Crystal‐to‐Crystal Transformation: An HgII Metal–Organic Polymer Constructed with a Triazole Ligand

A new one‐dimensional double‐chain Hg^II coordination polymer containing the ligand 3,5‐bis(4‐pyridyl)‐4‐amino‐1,2,4‐triazole (bpatrz) and thiocyanate anions, namely, {[Hg₂(μ‐bpatrz)(μ‐SCN)₂(SCN)₂] · MeOH}_n ( 1 ), has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. Compound 1 displays bright blue luminescence with emission maxima around 370 and 440 nm in solution and the solid state, respectively. Uptake and release of MeOH by 1 were investigated by powder X‐ray diffraction, thermogravimetric analysis, elemental analysis, and IR and NMR spectroscopy.     

Cerium (III) doping effects on optical and thermal properties of PVA films

Cerium chloride (CeCl₃) doped polyvinyl alcohol (PVA) films were prepared by casting technique. The effect of CeCl₃ concentrations on the structural, optical and thermal properties of the PVA films was studied by X-ray diffraction (XRD), FT-IR, UV-visible, transmittance (T), reflectance (R), differential scanning calorimetry (DSC) and thermogravimetry (TG). Both of the XRD and the DSC results affirm the increase in amorphousity. Absorption spectra of the doped films have shown an absorption band at 260 nm assigned to the trivalent state of cerium ions. Absorption, transmittance and reflectance spectra were used for the determination of the optical constants. The results indicate that the optical band gap (E_g) was derived from Tauc's extrapolation and decreases with the cerium content. The refractive index increases with monotonic behavior as the cerium content increases. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomernico model for obtaining the dispersion parameters. The obtained optical parameters were found to be strongly affected by CeCl₃ dopant. Thermal analysis showed that the thermal parameters of PVA are enhanced by CeCl₃. The dependence of the activation energy of the decomposition temperature on doping level was estimated.     

Chemoselective synthesis of xanthenes and tetraketones in a choline chloride-based deep eutectic solvent

A chemoselective synthesis of tetraketone and xanthene derivatives, by means of tandem Knoevenagel condensation and Michael addition in choline chloride-based deep eutectic solvents (DESs), is presented. The reaction of readily available aldehydes and active methylene compounds in malonic acid- and ZnCl₂-based DES gives various xanthenes derivatives with good to excellent yields under mild reaction conditions. On the other hand, tetraketones were synthesized in almost quantitative yields by simple condensation of an aldehyde and active methylene compounds in milder deep eutectic solvents of urea and SnCl₂. In addition, the reaction of other types of choline chloride-based DES leads to a mixture of tetraketone and xanthene.     

REACTIONS WITH 2-THIOHYDANTOIN DERIVATIVES: SYNTHESIS OF MANNICH BASES AND IMIDAZOTHIAZOLE DERIVATIVES

Abstract

5-Arylidene-2-thiohydantoins (la-c) and 5-arylazo-1-phenyl-2-thiohydantoins (7a, b) were condensed with formaldehyde and primary or secondary aromatic amines to give the corresponding Mannich bases (2a-f) and (8a, b) respectively, which could also be converted into the educts (la-c) and (7a, b) by boiling in ethanolic HCI. On treatment of (2a-f), (5a-c) and (8a, b) with an ethereal diazomethane the colourless cyclopropane products (3a-c) and yellow N-methyl substituted compounds (9, b) were isolated respectively. Alkylation of (2d-f) with methyl iodide and (la-e) with 3-chloropentane-2,4 dione gave the corresponding 2-alkylmercapto derivatives (5a-c) and (2a-c) respectively, the former of which on hydrolysis by boiling ethanolic HCI afforded the hydantoin derivatives (6a-c). Cyclization of (12a-c) using polyphosphoric acid resulted in the formation of imidazothiazole derivatives (13a-c). The structure of the isolated products were established by elemental analyses and spectral data studies.     

A Facile Synthesis of Stable Phosphorus Ylides Containing Chlorine and Sulfur Derived from 6-Chloro-2-benzoxazolethiol and 2-Chloro-phenothiazine

Stable crystalline phosphorus ylides containing chlorine and sulfur were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylene-dicarboxylates in the presence of 6-chloro-2-benzoxazolethiol and 2-chloro-phenothiazine. These stable ylides exist in solution as a mixture of two geometrical isomers. This is caused by the conjugation of the ylide moiety with the adjacent carbonyl group, which results in a restricted rotation around the respective carbon-carbon bond.     

Influence of the semiconductor/metal rear contact on the performance of n(a-Si:H)/i(a-Si:H)/p(c-Si) heterojunction solar cells

The aim of this work is to analyze on the results of using of Al/Ag layer as a rear contact to improve the performance of heterojunction silicon solar cells. An analytical method is presented to extract the physical parameters of the equivalent circuit. These parameters are extracted to simulate the I(V) characteristic of heterojunction silicon solar cells, with Al and Al/Ag rear-metal contact. A good agreement between our analytical method and experimental measurement of electrical characteristics is obtained which show clearly how the Al/Ag rear contact can improve the characteristics of silicon solar cells. The influence of the rear-metal contact on the performance of the c-Si(p)-based bifacial HIT solar cell, i.e., the ZnO/Al/a-Si:H(n)/a-Si:H(i)/c-Si(p)/metal solar cell, is investigated in detail by computer simulation using the AFORS-HET software. Accordingly, the design optimization of the bifacial HIT solar cells on c-Si(p) substrates is provided. These simulation show an optimal conversion efficiency of 23% when the rear-metal contact is perfectly ohmic.     

A numerical study on nonlinear dynamics of three-dimensional time-depended viscoelastic Taylor-Couette flow

In this paper, three-dimensional viscoelastic Taylor-Couette instability between concentric rotating cylinders is studied numerically. The aim is to investigate and provide additional insight about the formation of time-dependent secondary flows in viscoelastic fluids between rotating cylinders. Here, the Giesekus model is used as the constitutive equation. The governing equations are solved using the finite volume method (FVM) and the PISO algorithm is employed for pressure correction. The effects of elasticity number, viscosity ratio, and mobility factor on various instability modes (especially high order ones) are investigated numerically and the origin of Taylor-Couette instability in Giesekus fluids is studied using the order of magnitude technique. The created instability is simulated for large values of fluid elasticity and high orders of nonlinearity. Also, the effect of elastic properties of fluid on the time-dependent secondary flows such as wave family and traveling wave and also on the critical conditions are studied in detail.     

Hemisynthesis,crystal structure and inhibitory effect of sesquiterpenic thiosemicarbazones and thiazolidin‐4‐ones on the corrosion behaviour of stainless steel in 1 M H2SO4 solution

Treatment of thiosemicarbazones prepared from sesquiterpenes with ethyl 2‐bromoacetate in the presence of sodium acetate afforded the corresponding thiazolidin‐4‐ones. The structures of all the newly synthesized compounds were established by considering spectral and single‐crystal X‐ray diffraction data. The title compound, ethyl 2‐((Z)‐2‐{(Z)‐[(1aR,5aR,9aS)‐1,1‐dichloro‐1a,5,5,7‐tetramethyl‐1a,2,3,4,5,5a,8,9‐octahydro‐1H‐benzo[a]cyclopropa[b][7]annulen‐8‐ylidene]hydrazono}‐4‐oxothiazolidin‐3‐yl)acetate, C₂₃H₃₁Cl₂N₃O₃S, 5 , crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2₁ with Z = 4. Within the molecule in the crystal structure, the cyclohexene ring has an envelope conformation and the cycloheptane ring, to which it is fused, has a boat conformation. In the crystal, molecules are linked by C—H…Cl hydrogen bonds forming chains propagating along the b‐axis direction. The absolute configuration of the molecule in the crystal could be fully confirmed from anomalous dispersion effects [Flack parameter = ?0.04 (2)]. Thiosemicarbazones 1 and 2 are efficient inhibitors for steel corrosion in 1 M H₂SO₄ solution, with a maximum efficiency of 92.28% at 10^?3 M. Furthermore, thiosemicarbazone compounds were found to be more efficient than thiazolidin‐4‐one derivatives. In addition, cyclic voltammetry was used to characterize the tested molecules, as well to estimate the experimental value of the energy band gap.     

Status of the scalar singlet dark matter model

One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a \(\mathbb {Z}_2\) symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above \(\sim \)1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.     

Phase-Controlled Transparent Superluminal Light Propagation in a Doppler-Broadened Four-Level N-Type System

The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence(SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature,the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.