Electronic Structure of Thiolate‐bridged Diiron Complexes and a Single‐electron Oxidation Reaction: A Combination of Experimental and Computational Studies

Single‐electron oxidation of a diiron‐sulfur complex [Cp*Fe(μ‐bdt)FeCp*] ( 1 , Cp*=η⁵‐C₅Me₅; bdt=benzene‐1,2‐dithiolate) to [Cp*Fe(μ‐bdt)FeCp*]⁺ ( 2 ) has been experimentally conducted. The bdt ligand with redox‐active character has been computationally proposed to be a dianion (bdt^2?) rather than previously proposed monoanion (bdt^·?) radical in 1 though it has un‐equidistant aromatic C? C bond lengths. The ground state of 1 is predicted to be two low‐spin ferrous ions (S_Fe=0) and 2 has a medium‐spin ferric ion (S_Fe=1/2) and a low‐spin ferrous center (S_Fe=0), and the oxidation of 1 to 2 is calculated to be a single‐metal‐based process. Both complexes have no significant antiferromagnetic coupling character.     

Fast,Reversible Lithium Storage with a Sulfur/Long‐Chain‐Polysulfide Redox Couple

The cathodic reactions in Li–S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long‐chain polysulfides (S₈?Li₂S₄), which are highly soluble in the electrolyte. Next, long‐chain polysulfides undergo nucleation reaction and convert into solid‐state Li₂S₂ and Li₂S (Li₂S₄?Li₂S) by slow processes. As a result, the second‐step of the electrochemical reaction hinders the high‐rate application of Li–S batteries. In this report, the kinetics of the sulfur/long‐chain‐polysulfide redox couple (theoretical capacity=419 mA h g^?1) are experimentally demonstrated to be very fast in the Li–S system. A Li–S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso‐/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long‐chain polysulfide redox couple with an efficient interlayer configuration in Li–S batteries may be a promising choice for high‐power applications.     

The First Step of the Oxidation of Elemental Sulfur: Crystal Structure of the Homopolyatomic Sulfur Radical Cation [S8].+

The oxidation of elemental sulfur in superacidic solutions and melts is one of the oldest topics in inorganic main group chemistry. Thus far, only three homopolyatomic sulfur cations ([S₄]²⁺, [S₈]²⁺, and [S₁₉]²⁺) have been characterized crystallographically although ESR investigations have given evidence for the presence of at least two additional homopolyatomic sulfur radical cations in solution. Herein, the crystal structure of the hitherto unknown homopolyatomic sulfur radical cation [S₈]^.+ is presented. The radical cation [S₈]^.+ represents the first step of the oxidation of the S₈ molecule present in elemental sulfur. It has a structure similar to the known structure of [S₈]²⁺, but the transannular sulfur⋅⋅⋅sulfur contact is significantly elongated. Quantum-chemical calculations help in understanding its structure and support its presence in solution as a stable compound. The existence of [S₈]^.+ is also in accord with previous ESR investigations.     

Isolable Boron Persulfide: Activation of Elemental Sulfur with a 2‐Chloro‐Azaborolyl Anion

The novel boron persulfide 2 LB(η²‐S₂) (L=[ArNC(R)CHC(R)]^?; Ar=2,6‐Me₂C₆H₃, R=tBu) was obtained by the reaction of the 2‐chloro‐azaborolyl anion 1 (LBCl)K(THF) with 0.25 equiv of elemental sulfur (S₈). Persulfide 2 is labile in solution and could be converted to the cyclic tetrasulfide LBS₄ ( 3 ) and hexasulfide LBS₆ ( 4 ) in the presence of sulfur at room temperature and 50 °C, respectively. Desulfination of 2 with triphenylphosphine resulted in the formation of the thioxoborane LB=S ( 5) . Alternatively, 3 and 4 could be obtained by the reaction of 1 with an excess of sulfur. Structural analysis of 2 disclosed the relatively long S?S bond of 2.1004(8) Å due to the lone‐pair repulsions of the two sulfur atoms, as disclosed by DFT calculations.     

A Facile Synthesis of High‐Surface‐Area Sulfur–Carbon Composites for Li/S Batteries

Small‐grained elemental sulfur is precipitated from sodium thiosulfate (Na₂S₂O₃) in a carbon‐containing oxalic acid (HOOC?COOH) solution through a novel spray precipitation method. Surface area analysis, elemental mapping, and transmission electron micrographs revealed that the spray‐precipitated sulfur particles feature 11 times higher surface area compared to conventional precipitated sulfur, with homogeneous distribution in the carbon. Moreover, the scanning electron micrographs show that these high‐surface‐area sulfur particles are firmly adhered to and covered by carbon. This precipitated S–C composite exhibits high discharge capacity with about 75 % capacity retention. The initial discharge capacity was further improved to 1444 mA h g^?1 by inserting a free‐standing single‐walled carbon nanotube layer in between the cathode and the separator. Moreover, with the help of the fixed capacity charging technique, 91.6 % capacity retention was achieved.     

O→S Relay Deprotection: A General Approach to Controllable Donors of Reactive Sulfur Species

Reactive sulfur species (RSS) are biologically important molecules. Among them, H₂S, hydrogen polysulfides (H₂S_n, n>1), persulfides (RSSH), and HSNO are believed to play regulatory roles in sulfur‐related redox biology. However, these molecules are unstable and difficult to handle. Having access to their reliable and controllable precursors (or donors) is the prerequisite for the study of these sulfur species. Reported in this work is the preparation and evaluation of a series of O‐silyl‐mercaptan‐based sulfur‐containing molecules which undergo pH‐ or F^?‐mediated desilylation to release the corresponding H₂S, H₂S_n, RSSH, and HSNO in a controlled fashion. This O→S relay deprotection serves as a general strategy for the design of pH‐ or F^?‐triggered RSS donors. Moreover, we have demonstrated that the O‐silyl groups in the donors could be changed into other protecting groups like esters. This work should allow the development of RSS donors with other activation mechanisms (such as esterase‐activated donors).     

Two‐Step Oxidation Synthesis of Sulfur with a Red Aggregation‐Induced Emission

Sulfur is not normally considered a light‐emitting material, even though there have been reports of a dim luminescence of this compound in the blue‐to‐green spectral region. Now, it is shown how to make red‐emissive sulfur by a two‐step oxidation approach using elemental sulfur and Na₂S as starting materials, with a high photoluminescence quantum yield of 7.2 %. Polysulfide is formed first and is partially transformed into Na₂S₂O₃ in the first step, and then turns back to elemental S in the second step. The elevated temperature and relatively oxygen‐deficient environment during the second step transforms Na₂S₂O₃ into Na₂SO₃ incorporated with oxygen vacancies, thus resulting in the formation of a solid‐state powder consisting of elemental S embedded in Na₂SO₃. It shows aggregation‐induced emission properties, attributed to the influence of oxygen vacancies on the emission dynamics of sulfur by providing additional lower energy states that facilitate the radiative relaxation of excitons.     

Polyesters containing sulfur. VII. New aliphatic‐aromatic polyesters for synthesis of polyester‐sulfur compositions and polyurethanes

New linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane‐4,4′‐bis(methylthioacetic acid) (DBMTAA) or diphenylmethane‐4,4′‐bis(methythiopropionic acid) (DBMTPA) and diphenylmethane‐4,4′‐bis(methylthioethanol) (DBMTE) at equimolar ratio of reagents (polyesters E‐A and E‐P) as well as at 0.15 molar excess of diol (polyesters E‐A_OH and E‐P_OH). The kinetics of these reactions was studied at 150, 160, and 170°C. Reaction rate constants (k₂) and activation parameters (ΔG^≠, ΔH^≠, ΔS^≠) from carboxyl group loss were determined using classical kinetic methods. E‐A and E‐P (M̄_n = 4400, 4600) were used for synthesis of new rubber‐like polyester‐sulfur compositions, by heating with elemental sulfur, whereas oligoesterols E‐A_OH and E‐P_OH (M̄_n = 2500, 2900) were converted to thermoplastic polyurethane elastomers by reaction with hexamethylene diisocyanate (HDI) or methylene bis(4‐phenyl isocyanate) (MDI). The structure of the polymers was determined by elemental analysis, FT‐IR and liquid or solid‐state ¹H‐, ¹³C‐NMR spectroscopy, and X‐ray diffraction analysis. Thermal properties were measured by DTA, TGA, and DSC. Hardness and tensile properties of polyurethanes and polyester‐sulfur compositions were also determined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 835–848, 1999     

Synthesis of an All‐Ferric Cuboidal Iron–Sulfur Cluster [FeIII4S4(SAr)4]

An unprecedented, super oxidized all‐ferric iron–sulfur cubanoid cluster with all terminal thiolates, Fe₄S₄(STbt)₄ ( 3 ) [Tbt=2,4,6‐tris{bis(trimethylsilyl)methyl}phenyl], has been isolated from the reaction of the bis‐thiolate complex Fe(STbt)₂ ( 2 ) with elemental sulfur. This cluster 3 has been characterized by X‐ray crystallography, zero‐field ⁵⁷Fe Mössbauer spectroscopy, cyclic voltammetry, and other relevant physico‐chemical methods. Based on all the data, the electronic ground state of the cluster has been assigned to be S_tot=0.     

Low‐Spin Pseudotetrahedral Iron(I) Sites in Fe2(μ‐S) Complexes

Fe^I centers in iron–sulfide complexes have little precedent in synthetic chemistry despite a growing interest in the possible role of unusually low valent iron in metalloenzymes that feature iron–sulfur clusters. A series of three diiron [(L₃Fe)₂(μ‐S)] complexes that were isolated and characterized in the low‐valent oxidation states Fe^II? S? Fe^II, Fe^II? S? Fe^I, and Fe^I? S? Fe^I is described. This family of iron sulfides constitutes a unique redox series comprising three nearly isostructural but electronically distinct Fe₂(μ‐S) species. Combined structural, magnetic, and spectroscopic studies provided strong evidence that the pseudotetrahedral iron centers undergo a transition to low‐spin S=1/2 states upon reduction from Fe^II to Fe^I. The possibility of accessing low‐spin, pseudotetrahedral Fe^I sites compatible with S^2? as a ligand was previously unknown.     

Heterocyclic Bismuth(III) Dithiocarbamato Complexes as Single‐Source Precursors for the Synthesis of Anisotropic Bi2S3 Nanoparticles

New complexes catena‐(μ₂‐nitrato‐O,O′)bis(piperidinedithiocarbamato)bismuth(III) ( 1 ) and tetrakis(μ‐nitrato)tetrakis[bis(tetrahydroquinolinedithiocarbamato)bismuth(III)] ( 2 ) were synthesised and characterised by elemental analysis, FTIR spectroscopy and thermogravimetric analysis. The single‐crystal X‐ray structures of 1 and 2 were determined. The coordination numbers of the Bi^III ion are 8 for 1 and ≥6 for 2 when the experimental electron density for the nominal 6s² lone pair of electrons is included. Both complexes were used as single‐source precursors for the synthesis of dodecylamine‐, hexadecylamine‐, oleylamine and tri‐n‐octylphosphine oxide‐capped Bi₂S₃ nanoparticles at different temperatures. UV/Vis spectra showed a blueshift in the absorbance band edge characteristic of a quantum size effect. High‐quality, crystalline, long and short Bi₂S₃ nanorods were obtained depending on the thermolysis temperature, which was varied from 190 to 270 °C. A general trend of increasing particle breadth with increasing reaction temperature and increasing length of the carbon chain of the amine (capping agent) was observed. Powder XRD patterns revealed the orthorhombic crystal structure of Bi₂S₃.     

Synthesis,Structural Characterization,and Physical Properties of Cs2Ga2S5, and Redetermination of the Crystal Structure of Cs2S6

The reaction of CsN₃ with GaS and S at elevated temperatures results in Cs₂Ga₂S₅. Its crystal structure was determined from single‐crystal X‐ray diffraction data. The colorless solid crystallizes in space group C2/c (no. 15) with V=1073.3(4) ų and Z=4. Cs₂Ga₂S₅ is the first compound that features one‐dimensional chains ${{{\hfill 1\atop \hfill \infty }}}$ [Ga₂S₃(S₂)^2?] of edge‐ and corner‐sharing GaS₄ tetrahedra. The vibrational band of the S₂^2? units at 493 cm^?1 was revealed by Raman spectroscopy. Cs₂Ga₂S₅ has a wide bandgap of about 3.26 eV. The thermal decomposition of CsN₃ yields elemental Cs, which reacts with sulfur to provide Cs₂S₆ as an intermediate product. The crystal structure of Cs₂S₆ was redetermined from selected single crystals. The red compound crystallizes in space group ${P\bar 1}$ with V=488.99(8) ų and Z=2. Cs₂S₆ consists of S₆^2? polysulfide chains and two Cs positions with coordination numbers of 10 and 11, respectively. Results of DFT calculations on Cs₂Ga₂S₅ are in good agreement with the experimental crystal structure and Raman data. The analysis of the chemical bonding behavior revealed completely ionic bonds for Cs, whereas Ga?S and S?S form polarized and fully covalent bonds, respectively. HOMO and LUMO are centered at the S₂ units.     

Heterobimetallic Nickel(II) Complexes of Ferrocenyldithiophosphonates. Molecular Structures of [{FcP(OR)S2}2Ni] [Fc = Fe(η5‐C5H4)(η5‐C5H5), R = Et,Pri, Bus,Bui]

The reaction of 2,4‐diferrocenyl‐1,3‐dithiadiphosphetane 2,4‐disulfide [FcPS(μ‐S)]₂ [Fc = Fe(η⁵‐C₅H₄)(η⁵‐C₅H₅)] with alcohols ROH gave the corresponding ferrocenyldithiophosphonic acids [FcPS(OR)(SH)], which were treated in situ with Ni(CH₃COO)₂·4H₂O in acetic acid to yield the square‐planar heterobimetallic trinuclear complexes [{FcP(OR)S₂}₂Ni] (R = Me ( 1 ), Et ( 2 ), Prⁱ ( 3 ), Bu^s ( 4 ) and Buⁱ ( 5 )). Compounds 1‐5 were characterized by elemental analysis, MS, NMR (¹H, ¹³C and ³¹P), IR spectroscopy, and 2‐5 also by X‐ray crystallography. Cyclovoltammetric studies on the heterobimetallic nickel(II) complexes 1‐5 showed irreversible reduction to unstable nickel(I) complexes and an irreversible two‐electron oxidation of the sulfur‐containing nickel fragments, followed by a reversible one‐electron oxidation of the two ferrocenyl groups.     

Activation of Elemental Sulfur at a Two‐Coordinate Platinum(0) Center

Platinum dichalcogenides have been known to exhibit two‐dimensional layered structures. Herein, we describe the syntheses, isolation, and characterization of air‐stable crystalline cyclic alkyl(amino) carbene (cAAC)‐supported monomeric platinum disulfide three‐membered ring complex [(cAAC)₂Pt(S₂)] ( 2 ). The highly reactive platinum(0) [(cAAC)₂Pt] complex ( 1 ) with two‐coordinate platinum activates elemental sulfur to give 2 . The brown crystals of bis‐carbene platinum(II)monosulfate [(cAAC)₂Pt(SO₄)_x(S₂)_1?x] ( 4 ) have been isolated when the reaction was performed in air. The dioxygen analogue of 2 was formed upon exposing the THF solution of 1 to aerial oxygen (O₂). The binding of oxygen at the Pt⁰ center was found to be reversible. Additionally, DFT study has been performed to elucidate the electronic structure and bonding scenario of 2 , 3 , and 4 . Quantum chemical calculations showed donor–acceptor‐type interaction for the Pt?S bonds in 2 and Pt?O bonds in 3 and 4 .     

A non‐oxo methanolate‐bridged divanadium(IV) complex with tris(2‐sulfanidylphenyl)phosphane ligands: synthesis,structural characterization and magnetic investigation

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high‐valent vanadium ions with sulfur‐containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium‐containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high‐valent vanadium–sulfur chemistry, we have synthesized and characterized the non‐oxo divanadium(IV) complex salt tetraphenylphosphonium tri‐μ‐<!?tlsb=‐0.11pt>methanolato‐κ⁶O:O‐bis({tris[2‐sulfanidyl‐3‐(trimethylsilyl)phenyl]phosphane‐κ⁴P,S,S′,S′′}vanadium(IV)) methanol disolvate, (C₂₄H₂₀P)[V^IV₂(μ‐OCH₃)₃(C₂₇H₃₆PS₃)₂]·2CH₃OH. Two V^IV metal centres are bridged by three methanolate ligands, giving a C2‐symmetric V₂(μ‐OMe)₃ core structure. Each V^IV centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S = 1 spin state.     

Dual Protection of Sulfur by Carbon Nanospheres and Graphene Sheets for Lithium–Sulfur Batteries

Well‐confined elemental sulfur was implanted into a stacked block of carbon nanospheres and graphene sheets through a simple solution process to create a new type of composite cathode material for lithium–sulfur batteries. Transmission electron microscopy and elemental mapping analysis confirm that the as‐prepared composite material consists of graphene‐wrapped carbon nanospheres with sulfur uniformly distributed in between, where the carbon nanospheres act as the sulfur carriers. With this structural design, the graphene contributes to direct coverage of sulfur to inhibit the mobility of polysulfides, whereas the carbon nanospheres undertake the role of carrying the sulfur into the carbon network. This composite achieves a high loading of sulfur (64.2 wt %) and gives a stable electrochemical performance with a maximum discharge capacity of 1394 mAh g^?1 at a current rate of 0.1 C as well as excellent rate capability at 1 C and 2 C. The improved electrochemical properties of this composite material are attributed to the dual functions of the carbon components, which effectively restrain the sulfur inside the carbon nano‐network for use in lithium–sulfur rechargeable batteries.     

Synthesis and characterization of coordination compounds of organotin(IV) with nitrogen and sulfur donor ligands

The reactions of dimethyltin dichloride with nitrogen and sulfur donor ligands derived by condensation of S‐benzyldithiocarbazate with indol‐3‐carboxylaldehyde, thiophene‐2‐aldehyde and furfuraldehyde have been investigated in 1:1 and 1:2 molar ratios in anhydrous alcohol. These ligands act as mononegatively charged bidentate species and coordinate to the central tin(IV) atom through the thiosulfur by proton exchange with the azomethine nitrogen. The newly synthesized complexes have been characterized by elemental analysis, conductance measurements and molecular weight determinations. The mode of bonding and the geometry of the complexes have been suggested on the basis of infrared, electronic and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, and probable structures have been assigned to these complexes. A few representative ligands and their tin(IV) complexes have also been screened for their antifungal and antibacterial activities and found to be quite active in this respect. Copyright © 2001 John Wiley & Sons, Ltd.     

A new route towards redox bistability through the inspection of manganese-porphyrin complexes

The redox and spin versatilities of manganese–porphyrin complexes [Mn^IIP] are examined to construct a redox‐switchable device. The electronic structure of [Mn^IIIP]⁺ was analyzed by using wavefunction‐based calculations (complete active spaces plus single excitations on top of the active spaces, that is, CAS+singles). A non‐negligible σ‐type electron‐transfer configuration is present in the [Mn^IIIP]⁺ S=2 ground state. By contrast, the [Mn^IIP^.]⁺ valence tautomer is a purely π‐type intramolecular charge transfer, thus reflecting an S=3 spin state as a result of the strong ferromagnetic interaction (J=30 meV) between the S=5/2 Mn^II ion and the S=1/2 porphyrin radical cation P^.+. The change of the redox‐sensitive site in the valence tautomer leads to a ‘triangular scheme’ that involves a critical step in which a simultaneous electron transfer and spin change are expected to induce bistability. From the wavefunction inspection, a meso‐substituted porphyrin candidate was designed to support this scenario. The complete active‐space second‐order perturbation theory (CASPT2) adiabatic energy difference between the S=2 and the S=3 spin states was reduced down to 0.15 eV, thereby giving rise to a metastable S=3 state characterized by a 0.10 Å extension of the porphyrin cavity radius. These results not only confirm the rather versatile nature of these inorganic systems but also demonstrate that redox and spin changes are intermingled in this class of compounds and can be used for applied devices.     

An Integrated Photoelectrochemical–Chemical Loop for Solar‐Driven Overall Splitting of Hydrogen Sulfide

Abundant and toxic hydrogen sulfide (H₂S) from industry and nature has been traditionally considered a liability. However, it represents a potential resource if valuable H₂ and elemental sulfur can be simultaneously extracted through a H₂S splitting reaction. Herein a photochemical‐chemical loop linked by redox couples such as Fe²⁺/Fe³⁺ and I^?/I₃^? for photoelectrochemical H₂ production and H₂S chemical absorption redox reactions are reported. Using functionalized Si as photoelectrodes, H₂S was successfully split into elemental sulfur and H₂ with high stability and selectivity under simulated solar light. This new conceptual design will not only provide a possible route for using solar energy to convert H₂S into valuable resources, but also sheds light on some challenging photochemical reactions such as CH₄ activation and CO₂ reduction.     

Sulfur and Ti3+ co‐Doping of TiO2 Nanotubes Enhance Photocatalytic H2 Evolution Without the Use of Any co‐catalyst

TiO₂ nanotubes were successfully co‐doped with sulfur and Ti³⁺ states using a facile annealing treatment in H₂/H₂S gas mixture. The obtained nanotubes were investigated for their photocatalytic performance and characterized by SEM, XRD, XPS, EPR, IPCE, IMPS and Mott‐Schottky measurements. The synthesized co‐doped TiO₂ nanotubes show an enhanced photocatalytic hydrogen production rate compared to tubes that were treated only in pure H₂ or H₂S atmosphere—this without the presence of any co‐catalyst. It was found that sulfur in co‐doped TiO₂ exists in the form of S^2? and a small quantity of S⁴⁺/S⁶⁺, which leads to a narrowing of the band gap. However, the enhanced absorption of light in the visible range is not the key reason for the improved photocatalytic performance. We ascribe the enhanced photocatalytic activity to a synergetic effect of S mid‐gap states and disordered Ti³⁺ defects that facilitate photo generated electron transfer.