Electronic charge distribution in the intermetallic compound MnHg

The Electron Density Distribution (EDD) of the Mn and Hg atoms in MnHg has been elucidated for the first time using the statistical approach MEM (Maximum Entropy Method). Reported powder X‐ray data have been used for the present analysis. Presently, MEM studies are gaining momentum because of the feasibility of mapping the refined electron densities with very high accuracy, well resolved and clear electron density distributions obtainable from this method, etc. Moreover, the MEM results resemble very nearly the true structure/electron densities unlike the conventional Fourier methods, which give biased information due to many reasons, the major one being the series termination error. In the present analysis, the bonding between Mn and Hg, and the electron content for different radii of the two atoms has been investigated. The thermal vibration of the two atoms has also been analyzed and reported. The thermal parameter of Hg has been more accurately determined than that of Mn, which is in consistent with the electron density distribution of the atoms.     

Schottky diode characteristics: Aluminium with 500 and 1000 Å thicknesses on p type WSe2 crystal

The conduction properties of Al‐p WSe₂ Schottky barrier diodes prepared identically but with different metal thickness are reported here. The p type WSe₂ semiconducting crystals used in the present study was grown by direct vapour transport technique. The current‐voltage characteristics of these diodes were analyzed from 140 K to 300 K on the basis of thermionic emission theory applying Gaussian distribution. Below 200 K, deviations were observed in barrier height, ideality factor and Richardson plot. Hence at lower temperatures, a model has been considered where the total current is assumed to be the sum of thermionic emission, generation recombination and tunneling components. The observed deviations in the diode parameters were successfully interpreted in terms of the contribution of these multiple charge transport mechanisms across the interface of the fabricated diodes. The diode with a thickness of 500 Å Al showed more homogeneous nature than with 1000 Å. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cd‐Doping Effects on The Properties of Polycrystalline α‐In2Se3 Thin Films

The X‐ray diffraction has revealed that the polycrystalline hexagonal structured α‐In₂Se₃ thin films grown at substrate temperature of 200 °C with the unit cell parameters a = 4.03 Å and c = 19.23 Å becomes polycrystalline hexagonal structured InSe with a unit cell parameters of a = 4.00 Å and c = 16.63 Å by Cd‐doping. The analysis of the conductivity temperature dependence in the range 300‐40 K revealed that the thermionic emission of charged carriers and the variable range hopping are the predominant conduction mechanism above and below 100 K, respectively. Hall measurements revealed that the mobility is limited by the scattering of charged carriers through the grain boundaries above 200 K and 120 K for the undoped and Cd‐doped samples, respectively. The photocurrent (I_ph) increases with increasing illumination intensity (F) and decreasing temperature up to a maximum temperature of ∼100 K, below which I_ph is temperature invariant. It is found to have the monomolecular and bimolecular recombination characters at low and high illumination intensities, respectively. The Cd‐doping increases the density of trapping states that changes the position of the dark Fermi level leading to the deviation from linearity in the dependence of I_ph on F at low illumination intensities.     

Synthesis and crystal structure investigation of pyridine‐2‐(3′‐mercaptopropanoic acid)‐N ‐oxide

Pyridine‐2‐(3′‐mercaptopropanoic acid)‐N ‐oxide (I), is a higher homologue of 1‐oxopyridinium‐2‐thioacetic acid (II) [1]. It crystallizes in monoclinic space group P2₁ with a = 9.2168(2) Å, b = 4.1423(2) Å, c = 11.3904(4) Å, β = 98.65(2)°, V = 429.93(3) ų and Z = 2. The least‐squares refinement gave residual index R = 0.024 for 1070 observed reflections. The introduction of an additional methylene group in (II) causes a flip in the carboxylic acid group of (I) that facilitates the molecules to align infinite antiparallel chains through strong C–H···O interactions. The molecules are interlinked by O–H···O hydrogen bonding across the chains and forming an infinite screw chain along y‐direction. The molecular packing is stabilized by O–H···O and C–H···O hydrogen bonding and π‐π electron interactions. This is an important facet of the crystal packing. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and structural study of 1-(N,N-diethylamino)-2,2-bis(2-nitrophenylthio)ethene

The synthesis, variable temperature NMR spectra, and crystal structures of two crystalline forms, 2a and 2b, of the enamine 1-(N,N-diethylamino)-2,2-bis(2-nitrophenylthio)ethene have been obtained. Both forms crystallize in the monoclinic space group P2₁/a. The two phases have similar molecular structures but possess different intermolecular C–H······O hydrogen bonding interactions. Both forms exhibit disorder within the NEt₂ fragment at 298 K: sufficient disorder persisted with 2a (orange needles) down to 100 K to make the geometric parameters pertaining to the enamine fragment unreliable. The disorder was effectively eliminated on cooling 2b down (red colored blocks) to 150 K. Cell dimensions for the 2a-phase are at 100 K: a = 11.1030(4) Å, b = 15.1325(7) Å, c = 12.4504(7) Å, β = 114.606(3)°, while for the 2b-phase at 150 K, a = 15.5206(4) Å, b = 7.6958(2) Å, c = 15.7137(3) Å, β = 92.580(7)°. The C–N bond length in the β-form at 150 K of 1.335(3) Å indicates considerable double bond character: the rotational barrier of the C–N bond in CDCl₃ was calculated to be 52.4 kJ mol^?1.     

Crystal structure and electrochemical property of one‐dimensional complex: [K(cis‐syn‐cis‐ dicyclohexyl‐18‐crown‐6)]2[Cu(mnt)2]

One metalorganic complex [K(cis‐syn‐cis‐ dicyclohexyl‐18‐crown‐6)]₂[Cu(mnt)₂] (mnt = maleonitriledithiolate) has been obtained by the reaction of dicyclohexyl‐18‐crown‐6 with K₂mnt and CuCl₂·2H₂O. The title complex has been characterized by elementary analysis, FT‐IR, UV‐Vis spectroscopy and x‐ray single crystal diffraction. The title complex crystallizes in the triclinic space group P1 with crystallographic data: a = 10.870(6) Å, b = 11.536(6) Å, c = 12.904(7) Å, α = 101.541(10)°, β = 110.573(9)°, γ = 99.441(9)°, V = 1435.2(13) ų, Z = 1, D_calcd = 1.350 g/cm³, F(000) = 615, R₁ = 0.0641, wR₂ = 0.1475. It displays one‐dimensional chain‐like structure formed by [K(cis‐syn‐cis‐ dicyclohexyl‐18‐crown‐6)]⁺ complex cations and [Cu(mnt)₂]^2‐ complex anions through N‐K‐N interactions. Its electrochemical behavior has also been studied by the cyclic voltammetry. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure and electrochemical behavior of a novel polyoxometalate [Ni(bpy)3]2[W4V2O19] with Lindqvist‐type structure

A novel polyoxometalate [Ni(bpy)₃]₂[W₄V₂O₁₉] (Ni₂V₂W₄) has been synthesized by the hydrothermal method and the structure determined by X‐ray crystallography. Ni₂V₂W₄ crystallizes in a trigonal system with space group R ‐3c (a = 15.8984 (5) Å, b = 15.8984 (5) Å, c = 43.855 (3) Å). In the structure of the compound, terminal and bridging oxygen atoms are bond to the metal centers by σ or π bonds. The W⁶⁺ and V⁵⁺ ions in isopolyanion [W₄V₂O₁₉]^4‐ statistically distribute over the six metal centers. Using cathodic adsorptive voltammetric method with a carbon paste electrode, the redox property and the electron transferring process were studied. The results show that electrochemical behavior about W(VI) and V(V) atoms give one‐electron, three‐electron and two‐electron reduction waves. Three successive oxidation waves are observed too. The compound was also characterized by thermal gravimetric analysis and IR spectra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of MIGe2(PO4)3 (MI – Na,K, Ag) from molten phosphate media

A number of NASICON‐related M^IGe₂(PO₄)₃ (M^I – Na, K, Ag) have been prepared using a high‐temperature solution method in the molten system M^I‐Ge‐P‐O (M^I – Na, K) based on the solubility data for GeO₂ at 1123 K for the Na‐P‐O system and 1173 K for the K‐P‐O one. The single crystals of AgGe₂(PO₄)₃ were obtained after crystallization of a melt with Ag/P = 1.4. It crystallizes in the trigonal system, space group R‐3, cell parameters a = 8.06340(1) Å, c = 21.8385(4) Å, Z = 6. The framework is built up from two GeO₆ units that are isolated from each other by PO₄ tetrahedra to form the main building block of the structure [Ge₂(PO₄)₃]⁻. Two types of silver cations M1 and M2 are found to have different coordination requirements shown by the bond valence sum calculations.     

Modifications of epitaxy in evaporated films by electric charge effects

Modifications of epitaxy in Ge, Si, CdS, β-Sn, and α-Fe films, 100–600 Å in thickness, evaporated onto air-cleaved and vacuum-cleaved (001) NaCl substrates under electron bombardment (∽10¹⁵ electrons/cm² sec, at 200–400 V) or an electric field (dc 100–300 V/cm) applied to the substrate surface were investigated by reflection electron diffraction, transmission electron microscopy and selected-area diffraction. Results indicated that epitaxial temperatures of Ge and Si films were considerably lowered, and a monocrystalline β-Sn film was produced by the application of electron bombardment. The application of electric field resulted in the formation of an epitaxial cubic CdS phase, and a single orientation in an α-Fe film. These results are discussed in terms of current speculation concerning the electric charge effects on alkali halide substrates.     

Carrier Scattering Mechanisms in GaS0.5Se0.5 Layered Crystals

Systematic dark electrical resistivity and Hall mobility measurements have been carried out in the temperature range 150‐400 K on n‐type GaS_0.5Se_0.5 layered crystals. The analysis of temperature dependent electrical resistivity and carrier concentration reveals the extrinsic type of conduction with a donor impurity level located at 0.44 eV, donor and acceptor concentrations of 3.4 ×10¹⁷ and 4.1×10¹⁶ cm^‐3, respectively, and an electron effective mass of 0.41 m₀. The Hall mobility is limited by the electron‐phonon short‐range interactions scattering at high temperatures combined with the ionized impurity scattering at low temperatures. The electron‐phonon short‐range interactions scattering mobility analysis reveals an electron‐phonon coupling constant of 0.25 and conduction band deformation potential of 5.57 eV/Å.     

Growth and XRD analysis of the diluted magnetic semiconductor Zn1‐xNixO

Diluted magnetic semiconductor compound Zn_1‐xNi_x O (x =0.01, 0.02, 0.03, 0.04 and 0.05) was prepared by sol‐gel method and characterized using powder XRD for the distribution of electrons and bonding in the unit cell. The electronic structural studies of this material were carried out by maximum entropy method (MEM) for the quantitative and qualitative measurement on the inclusion and the effect induced on bonding by Ni doping. The spatial arrangement of charge and the bonding behavior of this material were analyzed from 3D, 2D and 1D density distributions. The evidence for the addition of Ni in the host lattice of Zn is realized. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and crystal structure determination of 6,7‐dihydro‐2‐methoxy‐4‐(substituted)‐5H ‐benzo[6,7]cyclohepta[1,2‐b ]pyridine‐3‐carbonitrile

The compounds 6,7‐dihydro‐2‐methoxy‐4‐(4‐methylphenyl)‐5H ‐benzo[6.7]cyclohepta[1,2‐b ]pyridine‐3‐carbonitrile (compound IIIa) and 4‐(4‐chlorophenyl)‐6,7‐dihydro‐2‐methoxy‐5H ‐benzo[6,7]cyclohepta[1,2‐b ]pyridine‐3‐carbonitrile (compound IIIb) were synthesized and their structures have been determined from three dimensional X‐ray data using direct method and refined by full matrix least squares with anisotropic thermal parameters for non‐hydrogen atoms to conventional R(gt) of 0.036 and 0.038 for the two compounds respectively. For compound (IIIa) the crystals are monoclinic, space group C_c, with a=11.2909 (5) Å, b=17.7755(8) Å, c=9.1437(4) Å and β=95.428(3)°, while the crystals of the second compound (IIIb) are triclinic, space group P1, with a=8.7465(3)Å, b=10.3958(3)Å, c=10.9011(4)Å, α= 108.3870(10)°, β=101.3741(12)°, γ=97.9594(12)°. The molecular structure of the two compounds have nearly the same configuration, where the cyclohepta ring takes the boat shape and the methoxy and the carbonitrile groups are attached at the same position C₂ and C₈. The difference occurs only at the position C₄, where the substituent is methylphenyl for compound (IIIa) and chlorophenyl for the other. The bond lengths, valency angles and the hydrogen bonding were calculated and fully discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transport Properties of (NH4)2 CuCl4.2H2O Low Dimensional Single Crystals

The X‐ray diffraction and Infrared (IR) spectral studies of (NH₄)₂ CuCl₄.2H₂O single crystals reveals that these crystals contains tetragonal crystal structure with the unit cell dimensions of a = 7.58Å, c = 7.95Å, z= 2, β =90° and two water molecules in the unit cell. The temperature dependence of thermally stimulated depolarization current (TSDC) and dc electrical conductivity (σ) studies of this two‐dimensional (NH₄)₂ CuCl₄.2H₂O single crystal have been carried out in 77K–300K temperature region. The TSDC thermograph shows only one sharp peak at 248K with a peak current of 130nA, which is attributed to the Maxwell‐Wagner peak. The activation energy (U), relaxation time (τ) are calculated as 0.78eV and 3.44×10^‐15 s respectively. Dc electrical conductivity studies of these crystals show a first order phase transition at about 248K.     

Solvothermal syntheses and crystal structures of two 4‐heterocyclic acylpyrazolone complexes

Many explorations of transition metal (M)‐L system under solvothermal condition, have led to the syntheses of two new 4‐heterocyclic acylpyrazolone complexes [Co(L)₂(CH₃OH)₂] (HL = 1‐phenyl‐3‐methyl‐4‐(2‐furoyl)‐5‐pyrazolone) ( 1 ) and [Cr(L)₃] ( 2 ). Single‐crystal X‐ray analyses reveal that crystal structures of compound 1 and 2 are respectively orthorhombic, Pbca, a = 15.0378(6) Å, b = 9.8405(4) Å, c = 20.7321(8) Å, V = 3067.9(2) ų, Z = 8 and triclinic, P‐1, a = 10.7966(18) Å, b = 13.023(2) Å, c = 15.520(3) Å, α = 73.011(4)°, β = 84.884(4)°, γ = 70.267(4)°, V = 1964.3(6) ų, Z = 2. Complex 1 has a two‐dimensional (2D) network structure that is formed by O–H···N H‐bonding interactions. Complex 2 makes a one‐dimensional (1D) zigzag chain structure by intermolecular π···π interactions, which is further interlinked via C–H···N H‐bonding interactions to generate a 2D sheet, and then a three‐dimensional (3D) supramolecular network structure is further linked by intermolecular C–H···π interactions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High field effects in amorphous germanium

Measurements of high field current have been made on amorphous Ge (a-Ge) films over the temperature range from 100 to 300 K. Non-ohmic conduction in a-Ge occurs at electric fields greater than 1–2 × 10⁴ V/cm. Field dependence of the conductivity has been explained in terms of the enhanced emission probability of carriers from the screened coulombic trap centers. Assuming the optical dielectric constant for a-Ge films, the screening length of the trap centers and the density of states at the Fermi level are estimated to be 12 Å and ～6.1 × 10²⁰ cm^?3 eV^?1, respectively.     

Influence of photonic excitations on the electrical parameters of TlInS2 crystals

The photo‐excitation effect on the current transport mechanism in TlInS₂ crystals has been studied by means of dark and illuminated conductivity measurements. The temperature‐dependent electrical conductivity analysis in the temperature region of 110‐340 K revealed the domination of the thermionic emission and the thermally assisted variable range hopping (VRH) of charge carriers above and below 160 K, respectively. Above 160 K, the conductivity activation energies in the dark are found to be 0.28 and 0.15 eV in the temperature regions of 340‐240 K and 230‐160 K, respectively. In the temperature region of 110‐150 K, the dark variable range hopping analysis revealed a density of localized states of 1.99×10²² cm^–3eV^–1, an average hopping distance of 0.53 nm and an average hopping energy of 79.65 meV. When the sample was photo‐excited, the values of the conductivity activation energies, the density of localized states near the Fermi level and the average hopping energy were observed to decrease sharply with increasing illumination intensity. On the other hand, the average hopping distance increased with rising illumination intensity. Such behaviours were attributed to the Fermi level shift and/or trap density reduction by electron‐hole recombination. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystal and molecular structure of SnBr[N(SiMe3)2]3

The crystal structure of SnBr[N(SiMe₃)₂]₃ has been determined from three-dimensional X-ray diffraction data collected by counter methods. This compound crystallizes in the rhombohedral space groupR3c witha=11.970(3) Å, α=99.06(3)°, andZ=2forD _c> =1.37 g cm^?3. The finalR value was 0.027 based on 608 independent observed reflections. The molecule lies on a crystallographic three-fold axis which contains the Sn and Br atoms. The bromine atom is covalently coordinated to the tin atom at a Sn-Br separation of 2.519(2) Å. The three nitrogen atoms complete the bonding to tin with an Sn-N bond length of 2.056(7) Å.     

An X-ray diffraction refinement of the crystal structure of natural apophyllite

The crystal structure of apophyllite (Andersberg — GDR), with a = 8.966(2), c = = 15.767(1) Å, P4/mnc, z = 2, Q = 2.35 gm · cm⁻³, has been refined (R = 0.035) by least squares with 976 reflections collected with a diffractometer. Apophyllite is a sheet structure with the bringing Si O bond lengths 1.6236 Å, while the non-bridging bond length Si O(3) is 1.5843 Å. The two independent Si O Si angles are 140.09, 140.76 degrees. The mean Si O bond length is 1.6138 Å. As it was not possible to locate unequivocally the H-atoms with the X-ray data, the interpretation of the of water in the structure was based on the charge balance approach of DONNAY and ALLMAN . Assuming that the fluorine ion is bonded to calcium ion (Ca-F = = 2.416 Å) and to H3 atom (F-H3 = 0.9145(1) Å) and water molecule hydrogen bonded to silicate framework. The average bond distances O-H are 0.962(2) Å and angle 105.24(1)°.     

Crystal structure and electrochemical properties of the supramolecular compound [Himi]6[As2Mo18O62]·11H2O

A supramolecular compound, [Himi]₆[As₂Mo₁₈O₆₂]·11H₂O ( 1 ) (imi = imidazole), has been synthesized and characterized by single crystal X‐ray analysis, IR spectra, thermal gravimetric analysis, electrochemical and elemental analysis. The crystals are monoclinic, P 2(1)/n, a = 14.9529(8) Å, b = 20.9521(11) Å, c = 25.2464(13) Å, β = 93.8130(10)°, V = 7892.1(7) ų, Z = 4. X‐ray diffraction indicated that protonated imidazole cation and polyanion were linked together through electrostatic interactions and intermolecular forces (hydrogen bonding). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray mapping in heterocyclic design: V. Diffractometric study of the crystal structure of 2-hydroxy-3-trifluoracetylimidazo[1,2-a]pyridine hydrochloride at 180 K

The crystal structure of 2-hydroxy-3-trifluoracetylimidazo[1,2-a]pyridine hydrochloride C₉H₆F₃ClN₂O₂ is determined by X-ray diffraction at 180 K. The structure is solved by the direct method and refined by the least-squares procedure to R = 0.0296. The alternation of bond lengths in the six-membered fragment of the molecule is observed. One of the specific features of the crystal structure is the formation of a system of the N-H?Cl^? (N?Cl, 3.09 Å; N-H, 0.83 Å; H?Cl, 2.33 Å; and N-H?Cl, 153°) and O-H?Cl^? (O?Cl, 2.87 Å; O-H, 0.95 Å; H?Cl, 1.92 Å; and O-H?Cl, 178°) hydrogen bonds in which the chlorine atoms are related to the reference atom by different symmetry transformations.