SC Bonds Research Articles

Plasmonic-mediated S[sbnd]C arylation and S[sbnd]S coupling on nanostructured silver electrodes monitored by in situ surface-enhanced Raman spectroscopy

Plasmon-mediated chemical reaction (PMCR) is a highly attractive field of research. Here we report in situ surface-enhanced Raman spectroscopic (SERS) monitoring of plasmonic-mediated SS bond-forming reaction. The reaction is thought to be a self-coupling reaction proceeding by photoinduced aromatic SC bond arylation. Surprisingly, the SC arylation and SS coupling are found to be occurred on both partially oxidized silver and silver nanoparticles. The results demonstrated that silver oxide or hydroxide and small molecule donor sacrifice agent played a crucial role in the reaction. This work facilitates the in-situ manipulation and characterization of the active silver electrode interface in conjunction with electrochemistry, and also establishes a promising new guideline for surface plasmon resonance photocatalytic reactions on metal nanostructures with high efficiency.

Deciphering reduction stability of sulfone and fluorinated sulfone electrolytes:Insight from quantum chemical calculations

Sulfones and fluorinated sulfones are preferred in high-voltage lithium-ion batteries, but the reasons for their decreased stability in various lithium salt electrolytes remain unknown. Twelve different sulfone-based solvents, Li+-solvent and Li+-solvent-anion complexes were studied herein via quantum chemical calculations to compare reduction potentials and initial decomposition reactions. The results show that position of fluorination has significant effect on the reduction potentials and significant elongation (over 50 %) of SC bond is responsible for the abnormal increase of reduction potential for α-fluorinated sulfones, leading to their poor reduction stability. Li+-solvent-FSI-/PF6- complexes have the preference for anionic reduction, spontaneous defluorination and production of LiF, which can produce a LiF-rich solid-electrolyte interface on graphite. Therefore, most β-fluorinated sulfones and regular sulfones are stable to graphite at high lithium salt concentrations, while only β-fluorinated sulfones are stable to graphite at low salt concentrations.

Al-Sc Bonded Complexes: Synthesis, Structure, and Reaction with Benzene in the Presence of Alkyl Halide.

An alumanyl anion possessing N,N'-bis(2,6-diisopropylphenyl)-1,3-propanediamine ligand was synthesized and characterized. Transmetalation of this Al anion with diaminoscandium chloride precursors afforded the corresponding Al-Sc complexes possessing an unprecedented Al-Sc bond. The Al-Sc[N(SiMe3)2] complex underwent intramolecular C-H cleavage to form a bridged dinuclear complex with μ-hydrido and μ-methylene ligands. The Al-Sc(NiPr2)2 complex reacted with benzene in the presence of alkyl bromide to furnish a 1,4-dialuminated cyclohexadiene product with a concomitant formation of the alkyl-alkyl coupled product. Although the latter product seems to form through the radical mechanism, DFT calculations revealed an ionic mechanism involving bimetallic reaction pathways to react with alkyl bromide and benzene, which provides new insight into the chemistry of metal-metal bonded compounds.

Surface deposit formation of sulfur compounds in both air-saturated and oxygen-free aviation fuels

Trace sulfur compounds in aviation fuel play a key role in the surface deposit formation by aviation fuel. The effects of sulfide and disulfide on the surface deposition of aviation fuel in a horizontal heat exchange tube at temperatures from 20 to 420 °C were studied by adding a certain amount of methyl phenyl sulfide and dibenzyl disulfide (DBDS) to a baseline aviation fuel. The deposition characteristics of each fuel under both air-saturated and oxygen-free conditions were compared to analyze the relationship between sulfur compounds and the oxidation reaction in the formation of deposits. The distribution of the carbon deposition rate in the heat exchange tube was measured, and the morphology and sulfur: carbon ratio of the deposits were obtained using scanning electron microscopy and energy dispersive spectrometry, respectively. The experimental results show that the added sulfur compounds promote oxidative deposition, but sulfur is not transformed into deposits. The high-sulfur deposits appear after the bulk temperature exceeds 250 °C. This indicated that sulfur compounds dominate the deposition pathway in the high-temperature region. A large amount of sulfur-containing deposits is observed in the high-temperature region under both air-saturated and oxygen-free conditions after the DBDS with weak SS and SC bonds is added to the fuel. The presence of a fuel autoxidation reaction can inhibit the formation of sulfur deposits. Sulfur-containing deposits increase significantly after the deoxygenation of fuel.

L-cysteine boosted Fe(III)-activated peracetic acid system for sulfamethoxazole degradation: Role of L-cysteine and mechanism

Sulfamethoxazole (SMX), a widely used and frequently detected antibiotics, may pose threat to water safety and environmental sustainability. In this study, L-cysteine (L-Cys) was used to boost the Fe(III)/peracetic acid (PAA) system for SMX degradation. After the addition of L-Cys, the degradation efficiency of Fe(III)/PAA system for SMX increased from 26.2% to 96.7%. Appropriate increase in initial concentration of Fe(III), L-Cys or PAA promoted the SMX degradation. The role of L-Cys, including the promotion of Fe(III)/Fe(II) cycle and the improvement of pH suitability by complexation, in boosted SMX degradation was proposed. Results of methyl phenyl sulfoxide probe assays, electron paramagnetic resonance tests and quenching experiments showed that FeIVO2+ as well as HO play major roles while carbon-centered radicals hardly contribute in SMX degradation. Degradation intermediates identified by LC/MS showed that SMX was degraded to less toxic small molecules through SN bond breaking, SC bond breakage, self-coupling and hydroxylation. Besides, L-Cys/Fe(III)/PAA system showed ideal tolerance to Cl– and humic acid, while HCO3– significantly inhibited the SMX degradation. Further, the satisfactory degradations of SMX were obtained in three real waters. This study provides a feasible strategy for enhancing the oxidation capacity of the Fe(III)/PAA system and an effective technique for the treatment of SMX in real waters.

Degradation of sulfonamide antibiotics and a structurally related compound by chlorine dioxide: Efficiency, kinetics, potential products and pathways

Sulfonamides (SAs) detected in all kinds of environmental water matrix may cause potential risk for aquatic environment and organisms. In this research, the oxidation of three SAs of sulfamethoxazole (SMX), sulfadiazine (SD) and sulfaguanidine (SGD), and a structurally related compound of 4-methylsulfonylaniline (MSA) by chlorine dioxide (ClO2) was investigated to identify removal efficiency, kinetics, potential products and pathways. At pH 7.0, the highest removal rates of 99.36 %, 100 % and 97.29 % were acquired for SMX, SD and SGD at the initial ClO2 concentration of 50 μM, while that of MSA was only 48.25 %. The difference among three SAs and MSA can be explained by structural influences of substituent attached to the sulfonyl amido-nitrogen. The reactions of SMX, SD and SGD with ClO2 followed the second-order kinetic model (R2 greater than 0.98) with the apparent second-order rate constants range of 5.60 × 102 to 2.73 × 103 M−1 s−1 at pH 7.0 and 25 ℃. The reaction rates were highly dependent on the pH and the trend of activation energy was SGD > SMX > SD at pH 7.0. Products evaluation indicated that the main potential degradation pathways of three SAs were the cleavage of SN and SC bonds, deamination and hydroxylation of aniline group. The sulfonyl amido-nitrogen and aniline amino-nitrogen were prone to be attacked by ClO2. Aniline and sulfanilic acid were found to be the common products of three SAs degradation. The results suggest that ClO2 has the potential to serve as a chemical oxidant for removing sulfonamides in practical water treatment conditions.

Dry and hydrated defective molybdenum Disulfide/Graphene bilayer heterojunction under strain for hydrogen evolution from water Splitting: A First-principle study

In search of exploiting cost-effective, highly stable, efficient, and greatly active electrocatalysts for hydrogen evolution reaction (HER), molybdenum disulfide-graphene heterostructures (MoS2/graphene) are promising, in contrast to noble metals. We used density functional theory (DFT) to examine the changes in the electronic structure of MoS2/graphene under compressive strain for structural defects in the MoS2 and graphene layers, as well as from hydration of the MoS2 layer. In the pristine MoS2/graphene heterostructure, a small bandgap (minigap) is opened at the graphene Dirac point, which is located above the Fermi energy, for dry and hydrated configurations. The presence of sulfur and carbon vacancies in the MoS2/graphene upshifts the Dirac point and widens the minigap. However, additional sulfur vacancies further widen or shrink the minigap depending on the location of the MoS2 conduction band bottom and the presence of defect bands at the Dirac point. The minigap tunability in the MoS2/graphene heterostructure could be engineered for producing efficient HER electrocatalysts and beyond. The Quantum Theory of Atoms in Molecules (QTAIM) reveals SC bond critical points, which correspond to van der Waals forces interactions in agreement with the Non-covalent Interaction (NCI) analysis. A correlation is drawn between the minigap and the electron density at the SC bond critical points.

Atomically Precise Insights into Metal–Metal Bonds Using Comparable Endo-Units of Sc 2 and Sc 2 C 2

The precise identification of metal–metal bonds is critical to fully understanding the nature of metal–metal bonding but remains a fundamental challenge. Herein, we show the essence of Sc–Sc bonds ...

The binary aluminum scandium clusters Al x Sc y with x + y = 13: when is the icosahedron retained?

Geometrical and electronic structures of the 13-atom clusters AlxScy with x + y = 13, as well as their thermodynamic stabilities were investigated using DFT calculations. Both anionic and neutral isomers of AlxScy were found to retain an icosahedral shape of both Al13 and Sc13 systems in which an Al atom occupies the endohedral central position of the icosahedral cage, irrespective of the number of Al atoms present. Such a phenomenon occurs to maximize the number of stronger Al–Al and Sc–Al bonds instead of the weaker Sc–Sc bonds. NBO analyses were applied to examine their electron configurations and rationalize the large number of open shells and thereby high multiplicities of the mixed clusters having more than three Sc atoms. The SOMOs are the molecular orbitals belonged to the irreducible representations of the symmetry point group of the clusters studied, rather than to the cluster electron shells. Evaluation of the average binding energies showed that the thermodynamic stability of AlxScy clusters is insignificantly altered as the number y goes from 0 to 7 and then steadily decreases when y attains the 7–13 range. Increase of the Sc atom number also reduces the electron affinities of the binary AlxScy clusters, and thus they gradually lose the superhalogen characteristics with respect to the pure Al13.

Rare-Earth Metal Boroxide with Formal Triple Metal–Oxygen Orbital Interaction: Synthesis from B(C 6 F 5 ) 3 ·H 2 O and Radical-Anion Ligated Rare-Earth Metal Amides

Rare-earth metal boroxides are not only rare and of great synthetic challenge but also important theoretically due to their unrevealed bonding characteristics. In this paper, we report the synthesi...

Ion conductive polymer electrolyte membranes based on star-branched poly(ethylene-glycol tri-acrylate) and polysulfide macromonomers

This article presents star-branched polymeric co-networks consisting of a three-arm poly(ethylene glycol) acrylate macromonomers (PEG3A) and a three-arm polysulfide (PS) via UV photopolymerization for the development of ion conductive polymer electrolyte membrane (PEM) containing succinonitrile (SCN) plasticizer and lithium bis(trifluoromethane sulfonyl)imide (LITFSI) salt. The hyperbranched co-network (PS-co-PEG3A) exhibits a lower glass transition temperature (Tg = −49 °C at 50:50) relative to that of 3-arm (PEG3A), i.e., Tg of −32 °C, showing systematic variation with polysulfide addition. In the tensile tests, elongation-at-break of PEM – PS-co-PEG3A is higher, but it occurs at the expense of lower tensile strength and modulus. Moreover, PEM – PEG3A exhibits higher strength and modulus relative to those of PEM – PS-co-PEG3A copolymer, but its ionic conductivity is lower (i.e., 3.41 × 10−4 S/cm for PEM – PEG3A versus 1.35 × 10−3 S/cm for PEM – PS-co-PEG3A at 21 °C). This improved ionic conductivity may be attributed to reduced crosslinking density associated with the formation of SC bonds upon addition of polysulfide. The PEM – PS-co-PEG3A co-network is thermally stable up to 130 °C tested and exhibited reasonably good anodic stabilities up to 4.5 V versus Li/Li+. In the CV tests in half-cells configuration with LiFePO4 cathode against Li/Li+, the specific discharge capacity was found to be 120 mAh/g with capacity retention of about 97% for 50 cycles tested.

(S,C) co-doped ZnO properties and enhanced photocatalytic activity

(S,C) co-doped ZnO system was prepared by Sol-Gel method from a single source of dopant (thiourea). The X-Ray diffraction pattern was indexed in a wurtzite phase without secondary phases formation. The codoping was confirmed by the modification of the cell parameters and ZnC, ZnS, SC and CO bonds identification with XPS study. The electrical conductivity σe ~ 3 × 10−4(Ωm)−1 was improved at room temperature particularly for both compositions x = 0.05 and × = 0.1 which influenced positively the photo degradation of eosin under visible light. The proposed mechanism has led to a promising application of these materials as electrodes in the field of Dye Sensitized Solar Cells (DSSC). The optical constants were globally improved and impacted the photoactivity under UVA. The high performance of the catalyst (S,C)0.2ZnO which demonstrates electrical energy consumption per order of magnitude EE/O of 2.1 kWh m−3 was attributed to the lowest optical conductivity (σopt = 6.634 × 10+7), dissipation factor (tanδ = 2.75 × 10−7) and the highest relaxation time (τ = 1.242 × 10−15s). The prepared materials were stable under visible light and UVA irradiation even after five recycles. (S,C)0.2ZnO was found to remove eosin, Bisphenol A, Acetamiprid and 4-hydroxy benzoïc Acid efficiently under sunlight.

Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: The effect of the supercell size

Scandium fluoride (ScF3) belongs to a class of negative thermal expansion (NTE) materials. It shows a strong lattice contraction up to about 1000 K switching to expansion at higher temperatures. Here the NTE effect in ScF3 is studied in the temperature range from 300 K to 1600 K using ab initio molecular dynamics (AIMD) simulations in the isothermal-isobaric (NpT) ensemble. The temperature dependence of the lattice constant, inter-atomic Sc–F–Sc bond angle distributions and the Sc–F and Sc–Sc radial distribution functions is obtained as a function of supercell size from 2a × 2a × 2a to 5a × 5a × 5a where a is the lattice parameter of ScF3. A comparison with the experimental Sc K-edge EXAFS data at 600 K is used to validate the accuracy of the AIMD simulations. Our results suggest that the AIMD calculations are able to reproduce qualitatively the NTE effect in ScF3, however a supercell size larger than 2a × 2a × 2a should be used to account accurately for dynamic disorder. The origin of the NTE in ScF3 is explained by the interplay between expansion and rotation of ScF6 octahedra.

A Scandium Metalloligand-Based Heterobimetallic Pd-Sc Complex: Electronic Tuning Through a Very Short Pd→Sc Dative Bond.

The first heterobimetallic Pd-Sc complex featuring a very short Pd→Sc dative bond has been synthesized and characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, and electrochemistry. Computational studies elucidated the nature of the Pd→Sc bond as a donor-acceptor interaction, which generates a more electron-deficient Pd0 metal center as compared to that in the mono Pd0 complex in their reactions with isonitrile and carbon monoxide. Cooperative reactivity has been demonstrated in the reaction with MeI.

Negative thermal expansion of ScF3: first principles vs empirical molecular dynamics

The crystal lattice of cubic scandium fluorine (ScF3) exhibits negative thermal expansion (NTE) over a wide range of temperatures from 10 K to 1100 K. Here the NTE effect in ScF3 is studied using atomistic simulations based on empirical and ab initio molecular dynamics (AIMD) in the isobaric-isothermal (NpT) ensemble. The temperature dependence of the average lattice constant, the Sc–F–Sc bond angle distribution and the radial distribution functions were obtained. Crossover from the NTE to positive thermal expansion occurring at about 1100 K is reproduced by AIMD simulations in agreement with the known experiment data. At the same time, empirical MD model fails to reproduce the NTE behaviour and suggests an expansion of the ScF3 lattice with increasing temperature. However, both MD models predict strong anisotropy of fluorine atom thermal vibration amplitude, being larger in the direction orthogonal to the Sc–F–Sc atom chain.

Mechanistic study of the atomic layer deposition of scandium oxide films using Sc(MeCp)2(Me2pz) and ozone

The atomic layer deposition (ALD) of scandium oxide (Sc2O3) thin films is investigated using Sc(MeCp)2(Me2pz) (1, MeCp = methylcyclopentadienyl, Me2pz = 3,5-dimethylpyrazolate) and ozone on hydroxyl-terminated oxidized Si(111) substrates at 225 and 275 °C. In situ Fourier transform infrared spectroscopy reveals that 1 not only reacts with surface hydroxyl groups at 275 °C, as expected but also with the SiO2 layer, as evidenced by losses in the SiO2 longitudinal optical and transverse optical phonon modes, resulting in the partial transformation of near-surface SiO2 to an ScSixOy interface layer. Ozone then combusts the MeCp groups of the O–Sc(MeCp)2 chemisorbed species, yielding surface carbonates, and oxidizes some of the underlying silicon, evidenced by gains in the SiO2 phonon modes. The Me2pz group from the next pulse of 1 reacts with these surface carbonates, leading to Sc–O–Sc bond formation (Sc2O3 deposition) and the restoration of an O–Sc(MeCp)2 surface. The reaction of the SiO2 substrate with 1 and the oxidation of silicon by ozone are temperature-dependent processes that occur during the initial cycles of film growth and directly impact the changes in the intensities of the SiO2 phonon modes. For instance, the intensity of the net gains in the phonon modes following ozone exposure is greater at 275 °C than at 225 °C. As the ALD cycle is repeated, the formation of an ScSixOy interface layer and deposition of an Sc2O3 film result in the gradual attenuation of the reaction of the SiO2 substrate with 1 and the oxidation of the underlying silicon by ozone. In addition to the ALD process, characterized by ligand exchange and self-limiting reactions, there are gas-phase reactions between 1 and residual water vapor near the substrate surface that lead to deposition of additional Sc2O3 and surface carbonates, the extent of which are also dependent on the temperature of the substrate. After 20 cycles of 1/ozone, the film thicknesses derived from ex situ X-ray photoelectron spectroscopy measurements are 2.18 nm (225 °C) and 3.88 nm (275 °C). This work constitutes the first mechanistic study of an Sc2O3 ALD process using ozone as the oxidant and emphasizes the significance of atypical reactions between the substrate and the reactants that influence the growth rate and near-surface stoichiometry during the initial cycles of film deposition.

Polyoxometalate hybrid catalyst for detection and photodecomposition of mustard gas surrogate vapors

The polyoxometalate hybrid (POM-h) nanorods were synthesized and tested as reactive adsorbents of the vapors of mustard gas surrogates, and in particular against 2-chloroethyl ethyl sulfide (CEES) and ethylethyl sulfide (EES). They were found to promote the photo-oxidation of the surrogates’ vapors to sulfoxide under ambient conditions and in the absence of an additional oxidation agent. The structural and morphological analysis by SEM, TEM, XRD, and BET showed that the non-porous bright-yellow powder consists of nanorods with diameter of 50–100 nm and length of around 1 μm, stacked together by forming star-like nanostructured aggregates. The FTIR, XRD, thermal analysis, and EDX mapping revealed that the obtained material consists of the Keggin-type cobalt containing heteropolytungstate polyoxometalate phase (K5CoW12O40·20H2O) and potassium persulfate. The estimated indirect band gap was in the blue region of the visible light. The decomposition/detoxification of CEES and EES vapors by POM-h occurred through various and complex photo-catalytic and photo-oxidative pathways. The degradation of the surrogates’ toxic vapors to non-toxic molecules was linked to the elevated surface photo-reactivity and the ability of the nanorods to form hydroxyl radicals. The latter ones were responsible for the cleavage of SC bonds and further photo-oxidation of the formed fragments to ethanol, formaldehyde and acetic acid. A fast and gradual color change of the nanomaterial upon exposure to surrogate vapors or droplets could be used in sensing/detecting the presence of toxic species.

Selective modification of two-dimensional MoS2 nanosheets by polymer grafting

As an emerging two-dimensional (2D) nanomaterial, single layer or a few layers of molybdenum disulfide (MoS2) has drawn significant attention in the past decade. In the present work, we report a strategy in direct creating polymer brushes on MoS2 surfaces via SC bond in the presence of UV light. The modification of MoS2 nanosheets can be achieved bilaterally or homolaterally by performing the UV-grafting polymerization on exfoliated MoS2 nanosheets or a single layer of MoS2 deposited on a silicon substrate. A series of vinyl monomers including methyl methacrylate (MMA), styrene (St) and 2-isopropenyl-2-oxazoline (IPOx) could be applied to this approach, leading to the formation of poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(2-isopropenyl-2-oxazoline) (PIPOx) brushes. AFM, IR, and XPS characterizations indicate the successful formation of homogeneous brush layers on MoS2 surfaces. The polymer brushes modified MoS2 may found potential applications in photo dynamic therapy and sensing technologies.

Nitrogen and sulfur dual-doped carbon films as flexible free-standing anodes for Li-ion and Na-ion batteries

Heteroatom doping is considered to be one of the most effective approaches to improve the electrochemical activity of carbon-based electrode materials for both Li-ion batteries (LIBs) and Na-ion batteries (SIBs) due to introduction of unbalanced electron atmosphere and enlarged interlayers of carbon materials. Here, we present nitrogen and sulfur dual-doped flexible carbon (NSC) film as a promising free-standing anode for stable high-power and high-energy LIBs or SIBs. The NSC film delivers high reversible capacities of 965.7 mAh g−1 in LIBs and 520.1 mAh g−1 in SIBs at a current density of 100 mA g−1. Particularly, the film electrodes exhibit excellent high-rate capability and remarkable long-term cyclability. For instance, as a LIBs anode, the NSC film remained a high capacity of 357.2 mAh g−1 at 2.0 A g−1 (∼10 min to full charge) after 2000 cycles; even in SIBs, a capacity of 155 mAh g−1 can also be reached at 1.0 A g−1. It is believed that the interconnected conducting structure of carbon backbones, heteroatomic defects and increased carbon interlayers distance by stable SC and NC bonds are beneficial to ultrafast ion diffusion and electron transport, making the NSC film become a high performance free-standing anode for LIBs or SIBs application.

Hindered C[sbnd]N bond rotation in triazinyl dithiocarbamates

The substituent and solvent effects on the rotation around a CN amide bond were studied for a series of triazine dibenzylcarbamodithioates. The Gibbs free energies (ΔG‡) were measured to be 16–18 kcal/mol in DMSO-d6 and toluene-d8 using variable-temperature nuclear magnetic resonance (VT-1H NMR) spectroscopy. Density functional theory (DFT) calculations reproduced the experimental observations with various substituents, as well as solvents. From the detailed analysis of the DFT results, we found that the electron donating dibenzyl amine group increased the electron population on the triazinyl ring, which decreased the rotational barrier of the CN bond in the dithiocarbamate group attached to the triazinyl ring. The higher electron population on the triazine moiety stabilizes the partial double bond character of the SC bond, which competitively excludes the double bond character of the CN bond. Therefore, the rotational dynamics of the CN bond in dithiocarbamates can be a sensitive probe to small differences in the electron population of substituents on sulfur.