Search

Five samples of differently colored sodalite-group minerals from gem lazurite deposits were studied by means of electron microprobe and wet chemical analyses, infrared, Raman, electron spin resonance (ESR) and UV-Visible spectroscopy, and X-ray diffraction. Various extra-framework components (SO42&ndash, S2&ndash, and Cl&ndash, anions, S3&middot, &ndash, S2&middot, and SO3&middot, radical anions, H2O, CO2, COS, cis- as well as trans- or gauche-S4 neutral molecules have been identified. It is shown that S3&middot, and S4 are the main blue and purple chromophores, respectively, whereas the S2&middot, yellow chromophore and SO3&middot, blue chromophore play a subordinate role. X-ray diffraction patterns of all samples of sodalite-group minerals from lazurite deposits studied in this work contain superstructure reflections which indicate different kinds of incommensurate modulation of the structures.

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.

Correction for ‘The role of polysulfide dianions and radical anions in the chemical, physical and biological sciences, including sulfur-based batteries’ by Ralf Steudel et al., Chem. Soc. Rev., 2019, 48, 3279–3319.

The radical HSO is an oxidation product of pollutants such as H(2)S and CH(3)SH in Earth's atmosphere. For the first time, the interaction of HSO and its tautomer HOS with single water molecules to yield the hydrates HSO.nH(2)O and HOS.nH(2)O was studied for n = 1-3, applying the high-level G3X(MP2) theory. A large number of structures corresponding to local minima on the potential energy surfaces has been identified. While gaseous HSO is more stable than HOS, the enthalpy diffference between HSO.nH(2)O and HOS.nH(2)O decreases with increasing degree of hydration and becomes practically zero for n = 3. Thus, in aqueous solution as well as in fog and rain droplets, HOS is expected to compete with HSO. The barrier for the tautomerization of HSO to HOS is dramatically lowered by the presence of water molecules since a cyclic transition state allows a concerted proton shift within the system of neighboring hydrogen bonds. The corresponding activation enthalpy of only 73.5 kJ mol(-1) predicted for the transformation of HSO.2H(2)O into HOS.2H(2)O may be compared to the 202 kJ mol(-1) reported for the tautomerization of the unhydrated gaseous HSO/HOS molecules. The impact of water of hydration on the fundamental vibrational modes of HSO and HOS has also been studied. Furthermore, HOS is predicted to dimerize at low temperatures to give two van der Waals molecules with singlet (symmetry C(2)) or triplet configuration (symmetry C(2h)), the latter being more stable than the singlet isomer. The disproportionation of 2HSO to H(2)S and SO(2) is predicted to be exothermic by -263.5 kJ mol(-1). The reaction of HSO with ozone to HSO(2) and O(2) is also strongly exothermic by -274.0 kJ mol(-1) and seems to proceed without any barrier. HOS forms a 1:1 van der Waals complex with O(3); the redox reaction of its two components is calculated as exothermic by -410.9 kJ mol(-1) and results in a rather stable adduct between HOSO and O(2) with the structure of a peroxo isomer of HOSO(3). This unprecedented hydrogen peroxosulfite radical might open a novel route to atmospheric sulfate without the intermediate formation of SO(2) and SO(3).

Certain sulfur bacteria oxidize thiosulfate enzymatically to sulfate, and derivatives of the amino acid cysteine play an important role as intermediates in this process. Since some of the proposed intermediates have so far been of hypothetical nature, we have investigated the structures and thermodynamic properties of more than 60 related derivatives of cysteine (CysH) by high-level quantum chemical calculations both in the gas phase and in a polarizable continuum using the PCM method to simulate an aqueous solution. Most of these molecules and anions were studied for the first time. Especially for the smaller species several conformational isomers of similar energy were identified; their relative stabilities are mainly determined by intramolecular hydrogen bonds. In contrast to the thiolate ion [Cys](-), the gaseous anions [CysS](-), [CysSO(2)](-), [CysSO(3)](-) and [CysSSO(3)](-) are most stable as zwitterions containing an NH(3) rather than an NH(2) group. This result also holds for the polarizable continuum. On the other hand, the related neutral molecules CysH, CysSH and CysSO(2)H are predicted to exist as NH(2) derivatives rather than zwitterions in the gas phase and this connectivity is predicted for CysH and CysSH also in the polarizable continuum. A model molecule of composition C(4)H(7)N(2)O(2)SH (abbreviated as RSH) simulating the structural environment of a cysteine residue within the peptide chain near the corresponding reaction center of the thiosulfate oxidizing enzyme complex "Sox" was used to elucidate the geometry of the proposed reaction intermediates as well as their thermodynamic properties. In the polarizable phase, the S-sulfonate ions [CysSO(3)](-) and [RSSO(3)](-) are predicted to react exothermically with water to the corresponding thiol and hydrogensulfate ions. These results support the proposed mechanism for enzymatic thiosulfate metabolism. Sulfur dioxide and hydrogensulfite anions are predicted to react exothermically and exergonically with thiolate and persulfide anions to give the corresponding S-sulfinate species [RSSO(2)](-) and [RSSSO(2)](-), respectively. The latter ions help to explain the inhibition of certain thiolate based enzymes by aqueous sulfite, disulfite and dithionite anions in sulfur oxidizing microorganisms.

The structures of a large number of hydrates of sulfur dioxide (SO2·nH2O), of the sulfonate ion ([HSO3]–·nH2O), of the tautomeric hydrogensulfite anion ([SO3H]–·nH2O), and of sulfurous acid (H2SO3·nH2O) with up to eight water molecules attached to these species have been optimized at the B3LYP/6-31G(2df,p) level of theory (DFT). The calculated vibrational frequencies allow the definite assignment of certain characteristic modes, and in this way a convincing interpretation of published spectra of aqueous SO2 as well as of SO2 adsorbed on very cold ice crystals has been achieved for the first time. Single-point calculations at the G3X(MP2) level of theory were used to calculate the binding energies of the water molecules in SO2·nH2O as well as the relative stabilities of the isomeric anionic species [HSO3]–·nH2O and [SO3H]–·nH2O. Generally, the water molecules tend to stick together forming clusters, whereas the particular sulfur-containing molecule remains at the surface of the water cluster, but it is always strongly hydrogen-bonded. Only when there are more than six water molecules are the anions more or less completely surrounded by water molecules. DFT calculations erroneously predict that the gaseous hydrated sulfonate ions are more stable than the isomeric hydrogensulfite ions, even when hydrated with six water molecules. However, if these hydrated species are calculated as being embedded in a polar continuum simulating the aqueous phase, the hydrogensulfite ions are more stable than the sulfonate ions, in agreement with various spectroscopic observations on aqueous sulfite solutions. On the other hand, at the higher G3X(MP2) level, the gaseous hydrated hydrogensulfite anions are more stable than the corresponding sulfonate ions only if the number of water molecules is larger than four, whereas for the weakly hydrated anions the order of relative energies is reversed. The possible implications of these results for the enzymatic oxidation of “sulfite ions” ([HSO3]– and [SO3H]–) by sulfite oxidase are discussed. The conversion of SO2·6H2O into its isomer H2SO3·5H2O is predicted to be exothermic (ΔH°298 = –56.1 kJ mol–1) and exergonic (ΔG°298 = –22.5 kJ mol–1). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The formation of adducts between the acceptor molecules SO2, S2O, S3, and SOCl2 and the donor molecules ammonia and trimethylamine has been studied by high-level G3X(MP2) theory, in most cases for the first time. Minimum energy structures with a 1:1 composition and with sulfur–nitrogen bonds have been located for all complexes. The thermodynamic properties, vibrational spectra, and atomic charges of these molecules have been calculated. Of the 10 investigated complexes, only SO2·NMe3 (2) and S2O·NMe3 (4) are predicted to be thermodynamically stable in the gas phase under standard conditions (ΔG°298 < 0). However, all adducts except S3·NH3 (5), SOCl2·NH3 (7), and SOCl2·NMe3 (8) are stable thermodynamically at 77 K. In a polar continuum with a dielectric constant (ϵ) of 40, complexes 2, 4, and S3·NMe3 (6) are stable even at 25 °C. However, if the adducts are formed in the polar continuum from the gaseous components, all adducts except S3·NH3 are formed not only exothermally but also exergonically. Complexes 2, 4, and 8 are the only species known in the solid state so far. The charge transfer from donor to acceptor in the various complexes in the gas phase ranges from 0.08 to 0.39 electrostatic units and correlates inversely with the S–N bond length, which ranges from 198 to 295 pm. In general, the charge transfer weakens the bonds within the acceptor molecule, which therefore may be considered to become activated. The formation of thionyl imide (SONH) from SOCl2 and NH3 is exergonic in the gas phase and the interaction between SONH and NH3 is very weak. In the case of SO2, the 1:2 complexes SO2·2NH3 (1a) and SO2·2NMe3 (2a), which contain two S–N bonds, are unstable with respect to their three-component molecules both in the gas phase and in a polar medium at 25 °C, but they are stable in the polar phase with respect to the gaseous components.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The structures of a large number of isomers of the sulfur oxides S(n)O with n = 4-9 have been calculated at the G3X(MP2) level of theory. In most cases, homocyclic molecules with exocyclic oxygen atoms in an axial position are the global minimum structures. Perfect agreement is obtained with experimentally determined structures of S(7)O and S(8)O. The most stable S(4)O isomer as well as some less stable isomers of S(5)O and S(6)O are characterized by a strong pi*-pi* interaction between S==O and S==S groups, which results in relatively long S--S bonds with internuclear distances of 244-262 pm. Heterocyclic isomers are less stable than the global minimum structures, and this energy difference approximately increases with the ring size: 17 (S(4)O), 40 (S(5)O), 32 (S(6)O), 28 (S(7)O), 45 (S(8)O), and 54 kJ mol(-1) (S(9)O). Owing to a favorable pi*-pi* interaction, preference for an axial (or endo) conformation is calculated for the global energy minima of S(7)O, S(8)O, and S(9)O. Vapor-phase decomposition of S(n)O molecules to SO(2) and S(8) is strongly exothermic, whereas the formation of S(2)O and S(8) is exothermic if n

Ab initio MO calculations (MP 2/6–311 G**//HF/6–311 G**) have been performed for several isomers (including rotamers) of Me2S3O and Me2S3O2. MeS(O)SSMe exists as five rotamers; the most stable form (1a) has a helical backbone CSSSC with S-S bond lengths of 206.0 (SIISII) and 212.4 pm (SIISII). The most stable rotamer of MeS-S(O)SMe (2a), is less stable than 1a by 10.7 kJ mol-1; it is of Cs, symmetry, while a rotamer of Cs symmetry (2b) is less stable than 2a by only 1.4 kJ mol-1. Both 2a and 2b are stabilized by O H hydrogen bonds. The S-S bond lengths of 2a are 210.0 and 212.0 pm; the CSSSC chain is not helical (CSSS torsion angles 166.3 and –75.4°). The 1,3-dioxide MeS(O)-SS(O)Me (3) has two equivalent chiral centers and exists as diastereomers. The most stable isomer 3a (RR)/(SS) is of C2 symmetry with methyl groups trans to each other; the SO bonds form an angle of about 90°. The meso form 3b is less stable than 3a by 17.2 kJ mol-1 and the rotamers 3c and 3d are less stable by 25.6 kJ mol-1 and 28.4 kJ mol-1, respectively. The trisulfane-1.2–dioxide MeS(O)-S(O)SMe has two nonequivalent chiral centers and exists as five isomers. The most stable form, the (RS)/(SR) form 4a, is less stable than 3a by 21.4 kJ mol-1 and is characterized by SS bonds of 220.9 (SIIISIII) and 208.3 pm (SIIISII). The rotamer 4b is less stable by 5.9 kJ mol-1. The isomers 4c, 4d, and 4e are all of (SS)/(RR) configuration and are less stable than 4a by 6.3, 12.7, and 12.0 kJ mol-1. For comparison, ab initio MO calculations (HF/6–311 G*) for tBuS(O)SS(O)-tBu yielded two diastereomers of practically identically energy that both contain helical CSSSC backbones. The (RS) form is less stable than the (RR)/(SS) form by 1.8 kJ mol-1.

The potential energy hypersurfaces (PESs) of heptasulfur (S7) and of [LiS7]+ have been investigated by ab initio molecular orbital calculations at the G3X(MP2) level of theory. Besides the chair-like seven-membered ring (1a) as the global minimum structure, eight local minimum structures and one transition state have been located on the PES of S7. The barrier for pseudorotation of 1a is only 5.6 kJ mol(-1). The boat-like S7 ring (1b) is 12.1 kJ mol(-1) less stable than 1a, followed by three isomers of connectivity S6=S and four open-chain isomers. On the basis of multireference calculations at the MRCI(4,4)+Q/6-311G(d) level, the most stable open-chain form of S7 is a triplet of relative energy 133.1 kJ mol(-1). Thus, the reaction energy (deltaE0) for the ring opening of 1a is 133.1 kJ mol(-1), halfway between those of the highly symmetrical rings S6 and S8. Because of their strong multireference characters, the stabilities of the biradicalic singlet chains are significantly overestimated by the single-reference-based G3X(MP2) method. The calculated vibrational spectrum of 1a is in good agreement with experimental data. The various isomers of S7 form stable complexes with Li+ with coordination numbers of 1-4 for the metal atom and binding energies in the range of -93.8 to -165.7 kJ mol(-1). A total of 15 isomeric complexes have been located, with 13 of them containing cyclic ligands. The global minimum structure (2a) is composed of 1a, with the Li+ cation linked to the four negatively charged sulfur atoms (symmetry C(s)). The corresponding complex 2c containing the ligand 1b is by 23.4 kJ mol(-1) less stable than 2a, and a bicyclic crown-shaped LiS7 cation (2e) is by 34.9 kJ mol(-1) less stable than 2a. Even less stable are four complexes with the branched S6=S ligand. SS bond activation by polarization of the valence electrons takes place on coordination of Li+ to cyclo-S7 (1a).

The complex formation between the Li+ cation and the sulfur homocycle S8 has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Starting with various isomers of S8, the formation of LiS8 heterocycles and clusters is preferred over complexes with a monodentate ligand. The binding energies of the cation in the 23 complexes investigated range from –95 to –217 kJ·mol–1. The global minimum structure of [LiS8]+ is of C4v symmetry with the S8 homocycle in the well-known crown conformation and four Li–S bonds of length 254.2 pm (binding energy: –156.5 kJ·mol–1). The S–S bonds of the various ligands are slightly weakened by the complex formation and a more or less strong bond length alternation is induced. Relatively unstable isomers of S8 (chair, tub, exo–endo ring, branched rings, triplet chain) are partly stabilized and partly destabilized by complex formation with Li+. The interaction between the cation and the S8 ligands is mainly due to ion–dipole attraction with little to moderate charge transfer (0.04–0.27 electrostatic units). In the four most stable isomers of [LiS8]+, the number of sulfur–sulfur bonds is at a maximum and the coordination number of Li+ is either 4 or 3. Complexes of the type [Li(S4)2]+ are much less stable than isomers with an eight-atomic ligand. The Li–S bond lengths in all of these complex cations (230–273 pm) depend on the coordination number of Li and on the atomic charge of the donating sulfur atom(s). In contrast to [LiS8]+, the complexes of composition [MS8]+ with M = Ca, V, and Cu are more stable as [M(S4)2]+ than with an eight-atomic crown-shaped ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Crystals of diiodo-2,2’-dipyridyldisulfide mercury(II) [HgI2(C5H4N)2S2], dichloro-2,2’-dipyridyldisulfide zinc(II) [ZnCl2(C5H4N)2S2], dibromo-2,2’-dipyridyldisulfide cadmium(II) [CdBr2 (C5H4N)2S2], diiodo-2,2’-dipyridyldisulfide cadmium(II) [CdI2(C5H4N)2S2], and diaquo 2,2’-dipyridyldisulfide cadmium(II) trifluoromethanesulfonate [Cd(H2O)2(C5H4N)2S2](CF3SO3)2, were obtained by evaporation of solutions of the ligand and the appropriate metal salts, and their X-ray crystal structures determined

Crystals of 1,4,7,10-tetrathiacyclododecane silver(I) trifluoromethanesulfonate, Ag(C8H16S4)- (CF3SO3), 1,4,7,10-tetrathiacyclododecane iodo mercury(II) hexaiododimercurate(II)methylene chloride [HgI(C8H16S4)][Hg2I6] · CH2Cl2, 1,4,7,10,13,16-hexathiacyclooctadecane silver(I) trifluoromethanesulfonate [Ag(C12H24S6)](CF3SO3), 1,4,7,10,13,16-hexathiacyclooctadecane diiodocadmium, [Cd(C12H24S6)I2], and bis-3,6,9,14-tetrathiabicyclo[9.2.1]tetradeca-11-13-diene silver(I) trifluoromethanesulfonate [Ag(C10H14S4)2](CF3SO3) were obtained by reaction of solutions of the ligands and the appropriate metal salts and their X-ray crystal structures determined.

All chemically reasonable [2+2] and [2+3] dipolar addition reactions between two S2O molecules forming heterocyclic intermediates of composition S4O2, as well as the decomposition of these species to generate the observed products S3 and SO2, have been studied by gas-phase ab initio MO calculations at the G3X(MP2) level of theory. The reaction enthalpies, Gibbs energies and, partly, activation enthalpies of 17 reactions have been calculated. The [2+2] cycloadditions of S2O are all endothermic and are characterized by high barriers. The reaction of lowest activation enthalpy (ΔH#298 = 11 kJ·mol−1) is the exothermic [2+3] cycloaddition of two S2O molecules resulting in the five-membered heterocycle oxatetrathiolane 2-oxide S4O2 (7), which is predicted to decompose at 298 K exothermally and without any activation enthalpy to SO2 plus S3. The S3 molecule is predicted to add exothermally to S2O to give the five-membered homocycle S5O which has, in fact, been prepared in this way before. The bimolecular decomposition of S5O to SO2, S4 and S5 is also exothermic and may explain the formation of the red S4 molecule on condensation of S2O at temperatures below −130 °C. The implications of these results for the understanding of the chemistry on Jupiter’s moon Io are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The structures and thermodynamic properties of 32 cations of composition [HSn]+ with n = 2−8 have been studied by ab initio methods at the G3X(MP2) level of theory. In the global minimum structures, the proton binds to a single sulfur atom and, except for n = 2, this also holds for the less stable isomers. The binding energies at 0 K range from 619.4 kJ mol-1 in [HS2]+ to 835.6 kJ mol-1 in [S5−SH]+, which represents the global minimum structure of composition [HS6]+. The protonated branched rings are also the global minimum structures in the case of S7 and S8, whereas [HS5]+ is most stable with a five-membered homocycle. The smaller cations [HSn]+ (n = 2−4) are all chainlike with the hydrogen atom at a chain end. Unexpectedly, singlet chainlike structures of [HSn]+ (n = 2−8) with the hydrogen terminating the chain at one end are more stable than the corresponding triplet chains. The protonation of neutral sulfur molecules always takes place at the atom of highest negative charge and the charge transfer to...

Two novel Cp2Ti(Cl)S3R′S3Tr complexes have been prepared by reaction of the six-membered metallacycles Cp2TiS4R′ (Cp = η5-C5H5, R′ = CMe2, 1,1-C6H10) with the sulfenyl chloride TrSCl (Tr = CPh3) at 20 °C. These complexes were treated with: (a) sulfenyl chlorides (RSCl or RSSCl) to obtain 11 new thiaalkanes of the type R−Sx−R′−Sy−R (R = Tr, 4-ClC6H4, 2-C10H7; x = 3, y > 2), or (b) with SO2Cl2, SCl2 or S2Cl2 to prepare six sulfur-rich species of the type Tr−Sx−R′−Sy−R′−Sz−Tr (x, z = 3, y > 3), as well as Cp2TiCl2. The thiaalkanes decompose upon heating to give mixtures of various linear and cyclic polysulfanes R2Sn and R′Sm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Eight hypothetical persulfurane molecules of the type X2SY4 (X, Y = H, F, Me) have been studied by ab initio MO calculations at the G3(MP2) level of theory. Depending on the substituents either the cis or the trans isomers of these octahedral molecules are most stable. While H4SF2 is most stable as the cis isomer, the global minimum structures of H2SF4, Me2SH4, and Me2SF4 are the trans isomers. The enthalpy differences between the corresponding isomers are in the range 7−53 kJ·mol−1. The transition states for the intramolecular cis ⇋ trans isomerization have been located in all cases. Starting from the global minimum geometries the activation enthalpies (ΔH#298) for this isomerization are in the range 199−263 kJ·mol−1, indicating rather rigid structures. Therefore, it should be possible to isolate both isomers at low to moderate temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The structures and relative stabilities of eight S 4 isomers were investigated by G3X(MP2), CCSD(T)/cc-pVTZ and MRCI/CASSCF calculations. The cis -planar (C 2v ) structure is confirmed to be the global minimum of S 4 , while the rectangular D 2h structure is calculated to be a transition state. The predicted stability order of various singlet S 4 isomers is C 2v >C 2h >C s >D 2d >D 3h . Calculated electronic absorption spectra [CIS/6-311 + G(3df)] and vibrational spectra [B3LYP/6-31G(2df)] allow a convincing assignment of the observed green absorbing species as the cis -planar (C 2v ) structure (global minimum) and the red absorbing species as the trans -planar (C 2h ) isomer, in distinct contrast to the previous assignments.

At the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol−1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol−1 at 298 K. The decomposition of trans-SF4(CN)2 to SF2(CN)2 and F2 is endothermic (ΔHo298 = 395 kJ·mol−1) but the elimination of FCN from trans-SF4(CN)2 is exothermic by −7 kJ·mol−1. The elimination of (CN)2 from cis-SF4(CN)2 is exothermic by −137 kJ·mol−1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol−1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol−1 [SF3CN] or 58 kJ·mol−1 [SF2(CN)2]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

III. Structures of Organic Polysulfanes 3922 A. General 3922 B. Structures of Chain-Like R−Sn−R Molecules 3923 C. Structures of Cyclic R−Sn−R Molecules 3924 D. Conformational Studies 3925 IV. Analysis of Organic Polysulfanes 3925 A. General 3925 B. NMR Spectroscopy 3926 C. Chromatography 3926 D. Raman Spectroscopy 3928 E. XANES Spectroscopy 3928 V. Reactions of Organic Polysulfanes 3928 A. Interconversion Reactions 3928 B. Sulfur Transfer Reactions 3930 C. Replacement Reactions 3931 D. Nucleophilic Displacement Reactions at the Sulfur−Sulfur Bond 3931

Ab initio calculations at the G3X(MP2) level have been employed to examine the structures and energies of S 8 and H 2 S 6 isomers. A cluster structure with a spiraling chain of 8 atoms (C 2 symmetry) lies close in energy ( 33 kJ mol −1 ) to the eight-membered crown-S 8 global energy minimum. This cluster species is characterized by two three-coordinate atoms and a rectangular arrangement of four sulfur atoms at the formal chain-ends. This unusual cluster geometry can be rationalized in terms of a weak π * –π * bond between the two π * orbitals of the chain-end groups. A low-energy cluster-type structure is also predicted for hexasulfane.

The bimetallic complexes fc(μ2-S)2TiCp2 (1, fc = 1,1‘-ferrocenyl, Cp = cyclopentadienyl) and fc(μ2-S2)(μ2-S)TiCp2 (2) were synthesized by reaction of fc(SH)2 with Cp2TiCl2, and from fcS3 and Cp2Ti(CO)2, respectively. The novel tetrasulfane fcS4 was obtained from 2 and SCl2. 1,3-Dithia[3]ferrocenophane fcS2CH2 was obtained from fc(SH)2 and CH2Cl2 in the presence of Cp2TiCl2 and KOH. The molecular and crystal structure of fcS2CH2 was determined by X-ray crystallography; the molecular symmetry is Cs. Electrochemical studies on the recently prepared ferrocenophanes fcS2-1-SO, fcS2-1-SO2, and fcS2-2-SO show that, with respect to fcS3, the progressive oxidation of the trisulfane bridge makes more and more difficult the fc/fc+ oxidation, whereas insertion of a Cp2Ti fragment exerts the opposite effect.

Using high-level ab initio MO methods, we have identified two reaction pathways with different thermodynamic and kinetic properties for the thermal decomposition of the three-membered heterocycle thiirane (C 2 H 4 S) and related derivatives. A homolytic ring opening, followed by attack of the generated diradical on another thiirane molecule, and subsequent elimination of ethene in a fast radical chain reaction results in the formation of disulfur molecules in their triplet ground state ( 3 S 2 ) and requires activation enthalpies of ΔH # 2 9 8 = 222 kJ mol - 1 and ΔG # 2 9 8 = 212 kJ mol - 1 . This reaction mechanism would result in a first-order rate law in agreement with one reported gas-phase experiment but does neither match the experimental activation energy nor does it explain the observed retention of the stereochemical configuration in the thermal decomposition of certain substituted thiiranes. Alternatively, sulfur atoms can be transferred from one thiirane molecule to another with the intermediate formation of thiirane 1-sulfide (C 2 H 4 S 2 ). This molecule can either decompose unimolecularly to ethene and disulfur in its excited singlet state ( 1 S 2 ) or, by means of spin crossover, S 2 in its triplet ground state may be formed. On the other hand, the thiirane 1-sulfide may react with itself and transfer one sulfur atom from one molecule to another with formation of thiirane 1,1-disulfide (C 2 H 4 S 3 ), which is an analogue of thiirane sulfone; thiirane is formed as the second product. The 1,1-disulfide may then decompose to ethene and S 3 . In still another bimolecular reaction, the thiirane 1-sulfide may react with itself in a strongly exothermic reaction to give S 4 and two equivalents of ethene. This series of reactions results in a second-order rate law and requires activation enthalpies of ΔH # 2 9 8 = 109 kJ mol - 1 and ΔG # 2 9 8 = 144 kJ mol - 1 for the formation of thiirane 1-sulfide, while the consecutive reactions require less activation enthalpy. Elemental sulfur (S 8 ) is eventually formed by oligomerization of either S 2 . S 3 , or S 4 in spin-allowed reactions. These findings are in agreement with most experimental data on the thermal desulfurization of thiirane and its substituted derivatives. Thiirane 1-persulfide (C 2 H 4 S 3 ) with a linear arrangement of the three sulfur atoms as well as zwitterions and radicals derived from thiirane are not likely to be intermediates in the thermal decomposition of episulfides.

High level ab initio MO calculations at the G3(MP2) level of theory were employed to study the molecular structures of SF2, FSSF3, and SSF4, as well as the dimerization of gaseous SF2 to FSSF3 and the isomerization of FSSF3 to SSF4. The dimerization of SF2 was calculated to be an exothermic process (ΔH°298 = −77 kJ·mol−1) with an activation enthalpy (ΔH≠298) of 65 kJ·mol−1. The transition state of the dimerization reaction is characterized by a bridging fluorine atom that undergoes a 1,2-shift, and a weak sulfur-sulfur single bond. The calculated lowest-energy structure of FSSF3 (2a) is in excellent agreement with the experimentally derived structure, with the −SF group in an equatorial position of the distorted pseudo-trigonal-bipyramid at the central sulfur atom. A significantly less stable FSSF3 conformer 2b, 76 kJ·mol−1 higher in energy, has the −SF group in an axial position. Unimolecular rearrangement of FSSF3 (2a) to the trigonal-bipyramidal SSF4 (3), by a 1,2-fluorine shift (TS2), is endothermic by 37 kJ·mol−1 and is inhibited by a large activation barrier of 267 kJ·mol−1. SSF4 is predicted to be an observable species in the gas phase. Calculated infrared spectra of 2a and 3 are also reported.

The gas-phase geometries, dipole moments, enthalpies, and Gibbs free energies of thiosulfuric acid H2S2O3, peroxosulfuric acid H2SO5, fluorosulfuric acid HSO3F, and chlorosulfuric acid HSO3Cl as well as of their monoanions have been determined by ab initio MO calculations at various levels of theory. The most stable conformations of the four acid molecules are all of C1 symmetry. The acidities, defined as ΔG°298 of the deprotonation reaction, obtained by the G2 method are as follows [kJ mol−1]: HO−SO2−SH 1251 and HO−SO2−SH 1276, HO−SO(=S)−OH 1241, HO−SO2−OOH 1239, HO−SO2−F 1229, HO−SO2−Cl 1219. Good agreement of the calculated acidities of HSO3F and HSO3Cl is observed with the experimental gas-phase acidities, which are the only experimental values available. The OH acidities of all five species are higher than that of sulfuric acid (1268 kJ mol−1). Therefore, these compounds may be termed as superacids. In contrast to the liquid state, chlorosulfuric acid is a stronger proton donor than fluorosulfuric acid in the gas phase. The dissociation of the acid molecules HSO3X (X = SH, OOH, F, Cl) into SO3 and HX is endothermic and endergonic in all cases. The same holds for the dissociation of the anions SO3X− into SO3 and X−. From these dissociation enthalpies and literature data the enthalpies of formation of the mentioned sulfonic acids and their anions are calculated.

Using ab initio MO calculations at the MP2/6-311G(2df,2pd) level of theory the most stable structures of the following seven ions were determined: H3S+ (C3v), H2S–SH+ (Cs), H2S–S–SH+ (C1), HS–S(H)–SH+ (C1), H2S–S–S–SH+ (C1), HS–S(H)–S–SH+ (C1) and S(SH)3+ (C3). In the case of the isomeric H3S3+ cations the species protonated at the terminal sulfur atom is most stable while in the case of the H3S4+ ions the protonation at the β sulfur atom is energetically preferred. However, the energy differences between isomeric cations are rather small. At the same level of theory the wavenumbers of the harmonic fundamental vibrations were calculated and compared to the available experimental data leading to a support for the existing assignments in certain cases but in some cases to revisions. The reaction enthalpies and Gibbs free energies of the proton transfer reactions H2Sn + H2Sn+1 H3Sn+ + HSn+1– were calculated by the G2 method. For n = 1–3 the enthalpies are found in the range 639–731 kJ mol–1. Schwefelverbindungen. 215 Strukturen, Energien und Normalschwingungen der Sulfonium Ionen H3Sn+ (n = 1–4) [1] Mittels ab-initio-MO-Rechnungen auf dem Niveau MP2/6-311G(2df,2pd) wurden die stabilsten Strukturen der Ionen H3S+ (C3v), H2S–SH+ (Cs), H2S–S–SH+ (C1), HS–S(H)–SH+ (C1), H2S–S–S–SH+ (C1), HS–S(H)–S–SH+ (C1) und S(SH)3+ (C3) ermittelt. Im Falle der isomeren Kationen H3S3+ zeigt sich, dass das am terminalen Schwefelatom protonierte Sulfan am stabilsten ist, wahrend im Falle der Ionen vom Typ H3S4+ die Protonierung am β-Schwefelatom energetisch bevorzugt ist. Die Energiedifferenzen zwischen isomeren Kationen sind jedoch sehr klein. Auf dem gleichen Niveau wurden die Wellenzahlen der Normalschwingungen berechnet und mit den verfugbaren experimentellen Werten verglichen, wodurch die Zuordnung in einigen Fallen gesichert werden konnte, in anderen Fallen jedoch revidiert werden musste. Die Reaktionsenthalpien und freien Reaktionsenthalpien der Protontransferreaktionen H2Sn + H2Sn+1 H3Sn+ + HSn+1– wurden mit der G2-Methode berechnet. Fur n = 1–3 liegen die Enthalpien im Bereich 639–731 kJ mol–1.

The preparation of seven novel organic polysulfanes is reported. Bis(n-octyl)heptasulfane R2S71 is formed upon reaction of RSCl with [Cp2TiS5], while the corresponding nonasulfane R2S92 is obtained by reaction of RSSCl with [Cp2TiS5]. The bis(n-octyl)pentasulfane R2S53 is obtained from RSCl and [(Cp′2TiCl)2S3] by transfer of the S3 ligand at 20 °C. The new alkyl polysulfanes 1–3 have been obtained in quantitative yields. They are liquids at 20 °C, having freezing points below –50 °C, but do not form mesogenic phases. Reactions of [Cp2TiS5] with 2-naphthyl- and 4-chlorophenyl sulfenyl chloride furnish the corresponding heptasulfanes 4 and 5, respectively, which are solids at 20 °C. 1,2-Benzodisulfenyl chloride C6H4(SCl)2 reacts with [(Cp′2TiCl)2S3] to give the known 1,2,3,4,5-benzopentathiepin C6H4S56, with [Cp2TiS5] to give the novel 1,2,3,4,5,6,7-benzoheptathionin C6H4S77, and with [(TMEDA)ZnS6] to give the novel 1,2,3,4,5,6,7,8-benzooctathiecin C6H4S88. The cyclic polysulfanes 6–8 are solids at 20 °C and have been recovered in yields of 60–83%. The orthorhombic structure of 1,2-C6H4S7 has been investigated by single-crystal X-ray diffraction analysis. The molecules are found to be located at sites of Cs symmetry and the motif of the C2S7 heterocycle is +–+–+–+–, with the torsion angle of zero at the carbon–carbon bond. The three internuclear SS distances measure 205.0(1), 203.7(1), and 205.7(1) pm.

The gas-phase acidities of the most stable conformations of nine sulfur oxo acids were determined by ab initio MO calculations at the CBS-Q, G2(MP2), and G2 levels of theory. The most accurate G2 results are as follows (ΔG°298 of the deprotonation reaction in kJ mol–1): H–S–O–H 1468, H–S–O–H 1449, (HO)2S 1426, H–S(=O)OH 1406, H2S/O 1394, H–S(=O)OH 1361, (HO)2S/O 1324, H2S(=O)2 1321, H2OS 1294, H–S(=O)2OH 1287, H–S(=O)2OH 1279, (HO)2S(=O)2 1268. These values are in excellent agreement with the few experimental data that can be considered reliable. For molecules of analogous structure, the acidity increases with increasing oxidation number of the sulfur atom. While sulfenic acid, HSOH, is as weak an acid as HOCl, sulfurous acid, (HO)2SO, is as strong a proton donor as nitric acid, HNO3, and sulfonic acid, HS(O)2OH, is even stronger than hydrogen iodide, HI, surpassed only by sulfuric acid, H2SO4. These results are of relevance to phenomena such as acid rain and aerosol formation in the earth′s atmosphere.

The gas-phase acidities ΔGacid(298 K) of the sulfanes H2Sn (n = 1–4) have been calculated by ab initio molecular orbital theory using the G2 and G2(MP2) methods, which were applied to the geometries of lowest energy. The results show that the higher sulfanes are surprisingly strong proton donors. The acidities (in kJ mol−1) are as follows: H2S (1444), H2S2 (1406), H2S3 (1370), H2S4 (1347). The latter three values may be compared to those of other strong Bronsted acids like gaseous HNO2 (1396), HCl (1371), and HBr (1332). The monoanions HSn− exhibit an interesting bond length distribution as a consequence of the charge delocalization by hyperconjugation, which in turn may be responsible for the high acidities of the sulfanes.