Electronic structure and properties of NbS3 and Nb3S4

Electronic structure calculations for NbS₃ and Nb₃S₄ are reported. The NbS₃ structure is closely related to that of ZrSe₃. In the undistorted ZrSe₃ atomic arrangement, NbS₃ would be a metal; it is shown that the observed distortion, a pairing of Nb atoms along the b-axis relative to ZrSe₃, stabilizes the NbS₃ crystal by inducing a 0.5-eV semiconducting gap. Nb₃S₄ is found to be a metal with the Fermi level lying near a deep minimum in the density of electron states.     

First example of monodispersed (Mo3Se3)1∞ clusters

The close relationship of the structure of ternary molybdenum chalcogenides to molecular cluster compounds suggests that these chalcogenides might be synthesized from such clusters or be solubilized as clusters. However, in contrast to molybdenum halide clusters which can be obtained in solution from the solid phase, many attempts to solubilize these chalcogenide clusters were unsuccessful. This is the first report that some of the pseudo-one-dimensional compounds (M₂Mo₆X₆, X = Se, Te; M = Li, Na) can be dissolved when exposed to highly polar solvents such as dimethylsulfoxide or N-methylformamide. We show using optical microscopy, TEM, and light scattering that some of these solutions contain individual (Mo₃X₃)¹_∞ chains. This is also the first example of a purely inorganic transition-metal polymer solution. The behavior with respect to flocculation is consistent with the double layer theory. We show that the (Mo₃X₃)¹_∞ chains can be oriented in solution.     

Halogen in materials design: Chloroammonium lead triiodide perovskite (ClNH3PbI3) a dynamical bandgap semiconductor in 3D for photovoltaics

Methylammonium lead trihalides and their derivatives are photovoltaic materials. CH₃NH₃PbI₃ is the most efficient light harvester among all the known halide perovskites (PSCs). It is regarded as unsuitable for long‐term stable solar cells, thus it is necessary to develop other types of PSC materials to achieve stable PSCs (Wang et al., Nat. Energy 2016, 2, 16195). Because of this, various research efforts are on‐going to discover novel lead‐based or lead‐free single/double PSCs, which can be stable, synthesizable, transportable, abundant and efficient in solar energy conversion. Keeping these factors in mind, we report here the electronic structures, energetic stabilities and some materials properties (viz. band structures, density of states spectra and photo‐carrier masses) of the PSC chloroammonium lead triiodide (ClNH₃PbI₃). This emerges through compositional engineering that often focuses on B‐ and Y‐site substitutions within the domain of the BMY₃ PSC stoichiometry. ClNH₃PbI₃ is found to be stable as orthorhombic and pseudocubic polymorphs, which are analogous with the low and high temperature polymorphs of CH₃NH₃PbI₃. The bandgap of ClNH₃PbI₃ (values between 1.28 and 1.60 eV) is found to be comparable with that of CH₃NH₃PbI₃, (1.58 eV), both obtained with periodic DFT at the PBE level of theory. Spin orbit coupling is shown to have a pronounced effect on both the magnitude and character of the bandgap. The computed results show that ClNH₃PbI₃ may act as a competitor for CH₃NH₃PbI₃ for photovoltaics. © 2018 Wiley Periodicals, Inc.     

Multiferroicity Broken by Commensurate Magnetic Ordering in Terbium Orthomanganite

TbMnO₃ is an important multiferroic material with strong coupling between magnetic and ferroelectric orderings. Incommensurate magnetic ordering is suggested to be vital for this coupling in TbMnO₃, which can be modified by doping at the site of Tb and/or Mn. Our study shows that a self‐doped solid solution Tb_1?xMn_yMnO₃ (y≤x) can be formed with Mn doped into the site of Tb of TbMnO₃. When y is small Tb_1?xMn_yMnO₃ shows both ferroelectric and incommensurate magnetic orders at low temperature, which is similar to TbMnO₃. However, if y is large enough, a commensurate antiferromagnetic ordering appears along with the incommensurate magnetic ordering to prevent the appearance of multiferroicity in Tb_1?xMn_yMnO₃. That is to say, the magnetoeletric coupling can be broken by the co‐existence of a commensurate antiferromagnetic ordering. This finding may be useful to the study of TbMnO₃.     

Photofragmentation of CF3I in the A band

CF₃I is photodissociated in a molecular beam with 248 nm laser lighl. Fragmentation takes place into CF₃ and I(²P_3/2) or I(²P_1/2). The quantum yield for excited I (I* = I(²P_1/2)) formation is determined to be 0.92. The CF₃ fragments are found to be considerably vibrationally excited. Of the available energy in the CF₃ + I* channel 39% (0.69 eV) appears on the average as vibrational energy in the CF₃ radical. The angular distributions in both channels show predominantly parallel character. It can be concluded that at this wavelength 97% of the total absorption is due to the ³Q₀ ← ¹A₁ transition and only 3% to the ¹Q ← ¹A₁ transition. Most of the signal in the CF₃ + I channel originates from an effective crossing between the ³Q₀ and ¹Q states. A coupled channel calculation is performed to obtain a better insight into the dissociation dynamics of the CF₃I molecule. The results indicate that the CF₃ fragments from dissociation of CF₃I at 248 nm may be expected to be vibrationally excited. However, the experimental distribution has a higher average energy and is much broader. An explanation for this phenomenon is suggested.     

Spectra and structure of gallium compounds: Part VI. Infrared and Raman spectra of trimethylgalliumtrimethylphosphine

The infrared (50–4000 cm^?1 ) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaP(CH₃)₃ have been recorded for the solid state at the temperature of boiling liquid nitrogen. The spectra have been interpreted on the basis of C_3v molecular symmetry and a complete vibrational assignment except for the methyl torsional modes is presented. A modified valence force field model has been utilized in calculating the frequencies and potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis acid and the Lewis base moieties and the differences are shown to be consistent with structural changes upon adduct formation. Extensive coupling has been observed between the Ga-P stretching mode and the PtC₃ and GaC₃ deformational modes. Substantial coupling is also observed between the PC₃ and the GaC₃ rocking motions. The magnitude of the Ga-P stretching force constant is found to be much smaller (0.88 mdyn Å^?1) than that reported for (CH₃)₃PGaH₃ and the difference possibly reflects the relative stabilities of the donor-acceptor bond in the two complex species.The fact that none of the A, modes appear as doublets in the spectra, nor are any of the E modes split except for the GaC₃ antisymmetric stretch, which is believed to be due to the two isotopes of gallium, indicates that there is only one molecule per primitive cell sitting on a C_3v or C₃ site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

The Distorted Structure of [Au(GeCl3)3]2–

It is well known that [Au(PR₃)₃]⁺ compounds (R any organic ligand) adopt a trigonal planar AuP₃ arrangement, small distortions being only due to steric repulsion between the ligands R. This is supported by relativistic MP2 geometry optimizations for the free gas phase species which yield the ideal trigonal planar AuP₃ structure for the model compound [Au(PH₃)₃]⁺. Model calculations on the recently synthesized compound [Au(GeCl₃)₃]^2– which is isoelectronic to [Au(PR₃)₃]⁺ also reveal a trigonal planar AuGe₃ structure. However, the recently determined X‐ray structure of [Au₂(dppm)₂][Au(GeCl₃)₃] shows a T‐shaped AuGe₃ arrangement. We demonstrate that this distortion is caused by solid state effects, that is the influence of the counter cations are necessary in order to obtain the observed symmetry breaking. However, unlike AuF₃ which has recently been determined by electron diffraction to be T‐shaped in the gas phase caused by a first‐order Jahn‐Teller effect, this distortion cannot be so easily rationalized by a similar AuGe₃ Jahn‐Teller effect along the e′ distortion mode. Model calculations on Na₂[Au(GeCl₃)₃] show that the strong Coulomb interaction between the negatively charged chlorine atoms and the Na⁺ ions leads to a distortion from a trigonal planar to the T‐shaped AuGe₃ arrangement lowering the energy by 137 kJ mol^–1.     

The effect of impurities Pb,Bi, and PbO on erosion properties of Lead-Bismuth Eutectic alloy on Fe3O4 oxide film by first principle calculations

The first-principle calculation was performed to study the effect of impurities Pb, Bi, and PbO on erosion properties of liquid lead-bismuth eutectic alloy on the metal oxide (Fe₃O₄) and its surfaces. We found that whether in the bulk or on the surface of Fe₃O₄ the formation energy by substitution of Fe with Bi is slightly larger than that with Pb substitution and the formation energy by substitution of Fe with PbO is much larger than those with Pb and Bi, indicating that PbO has weaker corrosion potential than Pb/Bi. The calculation results show that a tetrahedral site in Fe₃O₄ should be the weakest position where Fe₃O₄ is attacked by these exotic impurities. The corrosion process on the oxide film will be initialized at that position. It can be seen that for the doping case the dissociation energy of Fe atom in the (110) surface has the smallest value, a medium value in (100) surface, and the largest value in (111) surface. Correspondingly, the corrosion resistance of doping Fe₃O₄ film in (110) surface is the weakest one among these surfaces. For the doping-free case, the (100) surface has the weakest corrosion resistance. By comparing the doping case with no-doping case it can be seen that the impurities of Pb, Bi, and PbO will weaken the corrosion resistance of Fe₃O₄ film further. The doping has a negative impact on the stability of the structure and on the corrosion resistance of Fe₃O₄ film. From present results, it is also seen that the replacement of Fe in Fe₃O₄ by multiple impurities is more likely to occur than the replacement of only single impurity.     

The thermal decomposition of azomethane-d6

The thermal decomposition of azomethane-d₆ has been studied. There is a short chain reaction, and measurements have been made of the rate of production of N₂, CD₄, and C₂D₆. A mechanism is suggested which accounts for these results fairly well. A comparison is made with some similar results of Forst for azomethane. Measurements have also been made of the reaction inhibited by NO. It is believed that the N₂ production, extrapolated to zero NO pressure, measures the rate of the initial step CD₃N₂CD₃ → 2 CD₃ + N₂. This has an activation energy at high pressures of 50.7 kcal per mole and an Arrhenius A·factor of 10^15.49 sec^?1. This is to be compared to values of 55.5 and 10^17.3 found by Forst and Rice for CH₃N₂CH₃ → 2 CH₃ + N₂. The pressure fall-off behavior for CD₃N₂CD₃ → 2 CD₃ + N₂ has also been investigated and compared to the theoretical curves, which seem to fit satisfactorily except at the lowest pressure, where experimental errors may be large. Unexpectedly, the fall-off curve crosses that for CH₃N₂CH₃ → 2 CH₃ + N₂. It is suggested that the extrapolation to zero NO pressure may not be entirely correct in the CH₃N₂CH₃ case where the chain is longer than with CD₃N₂CD₃. It is believed that the decomposition of azomethane-d₆ is a better example for unimolecular-rate theory than is that of azomethane.     

NITRATE EFFECT ON Pfr-MEDIATED AND GA3-INDUCED GERMINATION IN SPORES OF Anemia phyllitidis (L.) Sw*

Spore germination in Anemia phyllitidis can be induced by red light (R) via the phytochrome system and by gibberellic acid (GA₃) in the dark. An enhancing effect of NO₃-ions on the Pfr-mediated germination could be demonstrated. This NO₃-effect was found to be pronounced during the preinduction phase and could be described by biphasic kinetics depending on the formation of Pfr by the R-irradiation. Besides NO₃, other electron accepting substances also increased germination significantly. In contrast to Pfr-mediated germination, no enhancing effect by NO₃ could be obtained for the GA₃-induced germination response. The application of an inhibitor of gibberellic acid synthesis, AMO1618, as well as the analysis of combined R and GA₃ treatment, support the hypothesis that for germination of Anemia phyllitidis spores no synergism between the factors exists. Thus, it is proposed that the gibberellic acid receptor starts a signal-transduction pathway resulting in germination which is in part independent of the Pfr-mediated signal-transduction chain. The NO₃-effect is specific for the Pfr-mediated signal-transduction chain.     

AB initio molecular orbital studies of CF3O2H,CF3O2F and CF2(OF)2

Ab initio calculations employing an extended 4-31G basis set have been applied to the highly fluorinated molecules, CF₃O₂H, CF₃O₂F and CF₂(OF)₂. Partial geometry optimizations have also been carried out on these molecules allowing a comparison between theory and the recently completed gas-phase electron diffraction results. The O-O bond distance in CF₃O₂ H is found to be longer (by 0.02 Å) than the corresponding bond in CF₃O₂F while the CO bond is found to be shorter (by 0.02 Å) in CF₃O₂H. The OF bond in CF₃O₂F is found to be longer (by 0.03–0.04 Å) than the corresponding bond in CF₃OF or F₂O. Torsional barriers have been computed for CF₃O₂H and CF₃O₂F with the aid of Fourier analysis of the potential curves. CF₃O₂H is found to have a torsional potential about the peroxide bond rather similar to that found for H₂O₂ while in CF₃O₂F the cis and trans barriers are predicted to be much larger (14.6 and 8.4 kcal mol^?1, respectively). The threefold barrier to rotation of the CF₃ group in CF₃O₂F is predicted to be 4.4 kcal mol^?1. Various conformations of CF₂(OF)₂ have also been studied with conformations consistent with the operation of the gauche-effect being most stable. Bond separation energies and molecular properties have also been computed for these molecules.     

Determination of the maximum monolayer dispersion and dispersed state for WO3 on γ-Al2O3

The maximum monolayer dispersion (the threshold) for WO₃ on γ-Al₂O₃ calcined at 500°, 550°, 600°, and 640°C has been determined quantitatively by XRD (amount of crystalline phase) and XPS (intensity ratios I_w4f/I_Al2). The results show that if the amount of WO₃ loaded is lower than the maximum monolayer dispersion, WO₃ will react with γ-Al₂O₃ to form surface compound due to mutual ionic interaction, and will be dispersed on γ-Al₂O₃ surface as monolayer then. In case the amount is higher than this value, the residual crystalline WO₃ will remain. The maximum monolayer dispersion (threshold) is 0.21 g and 0.20 g WO₃/100 m² γ-Al₃O₃ by XRD and XPS respectively. It agrees with the value (0.189 g WO₃/100 m² or 4.90 × 10^?18 W atoms/m²) calculated from the model on assumption that the WO₃ is dispersed as a closed-packed monolayer on γ-Al₂O₃ surface. Inasmuch as WO₃/γ-Al₂O₃ system is stable up to higher temperature, e.g. 700°C, than MoO₃/γ-Al₂O₃ system, WO₃ seems unfavorable to form new bulk compound with γ-Al₂O₃ at that temperature. However, Al₂(MoO₄)₃ forms perceptibly in MoO₃/γ-Al₂O₃ system at 500°C. Besides, the size of residual crystalline WO₃ in WO₃/γ-Al₂O₃ is much smaller than that of MoO₃ in MoO₃/γ-Al₂O₃. It might be the reason that WO₃/γ-Al₂O₃ catalyst is superior to MoO₃/γ-Al₂O₃ in hydrodesulfurization (HDS) or hydrodenitrogenation (HDN) in some cases.     

A high-pressure modification of MgVO3

The preparation of a high-pressure form of MgVO₃ has been accomplished utilizing two independent synthesis methods. The triclinic, ilmenite-type phase has been characterized by its crystallographic, magnetic, and electrical properties. Its structure is believed to be similar to that previously observed for other ilmenite-type AVO₃ derivatives (CoVO₃, NiVO₃, and MnVO₃). The properties of MgVO₃ appear to be intermediate between the localized electron model found in MnVO₃, CoVO₃, and NiVO₃, and the delocalized electron regime observed in CuVO₃.     

Cationic polymerization with boron halides. IV. Elucidation and control of initiation and termination by the help of model experiments

The proposition that BCl₃-coinitiated olefin (isobutylene, styrene) polymerizations terminate by chlorination has been corroborated by model experiments. Key experiments showed that under simulated polymerization conditions neither tert-butyl chloride nor 2-chloro-2,4,4-trimethylpentane reacts with BCl₃; that H₂O/BCl₃ + 2,4,4-trimethyl-1-pentene (TMP) produce 2-chloro-2,4,4-trimethylpentane; and that H₂O/BCl₃ + isobutylene gives rise to tert-butyl chloride. Extended model studies demonstrated that certain alkyl and benzyl chlorides produce carbenium ions in the presence of BCl₃ and that TMP can readily be alkenylated by using 1-substituted allyl chlorides in conjunction with BCl₃. These experiments led to the discovery that olefin polymerizations may be initiated by suitable allyl or benzyl chlorides and BCl₃. Accordingly, polymerizations of isobutylene have been carried out with RCl/BCl₃, where R is allyl or benzyl. These experiments suggest that both controlled initiation and termination, i.e., initiation by alkenylation and termination by chlorination, can be achieved with the allyl chloride/BCl₃ initiator system opening new avenues toward the synthesis of asymmetric telechelic polymers.     

Determination of oxygen in oxides by carrier gas hot extraction analysis with simultaneous COx detection

The determination of oxygen by carrier gas hot extraction is the most popular method for oxygen analysis, but its application to high oxygen contents in oxides requires a critical look at the basic assumptions of the method. The process was studied for various oxides (Al₂O₃, Bi₂O₃, Cr₂O₃, Fe₂O₃, MoO₃, NiO, TiO₂, WO₃, Y₂O₃, and ZrO₂) using a modern analyser with IR-detectors for CO₂ and CO. There was a difference specific to oxides that must be known to get the required analytical results with high precision and accuracy. High amounts of CO₂ were formed particularly from Bi₂O₃, Fe₂O₃, MoO₃, NiO, and WO₃. The reaction rate can be controlled with delayed heating of the furnace, so that an oxide sample weight of up to 100 mg can be used. Received: 13 April 1999 / Revised: 24 June 1999 / Accepted: 28 June 1999     

Direct Measurement of Emission of Endogenous Ozone from Plants by GC–MS-SIM

According to recent observations antibodies can catalyze the formation of previously unknown oxidants, dihydrogen trioxide (H₂O₃) and ozone (O₃), formed in the interaction between singlet oxygen (¹O₂) and H₂O. The O₃ molecules can be detected indirectly e.g. in TLC/OPLC chromatographic spots in the simple BioArena operating system using O₃-eliminating molecules in the culture medium. It is currently supposed that plants can be used for the direct detection of O₃ during its eventual emission from stomata. Using the fresh primary leaves of different plant species O₃ could be really detected by means of GC–MS-SIM from the space above the the leaves which were prepared in a CO₂-containing headspace vessel. It has been also established that the CO₂ also contained O₃ molecules, and therefore, we had to use a correction to the observed data. These new findings indicate that not only formaldehyde but also O₃ and their related bioreactive compounds may play a crucial role in disease resistance (e.g. in the mechanism of action of antibodies), cell proliferation and differentiation.     

Structure types and phase transformations in KMnCl3 and TlMnCl3

KMnCl₃ and TlMnCl₃ are known to crystallize in tetragonal and cubic perovskite structures, respectively. Room temperature X-ray diffraction data obtained in our laboratory proved that the perovskite structure of KmnCl₃ is orthorhombic. The space group is Pnma and Z = 4. Unit cell parameters are a = 7.08(1), b = 9.97(1), and c = 6.98(1) Å. Experimental data showed that the perovskite structures of KMnCl₃ and TlMnCl₃ are not stable, and that both materials transform slowly into another orthorhombic, nonperovskite KCdCl₃ structure with space group Pnma and Z = 4. Cell parameters of these structures are a = 8.769(7), b = 3.883(9), and c = 14.42(1) Å for KMnCl₃ and a = 8.926(8), b = 3.839(9), and c = 14.77(1) Å for TlMnCl₃. The nonperovskite structures of KMnCl₃ and TlMnCl₃ transform on heating to the perovskite structures and these phase transitions are not immediately reversed. No correlation could be found between the KCdCl₃ structure and water incorporation in the crystal lattice as has been previously suggested. An analysis of the factors that cause the K structure to be exhibited in chloride and to be absent in the fluoride compounds is also presented.     

Experimental study of the gas phase chemistry of C3H3+ with several cyclic molecules

Rate coefficients and ion product distributions have been determined for the gas phase reactions of C₃H₃⁺ with several homocyclic and heterocyclic molecules in a selected ion flow tube (SIFT) at 298 K. The rate coefficients for both the linear and cyclic isomers of C₃H₃⁺ are given. l-C₃H₃⁺ reacts by association in the majority of the reactions. c-C₃H₃⁺ is shown to be more reactive than previously suggested by low pressure experiments. In fact, the cyclic isomer reacts at the gas kinetic rate when the reaction involves a nitrogen containing cyclic compound but is less reactive with oxygen containing cyclic compounds. It is noted this reactivity of both the cyclic and linear isomer should be included when modeling the atmosphere of Titan due to the large number of nitrogen containing molecules that are considered to be present. Currently, the models consider electron recombination to be the only loss channel for c-C₃H₃⁺.     

Concise and Additive-Free Click Reactions between Amines and CF3SO3CF3

Trifluoromethyl trifluoromethanesulfonate has proved to be an excellent reservoir of difluorophosgene and a promising click ligation for amines in the preparation of urea derivatives, heterocycles, and carbamoyl fluorides under metal- and additive-free conditions. The reactions are rapid, efficient, selective, and versatile, and can be performed in benign solvents, giving products in excellent yields with minimal efforts for purification. The characteristics of the reactions meet the requirements of a click reaction. The use of trifluoromethyl trifluoromethanesulfonate as a click reagent is advantageous over other “CO” sources (e.g., TsOCF₃, PhCO₂CF₃, CsOCF₃, AgOCF₃, and triphosgene) because this reagent is readily accessible; easy to scale up; and highly reactive, even under metal- and additive-free conditions. It is anticipated that CF₃SO₃CF₃ will be increasingly as important as SO₂F₂ as a click agent in future drug design and development.     

Ab initio quantum-mechanical calculations on trifluoromethylamine

Extensive ab initio molecular-orbital calculations were carried out on trifluoromethylamine (TFM) to elucidate changes in geometry and electronic structure upon fluorination. The calculations show that the decomposition of CF₃NH₂ is slightly endoenergetic, and the heats of atomization of CF₃NH₂ and CH₃NH₂ show decreased stability of the species upon fluorination. Characteristic of CF₃NH₂ is a highly polar, strong, short CN bond. More limited calculations were carried out on CF₃OH and CH₃OH, and the electronic structure of CF₃OH is found to be generally similar to that of CF₃NH₂. The reduced basicity of the fluorinated amine cannot be ascribed to the inductive effect; the enhanced acidity of the fluorinated alcohol reflects the weakening of the OH bond. No evidence leads to a confirmation of the existence of nitrogen–fluorine hyperconjugation in the fluorinated amine.