Sulfur-bridged Research Articles

Base Stabilized σ‐Borane Complex of Group 5 Metals: Synthesis and Structure of [(η5‐C5Me5)Ta(H3BNC5H4) (C5H4NS)(η2‐S2)

AbstractAzametallacyclopropane‐containing base stabilized borane complexes of group 5 transition metals have been synthesized and their structural aspects have been described. Treatment of Cp* based Ta and Nb chlorides, Cp*TaCl4 and Cp*NbCl4 with [LiBH4 ⋅ THF] followed by addition of ligands, such as 2‐mercaptobenzothiazole, MBT, (C7H5NS2) and 2‐mercaptobenzoxazole, MBO (C7H5NSO) led to the formation of complexes [Cp*M‐[BHS(CH2ENC6H4)(C7H4NSE)] (1: M=Ta, E=S; 2; M=Nb, E=S; 3: M=Ta, E=O; 4; M=Nb, E=O, Cp*=pentamethyl‐η5‐cyclopentadienyl). By means of UV‐vis absorption spectra, the electronic properties of these complexes associated with central metal atoms and heteroatoms (S or O) have been evaluated. In contrast, treatment of Cp*TaCl4 with 2‐mercaptopyridine, MP, (C5H5NS) under the same reaction conditions yielded the agostic σ‐borane Ta complex, [Cp*Ta(H3BNC5H4) (C5H4NS)(η2‐S2)], 5. Unlike 1–4, where the metals interact with boron through bridging sulphur, 5 shows a notable σ‐B−H bond interaction with Ta. All spectroscopic data of 1–5 along with the X‐ray diffraction studies suggest complexes 2, 4, and 5 are base (amine) stabilized borane species. Computational studies based on Density Functional Theory (DFT) also supported this conclusion.

Development of fluorochromic polymer doped materials as platforms for temperature sensing using three dansyl derivatives bearing a sulfur bridge

Three novel bis-dansyl derivatives bearing a sulfur bridge have been synthesized, fully characterized, and their photophysical characterization studied in solution, as well as, in the solid state. All compounds exhibit fluorescence emission with quantum yields up to 60%, which vary significantly depending on the solvent used, and the inherent molecular structure. Moreover, these compounds demonstrate positive solvatofluorochromic behaviour emitting from bluish-green to yellow. Kamlet-Taft studies were performed to better understand the solute–solvent interactions. Due to the intrinsic characteristics of the compounds, efforts were made to understand their potential usefulness for environmental remediation and thus metal ion sensing studies were investigated. Compounds L1 and L2 showed high sensitivity to Cu2+ and Hg2+ ions and were found to modulate their emission extensively, with L2 capable of detecting and quantifying up to 4 µM of Hg2+. Considering the solid-state emission of these compounds, the application towards temperature sensing was put forth. L3 was found to quench its emission in a linear relation with temperature up to 170 °C. Several doped polymer thin films were fabricated, which served as a platform to establish a linear relation with temperature beyond their melting point. Polymethylmetacrylate (PMMA) films emitted up to temperatures of 218 °C, which could be fully restored at room temperature. These results suggest the potential application of these bis-chromophoric compounds as molecular thermometers.

Study on molten salt oxidation process of simulated Co doped cation exchange resins

Cation exchange resins (CERs) are widely applied to purify waste liquids generated during the operation of nuclear reactors. The radioactive nuclides 60Co and 58Co are important corrosion activation products in reactor cooling water. In this study, the simulated Co doped CERs were oxidized with ternary carbonate. According to the thermogravimetric analysis (TG), the decomposition of Co doped CERs includes three processes: 1. Elimination of the osmotic water; 2. Pyrolysis of sulfonic acid group; 3. Destruction of styrene–divinylbenzene copolymer. The X-Ray Diffraction (XRD) patterns indicate that sulfur mainly exists in the form of sulfate in waste salt. The Co2+ undergoes the path of CoS2 → Co3O4 with the increase of temperature and the transition point is 650 °C. Combined with Fourier Transform Infrared Spectrometer (FT-IR) spectra and X-ray Photoelectron Spectroscopy (XPS) analysis, sulfonic acid groups begin to decompose at 350 °C. During the molten salt oxidation process, most of the sulfur in sulfonic acid groups is entrapped by carbonate as the form of sulfate, and a little of which remains as sulfone group, sulfoxide group and sulfur bridge in residue. When the resins are oxidized at 800 °C, the retention rate of Co2+ is 97.3%, indicating that the molten salt oxidation can effectively remain Co2+ and convert it into a more stable substance.

Lithium superoxide-based high rate Li-Air batteries enabled by Di-iridium sulfur bridge active sites

Li-oxygen (Li-O2) batteries can potentially provide much higher energy density than Li-ion batteries; however, the practical application of these batteries is hindered due to several drawbacks such as low current rates and high overpotential for the charging process. In this paper, we report a novel Li-Air battery system that operates under high current rates (up to 1mAcm−2) with LiO2 as the primary discharge product instead of the commonly reported Li2O2. This LiO2 based battery at high rates is through a combination of an as-synthesized new one-dimensional (1D) transition metal trichalcogenide mid-entropy alloy of SnIrS3.6 as a cathode catalyst and an electrolyte blend with a SnI2 bi-functional additive. It is revealed that SnIrS3.6 has a microporous structure composed of six- and five-coordinated metal atoms, forming octahedral and triangular bipyramids which has not been observed in other layered chalcogeide materials. DFT calculations reveal that the SnIrS3.6 structure can result in LiO2 formation through di-iridium sulfur bridge active sites that results in strong binding of O2 and LiO2 preventing disproportionation to Li2O2 and enabling high rates. This finding will open a new perspective in designing advanced LiO2-based Li-O2 batteries for real practices.

Simultaneous reactions of sulfonation and condensation for high-yield conversion of polystyrene into carbonaceous material

Polystyrene (PS) was chemically treated with sulfuric acid to prepare stabilized precursors, which were converted into carbonaceous materials with high yield via subsequent carbonization. In addition to sulfuric acid, paraformaldehyde (PFA) was used to increase the crosslink density within the sulfonated PS chain networks by forming methylene bridges between phenyl rings via condensation. This transformed PS into a black glassy powder with increased crosslinking points. The carbon yield of the stabilized PS obtained after carbonization showed was considerably higher (45.3 wt%) than those of pristine PS (0 wt%) and sulfonated PS without PFA (22.4 wt%). This was attributed to its superior degree of crosslinks and the additional contribution of sulfur bridges to its thermal stability during carbonization. Further thermal treatment up to 2800 °C resulted in the formation of an intermediate structure between hard and soft carbons, which was directly revealed by microscopic images. These simultaneous reactions of sulfonation and condensation can be universally applied to various PS wastes, regardless of their shape and morphology. This suggests that the solid-to-solid transformation from PS to carbonaceous substances can be an effective and affordable method of upcycling general PS wastes.

Studying stearic acid interaction with ZnO/SiO2 nanoparticles with tailored morphology and surface features: A benchmark for better designing efficient ZnO-based curing activators

The interaction between activators (ZnO) and co-activators (stearic acid, SA) represents a key step in the vulcanization process, to generate Zn(II) intermediate complexes that enhance the reaction kinetic and promote the shortening of sulfur bridges, leading to highly cross-linked materials. To understand the influence of the structural, morphological and surface properties of ZnO in the reactivity with SA, in this work, pure ZnO nanoparticles (NPs) and ZnO NPs anchored on SiO2 (ZnO/SiO2) were prepared through soft chemistry techniques. Tailoring of morphology and surface features was accomplished through a fine control of the synthetic parameters, as demonstrated by the careful characterization of the activators. Then, the interaction of pure ZnO and ZnO/SiO2 activators with SA in the absence of rubber was investigated by using Differential Scanning Calorimetry (DSC). The occurrence of Zn(II)-SA complexes with different thermal stability and structural properties was assessed by a comprehensive thermogravimetric and spectroscopic survey. The generation and the chemical structure of these specific vulcanization intermediates was related to the peculiar characteristics of the ZnO/SiO2 systems and, in turn, to their ability in imparting faster kinetics and higher curing efficiency to isoprene rubber nanocomposites, compared to bare ZnO.These results, besides proposing a valid benchmark for achieving further insights on the interaction of stearic acid with activators, pave the way to provide specific protocols for a better design and implementation of ZnO-based materials able to effectively enhance the rubber vulcanization process, with significant economic and environmental advantages.

Facile Synthesis of S‐Fused Multi‐Membered Polycyclic Heterocycles: A Construction Strategy towards Thermally Stable Thiepine Derivatives

Comprehensive SummaryS‐fused heterocycles have become popular building blocks to construct functional polycyclic compounds. In contrast to the abundant synthetic methodologies for thiophene‐fused aromatics, the synthesis of S‐heterocycles containing six‐membered thiopyran and seven‐membered thiepine rings is much less reported owing to their unfavorable synthetic protocols and the thermal instabilities. Herein, a series of thiepine‐containing polycyclic S‐heterocycles have been successfully synthesized via different synthetic routes which involve initial construction of sulfur bridges and final ring‐closure reactions. Therefore, the dilithium intermediates are excluded, which facilitates the fusion on the thiepine ring with different S‐heterocycles, including thiophene and thiopyran derivatives. Typically, a S‐fused multi‐membered polycyclic compound simultaneously involving thiophen, thiopyran, and thiepine rings has been successfully prepared. Interestingly, nucleus‐independent chemical shift calculations reveal that the incorporated thiopyran and thiepine rings demonstrate aromatic and nonaromatic characteristics, respectively. Moreover, the thermal stabilities of the thiepine derivatives have been tremendously improved after the fusion on the three vinyl groups in the thiepine unit, which is attributed to the enhancements of the activation energies for the S‐extrusion reactions, as revealed by density functional theory calculations. Therefore, our findings not only provide a facile synthetic methodology for S‐fused multi‐membered polycyclic heterocycles, but also furnish a novel construction strategy towards thermally stable thiepine derivatives.

Theoretical Study on the Structures, Electronic Properties, and Aromaticity of Thiophene Analogues of Anti-Kekulene

We predict the geometries, electronic properties, and aromaticity of thiophene analogues of anti-kekulene with six to nine thiophene rings 1–4, together with those of cyclobutadithiophenes (CDTs) and anti-kekulene as reference compounds, using density functional theory calculations. Investigation of the simplest reference compounds, CDTs, reveals that the local aromaticity of their thiophene rings is influenced by their fused position (b- or c-bond) to the four-membered ring (4MR). A thiophene ring fused at the b-position (b-TR) retains its aromatic character to some extent, whereas the aromatic character of one fused at the c-position is attenuated. The 4MR with two fused b-TRs retains a strong anti-aromatic character. Thiophene analogues of anti-kekulene with six to eight thiophene rings 1–3 favor bowl-shaped structures, in contrast to the planar structure of anti-kekulene, because of the shorter distances of the sulfur bridges. Compound 4, with nine thiophene rings, adopts a planar structure. The local aromaticity and anti-aromaticity of the thiophene ring and 4MR are significantly attenuated in 1–4 compared with the reference compounds, the CDTs and anti-kekulene. This can be attributed to the considerable contribution of the quinoidal electronic structure in 1–4. The present study provides new insight into the aromatic and electronic nature of systems containing cyclobutadienothiophene.

Thermal decomposition and oxidation of cation exchange resins with and without Na2CO3–K2CO3 salt

Owing to the capability of trapping sulfur and reducing the formation of sulfur bridges, the addition of carbonate salt is one of the ideal destruction technologies for the treatment of cation exchange resins (CERs). The oxidation processes of CERs with and without Na 2 CO 3 –K 2 CO 3 salt were investigated using TG, FT-IR and XPS. The results of these analyses indicate that in addition to the evaporation process, the oxidation process of CERs can be described as: during the thermal decomposition of the sulfonic acid groups, there are direct destruction of functional groups and the dehydration of functional groups. In addition to the destruction of styrene-divinylbenzene copolymer, the continuous oxidation process includes the direct thermal decomposition of sulfonyl bridges and the formation of sulfur bridges, which decompose at high temperature. The elemental analysis results confirmed that the presence of carbonate salt reduced the formation of sulfur bridges in residue. The SO 2 can be effectively adsorbed by carbonate salt to form sulfate in the salt. Moreover, the content of sulfate ions in waste salt were determined by ICP-MS, which proves that oxidation with Na 2 CO 3 –K 2 CO 3 at 550 °C for 1 h is the optimal oxidation condition to form the sulfate in carbonate salt. • The Na 2 CO 3 –K 2 CO 3 salt can effectively promote the oxidation of resins. • Carbonates can convert the sulfur bridge structure in residue into sulfate. • Four oxidation processes of resin are described by quantifying S content.

Physico-chemical Characterization of Some Metal Complexes Formed by Substituted Thiourea

In view of unique physico-chemical observations affecting the geometry and various properties of the substituted thiourea complexes in literature along with several biological activities, N-(hydroxy)-N,N-diphenyl thiourea was taken up for study. Complexes with geometries of high spin octahedral for iron(II), cobalt(II); tetrahedral & square planar for nickel(II); and dimeric square planar for copper chloride, copper perchlorate, copper acetate and distorted octahedral for copper nitrate were synthesized and characterized based on magnetic moments, visible spectra, diffuse reflectance spectra, electron spin resonance, infrared spectral studies, and thermal analysis.
 Interestingly, the nature of anion influenced the geometry, the complex from copper nitrate salt resulted in a distorted octahedral structure and complexes formed from copper chloride, copper perchlorate, copper acetate exhibited sub-normal magnetic moments, highly insoluble in the most common organic solvents and water. Based on these and spectral data, polymeric or square-planar dimeric geometry with sulfur bridging between copper atoms is proposed. It was confirmed by the application of Bleaney-Bower’s equation for magnetic susceptibility, applicable to dimeric copper complexes.
 The overall thermal behavior of the ligand and complexes were observed and the detailed calculations interestingly lead to confirmation of the above proposed geometrical structures.

Donor-acceptor organic polymer with sulfur bridge for superior photocatalytic CO2 reduction to CH4 under visible light illumination

Much progress has been made in the design and preparation of organic polymers for photocatalytic CO2 reduction. However, potocatalytic reduction of CO2 to CH4 using organic polymers is still a great difficulty due to poor CO2 adsorption/activation and eight electron transfer. A donor-acceptor (D-A) organic polymer (TOA-PC) was synthesized by combining cyclotriphosphazene (donor) with s-triazine (acceptor) via sulfur bridge. The photocatalytic activity of as-obtained polymers is remarkably dependent on the electron bridges between the donor and acceptor, effectively changing the photogenerated carrier mobility and CO2 adsorption/activation property of the polymers. When the electron bridge is sulfur atom, the TOA-PC exhibits a high CH4 yield of 2748 μmol g−1 (selectivity: near 100 %) under visible light irradiation without photosensitizers and cocatalysts, which represents the latest CH4-producing yield of photocatalysts. This study demonstrates that implantation of novel electron bridges in polymers is an effective way to enhance CH4 yields.

Structural study of Li2S-GeS2 glasses: Ge[sbnd]S network and local environment of Li

The static structures of (Li2S)x(GeS2)100-x glasses (x = 0, 20, 30, 40 and 50) were investigated by using a combination of diffraction measurements and simulation techniques. The X-ray diffraction results show that the host GeS network is formed by linkages of GeS4 tetrahedra. The three-dimensional structure models of GeS network were generated by using the X-ray diffraction data and reverse Monte Carlo (RMC) simulation. The RMC models show that the number of edge-sharing GeS4 tetrahedra decreases as Li2S content but its ratio to the number of connections between GeS4 tetrahedra remains substantially constant irrespective of the composition. The Li ion sites in the GeS network structures were determined by molecular dynamics (MD) simulation with reference to the previously reported neutron diffraction data. The MD results show that each Li ion is located in a deformed octahedral site consisting of bridging and non-bridging sulphur atoms.

Synthetic Efforts to Investigate the Effect of Planarizing the Triarylamine Geometry in Dyes for Dye-Sensitized Solar Cells.

The geometry of a dye for dye-sensitized solar cells (DSSCs) has a major impact on its optical and electronic properties. The dye structure also dictates the packing properties and how well the dye insulates the metal–oxide surface from oxidants in the electrolyte. The aim of this work is to investigate the effect of planarizing the geometry of the common triarylamine donor, frequently used in dyes for DSSC. Five novel dyes were designed and prepared; two employ conventional triarylamine donors with thiophene and furan π-spacers, two dyes have had their donors planarized through one sulfur bridge (making two distinct phenothiazine motifs), and the final dye has been planarized by forming a double phenoxazine. The synthesis of these model dyes proved to be quite challenging, and each required specially designed total syntheses. We demonstrate that the planarization of the triarylamine donor can have different effects. When planarization was achieved by a 3,7-phenothiazine and double phenoxazine structures, improved absorption properties were noted, and a panchromatic absorption was achieved by the latter. However, an incorrect linking of donor and acceptor moieties has the opposite effect. Further, electrochemical impedance spectroscopy revealed clear differences in charge recombination depending on the structure of the dye. A drawback of planarized dyes in relation to DSSC is their low oxidation potentials. The best photovoltaic performance was achieved by 3,7-phenothazine with furan as a π-spacer, which produces a power conversion efficiency of 5.2% (Jsc = 8.8 mA cm–2, Voc = 838 mV, FF = 0.70).

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

Terminal sulfur atoms formation via defect engineering strategy to promote the conversion of lithium polysulfides

The defect engineering shows great potential in boosting the conversion of lithium polysulfides intermediates for high energy density lithium-sulfur batteries (LSBs), yet the catalytic mechanisms remain unclear. Herein, the oxygen-defective Li4Ti5O12-x hollow microspheres uniformly encapsulated by N-doped carbon layer ([email protected]) is delicately designed as an intrinsically polar inorganic sulfur host for the research on the catalytic mechanism. Theoretical simulations have demonstrated that the existence of oxygen deficiencies enhances the adsorption capability of spinel Li4Ti5O12 towards soluble lithium polysulfides. Some -S-S- bonds of the Li2S6 on the defective Li4Ti5O12 surface are fractured by the strong adsorption force, which allows the inert bridging sulfur atoms to be converted into the susceptible terminal sulfur atoms, and reduces the activation energy of the polysulfide conversion in some degree. In addition, with the N-doped carbon layer, secondary hollow microspheres architecture built with primary ultrathin nanosheets provide a large amount of void space and active sites for sulfur storage, adsorption and conversion. The as-designed sulfur host exhibits a remarkable rate capability of 547 mAh g−1 at 4 C (1 C=1675 mA g−1) and an outstanding long-term cyclability (519 mAh g−1 after 1000 cycles at 3 C). Besides, a high specific capacity of 832 mAh g−1 is delivered even after 100 cycles under a high sulfur mass loading of 3.2 mg cm−2, indicating its superior electrochemical performances. This work not only provides a strong proof for the application of oxygen defect in the adsorption and catalytic conversion of lithium polysulfides, but offers a promising avenue to achieve high performance LSBs with the material design concept of incorporating oxygen-deficient spinel structure with hierarchical hollow frameworks.

Computational Approach for Probing Redox Potential for Iron-Sulfur Clusters in Photosystem I.

Simple SummaryMany biological systems contain iron–sulfur clusters, which are typically found as components of electron transport proteins. Continuum electrostatic calculations were used to investigate the effect of protein environment on the redox properties of the three iron–sulfur clusters in the cyanobacterial photosystem I. Our results show a good correlation between the estimated and the measured reduction potential. Moreover, the results indicate that the low potential of FX is shown to be due to the interactions with the surrounding residues and ligating sulfurs. Our results will help in understanding the electron transfer reaction in photosystem I.Photosystem I is a light-driven electron transfer device. Available X-ray crystal structure from Thermosynechococcus elongatus showed that electron transfer pathways consist of two nearly symmetric branches of cofactors converging at the first iron–sulfur cluster FX, which is followed by two terminal iron–sulfur clusters FA and FB. Experiments have shown that FX has lower oxidation potential than FA and FB, which facilitates the electron transfer reaction. Here, we use density functional theory and Multi-Conformer Continuum Electrostatics to explain the differences in the midpoint potentials of the FX, FA and FB clusters. Our calculations show that FX has the lowest oxidation potential compared to FA and FB due to strong pairwise electrostatic interactions with surrounding residues. These interactions are shown to be dominated by the bridging sulfurs and cysteine ligands, which may be attributed to the shorter average bond distances between the oxidized Fe ion and ligating sulfurs for FX compared to FA and FB. Moreover, the electrostatic repulsion between the 4Fe-4S clusters and the positive potential of the backbone atoms is lowest for FX compared to both FA and FB. These results agree with the experimental measurements from the redox titrations of low-temperature EPR signals and of room temperature recombination kinetics.

Microwave‐assisted alcoholysis of silicone rubber waste with geraniol for effective elastomer damping

AbstractThe first step in the mainstream end‐of‐life management of discarded silicone‐rubber‐based composite insulators involves grinding and modification of them into fine silicone rubber powders (SRPs). However, significant knowledge gaps have prevented researchers from developing direct efficient surface treatments for SRPs that do not involve time‐consuming and multi‐step processes. Herein, we report a straightforward method for the efficient modification of discarded SRPs through a microwave‐assisted alcoholysis process. Specifically, the siloxane moieties of the SRPs were cleaved using nucleophilic geraniol as a modifier, thereby facilitating the introduction of abundant alkoxysilyl groups on SRPs surface. During sulfur crosslinking, the intrachain vinyl functionalities of the modified SRPs co‐crosslinked with the rubber matrix via sulfur bridges, thereby improving the dispersion state of the SRPs and the interfacial adhesion between the SRPs and the rubber matrix. Accordingly, even for a high SRP loading (200 phr, parts per hundreds of gum), the mechanical performance of the resulting systems, and in particular the tensile strength and extensibility were significantly higher than those of the rubber matrix. Moreover, the interfacial adhesion of the resulting systems was improved, and the resulting systems presented remarkable damping performance (tan δ ≥ 0.3) over a broad temperature range (≥80°C).

Preparation of asphalt-based microporous organic polymers with sulfur bridges

The construction of microporous organic polymers (MOPs) with sustainable building blocks is essential for their scale-up preparation and practical applications.

Raman spectra of MCl-Ga2S3-GeS2(M = Na, K, Rb) glasses

AbstractRaman spectra of (MY)x(Ga2S3)0.2−0.2x(GeS2)0.8−0.8xpseudo-ternary glassy systems (M = Na, K, Rb; Y = Cl, Br, I) were investigated systematically as a function of MY nature and alkali content. Raman spectroscopy of the Ga3S3-GeS2glassy matrix shows a complicated local structure: corner-sharing CS- and edge-sharing ES-GeS4/2tetrahedra, Ga-S triclusters and ETH-Ga2S6/2ethane-like units. The Ga2S6/2population decreases with increasingxrelated to a substitution of some bridging sulfur atoms around central Ga by terminal Y species with a respective decrease of the network rigidity. The formation of mixed Ga-(S,Y) environment is affected by the M+ion size and the MY concentration.

Surface Hopping Dynamics with the Frenkel Exciton Model in a Semiempirical Framework.

We present an implementation of the Frenkel exciton model in the framework of the semiempirical floating occupation molecular orbitals-configuration interaction (FOMO-CI) electronic structure method, aimed at simulating the dynamics of multichromophoric systems, in which excitation energy transfer can occur, by a very efficient approach. The nonadiabatic molecular dynamics is here dealt with by the surface hopping method, but the implementation we proposed is compatible with other dynamical approaches. The exciton coupling is computed either exactly, within the semiempirical approximation considered, or by resorting to transition atomic charges. The validation of our implementation is carried out on the trans-azobenzeno-2S-phane (2S-TTABP), formed by two azobenzene units held together by sulfur bridges, taken as a minimal model of multichromophoric systems, in which both strong and weak exciton couplings are present.