The thioantimonate anion [Sb4S8]4− acting as a tetradentate ligand: Solvothermal synthesis,crystal structure and properties of {[In(C6H14N2)2]2Sb4S8}Cl2 exhibiting unusual uniaxial negative and biaxial positive thermal expansion

The new compound {[In(C₆H₁₄N₂)₂]₂Sb₄S₈}Cl₂ was prepared under solvothermal conditions reacting InCl₃, Sb and S using 1,2-trans-diaminocyclohexane as solvent and structure directing molecule. The compound crystallizes in the monoclinic space group C2/c with a = 29.0259(12), b = 6.7896(2), c = 24.2023(12) Å, β = 99.524(4)°, V = 4703.9(3) ų. The central structural motif is the thioantimonate(III) anion [Sb₄S₈]^4? acting as a tetradentate ligand thus joining two symmetry related In³⁺ centered complexes. This binding mode was never observed before for the [Sb₄S₈]^4? anion. The optical band gap was determined as 2.03 eV in agreement with the red color of the compound. The thermal decomposition was monitored with in-situ X-ray diffraction experiments. After the emission of the amine molecules an amorphous intermediate is formed followed by the crystallization of InSbS₃ which is stable up to about 590 °C. On further heating, InSbS₃ is destroyed and reflections of γ-In₂S₃ appear being contaminated with some elemental Sb. Temperature dependent in-situ X-ray powder diffractometry performed between 30 and 220 °C reveals an unusual reversible negative and positive thermal expansion. The decrease of the a-axis in the temperature range is about 0.74 Å and the increase of the c-axis ca. 0.54 Å. Interestingly, the b-axis exhibits also a thermal expansion, i.e., a biaxial positive and an uniaxial negative thermal expansion coexist which is very unusual. The relative negative expansion coefficients for the a-axis of ?194 × 10^?6K^?1 (30–120 °C) and ?82 × 10^?6K^?1 (120–220 °C) are in the region of so-called colossal thermal expansion.     

Optimization of parameters of sampling and determination of reduced sulfur compounds using cryogenic capture and gas chromatography in tropical urban atmosphere

Reduced sulfur compounds, RSCs (H₂S, COS, CH₃SH, CH₃SCH₃, CS₂ and CH₃S₂CH₃) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection.Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min^? 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H₂S, CH₃SH and CH₃S₂CH₃ the method showed a precision of 89%, limit of detection of 0.10 µg m^? 3 and limit of quantification 0.3 µg m^? 3. For CH₃SCH₃ and CS₂ the corresponding values were 89%, 0.15 µg m^? 3 and 0.5 µg m^? 3 and for COS were 75%, 0.18 µg m^? 3 and 0.8 µg m^? 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H₂S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics.     

Macroporous Co3O4 platelets with excellent rate capability as anodes for lithium ion batteries

This paper reports the microwave-assisted synthesis of Co₃O₄ nanomaterials with different morphologies including nanoparticles, rod-like nanoclusters and macroporous platelets. The new macroporous platelet-like Co₃O₄ morphology was found to be the best suitable for reversible lithium storage properties. It displayed superior cycling performances than nanoparticles and rod-like nanoclusters. More interestingly, excellent high rate capabilities (811 mAh g^?1 at 1780 mA g^?1 and 746 mAh g^?1 at 4450 mA g^?1) were observed for macroporous Co₃O₄ platelet. The good electrochemical performance could be attributed to the unique macroporous platelet structure of Co₃O₄ materials.     

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

The precursor [Fe^III(L)Cl] (LH₂ = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [Sb^V(X)₆]^? (X = CN^?, NCS^?) to yield star-shaped heptanuclear clusters [(LFe^III–X)₆Sb^V]Cl₅. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.     

Bi2O3 deposited on highly ordered mesoporous carbon for supercapacitors

A simple route has been employed to prepare nanosized Bi₂O₃ deposited on highly ordered mesoporous carbon. The electrochemical measurements reveal that, by loading only 10% Bi₂O₃ on the mesoporous carbon, the specific capacitance of the composite is improved by 62%, with the maximum value reaching 232 F g^?1 at a sweep rate of 5 mV s^?1. The specific capacitance of Bi₂O₃ is calculated and reaches 1305 F g^?1 at 1 mV s^?1. It is found that the mass transfer in the framework of the crystalline oxide is still difficult in spite of its nanosize, as evidenced by the decline of the specific capacitance of the Bi₂O₃ with the increase of the sweep rate. The cyclic life of composite materials is also measured and the capacitance only declines 21% after 1000 cycles.     

A Raman spectroscopic study of the mineral coquandite Sb6O8(SO4)·(H2O)

Raman spectra of coquandite Sb₆O₈(SO₄)·(H₂O) were studied, and related to the structure of the mineral. Raman bands observed at 970, 990 and 1007 cm^?1 and a series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes respectively. Raman bands at 629, 638, 690, 751 and 787 cm^?1 are attributed to the SbO stretching vibrations. Raman bands at 600 and 610 cm^?1 and at 429 and 459 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes. Raman bands at 359 and 375 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure.     

Li2ZnTi3O8 nanorods: A new anode material for lithium-ion battery

Spinel Li₂ZnTi₃O₈ nanorods were first synthesized using titanate nanowires as a precursor. The synthesized nanorods are highly crystalline and used as an anode material in a rechargeable Li-ion battery. A large capacity of 220 mA h g^? 1 was kept after 30 cycles at a current density of 0.1 A g^? 1, which is close to the theoretic capacity. The electrochemical measurements indicate that the anode material made of spinel Li₂ZnTi₃O₈ nanorods displayed a highly reversible capacity and excellent cycling stability.     

Excited states of pyrene excimer observed by photodissociation spectroscopy in a supersonic jet

The absorption spectrum of jet-cooled pyrene excimer was measured using photodissociation spectroscopy. Broad absorption bands were observed in the near-IR and visible regions, which were assigned to the B_2u^? ← B_3g^? and B_2u⁺ ← B_3g^? transitions of the excimer, respectively. Excitation of these bands results in rapid dissociation of the excimer into monomer fragments, one of which is an electronically excited monomer in the S₂ state. The formation mechanism of the pyrene excimer from the vdW dimer is also discussed.     

Molybdic acid doped polyaniline micro/nanostructures via a self-assembly process

Molybdic acid (H₂MoO₄, MA) doped polyaniline (PANI) micro/nanostructures were prepared by a self-assembly process in the presence of ammonium persulfate ((NH₄)₂S₂O₈, APS) as the oxidant. The morphology of PANI-MA changed from nanofibers or nanotubes (～160 nm in diameter) to co-existence of nanofibers and microspheres (～3 μm in diameter) and that accompanied an enhancement of the conductivity from 5.42 × 10^?3 S cm^?1 to 2.8 × 10^?1 S cm^?1as the molar ratio of MA to aniline varied from 0.01 to 1.5. With increasing the polymerization time, moreover, the pH value of the reaction solution not only decreased due to sulfuric acid produced during the course of the polymerization, but also accompanied a change in morphology from microspheres to nanofibers. All above-mentioned observations could be interpreted by spherical and cylindrical micelle composed of MA as the “soft-template” in forming the micro/nanostructures.     

High capacity and excellent cyclability of vanadium (IV) oxide in lithium battery applications

A VO₂ · 0.43H₂O powder with a flaky particle morphology was synthesized via a hydrothermal reduction method. It was characterized by scanning electron microscopy, electron energy loss spectroscopy, and thermogravimetric analysis. As an electrode material for rechargeable lithium batteries, it was used both as a cathode versus lithium anode and as an anode versus LiCoO₂, LiFePO₄ or LiNi_0.5Mn_1.5O₄ cathode. The VO₂ · 0.43H₂O electrode exhibits an extraordinary superiority with high capacity (160 mAh g^?1), high energy efficiency (95%), excellent cyclability (142.5 mAh g^?1 after 500 cycles) and rate capability (100 mAh g^?1 at 10 C-rate).     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

Raman spectroscopy of the Pb-Sb sulfosalts minerals: Boulangerite,jamesonite, robinsonite and zinkenite

Raman spectroscopy was used to investigate the lead–antimony sulfosalts minerals: boulangerite (Pb₅Sb₄S₁₁), jamesonite (FePb₄Sb₆S₁₄), robinsonite (Pb₄Sb₆S_l3) and zinkenite (Pb₉Sb₂₂S₄₂). Raman bands of the investigated minerals that have interconnected SbS₃ pyramids are found between 375 and 50 cm⁻¹. The stretching and bending modes of SbS₃ groups occur between 375 and 175 cm⁻¹ in boulangerite, 350 and 180 cm⁻¹ in jamesonite, 350 and 175 cm⁻¹ in robinsonite and zinkenite. The investigated minerals show approximate similarities in their spectral features with those of minerals containing pyramidal SbS₃ groups.     

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol^?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g^?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^°), enthalpy (ΔH^°), and entropy (ΔS^°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.     

Determination of traces of Sb(III) using ASV in Sb-rich water samples affected by mining

Chemical speciation [Sb(V) and Sb(III)] affects the mobility, bioavailability and toxicity of antimony. In oxygenated environments Sb(V) dominates whereas thermodynamically unstable Sb(III) may occur. In this study, a simple method for the determination of Sb(III) in non acidic, oxygenated water contaminated with antimony is proposed. The determination of Sb(III) was performed by anodic stripping voltammetry (ASV, 1–20 μg L⁻¹ working range), the total antimony, Sb(tot), was determined either by inductively coupled plasma mass spectrometry (ICP-MS, 1–100 μg L⁻¹ working range) or inductively coupled plasma optical emission spectrometry (ICP-OES, 100–10,000 μg L⁻¹ working range) depending on concentration. Water samples were filtered on site through 0.45 μm pore size filters. The aliquot for determination of Sb(tot) was acidified with 1% (v/v) HNO₃. Different preservatives, namely HCl, L(+) ascorbic acid or L(+) tartaric acid plus HNO₃, were used to assess the stability of Sb(III) in synthetic solutions.The method was tested on groundwater and surface water draining the abandoned mine of Su Suergiu (Sardinia, Italy), an area heavily contaminated with Sb. The waters interacting with Sb-rich mining residues were non acidic, oxygenated, and showed extreme concentrations of Sb(tot) (up to 13,000 μg L⁻¹), with Sb(III) <10% of total antimony. The stabilization with L(+) tartaric acid plus HNO₃ appears useful for the determination of Sb(III) in oxygenated, Sb-rich waters. Due to the instability of Sb(III), analyses should be carried out within 7 days upon the water collection. The main advantage of the proposed method is that it does not require time-consuming preparation steps prior to analysis of Sb(III).     

Propriétés thermiques et optiques des verres du système Sb2S3–As2S3–Sb2Te3

Thermal and optical properties of glasses of the Sb₂S₃–As₂S₃–Sb₂Te₃ system. The glass-forming region of Sb₂S₃–As₂S₃–Sb₂Te₃ is very wide. The As₂S₃ compound supports the formation of prepared glasses and their stability. They have only one glass-transition temperature (T_g), which varies from 167 to 214 °C. It drops when the content of Sb₂Te₃ increases. This semi-metal compound supports the crystallization of glasses in several stages. Whereas the optical gap (E_g) increases with the content of As₂S₃ in the Sb₂S₃–As₂S₃ and Sb₂Te₃–As₂S₃ binary systems, it is practically constant in the ternary one on the cut with 20% of Sb₂Te₃, and is worth on average 1.04 eV.     

Determination of Cr(VI) in plants by electrothermal atomic absorption spectrometry after leaching with sodium carbonate

The determination of chromium (VI) compounds in plants by electrothermal atomic absorption spectrometry (ET AAS) is proposed based on their leaching with 0.1 M Na₂CO₃. Due to the presence of relatively high amounts of Na₂CO₃ in the resulting samples, the temperature and time of pyrolysis and atomization stages must be optimized to minimize the influence of the matrix. A limit of detection (LOD) for determination of Cr(VI) in plants by ET AAS was found to be 0.024 μg g⁻¹.The concentration of Cr(VI) and total chromium in plants collected in different geographical areas (South Africa and Russia), grown on soils high in chromium was determined. The concentration of Cr(VI) and total Cr in stems and leaves of plants was in the range of 0.04–0.7 μg g⁻¹ and 0.5–10 μg g⁻¹, respectively. The limited uptake of Cr(III) by plants, in comparison to its concentration in soil, can be explained by the very low solubility of natural Cr(III) compounds.Results for the determination of Cr(VI) were confirmed by the analysis of BCR CRM 545 (Cr(VI) in welding dust) with good agreement between certified (39.5 ± 1.3 μg mg⁻¹) and found (38.8 ± 1.2 μg mg⁻¹) values. The total concentration of Cr in plants has also been determined by ET AAS after dry ashing of samples at 650 °C. Results were confirmed by the analysis of BCR CRM 281 (Trace elements in Rye Grass) with good agreement between the found (2.12 ± 0.16 μg g⁻¹) and certified value (2.14 ± 0.12 μg g⁻¹).     

Raman spectroscopic study of the antimonate mineral roméite

Raman spectroscopy has been sued to study the antimony containing mineral roméite Ca₂Sb₂O₆(OH,F,O) from three different origins. Roméite is a calcium antimonate mineral of the pyrochlore group. An intense Raman band at ～518 cm^?1 for roméite is assigned to the SbO ν₁ symmetric stretching mode and the band at 466 cm^?1 to the SbO ν₃ antisymmetric stretching mode. The Raman band at 303 cm^?1 is attributed to the OSbO bending mode. Some variation in band positions is observed and is attributed to the variation in composition between the three mineral samples.     

A novel gel electrolyte with lithium difluoro(oxalato)borate salt and Sb2O3 nanoparticles for lithium ion batteries

A new type of lithium difluoro(oxalate)borate salt was synthesized by solid state reaction method and has been incorporated into polyvinyledenefluoride–hexafluoropropylene (PVdF–HFP) skeleton. Ethylene carbonate (EC) and diethyl carbonate (DEC) mixture was used as plasticizing agent. Sb₂O₃ nanoparticle was used as the filler in the polymer host to prepare the nanocomposite polymer electrolytes (NCPE) for lithium ion batteries by solution casting technique. All the membranes were subjected to a.c. impedance, mechanical stability and morphological analysis. Among them 5 wt% Sb₂O₃ having NCPE exhibited enhanced conductivity of 0.298 mS cm⁻¹ at ambient temperature and Young's modulus increased from 1.32 to 2.31 MPa after the addition of Sb₂O_3. The conductivity enhancement is explained in terms of Vogel–Tamman–Fulcher (VTF) theory.     

Mesoporous Fe2O3 nanoparticles as high performance anode materials for lithium-ion batteries

This work introduces an effective, inexpensive, and large-scale production approach to the synthesis of Fe₂O₃ nanoparticles with a favorable configuration that 5 nm iron oxide domains in diameter assembled into a mesoporous network. The phase structure, morphology, and pore nature were characterized systematically. When used as anode materials for lithium-ion batteries, the mesoporous Fe₂O₃ nanoparticles exhibit excellent cycling performance (1009 mA h g^− 1 at 100 mA g^− 1 up to 230 cycles) and rate capability (reversible charging capacity of 420 mA h g^− 1 at 1000 mA g^− 1 during 230 cycles). This research suggests that the mesoporous Fe₂O₃ nanoparticles could be suitable as a high rate performance anode material for lithium-ion batteries.     

Jahn–Teller coupling and the influence of strain in Tg and Eg ground and excited states – A ligand field and DFT study on halide MIIIX6 model complexes [M = TiIII–CuIII; X = F−, Cl−]

In contrast to well established experimental results of vibronic coupling effects in octahedral dⁿ complexes with E_g ground states (Cu²⁺, Ag²⁺; Cr²⁺, Mn³⁺ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dⁿ cations – in particular for Ti^III, V^III and high-spin Co^III, Ni^III with T_2g and T_1g ground states, which involve, to first-order, solely splitting of the π-antibonding t_2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the T_g ? (?_g + τ_2g) vibronic interaction as well as in the E_g ? ?_g coupling case (Mn^III, low-spin Ni^III); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dⁿ ligand field matrices in O_h, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (Cr^III, ⁴A_2g ground state). The group-theoretical analysis of the interaction with the JT-active ?_g and τ_2g modes yields D_4h, D_3d and D_2h as the possible distortion symmetries in the case of a T_g ground state. The DFT-calculations give clear evidence, that the D_4h stationary points represent the absolute minima in the T_g ? (?_g + τ_2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited T_g states, can be presented for trivalent 3dⁿ cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding e_g MOs.The tetragonal splitting of T_g states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds A^IM^IIIF₄, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for Ti^III to Fe^III; the rather small electronegativity already of Co^III suggests a reducing ligand-to-metal (3dⁿ) electron transfer for n ≥ 6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the Cu^IIIF₆^3? complex and the reduced T_g ? ?_g coupling strength suggest a pronounced covalency of the Cu^III–F, and, even more distinctly, of the Cu^III–O bond, which is of interest for superconductivity. The Ni^IIIF₆^3? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative _a²A_1g(_a²E_g) and _a⁴A_2g (_a⁴T_1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong E_g ? ?_g as compared to the T_1g ? ?_g coupling, which finally stabilises a spin-doublet ground state in D_4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.