A Compact Tetrathiafulvalene–Benzothiadiazole Dyad and Its Highly Symmetrical Charge‐Transfer Salt: Ordered Donor π‐Stacks Closely Bound to Their Acceptors

A compact and planar donor–acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been synthesised and experimentally characterised by structural, optical, and electrochemical methods. Solution‐processed and thermally evaporated thin films of 1 have also been explored as active materials in organic field‐effect transistors (OFETs). For these devices, hole field‐effect mobilities of μ_FE=(1.3±0.5)×10^?3 and (2.7±0.4)×10^?3 cm² V s^?1 were determined for the solution‐processed and thermally evaporated thin films, respectively. An intense intramolecular charge‐transfer (ICT) transition at around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine‐induced oxidation of 1 leads to a partially oxidised crystalline charge‐transfer (CT) salt {( 1 )₂I₃}, and eventually also to a fully oxidised compound { 1 I₃} ? 1/2I₂. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm^?1. The one‐dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of the LUMO) along its ridge.     

Thermal and surface analysis of palladium pyrazolates molecular precursors

The reduction of molecular or ionic precursors represents one of the more suitable and effective methods to obtain small and uniform particles. In the present work, various palladium (Pd(II)) molecular precursors (MPs) were characterized before and after thermal reduction process, as an alternative to form Pd nanoparticles. These MPs are classified in two principal groups; those that contain 3,5-dimethylpyrazole and those that contain 3-phenyl or 3,5-diphenyl pyrazole with some chemical variations: Pd(3,5-Ph₂pzH)₂Cl₂ (MP(I)), Pd(3-PhpzH)₂Cl₂ (MP(II)), Pd(3,5-Me₂pzH)₂Cl₂ (MP(III)), Pd(4-Br-3,5-Me₂pzH)₂Cl₂ (MP(IV)), Pd₂(µ-3,5-Ph₂pz)₂(3,5-Ph₂pzH)₂Cl₂·H₂O (MP(V)), Pd₂(µ-3,5-Me₂pz)₂(3,5-Me₂pzH)₂Cl₂ (MP(VI)), and Pd₃(µ-Phpz)₆ (MP(VII)). In order to obtain Pd nanoparticles, these neutral MPs were reduced under hydrogen atmosphere. Thermogravimetric analyses were carried out to establish the thermal stability of these compounds, an important parameter in order to select the appropriate conditions to form metallic Pd nanoparticles. To confirm the reduction of the precursors, Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis were performed on the molecular cluster precursor powders. The present study is a preparatory guide to establish the appropriate conditions in order to promote the formation of Pd nanoparticles. The temperature of 600 °C emerges as an ideal temperature to reach the decomposition of organic groups in the Pd(II) MPs, as well as the formation of metallic Pd particles, as corroborated by FT-IR and XPS analysis. These Pd MPs represent a new alternative for the preparation of metallic Pd nanoparticles.     

Preparation,thermal characterization,and DFT study of the bacterial cellulose

A bifunctional comonomer 3-aminocarbonyl-3-butenoic acid methyl ester (ABM) was designed and synthesized to prepare poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] copolymer which can be used as carbon fiber precursor instead of poly(acrylonitrile–acrylamide–methyl acrylate) [P(AN–AM–MA)] terpolymer. The stabilization mechanism and structural evolution of P(AN-co-ABM) and P(AN–AM–MA) during stabilization were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetry. The activation energy (E _a) of the cyclization reactions was calculated by Kissinger method and Ozawa method. The results show that the stabilization of P(AN-co-ABM) has been remarkably improved by ABM compared with P(AN–AM–MA) terpolymer, such as lower initiation temperature, broadened exothermic peak, larger extent of stabilization, and smaller E _a of cyclization, which is attributed to the initiation of ABM through ionic mechanism. Moreover, the spinnability of P(AN-co-ABM) is also improved by ABM due to the lubrication of ester groups in ABM. This study clearly shows that P(AN-co-ABM) copolymer is a better material used as carbon fiber precursor than P(AN–AM–MA) terpolymer.     

Dismutational and Global‐Minimum Isomers of Heavier 1,4‐Dimetallatetrasilabenzenes of Group 14

Aromatic species with heavier Group 14 elements show remarkable differences in terms of stability, structure, and reactivity. Herein we report our experimental and theoretical investigations regarding isomers of germanium‐ and tin‐containing benzene analogues E₂Si₄R₆ (E=Ge, Sn). The germanium‐substituted dismutational isomer with a tricyclic six‐membered scaffold is isolable, but unlike the homonuclear Si₆ analogue slowly rearranges even at room temperature to give the propellane‐type global minimum isomer. In case of E=Sn the dismutational isomer may be an intermediate on the pathway to the propellane‐type species obtained, but cannot be detected even at low temperature. Unprecedentedly large chemical shift anisotropies in the ²⁹Si NMR spectra that increase from the Si₆ species through Ge₂Si₄ to Sn₂Si₄ are rationalized by progressively larger paramagnetic‐term contributions to the chemical shift tensor as a result of diminishing HOMO–LUMO gaps, which are also reflected in the absorption spectra, as well as by appearance and symmetry of these frontier orbitals.     

Potassium hydroxylamine complexes

Potassium complexes of N,N-dialkylhydroxylamines [KONR2, R=Me (1a), iPr (2a), CH2C6H5] were synthesized by the deprotonation of the corresponding N, N-dialkylhydroxylamines with KH. 1a and 1b [(KONMe2)(HONMe2)] dissolve in THF under the addition of an additional equiv of the parent hydroxylamine to give 1b and [(KONiPr2)(HONiPr2)(THF)] 2b. 1b, 2b and [(KONBn2)6(THF)4] (3) were characterized by NMR and IR spectroscopy, by elemental analyses, and by X-ray diffraction of single crystals. 1b and 2b crystallize as polymers, whereby compound 1b with smaller groups leads to higher coordination numbers at the potassium atoms (CN=7) and double-stranded more complex ladder-type aggregates, whereas 2b with the larger iPr groups contains potassium atoms with a coordination number of 5 and is a single-stranded polymer. The compound {[KON(CH2C6H5)2]6(THF)4} (3) exists in a hexameric bis-cubane-based form in the solid state. Quantum chemical calculations were undertaken to examine the nature of the hydrogen bonding in the (R2NO...H...ONR2) units of 1b and 2b, which is asymmetric in the first and symmetric in the second case.     

Solution identification and solid state characterisation of a heterometallic polyoxometalate {Mo(11)V(7)}: [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(mu(9)-SO(3))](7-)

A polyoxomolybdenum/vanadium-sulfite {M(18)} cluster-based compound, [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(mu(9)-SO(3))](7-), is reported that exhibits a unique structural motif, arising from the incorporation of five V(V) and two V(IV) ions into a {M(18)} cluster framework templated by SO(3)(2-); this cluster compostion was first identified using cryospray mass spectrometry.     

Temperature (over)compensation in an oscillatory surface reaction

Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. We study the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25 °C, and the oscillations are studied under galvanostatic control. Under oscillatory conditions, only non-Arrhenius behavior is observed. Overcompensation with temperature coefficient (q(10), defined as the ratio between the rate constants at temperature T + 10 °C and at T) < 1 is found in most cases, except that temperature compensation with q(10) ≈ 1 predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, nonoscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than from a weak temperature dependence of the individual steps.     

Rainbow decompositions

A rainbow coloring of a graph is a coloring of the edges with distinct colors. We prove the following extension of Wilson's Theorem. For every integer there exists an so that for all , if

then every properly edge-colored contains pairwise edge-disjoint rainbow copies of .

Our proof uses, as a main ingredient, a double application of the probabilistic method.

     

Alterations in the fat body cells of Rhinocricus padbergi (Diplopoda) resulting from exposure to substrate containing sewage sludge

The final disposal of residues generated at sewage treatment plants (STPs) has become a major problem for cities, due to the increase in the amount of treated sewage. One of the alternatives for the residue, labeled "sewage sludge," is its reuse in agriculture and in degraded soil. However, not all pathogens and metals present in it are eliminated during treatment. Diplopods have been used as bioindicators in ecotoxicological tests as they are constantly in close contact with the soil. Owing to this fact, the purpose of this study was to expose specimens of the diplopod Rhinocricus padbergi to substrate containing sewage sludge collected at STPs to analyze morphological alterations in their parietal and perivisceral fat body, where substances are stored. The exposures were held for 7, 15, or 90 days at different concentrations of sewage sludge (control, 1%, 10%, and 50%). The parietal fat body showed no alterations in any of the three exposure periods or concentrations. Alterations in the perivisceral fat body were observed for all exposure periods. According to the results, we suggest that the sludge used has toxic agents responsible for changing the animal's perivisceral fat body.