Mechanism of the emergence of the photo-EMF upon silicon liquid crystal–single crystal contact

The effect light has on a silicon liquid crystal–single crystal contact at different temperatures of the surface doping of silicon, and when BaTiO₃ nanoparticles are added to the composition of a liquid crystal, is studied. The mechanism of the emergence of the photo-EMF in the liquid crystal–silicon structure is explained.

     

Electrochemical intercalation of O2− in CuAlO2 single crystal and photoelectrochemical properties

The delafossite CuAlO₂ single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹. The chronoamperometry showed an electrochemical O²⁻ insertion with a diffusion coefficient D _303K of 3.3 × 10⁻¹⁸ cm² s⁻¹. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol⁻¹. CuAlO₂ is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and a holes density (N _A) of 10¹⁶ cm⁻³. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration depth (12 μm).     

Thermal, UV and FTIR spectral studies of urea–thiourea zinc chloride single crystal

A single crystal of urea–thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterised by TG–DTA, UV and FTIR spectral analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage mass loss between 200 and 750 °C. DTA curve shows exothermic peaks supporting the formulated decomposition pattern in this temperature range. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea–thiourea zinc chloride crystals. Detailed structural analysis of the compound is under progress.     

Preparation and characterization of a novel single crystal of Th(Ⅳ) with cucurbit[6]uril

One single crystal based on Th~(4+) and cucurbit[6]uril(CB6) in nitric acid aqueous solutions was synthesized by slow evaporation method. The single crystal was characterized by elemental analysis,single crystal X-ray diffraction, XRD, FT-IR and TGA. The complexed cation of Th~(4+) is a ten coordinated structure, in which the central thorium ion is coordinated by six monodentate water molecules and two bidentate nitrates. While CB6, as a second-sphere ligand, coordinates with the water molecules of [Th(NO_3)_2(H_2 O)_6]~(2+) through the formation of hydrogen bonding. Two other nitrate ions act as the counter anions. Besides, there are two free water molecules in the crystal system. The formation of the Th~(4+)-CB6 complex can contribute to the study of the coordination of CB6 and the extraction of Th~(4+) in HNO_3 system     

Synthesis and crystal structure of β-hexanitrohexaazaisowurtzitane

A polycyclic caged compound with high strain—hexanitrohexaazaisowurtzitane (HNIW)—has been synthesized via a three-step reaction: condensation, hydrogenolysis debenzylation and nitrolysis, starting with benzylamine and glyoxal. HNIW is the most powerful high energy density compound (HEDC) ever tested. β-HNIW possesses a caged structure consisting of two five-membered rings and one six-membered ring with a nitro group attached to each of the six bridging nitrogens. The nitro group lies basically within a plane. The lengths of C—C bonds of β-HNIW range from 0. 156 nm to 0.159 nm, 0.002–0.005 nm longer than the sp³ C-C bond. The β-HNIW’s crystal belongs to orthorhombic system and space groupPca2₁ with parameters:a = 0.9670 (2),b = 1.1616 (2),c = 1.3032 (3) nm;V = 1.4638(5) nm³,Z = 4; D_c = 1.989 g/cm³ and D_m = 1.982 g/cm³. Project supported by the Advanced Research Funds (12060451867) from the Commission of Science and Technology for National Defence.     

Synthesis and crystal structure of β-hexanitrohexaazaisowurtzitane

A polycyclic caged compound with high strain——hexanitrohexaazaisowurtzitane (HNIW)——has been synthesized via a three-step reaction: condensation, hydrogenolysis debenzylation and nitrolysis, starting with benzylmine and glyoxal. HNIW is the most powerful high energy density compound (HEDC) ever tested. β-HNIW possesses a caged structure consisting of two five-membered rings and one six-membered ring with a nitro group attached to each of the six bridging nitrogens. The nitro group lies basically within a plane. The lengths of C--C bonds of β-HNIW range from 0.156 nm to 0.159 nm, 0.002--0.005 nm longer than the sp~3 C-C bond. The β-HNIW's crystal belongs to orthorhombic system and space group Pca2_1 with parameters: a=0.9670 (2), b=1.1616 (2), c=1.3032 (3) nm; V=1.4638(5) nm~3, Z=4; D_c=1.989 g/cm~3 and D_m=1.982 g/cm~3.     

X-ray crystal structure of tribenzylaluminum · diethyl etherate

The crystal structure of tribenzylaluminum · diethyl etherate has been determined by single crystal X-ray diffraction techniques. It crystallizes in the monoclinic system, space group P2₁, with unit cell dimensions of a 8.106(1), b 15.098(2), c 10.037(1) Å, β 111.02(1)°, V 1146.6(3) ų, and Z = 2. The final full matrix least-squares refinement on 1139 data gave R_F 3.8 and R _wF 5.2%. The compound is similar to other organoaluminum adducts yielding a four coordinate aluminum atom with average AlC distances of 1.986 and an AlO distance of 1.901(4) Å which is significantly shorter than the AlO distance observed in other ether adducts. The average CAlC and CAlO angles are 113 and 106°, respectively.     

Polarised vibrational spectra of Bet·H3AsO4 single crystal: Part II. Low temperature studies

Polarised infrared transmission (4000–400 cm⁻¹) and Raman (3500–10 cm⁻¹) spectra of betaine ortho-arsenic acid crystal ((CH₃)₃NCH₂COO·H₃AsO₄; abbreviated as BA) were measured at various temperatures and analysed. The temperature evolution of the hydrogen bonds stretching vibrations (νOH) apparent in the polarised infrared transmission spectrum (||c axis) shows that the O(4)⋯O(4) hydrogen bonds being almost parallel to the spontaneous polarisation direction plays an important role in the ferroelectric phase transition. New experimental proofs for the deformation of the AsO₄ group in H₃AsO₄ acid and rotation of betaine molecules related to the ordering of the hydrogen bonds at the ferroelectric phase transition were found.     

Synthesis and mesomorphic properties of trifluorobenzoate liquid crystal

Four series of trifluorobenzoate liquid crystals have been synthesized. Their phase transition temperatures have been also measured by texture observation in a polarizing microscope and confirmed by DSC. The influence of the lateral fluoro-substitution and triple bond has been also discussed.     

Does Gd@C82 have an anomalous endohedral structure? Synthesis and single crystal X-ray structure of the carbene adduct

We report here the results on single crystal X-ray crystallographic analysis of the Gd@C82 carbene adduct (Gd@C82(Ad), Ad = adamantylidene). The Gd atom in Gd@C82(Ad) is located at an off-centered position near a hexagonal ring in the C2v-C82 cage, as found for M@C82 (M = Sc and La) and La@C82(Ad). Theoretical calculation also confirms the position of the Gd atom in the X-ray crystal structure.     

Formation and structure of a Pd(I) complex: The crystal structure of (C5H8N2S)4Pd(II)Cl2·H2O and the ESR study of the X-irradiated single crystal

The crystal structure of tetrakis(tetrahydro-1H-pyrimidine-2-thione)palladium(II) dichloride monohydrate has been determined. X-irradiation of a single crystal, at liquid-nitrogen temperature, leads to formation of a paramagnetic species whose ESR study has been performed at 77 K. The g and ¹⁰⁵Pd-hyperfine tensors have been obtained. Their eigenvalues are consistent with the trapping of a d⁹ ion. Comparison of the eigenvectors with the crystallographic bond directions shows that the paramagnetic species results from the reduction of Pd(II) to Pd(I) which remains at the center of a square formed by four sulphur atoms.     

Structure and properties of lanthanide catalysts: the crystal and molecular structure of SmBr3·4iPr(OH)

The crystal of the title compound is monoclinic (space group C2/c), with a = 22,067(17), b = 10.111 (10), c = 16.886(11) Å,=142.95(5)°, and Z = 4. Its structure is based on the packing of SmBr₃·4iPr(OH) (iPr = isopropyl) molecules. The metal atom is coordinated by three Br ions and by the oxygen atoms of the four iPr(OH) ligands. The coordination polyhedron is a distorted pentagonal bipyramid of C2 symmetry, with Sm and one of the Br atoms lying on the twofold axis of crystallographic symmetry. Polymerization experiments are reported showing that the activity of the catalytic system based on the title complex is much lower than that shown by systems based on similar Nd complexes. A possible rationalization of this fact is given in terms of the oxidation capacity of the rare-earth ions.     

Synthesis, crystal growth, and structure of Ta3Al2CoC—An ordered quarternary cubic η-carbide and the first single crystal study of a η-carbide

Single crystals of the new carbide Ta₃Al₂CoC were synthesised from metallic melt and characterized by XRD, EDX and WDX measurements. The crystal structure of Ta₃Al₂CoC was refined on the basis of single crystal data (cF112, Fd3¯m, a=11.6153(13) Å, Z=16, 169 reflections, 13 parameters, R₁(F)=0.0315, wR₂(F²)=0.0857). Ta₃Al₂CoC belongs to the great family of η-carbides or which are important components for cermets. Its crystal structure is characterised by TaC₆-octahedra, which are connected to a three-dimensional net. Co and Al have icosahedral surroundings without contacts to C-atoms. All positions show full occupation. Ta₃Al₂CoC represents the first η-carbide with a complete structure refinement on the basis of single crystal data.     

Synthesis and crystal structure of the lithium perrhenate monohydrate LiReO4·H2O

A new monohydrate of lithium perrhenate LiReO₄·H₂O was prepared by dehydration of LiReO₄·1.5H₂O at room temperature. The single crystals of LiReO₄·H₂O were obtained by crystallisation from the isoamyl acetate solution of LiReO₄·1.5H₂O. The structure of monohydrate (a=5.6674(4), b=10.771(1), c=7.4738(7) Å, β=102.422(7)°, R₁=0.0414, space group P2₁/a, Z=4) is built up from LiO₃(H₂O)₂ trigonal bipyramids and ReO₄ tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO₄ are discussed.     

Growth of germanium dioxide single crystals with α-quartz structure and investigation of their crystal structure,optical, elastic,piezoelectric, dielectric and mechanical properties

The optimal growing conditions for α-GeO₂ single crystals and Si-substituted α-GeO₂ crystals have been found. The quality and sizes of the grown crystals of α-GeO₂ have allowed studying their morphology, internal constitution and measuring their piezoelectric, dielectric, elastic and other physical properties.     

Syntheses and crystal structures of transition metal complexes of 1,1′-bisacetylacetoferrocene

Bimetallic complexes 3a–e of 1,1′-bisacetylacetoferrocene (2) were prepared by reactions of transition metal acetates M(OAc)₂ (M?=?Co²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Zn²⁺) with the 2 in refluxing methanol. The X-ray structures of the cobalt and manganese complexes were determined showing very similar centrosymmetric macrocyclic dimeric frameworks constituted by linkage of two Co²⁺ or Mn²⁺ ions and two 1,1′-diacetoacetylferrocene units with two additional methanols as bridges dividing this macrocyclic framework into two small cyclic subunits. The UV-Vis spectra and electronic properties were also studied.     

Molecular structure of imidazolate bridged binuclear zinc complex and its single crystal ESR spectra doped with bridged Cu—Zn complex

The X-ray crystal structure of [(dtma)ZnImZn(dtma)]ClO_4·2.5H_2O (Hdtma=4-Diethyl-enetriamineacetic acid) was determined.The crystal is of orthorhombic,space group Pbcn with a-14.104(5),b=14.897(5),c=25.384(9),and Z=8.The least-square refinement of the structureleads to conventional R factor of 0.066.The magnetic properties of [(dtma)CulmZn(dtma)]CIO_4·2.5H_2Owere investigated.From the single crystal ESR spectra of Zn—Im—Zn dimer doped withCu—Im—Zn complex,the anisotropic g and A tensors and electronic spin-density of the Cu—Zncomplex are obtained and the bonding nature of Cu is discussed.     

First-principles study of the crystal and electronic structures of α-tetragonal boron

The crystal and electronic structures of α-tetragonal (α-t) boron were investigated by first-principles calculation. Application of a simple model assuming 50 atoms in the unit cell indicated that α-t boron had a metallic density of state, thus contradicting the experimental fact that it is a p-type semiconductor. The presence of an additional two interstitial boron atoms at the 4c site made α-t boron semiconductive and the most stable. The cohesive energy per atom was as high as those of α- and β-rhombohedral boron, suggesting that α-t boron is produced more easily than was previously thought. The experimentally obtained α-t boron in nanobelt form had about two interstitial atoms at the 8i sites. We consider that the shallow potential at 8i sites generates low-energy phonon modes, which increase the entropy and consequently decrease the free energy at high temperatures. Calculation of the electronic band structure showed that the highest valence band had a larger dispersion from Γ to Z than from Γ to X; this indicated a strong anisotropy in hole conduction.