The crystal structure of realgar

Cluster Modeling of Network-Forming Amorphization Pathways in AsxS100−x Arsenicals (50 ≤ x ≤ 57) Diven by Nanomilling

Complete hierarchy of network amorphization scenarios initiated in AsxS100-x nanoarsenicals within As4S4-As4S3 cut-Sect. (50 ≤ x ≤ 57) is reconstructed employing materials-computational approach based on ab-initio quantum-chemical modeling code (CINCA). Under nanostructurization due to high-energy mechanical milling, the inter-crystalline transformations to nanoscopic β-As4S4 phase accompanied by appearance of covalent-network amorphous matrix are activated. General amorphization trend under nanomilling obeys tending from molecular cage-like structures to optimally-constrained covalent-bonded networks compositionally invariant with parent arsenical. The contribution of amorphization paths in nanoarsenicals is defined by their chemistry with higher molecular-to-network barriers proper to As4S3-rich alloys. The generated amorphous phase is intrinsically decomposed, possessing double-Tg relaxation due to stoichiometric (x = 40) and non-stoichiometric (x > 40) sub-networks, which are built of AsS3/2 pyramids and As-rich arrangement keeping (i) two separated As-As bonds derived from realgar-type molecules, (ii) two neighboring As-As bonds derived from pararealgar-type molecules or (iii) three neighboring As-As bonds in triangle-like geometry derived from dimorphite-type molecules. Compositional invariance of nanoamorphous phase is ensured by growing sequence of network-forming clusters with average coordination numbers Z in the row (As2S4/2,Z = 2.50) – (As3S5/2, Z = 2.55) – (As3S3/2, Z = 2.67). Diversity of main molecular-to-network amorphizing pathways in nanoarsenicals is reflected on the unified potential energy landscape specified for boundary As4S4 and As4S3 components.

Thermochemical study of gaseous indium-arsenic sulfosalt

RATIONALE

Sulfide systems are often used at high temperatures, when vaporization of the components is enabled. Sulfide ores are used as sources of various metals and nonmetals and gaseous sulfides, and sulfosalts may also play a role in the atmosphere chemistry of hot rocky exoplanets. To predict the existence and thermal stability of gaseous sulfides and sulfosalts it is important to know their thermodynamic characteristics. In this study the sulfosalt of indium and arsenic was obtained in the gaseous phase for the first time.

METHODS

High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over indium and arsenic sulfides. A molybdenum double two-temperature cell was used to create the conditions of coexistence of indium and arsenic sulfides. A theoretical study of gaseous As₄ S₄ and In₂ AsS₂ was performed using both B3LYP, M06, PBE0 and TPSSh hybrid DFT functionals and an ab initio wave function-based MP2(Full) method.

RESULTS

Gaseous In₂ AsS₂ has been identified during vaporization of In₆ S₇ and As₂ S₃ from the molybdenum double two-temperature cell. The structure and molecular parameters of gaseous In₂ AsS₂ were determined using quantum chemical calculations. Energetically favorable structures of gaseous In₂ S, AsS, As₄ S₄ and In₂ AsS₂ were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous In₂ AsS₂ (186 ± 37 kJ mol^-1 ) was derived as a result of measurements of the equilibrium constants of two independent gas-phase reactions.

CONCLUSIONS

The gaseous sulfosalt of indium and arsenic was obtained for the first time. The formation enthalpy of the In₂ AsS₂ (g) molecule at 298 K was evaluated both experimentally and theoretically. The thermal stability of the gaseous sulfosalt is less than that of the gaseous oxyacid salts.

Infrared and Raman spectroscopy study of AsS chalcogenide films prepared by plasma-enhanced chemical vapor deposition

AsS chalcogenide films, where As content is 60-40at.%, have been prepared via a RF non-equilibrium low-temperature argon plasma discharge, using volatile As and S as the precursors. Optical properties of the films were studied in UV-visible-NIR region in the range from 0.2 to 2.5μm. Infrared and Raman spectroscopy have been employed for the elucidation of the molecular structure of the newly developed material. It was established that PECVD films possess a higher degree of transparency (up to 80%) and a wider transparency window (>20μm) in comparison with the "usual" AsS thin films, prepared by different thermal methods, which is highly advantageous for certain applications.

Phosphorus-based materials for high-performance rechargeable batteries

A review of P based materials used in LIB/NIB and their synthesis strategies, tailored materials properties and different electrochemical performances.

Compressibility and polymorphism of α-As(4)S(4) realgar under high pressure

The energy-dispersive x-ray diffraction technique has been employed to study the structure and equation of state of realgar As(4)S(4) under pressures up to 8 GPa at room temperature. We have obtained pressure dependences of the unit cell parameters and volume for the monoclinic structure of realgar. An approximation of the equation of state through the Murnaghan equation gives the bulk modulus and its derivative, B(0) = 8.1 ± 0.5 GPa and B(0)(') = 9.0 ± 0.5, respectively. A comparison of the obtained values with the corresponding values for other molecular crystals is drawn and discussed. At a pressure of around 7 GPa, realgar showed a polymorph transition to a new molecular phase with a supposedly orthorhombic structure. Such identification is evidenced by the presence of geometrical correlations between the parameters of the parent monoclinic phase and those of the new phase, and the phase transition is likely to be associated with the removal of a monoclinic distortion in the unit cell.

Structural rearrangements in triple-decker-like complexes with mixed group 15/16 ligands: synthesis and characterization of the redox couple

The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Hückel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: significant shortening of the Fe-Fe distance (deltad(Fe-Fe)> 0.3 A) and weakening of the As-As bond length ((deltad(As-As) > 0.3 A) suggests the formal presence of two diatomic AsSe ligands and a Fe-Fe bond. DFT and EHMO calculations confirm that an electron is removed from an occupied Fe-Fe orbital of antibonding character during oxidation. All molecular orbitals lower their energies upon oxidation, but the energy drop is relatively small for those involving the As-As bond. An additional structural feature in 4 consists of an electronic interaction of the iodide with both As atoms which suggests a formally neutral ion pair. Electrochemical studies confirm that the oxidation of 1 is a reversible one-electron process with E(1/2)= +0.07 V (in THF). These studies also reveal that 4 dissociates in polar solvents, such as THF, into [1]+ and I-, which is followed by transformation into 1 and I3.