Three types of ladder-like organostannoxanes, [C5H4N(p-CO2)]2[Bu2Sn]4(μ 3-O)2(μ 2-OH)2 (1), [Ph2CHCO2]4[Bu2Sn]4(μ 3-O)2 (2), and [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ 3 -O)2(μ 2 -OH)2 (3), have been synthesized and characterized using elemental analyses, Fourier-transform infrared spectroscopy, nuclear magnetic resonance (1H, 13C) experiments, and, for 1 and 2, single-crystal X-ray diffraction analysis. X-Ray diffraction discloses that complexes adopt tetranuclear tin(iv) ladder-like structures containing two (1) or four (2) deprotonated ligands. The essential difference between their molecular structures is that in 2 there are four carboxylate ligands, while in 1 and 3 there are two. The crystal structure of 1 reveals them to be a tetranuclear structure containing a three-rung-staircase Sn4O4 core. The Sn4O4 cluster consists of a ladder of four Sn2O2 units. For 2, the structure is a tetranuclear centrosymmetric dimer of an oxoditin unit having a central four-member ring. In this complex, the central Sn2O2 core is fused with two four-member and two six-member rings. In the structures, there are two types of tin ions arranged in distorted trigonal bipyramid geometry or octahedron geometry. A series of O–H⋯N, C–H⋯O, and C–H⋯π intermolecular hydrogen bonds in these complexes play an important function in the supramolecular, or two-dimensional network structures are formed by these interactions.

Calix[4]arenes have the ability to encapsulate biomimetic guests, offering interesting opportunities to explore their molecular recognition, very close to biological scenarios. In this study, p-sulfonatocalix[4]arene (C4 A) anions and hydrated alkali cations have been used for the in situ recognition of cationic 1,ω-diammonium-alkanes and 1,ω-amino-acids of variable lengths. NMR spectroscopy illustrates that these systems are stable in aqueous solution and the interaction process involves several binding states or stabilized conformations within the C4 A anion, depending of the nature of the guest. DOSY experiments showed that monomeric 1 : 1 host-guest species are present, while the cation does not influence their self-assembly in solution. The folded conformations observed in the solid-state X-ray single-crystal structures shed light on the constitutional adaptivity of flexible chains to environmental factors. Futhermore, a comprehensive screening of 30 single crystal structures helped to understand the in situ conformational fixation and accurate determination of the folded structures of the confined guest molecules, with a compression up to 40 % compared with their linear conformations.

First principles calculations of the α-quartz phase of Si1−xSnxO2 predict great benefits of the substitution of Si by Sn with d11 piezoelectric constant. Moreover, the substitution with Sn atoms is more efficient than with Ge atoms.

Tellurium (IV) complexes with pyridine-2,6-dicarboxylate ligand were synthesized by slow evaporation from aqueous solutions yielding a new compound: [(C7H6NO4)2TeBr6·4H2O]. The structure of this compound was solved and refined by single-crystal X-ray diffraction. The compound is centrosymmetric P21/c (N°: 14) with the parameters a = 8.875(5) Å, b = 15.174(5) Å, c = 10.199(5) Å, β = 94.271° (5) and Z = 2. The structure consists of isolated H2O, isolated [TeBr6]2− octahedral anions and (pyridine-2,6-dicarboxylate) [C7H6NO4]+ cations. The stability of the structure was ensured by ionic and hydrogen bonding contacts (N–H⋯Br and O–H⋯Br) and Van-Der Walls interaction. The thermal decomposition of the compound was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The FTIR and Raman spectroscopy at different temperatures confirm the existence of vibrational modes that correspond to the organic, inorganic and water molecular groups. Additionally, the UV–Vis diffuse reflectance spectrum was recorded in order to investigate the band gap nature. The measurements show that this compound exhibits a semiconducting behavior with an optical band gap of 2.66 eV.

Tellurium (IV) complexes with pyridine-2,6-dicarboxylate ligand were synthesized by slow evaporation from aqueous solutions yielding a new compound: [(C7H6NO4)(2)TeBr6 center dot 4H(2)O]. The structure of this compound was solved and refined by single-crystal X-ray diffraction. The compound is centrosymmetric P2(1)/c (N degrees: 14) with the parameters a = 8.875(5) angstrom, b = 15.174(5) angstrom, c = 10.199(5) angstrom, beta = 94.271 degrees (5) and Z = 2. The structure consists of isolated H2O, isolated [TeBr6](2-) octahedral anions and (pyridine-2,6-dicarboxylate) [C7H6NO4](+) cations. The stability of the structure was ensured by ionic and hydrogen bonding contacts (N-H center dot center dot center dot Br and O-H center dot center dot center dot Br) and Van-Der Walls interaction. The thermal decomposition of the compound was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The FTIR and Raman spectroscopy at different temperatures confirm the existence of vibrational modes that correspond to the organic, inorganic and water molecular groups. Additionally, the UV-Vis diffuse reflectance spectrum was recorded in order to investigate the band gap nature. The measurements show that this compound exhibits a semiconducting behavior with an optical band gap of 2.66 eV. (C) 2016 Production and hosting by Elsevier B.V. on behalf of King Saud University.

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes ( 10 B and 11 B) compared to those with the natural distribution of boron (20 at% 10 B and 80 at% 11 B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10 BN than in 11 BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

Tellurium (IV) complexes with pyridine-2,6-dicarboxylate ligand were synthesized by slow evaporation from aqueous solutions yielding a new compound: [(C7H6NO4)2TeBr6·4H2O]. The structure of this compound was solved and refined by single-crystal X-ray diffraction. The compound is centrosymmetric P21/c (N°: 14) with the parameters a=8.875(5)Å, b=15.174(5)Å, c=10.199(5)Å, β=94.271° (5) and Z=2. The structure consists of isolated H2O, isolated [TeBr6]2− octahedral anions and (pyridine-2,6-dicarboxylate) [C7H6NO4]+ cations. The stability of the structure was ensured by ionic and hydrogen bonding contacts (N–H⋯Br and O–H⋯Br) and Van-Der Walls interaction. The thermal decomposition of the compound was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The FTIR and Raman spectroscopy at different temperatures confirm the existence of vibrational modes that correspond to the organic, inorganic and water molecular groups. Additionally, the UV–Vis diffuse reflectance spectrum was recorded in order to investigate the band gap nature. The measurements show that this compound exhibits a semiconducting behavior with an optical band gap of 2.66eV.

. The present paper is aimed to analyze the effects of sodium substitution on the magnetic entropy change between La_0.9Na_0.1SrMn_2O_5+δ and La_0.8Na_0.2SrMn_2O_5+δ polycrystalline samples. Evaluation of the potential magnetocaloric effects is sought through identifying the magnetic entropy change Δ S_M , which was basically determined from the magnetic field dependences of magnetization at different temperatures M(H,T) near T_C . Interestingly, the substitution of a small amount of Na in La_1-xNa_xSrMn_2O_5+δ nanocrystalline samples (with x=0.1 , 0.2 and 0.3) reduced the maximum magnetic entropy |Δ S_Max^M| from 2.2 J kg -1 K -1 (for x=0.1 to 0.8 Jkg -1 K -1 (for x=0.3 for a field change Δ H=5 T. The relative cooling power (RCP) decreases with increasing Na content reaching 53.13J kg^-1 for x=0.3 ( Δ H=5 T), respectively.

The present paper is aimed to analyze the effects of sodium substitution on the magnetic entropy change between \(La_{0.9}Na_{0.1}SrMn_{2}O_{5+\delta}\) and \(La_{0.8}Na_{0.2}SrMn_{2}O_{5+\delta}\) polycrystalline samples. Evaluation of the potential magnetocaloric effects is sought through identifying the magnetic entropy change \( \Delta S_{M}\), which was basically determined from the magnetic field dependences of magnetization at different temperatures \( M(H,T)\) near \( T_{C}\). Interestingly, the substitution of a small amount of Na in \(La_{1-x}Na_{x}SrMn_{2}O_{5+\delta}\) nanocrystalline samples (with \( x=0.1\), 0.2 and 0.3) reduced the maximum magnetic entropy \( \vert\Delta S_{Max}^{M}\vert\) from 2.2 J kg-1K-1 (for \( x=0.1\) to 0.8 Jkg-1K-1 (for \( x=0.3\) for a field change \( \Delta H=5\) T. The relative cooling power (RCP) decreases with increasing Na content reaching 53.13J kg^-1 for \( x=0.3\) (\( \Delta H=5\) T), respectively.

Layered compounds are stacks of weakly bound two-dimensional atomic crystals, with a prototypal hexagonal structure in graphene, transition metal dichalcogenides and boron nitride. This crystalline anisotropy results in vibrational modes with specific symmetries depending on the in-plane or out-of-plane atomic displacements. We show that polarization-resolved photoluminescence measurements in hexagonal boron nitride reflect the phonon symmetries in this layered semiconductor. Experiments performed with a detection on the sample edge, perpendicular to the c-axis, reveal the strong polarization-dependence of the emission lines corresponding to the recombination assisted by the three acoustic phonon modes. We elucidate the dipole orientation of the fundamental indirect exciton. We demonstrate evidence of the so-far missing phonon replica due to the optical out-of-plane phonon mode.

Na-doped brownmillerite oxides La1-xNaxSrMn2O6 (x = 0, 0.1, 0.2 and 0.3) were synthesized by the solid state reaction method at high temperature. The structural and magnetic properties of the samples were investigated by X-ray diffraction and magnetization experiments. The results from X-ray diffraction analysis showed that all samples were single phase and crystallized in the orthorhombic system, with space group Pnma. This structure can be described as an oxygen-deficient perovskite, resulting in a sequence of regular alternating layers of corner-sharing BO6 octahedra (O) and BO4 tetraedra (T) according to axis b. The results from magnetization versus temperature measurements in a magnetic applied field of 0.05 T indicated that the samples underwent a paramagnetic ferromagnetic transition with decreasing temperature. The Curie temperature T-c decreased from 365 to 345 K with Na content. An electronic phase separation model considering the formation of ferromagnetic clusters in the antiferromagnetic matrix was proposed to interpret the observed magnetization results for the Na-substituted samples. Overall, the present study provided an effective approach to achieve new functional materials based on naturally occurring layered systems such as La1-xNaxSrMn2O5+delta, for possible application in the spintronics industry. (C) 2015 Elsevier B.V. All rights reserved.

The present study investigates the effects of the substitution of iron in the B-site on the magnetic and magnetocaloric properties of the new brownmillerite LaSrMn2O5 powder. Our samples were synthesized using the conventional solid state reaction at high temperature. Magnetization measurements versus temperature in an applied magnetic field of 0.05T indicated that the samples underwent a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature TC decreased with more substitution of iron content. Arrott plots showed that all samples exhibited a second order magnetic phase transition. Magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. A large magnetocaloric effect was observed for x=0.1 and x=0.2 samples. The maximum magnetic entropy changes, |ΔSMMax|, obtained were 0.7Jkg−1K−1 and 0.75Jkg−1K−1 in magnetic field change of 5T for x=0.1 and x=0.2, respectively.

Zeolites exhibit an immense range of applications, such as those in the chemical industry, electronics and photonics among others. We used non-catalytic zeolites in an entirely new fashion. In fact, high pressure (0.5–26 GPa) chemical reactions of simple molecules in the pores of a pure SiO2 zeolite, silicalite were performed in the diamond anvil cell to obtain unique nano-composites with drastically modified properties. These materials were investigated using a combination of X-ray diffraction and optical spectroscopy. We will first show how silicalite can be easily filled by simple molecules at high pressures and how this filling deactivates pressure induced amorphization of the silica framework. We will then present a silicon carbonate phase synthesized by reacting silicalite and molecular CO2 that fills the nano-pores, at 18–26 GPa and 600–980 K; the resulting compound is slightly metastable at room pressure. On the other hand, a nano-composite, which is stable at room temperature and pressure, is obtained by photo-polymerizing ethylene at 0.5–1.5 GPa under UV (351–364 nm) irradiation in the channels of silicalite. The structure of this material is characterized by single polyethylene chains adapting very well to the confining channels, which significantly modifies the physical properties of the silicalite framework. These findings may pave the way to the high pressure synthesis of a unique generation of technological materials.

The crystal structure of lithium–ammonium hexabromotellurate[(NH4)0.63Li0.37]2TeBr6, has been determined by X-ray single crystal analysis at room temperature. The space group is Fm 3¯ m, with a = 10.7200(12) Å. Differential scanning calorimetry reveals three anomalies at 195, 395 and 498 K. Below 195 K the phase transition leads to a tetragonally distorted structure. This low temperature phase shows an anti-ferrorotative displacement ofTeBr62- octahedra with a tilt angle 6 °. The title compound has an anti-fluorite-type arrangement ofNH4+/Li+ and octahedralTeBr62- anions.

Iron doped brownmillerite oxides LaSrMn2-xFexO5 (0 <= x <= 0.5) have been prepared as pure powders by a conventional solid state reaction and studied by X-ray powder diffraction, scanning electronic microscope and Mossbauer spectroscopy. Rietveld analysis of X-ray diffraction patterns confirms that all samples crystallize in the orthorhombic system with Pnma space group and are isotypic with the Ca2Fe1.039Mn0.962O5 phase. Cell parameters and crystallite size show an anomaly around x = 0.2 which is explained by the partial substitutions of Mn2+ and Mn3+ by Fe3+ and small amounts of Fe4+. A detailed analysis of the M"ssbauer spectra for all compounds measured at room temperature shows that Fe3+ ions are located in distorted octahedral and tetrahedral sites. The environment and oxidation states of Mn and Fe are determined by bond valence sum calculations and the results for Fe are compared to the results from the Mossbauer study. (C) 2013 Elsevier B. V. All rights reserved.

In this work we probe the structural properties of amorphous hydrogenated carbon thin films prepared by plasma-enhanced chemical vapor deposition in a low pressure inductively coupled plasma using X-ray reflectometry in order to study the effect of varying the ion energy on the density of these films. The ion energy is varied by varying the RF power used to bias the substrate. It is shown that a very low ion energy is already sufficient to obtain a dense diamond-like carbon (DLC) film, in contrast with other deposition techniques where much higher ion energies are required to obtain a dense DLC film. The results of this study are corroborated by Raman spectroscopy and ellipsometry measurements. The X-ray reflectometry data analysis is detailed in order to highlight some methodological problems encountered during the data fitting which could lead to an incorrect interpretation of the measured curves.

Charge flipping can be routinely used for solving small-molecule structures measured at atomic resolution. It is shown by benchmark tests that its performance is at least equal to that of direct methods in terms of the speed of solution and the quality of the resulting structure. There are, however, cases where charge flipping may be more suitable than direct methods for solving structures, viz. where space-group symmetry is uncertain from the analysis of systematic extinct reflections. The latest charge-flipping enhancements, such as the minimum superposition map procedure and the AAR algorithm, are also tested against database structures and compared with the usual variant. Default parameters are determined which yield a maximum of solved structures.