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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 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.

For many years their so-called hyper-valent or hypercoordinate molecules have also been ofinterest to theoretical chemists: there seem to be more thaneight valence electrons at the central S atoms and therefore aviolation of the octet rule has been suspected. However, it isnow generally accepted that the covalent bonds in thesespecies can be understood on the basis of multi-centerinteractions of the 3s and 3p atomic orbitals of sulfur withthe 2p orbitals of the F atoms while the high-energy 3dvalence orbitals of sulfur play a minor role and, to a first ap-proximation, can be neglected. However, d and even f func-tions serve as polarization functions in the basis sets used.

The three isomeric benzene bis-sulfenyl chlorides C6H4(SC1)2 react with [Cp2TiS7NR] (R = H, Me) to give large sulfur-rich heterocycles C6H4S9NR.

The reaction of 1,4-S4(NR)2 with (η5-C5H5)2Ti(CO)2 yields [Cp2Ti(μ-S2)2NR] which on treatment with SCl2 or S2Cl2 provides the novel heterocycles S5NR and S6NR (R = Me, Oct).

Negative hyperconjugation of the type nN→σ* is responsible for the planar or almost planar geometry at nitrogen in certain S–N compounds.

Elemental sulfur - both in the solid, liquid, and gaseous state - shows highly unusual physical and chemical properties not matched by any other element. The reason for this unique behavior is the formation of molecules of different size -from S2 to S6, S7, and S8 up to macromolecules („S,”) - every size is possible. Which mixture is obtained depends on the temperature and other reaction conditions. These findings are important for the understanding of elemental sulfur produced industrially in huge quantities, certain astonishing observations made with bacteria that oxidize sulfur, the Stretford process for sulfur production, and the sulfur covering Ios surface.

The sodium-sulfur (NAS) battery is a candidate for energy storage and load leveling in power systems, by using the reversible reduction of elemental sulfur by sodium metal to give a liquid mixture of polysulfides (Na(2)S(n)) at approximately 320°C. We investigated a large number of reactions possibly occurring in such sodium polysulfide melts by using density functional calculations at the G3X(MP2)/B3LYP/6-31+G(2df,p) level of theory including polarizable continuum model (PCM) corrections for two polarizable phases, to obtain geometric and, for the first time, thermodynamic data for the liquid sodium-sulfur system. Novel reaction sequences for the electrochemical reduction of elemental sulfur are proposed on the basis of their Gibbs reaction energies. We suggest that the primary reduction product of S(8) is the radical anion S(8)(˙-), which decomposes at the operating temperature of NAS batteries exergonically to the radicals S(2)(˙-) and S(3)(˙-) together with the neutral species S(6) and S(5), respectively. In addition, S(8)(˙-) is predicted to disproportionate exergonically to S(8) and S(8)(2-) followed by the dissociation of the latter into two S(4)(˙-) radical ions. By recombination reactions of these radicals various polysulfide dianions can in principle be formed. However, polysulfide dianions larger than S(4)(2-) are thermally unstable at 320°C and smaller dianions as well as radical monoanions dominate in Na(2)S(n) (n=2-5) melts instead. The reverse reactions are predicted to take place when the NAS battery is charged. We show that ion pairs of the types NaS(2)˙, NaS(n)(-), and Na(2)S(n) can be expected at least for n=2 and 3 in NAS batteries, but are unlikely in aqueous sodium polysulfide except at high concentrations. The structures of such radicals and anions with up to nine sulfur atoms are reported, because they are predicted to play a key role in the electrochemical reduction process. A large number of isomerization, disproportionation, and sulfurization reactions of polysulfide mono- and dianions have been investigated in the gas phase and in a polarizable continuum, and numerous reaction enthalpies as well as Gibbs energies are reported.

Titanocene pentasulfide reacts with Ph3CCl and CCl3SCl to give (Ph3C)2S5 and (CCl3)2S7, respectively, the molecular structures of which show helical CSnC backbones. (Ph3C)2S6 and (CN)2S9 possess non-helical structures. C2H4(SCl)2, C6H4(SCl)2, C6H4(SSCl)2 and CH3C6H3(SCl)2 react with Cp2TiS5 to give the corresponding sulfur-rich heterocycles with up to nine sulfur atoms. Dicyclopentadiene trisulfane is used to prepare the dicyclopentadiene tetra-, penta-, hexa- and octa-sulfanes by (a) derivatization to SCl or SH compounds followed by sulfur transfer reactions using Cp2TiS5, (Cp′2ClTi)2S3 or S2Cl2 as reagents. Several cyclic, bicyclic and tricyclic organosulfur heterocycles are obtained from Cp4Ti2C2S4 or from Cp2TiS2C3H6 by reactions with SCl2, S2Cl2, C2H4(SCl)2, COCl2 or C6H4(SCl)2.

The chemistry of organic polysulfanes (or polysulfides) is thoroughly and critically reviewed. The synthesis of chain-like and cyclic polysulfanes with alkyl and aryl substituents as well as their analysis, molecular structures, reactions with nucleophiles, natural occurrence and potential applications are described. Keywords: polysulfides; synthesis; structures; spectra; application; reactions

Reaction of RSeCl (R = 4-Cl-C 6 H 4 ) with titanocene pentasulphide Cp 2 TiS 5 affords the novel RSeS 5 SeR as a yellow oil which is quite stable at 20°C. Using Cp 4 ′Ti 2 S 4 (Cp′ = CH 3 C 5 H 4 ) as a sulphur transfer reagent the reaction with RSeCl results in a mixture of (RSe) 2 S n molecules with n = 0–10, which on heating produces even longer chains as demonstrated by HPLC analysis. Titanocene pentaselenide Cp 2 TiSe 5 reacts with RSeCl at 4°C to give a mixture of R 2 Se x molecules (x = 1–7) and Se 8 , the relative concentrations sharply decrease with increasing x. 77 Se NMR and UV spectra as well as retention index data of the new molecules are reported.

Dithionite (S2O2−4) and hydroxymethanesulphinate (HOCH2SO−2) were separated from other sulphur oxyanions by ion-pair chromatography and determined using a UV absorbance detector. To circumvent the autoxidation of dithionite it was derivatized by quantitative reaction with formaldehyde to give hydroxymethanesulphinate; the UV spectrum of the latter is reported. The detection limit of HOCH2SO2Na · 2H2O (Rongalite) was 0.5 mg l−1 (0.5 ppm).

Chromatographic analyses and UV spectra show that alkaline aqueous solutions of cystine (or homocystine) and sulphide contain the anions HS − , RS − , RSS − , and RSSO − 3 (R = alanyl). The latter species originates from the autoxidation of the persulphide RSS − by air. Under special conditions, S 2 O 2− 3 and R 2 S 3 are observed in addition.

Careful chlorination of l,2-Se2,S5 with Cl2 in CS2 mainly yields Cl-Se-S5-Se-CI which reacts with (η5-CH3CSH4)2TiS5 to give the heterocycle 1,7-Se2,S10. ClSeS5SeCl was characterized by Raman, mass and 77Se NMR spectroscopy.

The silicon- and germanium-containing titanocene complexes Cp2TiS2Si(C6H5), and Cp2TiSHGe(C6H5), (Cp = Q5-C5H5) react with S2C12and (CH2SCl)2, respectively, to give five- and seven-membered heterocycles which have been characterized by mass and 1H NMR spectroscopy.

Reaction of Cp4Ti2Se4 with either SCl2 or S2Cl2 in a molar ratio of 1:1 provides the new complexes CpiTiSe4S or CpiTiSe3S2, the H NMR spectra of which and the structure of the second complex are reported.

The halides (C6H5)2SiCl2, (C6H5)2GeBr2, and (C6H5)2SnCl2, react with Li2S and (η5- C5H4R)2TiCl2 (R = H, CH3) to give respectively the four-membered titanacycles CP2TiS2Si(C6H5)2, Cp2 TiS2Ge(C6H5)2, and Cp′2TiS2Sn(C6H5)2 which have been characterized by 1H NMR, mass and UV spectroscopy. The new compounds form green crystals, which react with sulphur chlorides with precipitation of (C5H4-R)2TiCl2. This reaction provides a route to formerly unknown sulphur-rich heterocycles of Group 14 elements.

Oxidation of 1,2,3-trithia[3]ferrocenophane 1 by 3-chloroperoxobenzoic acid at 25 °C in dichloromethane yields the corresponding sulfoxide 2 and the sulfone 3 depending on the molar ratio. The oxid...

The cyclic polysulfanes exo-3,4,5,6,7,8,9-heptathiatricyclo[9.2. 1.02, 10]tetradecane (C7H10S7) and exo- 3,4,5,6,7,8,9,10-octathiatricyclo[10.2.1.02.11]-pentadecane (C7H10S3) have been prepared from the corresponding trisulfane C7H10S3 by chlorination resulting in the two sulfenylchlorides C7H10(SCI)2 and C7H10(SCI) (S2CI) which react with (C5H5)2TiS5 to yield the title compounds in good yields. Similarly, C7H10S5CI2 was obtained from C7H10S5 and Cl2 and yielded C7H10S10 on treatment with (C5H5)2TiS5. The hepta- and octasulfanes form pale-yellow microcrystals which have been characterized by UV, mass, Raman, and 1H NMR spectroscopy. The retention time of C7H10Sn molecules in reversed-phase HPLC is a function of the number of sulfur atoms (n = 3… 12).

(C5H4CH3)4Ti2Se4 reacts of 0°C in CS2 with CH3AsCl2 in a molar ratio of 1 : 1 to give the novel (C5H4CH3)2TiSe4AsCH3, which forms air-stable black-violet crystals that have been characterized by 1H NMR, mass, and infrared spectra. When a molar ratio of 1 : 2 is used the novel (CH3As)2Se3 rather than (CH3As)2Se4 is obtained, as orange crystals, together with elemental selenium. (CH3As)2Se3 can also be prepared from (C5H4CH3)2TiSe5 and CH3AsCl2 at 20°C in CS2; it probably contains five-membered 1,3-As2Se3 rings.

By analogy with the synthesis of [(η 5 -C 5 H 5 ) 2 Ti] 2 C 2 S 4 ( 1 ) from Cp 2 Ti(CO) 2 and CS 2 , the compounds [(MeC 5 H 4 ) 2 Ti] 2 C 2 S 4 ( 2 ) and [(Me 3 SiC 5 H 4 ) 2 Ti] 2 C 2 S 4 ( 3 ) were synthesized from the corresponding dicarbonyls (Me = CH 3 ). 1 and 2 react with SCl 2 in CH 2 Cl 2 to give the corresponding mononuclear complexes Cp 2 ′TiC 2 S 5 ( 4 : Cp′ = C 5 H 5 ; 5 : Cp′ = MeC 5 H 4 ) containing the previously unknown η 2 -C 2 S 5 2− ligand. Similarly, 1 and 2 react with S 2 Cl 2 to give compounds of type Cp 2 ′TiC 2 S 6 ( 6 : Cp′ = C 5 H 5 ; 7 : Cp′ = MeC 5 H 4 ) containing the novel ligand C 2 S 6 2− . UV-VIS, mass, and NMR ( 1 H and 13 C) spectra of the new compounds are reported. Compounds 1–7 can be separated by reversed-phase HPLC.

Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn(2+), ZnMe(2), Zn(OMe)(2), Zn(OOCMe)(2), and the heterocubane cluster Zn(4)O(4) with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me(2)NCS(2)(*), Me(2)NCS(3)(*), Me(2)NCS(2)(-), and Me(2)NCS(3)(-) 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 ZnMe(2)