Electrospray Ionization Mass Spectrometric Analysis of Aqueous Polysulfide Solutions

The speciation of polysulfides in aqueous solutions was investigated by electrospray – ion trap and electrospray – time of flight mass spectrometry. The pH dependence of the observed total dissolved polysulfides concentration followed the trend calculated based on reported thermodynamic constants. However, the observed species distributions were substantially different from those calculated based on thermodynamic coefficients derived by UV spectroscopy. Notably, large abundances of heptasulfide, octasulfide and nonasulfide species were observed throughout the pH range 6 to 11. The large molecular weight anions had not been reported before in aqueous solutions although indirect evidence had suggested their existence.     

LaS1.9, CeS1.9, PrS1.9, NdS1.9 und GdS1.9: Fünf neue Lanthanoidpolysulfide – Synthese und Kristallstrukturen und ihre Strukturbeziehung zum ZrSSi‐Typ

LaS_1.9, CeS_1.9, PrS_1.9, NdS_1.9, and GdS_1.9: Five new Lanthanide Polysulfides – Syntheses, Crystal Structures and their Structural Relationship to the ZrSSi Type Crystals of the five new lanthanide polysulfides LaS_1.9, CeS_1.9, PrS_1.9, NdS_1.9, and GdS_1.9 have been prepared by different synthetic routes. According to X‐ray structure analyses, the compounds adopt the tetragonal CeSe_1.9 type structure (space group: P4₂/n, no. 86) with the lattice parameters a = 9.111(1) Å, c = 16.336(2) Å (LaS_1.9), a = 9.015(3) Å, c = 16.168(4) Å (CeS_1.9), a = 8.947(3) Å, c = 16.054(4) Å (PrS_1.9), a = 8.901(3) Å, c = 16.022(4) Å (NdS_1.9), and a = 8.714(1) Å, c = 15.791(1) Å (GdS_1.9), respectively. The crystal structure consists of puckered [LnS] double slabs and planar sulfur layers alternating along [001]. Each planar sulfur layer contains disulfide dumbbells, isolated anions and ordered vacancies.     

Isoprene–Styrene Chain Shuttling Copolymerization Mediated by a Lanthanide Half‐Sandwich Complex and a Lanthanidocene: Straightforward Access to a New Type of Thermoplastic Elastomers

A lanthanide half‐sandwich complex and a ansa lanthanidocene have been assessed for isoprene–styrene chain shuttling copolymerization with n‐butylethylmagnesium (BEM). In the presence of 1 equiv BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene‐co‐styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (T_g) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self‐organize into nanostructures in the solid state.     

Capillary electrophoretic separation of inorganic sulfur-sulfide, polysulfides, and sulfur-oxygen species

A CE protocol was developed for the identification and separation of inorganic polysulfides simultaneously with other inorganic sulfur-bearing species coexisting in aqueous hydrosulfide/sulfur solutions. The electrophoretic separation of thiosulfate, sulfate, hydrosulfide, sulfite, tetrathionate, and polysulfides was achieved at pH values between 8.2 and 12.2. The peaks attributed to the polysulfide species were strongly sensitive to pH. CE analysis of hydrosulfide/sulfur solutions at different pH values permitted possible identification of two forms of polysulfides: S4(2-) and S3(2-). Upon exposure to air at ambient temperature, thiosulfate was the main oxidation product of hydrosulfide/sulfur solutions mainly in the first 60 min, when hydrosulfide was rapidly consumed. Analysis of the oxidation reaction products provided retrospectively tentative evidence that the peaks separated and identified as tri- and tetrasulfide may be ascribed to polysulfides.     

Half‐lanthanocene/dialkylmagnesium‐mediated coordinative chain transfer copolymerization of styrene and hexene

The Cp*La(BH₄)₂(THF)₂/n‐butylethylmagnesium (BEM) catalytic system has been assessed for the coordinative chain transfer copolymerization of styrene and 1‐hexene. Poly(styrene‐co‐hexene) statistical copolymers were obtained with number‐average molecular weight up to 7600 g/mol, PDI around 1.4 and 1.5 and up to 23% hexene content. The occurence of chain transfer reactions in the presence of excess BEM is established in the course of the statistical copolymerization. Thanks to this transfer process, the quantity of 1‐hexene in the copolymer is increased by a factor of about 3 for high ratio of hexene in the feed, extending the range of our concept of a chain transfer induced control of the composition of statistical copolymers to poly(styrene‐co‐hexene) copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

Radical formation is the initial step for conventional radical chemistry. Reported herein is a unified strategy to generate radicals in situ from aromatic β‐ketoesters by using a photocatalyst. Under visible‐light irradiation, a small amount of photocatalyst fac‐Ir(ppy)₃ generates a transient α‐carbonyl radical and persistent ketyl radical in situ. In contrast to the well‐established approaches, neither stoichiometric external oxidant nor reductant is required for this reaction. The synthetic utility is demonstrated by pinacol coupling of ketyl radicals and benzannulation of α‐carbonyl radicals with alkynes to give a series of highly substituted 1‐naphthols in good to excellent yields. The readily available photocatalyst, mild reaction conditions, broad substrate scope, and high functional‐group tolerance make this reaction a useful synthetic tool.     

Recent Advances and Perspectives in Lithium−Sulfur Pouch Cells

Lithium–sulfur batteries (LSBs) are considered one of the most promising candidates for next-generation energy storage owing to their large energy capacity. Tremendous effort has been devoted to overcoming the inherent problems of LSBs to facilitate their commercialization, such as polysulfide shuttling and dendritic lithium growth. Pouch cells present additional challenges for LSBs as they require greater electrode active material utilization, a lower electrolyte–sulfur ratio, and more mechanically robust electrode architectures to ensure long-term cycling stability. In this review, the critical challenges facing practical Li–S pouch cells that dictate their energy density and long-term cyclability are summarized. Strategies and perspectives for every major pouch cell component—cathode/anode active materials and electrode construction, separator design, and electrolyte—are discussed with emphasis placed on approaches aimed at improving the reversible electrochemical conversion of sulfur and lithium anode protection for high-energy Li–S pouch cells.     

An Organodiselenide Comediator to Facilitate Sulfur Redox Kinetics in Lithium–Sulfur Batteries with Encapsulating Lithium Polysulfide Electrolyte

Lithium–sulfur (Li–S) batteries are regarded as promising high-energy-density energy storage devices. However, the cycling stability of Li–S batteries is restricted by the parasitic reactions between Li metal anodes and soluble lithium polysulfides (LiPSs). Encapsulating LiPS electrolyte (EPSE) can efficiently suppress the parasitic reactions but inevitably sacrifices the cathode sulfur redox kinetics. To address the above dilemma, a redox comediation strategy for EPSE is proposed to realize high-energy-density and long-cycling Li–S batteries. Concretely, dimethyl diselenide (DMDSe) is employed as an efficient redox comediator to facilitate the sulfur redox kinetics in Li–S batteries with EPSE. DMDSe enhances the liquid–liquid and liquid–solid conversion kinetics of LiPS in EPSE while maintains the ability to alleviate the anode parasitic reactions from LiPSs. Consequently, a Li–S pouch cell with a high energy density of 359 Wh kg⁻¹ at cell level and stable 37 cycles is realized. This work provides an effective redox comediation strategy for EPSE to simultaneously achieve high energy density and long cycling stability in Li–S batteries and inspires rational integration of multi-strategies for practical working batteries.     

Cationic and Neutral Rotaxanes Having Different Functional Groups in the Axle Molecule and Their Coordination to PtII

Dibenzo[24]crown‐8 (DB24C8) forms rotaxanes with a linear molecule having a dialkylammonium group and a triazole group as well as with the acetylation product of a cationic axle molecule. The former cationic rotaxane is stabilized by multiple intermolecular hydrogen bonds between the NH₂⁺ and oxyethylene groups. The neutral rotaxane contains the macrocycle in the vicinity of the terminal aryl group. The co‐conformation of both the cationic and neutral rotaxanes can be fixed by coordination of the triazole group of the axle molecule to PtCl₂(dmso)₂. A ¹H NMR spectroscopic study on the thermodynamics of the Pt coordination revealed a larger association constant for the rotaxanes than for the corresponding axle molecules and a larger value for the neutral rotaxane than for the cationic rotaxane.