Sulfur-sulfur Bond Research Articles

Regulating Interface Dipole Interaction between Ethers and Active Species Toward Highly Stable Li-SPAN Batteries.

Sulfurized polyacrylonitrile (SPAN) is recognized as a promising organic cathode for long-lifespan lithium metal batteries. Nevertheless, the irreversible cleavage/formation of multiple sulfur-sulfur (S-S) bonds of SPAN within conventional ether-based electrolytes results in loss of active S species, severe capacity fading and shuttle effects. Herein, we propose a new electrolyte based on dipropyl ether (PE) solvent for Li-SPAN batteries. Benefiting from the particular chain-coordination structure and weak dipole interactions with Li+ and active species, the resulting electrolyte not only achieves low desolvation energy barrier and high Li+ transference number, but also displays stable electrolyte-electrode interface (EEI). Consequently, the full cells utilizing this electrolyte exhibit good cyclability, outstanding capacity retention and superior extreme-temperature (-50 °C to 50 °C) performance. Furthermore, the Ah-scale pouch cell with lean electrolyte (2.5 g Ah-1) achieves record cycle stability with 96.5 % capacity retention after 75 cycles, which deliver an initial specific energy density of 150 Wh kg-1 (based on the weight of the entire cell). Impressively, this strategy demonstrates universality in a series of organic electrodes employing with PE-based electrolytes. This work highlights the strategy for modulating the dipole interaction at EEI for long-lifespan Li-organic batteries at extreme conditions.

Inverse Vulcanization of Activated Norbornenyl Esters-A Versatile Platform for Functional Sulfur Polymers.

Elemental sulfur has shown to be a promising alternative feedstock for development of novel polymeric materials with high sulfur content. However, the utilization of inverse vulcanized polymers is restricted by the limitation of functional comonomers suitable for an inverse vulcanization. Control over properties and structure of inverse vulcanized polymers still poses a challenge to current research due to the dynamic nature of sulfur-sulfur bonds and high temperature of inverse vulcanization reactions. In here, we report for the first time the inverse vulcanization of norbornenyl pentafluorophenyl ester (NB-PFPE), allowing for post-modification of inverse vulcanized polymers via amidation of reactive PFP esters to yield high sulfur content polymers under mild conditions. Amidation of the precursor material with three functional primary amines (α-amino-ω-methoxy polyethylene glycol, aminopropyl trimethoxy silane, allylamine) was investigated. The resulting materials were applicable as sulfur containing poly(ethylene glycol) nanoparticles in aqueous environment. Cross-linked mercury adsorbents, sulfur surface coatings, and high-sulfur content networks with predictable thermal properties were achievable using aminopropyl trimethoxy silane and allylamine for post-polymerization modification, respectively. With the broad range of different amines available and applicable for post-polymerization modification, the versatility of poly(sulfur-random-NB-PFPE) as a platform precursor polymer for novel specialized sulfur containing materials was showcased.

Reactivity of hydrogen sulfide toward organic compounds with sulfur-sulfur bonds

The presence of organic molecules containing sulfur-sulfur bonds was documented in the water columns and sediments of the natural aquatic systems as well as in fossil fuels. These compounds range from small molecules of volatile organic compounds to polysulfide cross-linked macromolecules in the sediments. While processes leading to formation of these compounds were intensively studied during the last decades, kinetics and mechanisms of reactions which lead to their decomposition are poorly understood. In this work, the kinetics and products of the reactions of dimethyl disulfide, dimethyl trisulfide, and cyclic polysulfide lenthionine (1,2,3,5,6-pentathiepane) with hydrogen sulfide at the environmental pH and temperature ranges were studied. It was shown that at pH ≥ 5, the reaction of bisulfide anion (HS–) rather than that of hydrogen sulfide controls the overall reaction rates. The activation energy and the order of the reaction with respect to bisulfide anion is dimethyl disulfide– < dimethyl trisulfide < lenthionine, while the order of the reaction with respect to organosulfur compounds is lenthionine < dimethyl trisulfide < dimethyl disulfide. The obtained results suggest that bisulfide anion is responsible for fast decomposition of organosulfur compounds in aphotic natural aquatic systems. This observation leads to the conclusion that sulfurization of sedimentary organic matter during the early diagenesis is not an unidirectional but a dynamic process, and concentrations of organic compounds with sulfur-sulfur bonds are controlled by the polysulfide to sulfide sulfur concentrations ratio in the sedimentary pore waters. In addition, the cyclic polysulfides were shown to be more stable than their linear analogs that results in preferential preservation of these compounds during the maturation process.

PPh3/I2 Promoted Synthesis of Unsymmetrical Disulfides from Sodium Sulfites and 2-Mercaptobenzo Heterocyclics.

A simple and efficient method for the synthesis of unsymmetrical disulfides is reported. Using sodium sulfites and 2-mercaptobenzo heterocyclic compounds as starting materials, the unsymmetrical sulfur-sulfur bonds could be quickly constructed in the PPh3/I2 reaction system under transition-metal-free conditions. This protocol has the advantages of mild reaction conditions, easily available starting materials, and wide substrate scope, showing potential synthetic value for the synthesis of a diversity of biologically or pharmaceutically active compounds.

Increased intracellular persulfide levels attenuate HlyU-mediated hemolysin transcriptional activation in Vibrio cholerae

The vertebrate host's immune system and resident commensal bacteria deploy a range of highly reactive small molecules that provide a barrier against infections by microbial pathogens. Gut pathogens, such as Vibrio cholerae, sense and respond to these stressors by modulating the expression of exotoxins that are crucial for colonization. Here, we employ mass-spectrometry-based profiling, metabolomics, expression assays and biophysical approaches to show that transcriptional activation of the hemolysin gene hlyA in V. cholerae is regulated by intracellular forms of sulfur with sulfur-sulfur bonds termed reactive sulfur species (RSS). We first present a comprehensive sequence similarity network analysis of the arsenic repressor (ArsR) superfamily of transcriptional regulators where RSS and H2O2 sensors segregate into distinct clusters. We show that HlyU, transcriptional activator of hlyA in V. cholerae, belongs to the RSS-sensing cluster and readily reacts with organic persulfides, showing no reactivity and or DNA-dissociation following treatment with GSSG or H2O2. Surprisingly, in V. cholerae cell cultures, both sulfide and peroxide treatment downregulate HlyU-dependent transcriptional activation of hlyA. However, RSS metabolite profiling shows that both sulfide and peroxide treatment raise the endogenous inorganic sulfide and disulfide levels to a similar extent, accounting for this crosstalk, and confirming that V. cholerae attenuates HlyU-mediated activation of hlyA in a specific response to intracellular RSS. These findings provide new evidence that gut pathogens may harness RSS-sensing as an evolutionary adaptation that allows them to overcome the gut inflammatory response by modulating the expression of exotoxins.

A computational mechanistic study of the cleavage of sulfur-sulfur bond by Frustrated Lewis Pairs

A computational mechanistic study of the cleavage of sulfur-sulfur bond by Frustrated Lewis Pairs

Organosulfur Materials for Rechargeable Batteries: Structure, Mechanism, and Application.

Lithium-ion batteries have received significant attention over the last decades due to the wide application of portable electronics and increasing deployment of electric vehicles. In order to further enhance the performance of the batteries and overcome the capacity limitations of inorganic electrode materials, it is imperative to explore new cathode and functional materials for rechargeable lithium batteries. Organosulfur materials containing sulfur-sulfur bonds as a kind of promising organic electrode materials have the advantages of high capacities, abundant resources, tunable structures, and environmental benignity. In addition, organosulfur materials have been widely used in almost every aspect of rechargeable batteries because of their multiple functionalities. This review aims to provide a comprehensive overview on the development of organosulfur materials including the synthesis and application as cathode materials, electrolyte additives, electrolytes, binders, active materials in lithium redox flow batteries, and other metal battery systems. We also give an in-depth analysis of structure-property-performance relationship of organosulfur materials, and guidance for the future development of organosulfur materials for next generation rechargeable lithium batteries and beyond.

On the Electronic Structure of 2H-MoS2: Correlating DFT Calculations and In-Situ Mechanical Bending on TEM.

We present a systematic density functional theory study to determine the electronic structure of bending 2H-MoS2 layers up to 75° using information from in-situ nanoindentation TEM observations. The results from HOMO/LUMO and density of states plots indicate a metallic transition from the typical semiconducting phase, near Fermi energy level (EF) as a function of bending, which can mainly occur due to bending curvatures inducing a stretching and contracting of sulfur-sulfur chemical bonds located mostly over basal (001)-plane; furthermore, molybdenum ions play a major role in such transitions due to reallocation of their metallic d-character orbitals and the creation of “free electrons”, possibly having an overlap between Mo-dx2-y2 and Modz2 orbitals. This research on the metallic transition of 2H-MoS2 allows us to understand the high catalytic activity for MoS2 nanostructures as extensively reported in the literature.

Commonly Used Alkylating Agents Limit Persulfide Detection by Converting Protein Persulfides into Thioethers.

Protein persulfides (R‐S‐SH) have emerged as a common post‐translational modification. Detection and quantitation of protein persulfides requires trapping with alkylating agents. Here we show that alkylating agents differ dramatically in their ability to conserve the persulfide's sulfur–sulfur bond for subsequent detection by mass spectrometry. The two alkylating agents most commonly used in cell biology and biochemistry, N‐ethylmaleimide and iodoacetamide, are found to be unsuitable for the purpose of conserving persulfides under biologically relevant conditions. The resulting persulfide adducts (R‐S‐S‐Alk) rapidly convert into the corresponding thioethers (R‐S‐Alk) by donating sulfur to ambient nucleophilic acceptors. In contrast, certain other alkylating agents, in particular monobromobimane and N‐t‐butyl‐iodoacetamide, generate stable alkylated persulfides. We propose that the nature of the alkylating agent determines the ability of the disulfide bond (R‐S‐S‐Alk) to tautomerize into the thiosulfoxide (R‐(S=S)‐Alk), and/or the ability of nucleophiles to remove the sulfane sulfur atom from the thiosulfoxide.

Synthesis and Structure of Platinum (II) Complexes with Dithiodiethylamine

The interaction of dithiodiethylamine (cystamine) (L1) with platinum compounds in non-aqueous and aqueous media has been studied. It was shown that in aqueous solutions the disulfide bond L1 cleaves with the subsequent coordination of platinum of the resulting β-mercaptoethylamine (mercamine, LH). Depending on the reaction conditions, binuclear complexes of the composition [Рt2(LН)2С14] with bridging chlorine or sulfur atoms or [Рt2L2С12] with bridging chlorine atoms are formed. An X-ray structural analysis of the complex [Рt2(LН)2С14] (I) was carried out. Crystals of I are rhombic, at 20°С а = 17.283(1), b = 9.987(1), с = 8.0187(9) Å; R = 0.030. Molecule I is a binuclear complex in which platinum atoms are linked by a pair of bridging thiolate ligands (-SСН2-СН2-МН3+). The Рt2S2 metal cycle is bent along the sulfur-sulfur line, so that the dihedral angle between the coordination planes of platinum atoms is 138 °. The S-S distance, equal to 2.909 (1) Å, is noticeably shorter than the double van der Waals radius of the sulfur atom (3.60 Å). Carrying out the reaction in benzene makes it possible to obtain the complex (L1Н2)[РtХ4] (X = С1, Вг) with the retention of the sulfur-sulfur bond in the ligand. The structure of the complexes is confirmed by the data of IR spectroscopy.

SYNTHESIS AND STRUCTURE OF PLATINUM(ii) COMPLEXES WITH DITHIODIETHYLAMINE

The interaction of dithiodiethylamine (cystamine) (L1) with platinum compounds in non-aqueous and aqueous media has been studied. It is shown that in aqueous solutions, the L1 disulfide bond is cleaved, followed by platinum coordination of the resulting β-mercaptoethylamine (mercamine, HL). Depending on the reaction conditions, binuclear complexes of the composition [Pt2(LH)2C14] with bridged chlorine or sulfur atoms or [Pt2L2C12] with bridged chlorine atoms are formed. An X-ray diffraction analysis of the [Pt2(LH)2C14] (I) complex was carried out. Crystals I are rhombic, at 20 °C a=17.283(1), b=9.987(1), c=8.0187(9) Å; R=0.030. Molecule I is a binuclear complex in which platinum atoms are united by a pair of bridged thiolate ligands (-SCH2-CH2-NH+3). The metallocycle Pt2S2 is bent along the sulfursulfur line, so that the dihedral angle between the coordination planes of platinum atoms is 138°. The S-S distance equal to 2.909(1) Å is noticeably shorter than the doubled van- der- vaals radius of the sulfur atom (3.60 Å). The implementation of the reaction in benzene makes it possible to obtain a complex (L1H2)[PtX4] (X=C1, Вг) with the preservation of the sulfur-sulfur bond in the ligand. The structure of the complexes is confirmed by IR spectroscopy data.

Is sulfur the responsible for color of yellow Chiapas Amber?

Amber is a fossilized natural resin found in specific areas of the world; its geographical origin is associated to a characteristic color. Amber all over the world share basic characteristics due to a common polymeric matrix; however, its color is associated to the environment where it was formed. In this work, based on a compositional analysis, it is proposed that yellow color of Mexican amber is originated from the sulfur physical and chemical interaction within its polymeric matrix. The effect of sulfur present in yellow Mexican amber is studied by employing X-ray photoelectron and UV-Vis spectroscopies. Results show that sulfur is incorporated inside the polymer matrix with two different chemical environments; one related with sulfur-carbon bonds and the other with sulfur-sulfur bonds. The optical transmission spectrum simulated considering amber as a composite material reproduce the scattering contribution observed experimentally.

Production of Alkyl Aryl Sulfides from Aromatic Disulfides and Alkyl Carboxylates via a Disilathiane-Disulfide Interchange Reaction.

The results of this study show that disilathiane is an effective mediator in the synthesis of alkyl aryl sulfides with disulfides and alkyl carboxylates. Mechanistic studies suggest that disilathiane promotes cleavage of the sulfur-sulfur bond of disulfides to generate thiosilane as a key intermediate. Diselenides were also applicable to this transformation to produce the corresponding selenides.

Allium hooshidaryae (Alliaceae); Chemical compositions, biological and ethnomedicine uses

Ethnopharmacological relevanceAllium hooshidaryae (sect. Pseudoprason) is a wild plant in northwestern Iran. The plant is traditionally used, besides as spice, also for its medicinal properties. Aim of the studyDue to the shortcoming evidence in scientific research and the importance of this plant in folk medicine, this study aims to assess the chemical compositions and biological activities, which have no longer reported to date. Materials and methodsThe bulbs of A. hooshidaryae were collected from West Azerbaijan, Iran. The plant essential oil was obtained by hydrodistillation using Clevenger-type apparatus according to the European pharmacopeia. The plant hydromethanolic extract was obtained using maceration method. The volatile oil compositions of A. hooshidaryae bulbs were evaluated by use of combined gas chromatography/flame ionization detector (GC/FID) and gas chromatography/mass spectrometry (GC/MS) techniques. Furthermore, different biological activities of the yielded essential oil and hydromethanolic extract were in vitro evaluated. The antibacterial and antifungal activities were assessed using disc diffusion assay, tube dilution assay, minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), and minimal fungicidal concentration (MFC). The cytotoxic activities were assayed by reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) toward two human cancerous cell lines (MOLT-4 and MCF-7). Antioxidant activity was investigated using 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging assay. ResultsGC/FID and GC/MS analyses allowed detecting 62 components in the A. hooshidaryae essential oil representing the 91.87% of the total oil. The volatile compounds were identified by comparison of the relative retention indices (RRI), mass spectra with those in NIST08/NIH and Wiley (257 and 7 L) libraries and co-elution with authentic samples where available. Surprisingly, the most abundant compound was obtained as menthol (19.0%) followed by carvacrol (10.1%), menthone (6.4%), methyl (methylthiomethyl) disulfide (4.2%), dimethyl disulfide (3.8%), and thymol (3.8%). Contrary to the other Allium species enriched by sulfur compounds, just three compounds accounting for 10.7% of the total oil were obtained as the sulfur-sulfur bond containing components (Dimethyl disulfide, Methyl (methylthio) methyl disulfide, Bis-methylthiomethyl disulfide). The hydromethanolic extract of A. hooshidaryae showed higher anti-radical (IC50DPPH of 9.81 μg/mL) and cytotoxic (for MOLT-4 and MCF-7, IC50s were 76.3 and 128.6 μg/mL, respectively) activities rather than that of the obtained essential oil (IC50 DPPH of 39.9 μg/mL; IC50 MOLT-4 of 109.2 μg/mL, and IC50 MCF-7 of 297.5 μg/mL). While, the essential oil exhibited the anti-Staphylococcus aurous and anti-Escherichia coli activities approximately the same as Chloramphenicol (positive control). The MIC values were 31.25 and 62.5 μg/mL and the disk inhibition zone values were 23 and 21 mm, respectively. In addition, Candida albicans had moderate sensitivity (MFC of 62.5 μg/mL) for the essential oil. ConclusionsThe hydromethanolic extract of A. hooshidaryae shows the potency to be used for food protection in addition to further cytotoxic investigations. Associated with antimicrobial abilities of both A. hooshidaryae products, the compatible results was observed with the traditional claim having being not investigated to date. These findings will facilitate the development of A. hooshidaryae for further deep investigations.

Formation of protein cross-links by singlet oxygen-mediated disulfide oxidation

Cross-links formed within and between proteins are a major cause of protein dysfunction, and are postulated to drive the accumulation of protein aggregates in some human pathologies. Cross-links can be formed from multiple residues and can be reversible (usually sulfur-sulfur bonds) or irreversible (typically carbon-carbon or carbon-heteroatom bonds). Disulfides formed from oxidation of two Cys residues are widespread, with these formed both deliberately, via enzymatic reactions, or as a result of unintended oxidation reactions. We have recently demonstrated that new protein-glutathione mixed disulfides can be formed through oxidation of a protein disulfide to a thiosulfinate, and subsequent reaction of this species with glutathione. Here we investigate whether similar reactions occur between an oxidized protein disulfide, and a Cys residues on a second protein, to give novel protein cross-links. Singlet oxygen (1O2)-mediated oxidation of multiple proteins (α-lactalbumin, lysozyme, beta-2-microglobulin, C-reactive protein), and subsequent incubation with the Cys-containing protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH), generates inter-protein cross-links as detected by SDS-PAGE, immunoblotting and mass spectrometry (MS). The cross-link yield is dependent on the 1O2 concentration, the presence of the original protein disulfide bond, and the free Cys on GAPDH. MS with 18O-labeling has allowed identification of the residues involved in some cases (e.g. Cys25 from the Cys25-Cys80 disulfide in beta-2-microglobulin, with Cys149 or Cys244 of GAPDH). The formation of these cross-links results in a loss of GAPDH enzymatic activity. These data provide ‘proof-of-concept’ for a novel mechanism of protein cross-link formation which may help rationalize the accumulation of cross-linked proteins in multiple human pathologies.

A Fast and Ratiometric Method for Quantification of Cysteine-Bound Persulfides Based on Alkylation and Gel-Shift Assays.

Cysteine-bound persulfides (Cys-SSH) in proteins are sulfur carrier intermediates in the synthesis of essential cofactors such as iron-sulfur clusters, molybdenum cofactor, vitamin (thiamine), and thionucleosides (thiolated tRNA). Protein-bound persulfides are also used for signaling purposes as a carrier of the "H2S" signal. Several methods have been developed to detect and quantify cysteine-bound persulfides in protein and monitor their exchange. The main challenge in developing these techniques is to discriminate persulfidated cysteine from cysteine and other cysteine modifications. It is also critical to develop ratiometric methods to quantify the level of persulfidation in the protein of interest. We describe here a ratiometric method to label and quantify protein-bound persulfides relying on alkylation and gel-shift assays. This method is based on the derivation of cysteine and persulfides with "heavy" alkylating agents, followed by specific cleavage of the sulfur-sulfur bond of the alkylated persulfide by a reducing agent and separation of the alkylated species by electrophoresis. A persulfide is thus revealed by the appearance of a species lacking one alkylation unit under reducing conditions. We call this alkylation-reduction band-shift (ARBS) assay. Moreover, the quantification of the bands corresponding to the persulfidated and non-persulfidated species in the same lane provides a ratiometric quantification allowing determination of the level of persulfidation of individual cysteine. Other cysteine modifications such as disulfides, sulfenic, sulfinic, sulfonic acids, nitrosothiols, and sulfenamides preclude alkylation. Thus, they may appear as false positives, but they are ruled out by the analysis under nonreducing conditions since these species do not behave as persulfides under these conditions.

Unsymmetrical polysulfidation via designed bilateral disulfurating reagents

Sulfur-sulfur motifs widely occur in vital function and drug design, which yearns for polysulfide construction in an efficient manner. However, it is a great challenge to install desired functional groups on both sides of sulfur-sulfur bonds at liberty. Herein, we designed a mesocyclic bilateral disulfurating reagent for sequential assembly and modular installation of polysulfides. Based on S-O bond dissociation energy imparity (mesocyclic compared to linear imparity is at least 5.34 kcal mol−1 higher), diverse types of functional molecules can be bridged via sulfur-sulfur bonds distinctly. With these stable reagents, excellent reactivities with nucleophiles including C, N and S are comprehensively demonstrated, sequentially installing on both sides of sulfur-sulfur motif with various substituents to afford six species of unsymmetrical polysulfides including di-, tri- and even tetra-sulfides. Life-related molecules, natural products and pharmaceuticals can be successively cross-linked with sulfur-sulfur bond. Remarkably, the cyclization of tri- and tetra-peptides affords 15- and 18-membered cyclic disulfide peptides with this reagent, respectively.

Molecular Damage Detection in an Elastomer Nanocomposite with a Coumarin Dimer Mechanophore.

Molecular force probes that generate optical responses to critical levels of mechanical stress (mechanochromophores) are increasingly attractive tools for identifying molecular sites that are most prone to failure. Here, a coumarin dimer mechanophore whose mechanical strength is comparable to that of the sulfur-sulfur bonds found in vulcanized rubbers is reported. It is further shown that the strain-induced scission of the coumarin dimer within the matrix of a particle-reinforced polybutadiene-based co-polymer can be detected and quantified by fluorescence spectroscopy, when cylinders of the nanocomposite are subjected to unconstrained uniaxial stress. The extent of the scission suggests that the coumarin dimers are molecular "weak links" within the matrix, and, by analogy, sulfur bridges are likely to be the same in vulcanized rubbers. The mechanophore is embedded in polymer main chains, grafting agent, and cross-linker positions in a polymer composite in order to generate experimental data to understand how macroscopic mechanical stress is transferred at the molecular scale especially in highly entangled cross-linked polymer nanocomposite. Finally, the extent of activation is enhanced by approximately an order of magnitude by changing the regiochemistry and stereochemistry of the coumarin dimer and embedding the mechanophore at the heterointerface of the particle-reinforced elastomer.

Alternating Current Electrolysis for the Electrocatalytic Synthesis of Mixed Disulfide via Sulfur-Sulfur Bond Metathesis towards Dynamic Disulfide Libraries.

A novel approach of electrolysis using alternating current was applied in the sulfur–sulfur bond metathesis of symmetrical disulfides towards unsymmetrical disulfides. As initially expected, a statistical distribution in disulfides was obtained. Furthermore, the influence of electrode polarisation by alternating current was investigated on a two‐disulfide matrix. The highly dynamic nature of this chemistry resulted in the creation of dynamic disulfide libraries by expansion of the matrices, consisting of up to six symmetrical disulfides. In addition, mixing of matrices and stepwise expanding of a matrix by using alternating current electrolysis were realised.

Unveiling the Sulfur-Sulfur Bridge: Accurate Structural and Energetic Characterization of a Homochalcogen Intermolecular Bond.

By combining rotational spectroscopy in supersonic expansion with the capability of state-of-the-art quantum-chemical computations in accurately determining structural and energetic properties, the genuine nature of a sulfur-sulfur chalcogen bond between dimethyl sulfide and sulfur dioxide has been unveiled in a gas-jet environment free from collision, solvent and matrix perturbations. A SAPT analysis pointed out that electrostatic S⋅⋅⋅S interactions play the dominant role in determining the stability of the complex, largely overcoming dispersion and C-H⋅⋅⋅O hydrogen-bond contributions. Indeed, in agreement with the analysis of the quadrupole-coupling constants and of the methyl internal rotation barrier, the NBO and NOCV/CD approaches show a marked charge transfer between the sulfur atoms. Based on the assignment of the rotational spectra for 7 isotopologues, an accurate semi-experimental equilibrium structure for the heavy-atom backbone of the molecular complex has been determined, which is characterized by a S⋅⋅⋅S distance (2.947(3) Å) well below the sum of van der Waals radii.