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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 B3LYP631G2df,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 SO2as well as of SO2adsorbed on very cold ice crystals has been achieved for the first time. Singlepoint calculations at the G3XMP2 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 sulfurcontaining molecule remains at the surface of the water cluster, but it is always strongly hydrogenbonded. 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 G3XMP2 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. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn2+, ZnMe2, Zn(OMe)2, Zn(OOCMe)2, and the heterocubane cluster Zn4O4with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me2NCS2., Me2NCS3., Me2NCS2−, and Me2NCS3−have been studied by quantum chemical methods at the MP2/6‐31+G(2df,p)//B3LYP/6‐31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe2

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 SnO 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 S7O and S8O. The most stable S4O isomer as well as some less stable isomers of S5O and S6O are characterized by a strong π*–π* 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 (S4O), 40 (S5O), 32 (S6O), 28 (S7O), 45 (S8O), and 54 kJ mol−1(S9O). Owing to a favorable π*–π* interaction, preference for an axial (or endo) conformation is calculated for the global energy minima of S7O, S8O, and S9O. Vapor‐phase decomposition of SnO molecules to SO2and S8is strongly exothermic, whereas the formation of S2O and S8is exothermic if n<7, but slightly endothermic for S7O, S8O, and S9O. The calculated vibrational spectra of the most stable isomers of S6O, S7O, and S8O are in excellent agreement with the observed data.

The vulcanization of rubber by sulfur is a large‐scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn4O4(Td) as a model species to study the thermodynamics of the initial interaction of various vulcanization‐related molecules with ZnO by DFT methods, mostly at the B3LYP/6‐31+G* level. The interaction energy of Lewis bases with Zn4O4increases in the following order: COCSSH.

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)

Complex formation between gaseous Li+ions and sulfur‐containing neutral ligands, such as H2S, Me2Sn(n= 1–5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiSnheterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from −88 kJ mol−1for [H2SLi]+to −189 kJ mol−1for the most stable isomer of [Me2S5Li]+which contains three‐coordinate Li+. Of the various S6ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5S ligand have the highest binding energies (−163±1 kJ mol−1). However, the global minimum structure of [LiS6]+is of C3vsymmetry with the six‐membered S6homocycle in the well‐known chair conformation and three LiS bonds with a length of 256 pm (binding energy: −134 kJ mol−1). Relatively unstable isomers of S6are stabilized by complex formation with Li+. The interaction between the cation and the S6ligands is mainly attributed to ion–dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4units, as in [Li(S3)2]+and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+complexes, the number of SS bonds is at maximum and the coordination number of Li+is either 3 or 4. A topological analysis of all investigated complexes revealed that the LiS bonds of lengths below 280 pm are characterized by a maximum electron‐density path and closed‐shell interaction.

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)

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 &lrhar2; 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)

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 (ΔH^o298 = 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)

Ab initio MO calculations at the G3(MP2) level of theory show that sulfur tetraamide S(NH2)4 is a local minimum energy structure but thermodynamically unstable with respect to both sulfur diamide S(NH2)2 plus hydrazine and sulfurimidediamide S(NH)(NH2)2 plus ammonia. The activation enthalpy of the latter reaction is 63 kJ·mol⁻¹ at 298 K. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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 (C2H4S) 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 (³S2) and requires activation enthalpies of ΔH$\rm{_{298}^{\char 35}}$=222 kJ mol⁻¹ and ΔG$\rm{_{298}^{\char 35}}$=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 (C2H4S2). This molecule can either decompose unimolecularly to ethene and disulfur in its excited singlet state (¹S2) or, by means of spin crossover, S2 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 (C2H4S3), which is an analogue of thiirane sulfone; thiirane is formed as the second product. The 1,1-disulfide may then decompose to ethene and S3. In still another bimolecular reaction, the thiirane 1-sulfide may react with itself in a strongly exothermic reaction to give S4 and two equivalents of ethene. This series of reactions results in a second-order rate law and requires activation enthalpies of ΔH$\rm{_{298}^{\char 35}}$=109 kJ mol⁻¹ and ΔG$\rm{_{298}^{\char 35}}$=144 kJ mol⁻¹ for the formation of thiirane 1-sulfide, while the consecutive reactions require less activation enthalpy. Elemental sulfur (S8) is eventually formed by oligomerization of either S2, S3, or S4 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 (C2H4S3) 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.

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 (C2H4S) 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 (3S2) and requires activation enthalpies of ΔH$\rm{_{298}^{\char 35}}$=222 kJ mol−1and ΔG$\rm{_{298}^{\char 35}}$=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 (C2H4S2). This molecule can either decompose unimolecularly to ethene and disulfur in its excited singlet state (1S2) or, by means of spin crossover, S2in 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 (C2H4S3), which is an analogue of thiirane sulfone; thiirane is formed as the second product. The 1,1‐disulfide may then decompose to ethene and S3. In still another bimolecular reaction, the thiirane 1‐sulfide may react with itself in a strongly exothermic reaction to give S4and two equivalents of ethene. This series of reactions results in a second‐order rate law and requires activation enthalpies of ΔH$\rm{_{298}^{\char 35}}$=109 kJ mol−1and ΔG$\rm{_{298}^{\char 35}}$=144 kJ mol−1for the formation of thiirane 1‐sulfide, while the consecutive reactions require less activation enthalpy. Elemental sulfur (S8) is eventually formed by oligomerization of either S2, S3, or S4in 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 (C2H4S3) 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.

Ab initio MO calculations at the CCSD(T)/6‐311++G(2df,p)//MP2/6‐311++G** level have been carried out to determine the reaction energies and Gibbs energies of the homolytic dissociation of the S−S bonds in the chainlike sulfanes H2Sn(n=2–4). Good agreement with the experimental data is observed. At the same level of theory, the formation of the hypothetical sulfuranes H2S(SH)2, H2S(SSH)2, and S(SH)4from H2S and the mentioned sulfanes has been studied. Species of this type had been proposed as intermediates in the interconversion reactions of polysulfur compounds (e.g., formation of S7from S8and vice versa). The three sulfuranes serve here as model compounds. On the basis of the Gibbs energies and activation energies at 298 K, it is shown that the formation of the three sulfuranes from sulfanes requires too much energy and activation energy to successfully compete with homolytic dissociation reactions. In addition, the formation of the methyl‐substituted sulfurane S(SMe)4from the sulfanes Me2S2and Me2S3was studied to elucidate the mechanism of the formal exchange of sulfur atoms between polysulfane molecules. However, both the reaction energy of 199 kJ mol−1and the activation energy of 287 kJ mol−1, calculated at the MP2/6‐31G* level, are much higher than the homolytic dissociation energy of the S−S bonds in chain‐ and ringlike polysulfur compounds, such as Me2S4(140 kJ mol−1) and sulfur homocycles (150 kJ mol−1). Therefore, it is concluded that the observed interconversion reactions of sulfur rings and of chainlike polysulfanes do not proceed via sulfurane‐type intermediates. Instead, these reactions will take place by a radical chain mechanism at high temperatures, while at temperatures below 100 °C they are most probably initiated either by traces of nucleophiles that are present as impurities or by the polar surface groups usually present on the walls of the vessels used.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.