raman, UV-visible, EPR, NMR and X-ray absorption spectroscopy, X-ray crystallography, mass spectrometry, chromatography and high-level quantum-chemical calculations. This is followed by a discussion of recent advances in areas in which these anionic sulfur species play a crucial role, viz. alkali-metal–sulfur batteries, organic syntheses, biological chemistry, geochemical processes including metal transport, coordination complexes, atmospheric chemistry and materials science.TU Berlin, Open-Access-Mittel - 201

Equilibria between Sulfur Rings in Carbon Disulfide Solution at Elevated Temperatures

Cyclooctasulfur, S8, dissolved in CS2 reacts at 130-155 °C in sealed ampoules to give S6 and S7 whose concentrations have been determined by HPLC. The half-time of the reaction is independent of the initial S8 concentration and decreases from 232 min at 130 °C to 64 min at 150 °C. After long reaction times equilibrium concentrations are observed which are in agreement with the law of mass action. From the temperature dependence of the equilibrium constants the following reaction enthalpies (at 130-155 °C) have been calculated: 3/4S8⇌S6 ⊿H°=24kJ/mol 7/8S8⇌S7 ⊿H°=21kJ/mol

Photolyse von elementarem Schwefel (S6, S7, S8, S10, S12) in Kohlenstoffdisulfidlösung [1]

The photochemical decomposition of pure carbondisulfide as well as of solutions of pure S6 , S7 , S8 , S10 and S12 , respectively, in CS2 at 15 °C on irradiation by a high-pressure mercury lamp (200-600 nm) has been studied by quantitative HPLC analysis of the soluble products. In all cases mixtures of sulfur homocycles Sn (n = 5,6, ...) are formed with S8 , S7 and S6 being the dominating species, but traces of S5 , S9 , S10 and S12 have also been observed in most cases. S5 has been identified for the first time; it is formed in particular in the photolysis of S7 in CS2 . All irradiated sulfur solutions reach more or less the same photostationary equilibrium, but the decomposition of CS2 increases linearly with time and its effects are superimposed on the Sn interconversion reactions

Detection, of Se6, Se7 and Se8 in Selenium Solutions by High-Pressure Liquid Chromatography

Dissolution of crystalline Se8 or extraction of glassy or red amorphous selenium, prepared from aqueous SeO2 by reduction, by organic solvents yields solutions containing Se6, Se7 and Se8 in equilibrium as shown by HPLC. The equilibrium explains the concentration dependence of the molar absorbance of such solutions observed earlier. Since the Raman spectrum of red amorphous selenium does not show any lines due to Se6 Se7 and Se8 a rapid interconversion of selenium molecules in solution at 20 °C is postulated. Red amorphous selenium may consist of a mixture of small and medium sized ring molecules

X-ray Structural Analysis and Vibrational Spectra of Trisulfurdinitrogendioxide, S3N2O2 [1]

A redetermination of the crystal and molecular structure of the chain-like molecule S(NSO)2 resulted in the following molecular parameters: d(SO) = 146.5(2), d(S = N) = 153.4(2), d(S-N) = 165.7(2) pm, bond angles OSN = 117.5(1)°, SNS = 123.6(2)°, and NSN = 97.2(1)°, torsion angles OSNS = -0.3(2)°, and SNSN = -177.7(2)° (molecular symmetry C2). Infrared and Raman spectra of S(NSO)2 are reported and assigned; there is no evidence for conformational changes on dissolution of crystalline S(NSO)2

The Molecular Composition of Hydrophilic Sulfur Sols Prepared by Acid Decomposition of Thiosulfate [1]

Hydrophilic sulfur sols prepared from sodium thiosulfate and concentrated sulfuric acid and purified by repeated NaCl precipitation and peptization in water have been studied by chemical analysis, vibrational spectroscopy, ion-pair chromatography and reversed-phase HPLC. The composition of the sol is Na164S28.606 • 5.9In S„ • 1.0 NaCl. The elemental sulfur S„ (n = 6-14; mainly S8) accounts for 17% the total sulfur; 83% of the S are present as long-chain polythionates which form micelles in which the S„ molecules are dissolved. On aging of the sol at 20 °C the polythionate micelles decompose to give water-soluble short-chain polythionates and elemental sulfur which precipitates from the solution. The micelle structure of hydrophilic sulfur sols may serve as a model for the so-called sulfur globules (S°) formed intra- or extracellularly by many sulfur bacteria which oxidize reduced sulfur compounds to S°. — Infrared and Raman spectra of K2Sm06 (m = 3—6) are reported. The photodecomposition of aqueous tetrathionate yields sulfite, thiosulfate, and polythionates with up to 9 sulfur atoms