Distribution de la densite des electrons de valence dans Cu2As

The distribution of valency electron density in Cu₂As (C38) has been determined by Fourier synthesis using as coefficients the values ΔF = F_obs ? F_core (F_core corresponds to the structure factors of the inner orbitals). The bonding between the pyramidal-site copper atoms and the arsenic atoms is exposed, as well as the bonding between tetrahedral-site and pyramidal-site copper atoms.The structural evolution of the unit cell from the Cu₂Sb-type (C38) to the Fe₂P-type (C22) and Co₂P-type (C23) can be related to the metal-metalloid interaction. This interaction mainly involves the pyramidal-site metal atoms in the Cu₂Sb-type, and the tetrahedral-site metal atoms in the Fe₂P- and Co₂P-types.     

Synthesis and properties of BF2- & PO2-complexes of mono meso-heterocycle substituted 25-oxasmaragdyrins and derivatives

BF₂- and PO₂-smaragdyrins containing one five membered heterocycle such as pyrrole, thiophene and furan at one of the meso-position of corresponding 25-oxasmaragdyrins were synthesized by treating the appropriate mono meso-heterocycle substituted 25-oxasmaragdyrin with BF₃.OEt₂ and POCl₃ respectively in CH₂Cl₂ under mild reaction conditions. All macrocycles were thoroughly characterized by HR-MS and 1D and 2D NMR spectroscopy. The presence of a five membered heterocycle in place of a six membered aryl group significantly alters the electronic properties of the smaragdyrin macrocycle as reflected in their spectral and electrochemical properties. The meso-pyrrole BF₂-smaragdyrin was subjected to a Vilsmeier-Haack reaction to prepare meso-(α-formyl pyrrolyl) BF₂-smaragdyrin which was subsequently used to prepare meso-(α-dipyrromethanyl pyrrolyl) BF₂-smaragdyrin. The further use of meso-heterocycle substituted BF₂- and PO₂-oxasmaragdyrins was demonstrated by treating meso-pyrrolyl BF₂-smaragdyrin with pentafluorobenzaldehyde in CHCl₃ under mild acid catalysed conditions to afford an unusual dipyrromethanyl bridged BF₂-smaragdyrin dyad which exhibits excellent photophysical properties.     

Synthesis, Structures, and Thermal Expansion of the La2W2−xMoxO9 Series

The La₂W_2−xMo_xO₉ series has been synthesized by the ceramic method. An alternative synthesis using microwave radiation is also reported. La₂W₂O₉ has two polymorphs and the low-temperature phase (α) transforms to the high-temperature form (β) at 1077°C. The influence of the W/Mo substitution in this phase transition has been investigated by DTA. The β structure for x≥0.7 compositions can be prepared as single phase at any cooling rate. The β phase for 0.3≤x≤0.7 compounds can be prepared as single phase by quenching, whereas a mixture of α and β phases is obtained by slow cooling. The W/Mo ratio in both coexisting phases is different with the β-phase having a higher Mo content. The x=0.1 and 0.2 compounds have been prepared as mixtures of phases. The room temperature structure of β-La₂W_1.7Mo_0.3O₉ has been analyzed by the Rietveld method in P2₁3 space group. The final R-factors were R_WP=9.0% and R_F=5.6% with a structure similar to that of β-La₂Mo₂O₉. Finally, the thermal expansion of both types of structures has been determined from a thermodiffractometric study. The thermal expansion coefficients were 2.9×10⁻⁶ and 9.7×10⁻⁶°C⁻¹ for α-La₂W₂O₉ and β-La₂W_1.2Mo_0.8O₉, respectively.     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .     

Synthesis and characterization of 2-phosphonoethanesulfonic acid and a barium-hydrogenphosphonatoethanesulfonate — BaH(O3P-C2H4-SO3)

Following the strategy of using polyfunctional phosphonic acids for the synthesis of new metal phosphonates, the organic linker molecule 2-phosphonoethanesulfonic acid, H₂O₃P-C₂H₄-SO₃H (1) (H₃L), was synthesized and characterized in detail. The acid was used in a high-throughput (HT) investigation of the system BaCl₂/H₃L/NaOH/H₂O. The HT experiments comprising 48 individual hydrothermal reactions were performed to systematically investigate the influence of pH of the starting mixture as well as the molar ratio Ba²⁺: H₃L. Only two reaction products were observed: small amounts of BaCO₃ under basic conditions and BaH(O₃P-C₂H₄-SO₃) (2). For compounds 1 and 2 the crystal structures were determined from single-crystal X-ray diffraction data (H₂O₃P-C₂H₄-SO₃H: trigonal, P3₂, a=814.58(1), c=861.20(2) pm, Z=3, R1=0.0254, wR₂=0.0758 for I>2σ(I); BaH(O₃P-C₂H₄-SO₃): orthorhombic, Ibam, a=953.39(19), b=855.55(17), c=867.82(17) pm, Z=4, R1=0.0162, wR₂=0.0417 for I>2σ(I)). The structure of H₃L (1) is stabilized exclusively by strong hydrogen bonds. Compound 2 is built up by chains of edge sharing BaO₈ polyhedra. These chains are connected to a three-dimensional network by the -CH₂CH₂- linker of the ligand. Thermogravimetric investigation of compound 2, as well as IR spectra of 1 and 2 are presented.     

Ternary rare-earth alumo-silicides—single-crystal growth from Al flux, structural and physical properties

A number of rare-earth alumo-silicides (R-Al-Si) have been synthesized from the corresponding elements by high-temperature reactions, carried out in excess of aluminum to serve as a flux. Under these experimental conditions, large single crystals of all R-Al-Si ternary phases were readily produced. The crystal structures these ternaries adopt were studied by means of powder and single-crystal X-ray diffraction and were classified as follows: (1) the early rare-earths (R=La, Ce, Pr, Nd, Sm, Gd) yield RAl_xSi_2−x, x∼1, non-stoichiometric ternary derivatives of the body-centered α-ThSi₂-type; (2) the late rare-earths (R=Tb, Dy, Ho, Er, Tm) form stoichiometric R₂Al₃Si₂ compounds that crystallize in the C-centered monoclinic Y₂Al₃Si₂-type; (3) the divalent Eu and Yb produce EuAl₂Si₂ and YbAl₂Si₂ with the trigonal CaAl₂Si₂-type, whereas the last lanthanide element, Lu, forms LuAlSi with C-centered orthorhombic YAlGe-type. These structural trends are reviewed, and the evolution of the basic physical properties such as magnetism, heat capacity and electrical resistivity when moving across the series is described in detail.     

Stereocontrolled palladium(0)-catalyzed preparation of unsaturated azidosugars: an easy access to 2- and 4-aminoglycosides

The palladium-catalyzed substitution of alkyl 4,6-di-O-acetyl-α-d-erythro-hex-2-eno-pyranosides using NaN₃ as the nucleophile gave predominantly the corresponding alkyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-2-enopyranosides in the presence of Pd(PPh₃)₄. However, alkyl 6-O-acetyl-4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides were obtained as the major products using Pd(PPh₃)₄ as the catalyst in the presence of dppb as the added ligand. Conversely, alkyl 6-O-(tert-butyldimethylsilyl)-4-O-methoxycarbonyl-2,3-dideoxy-α-d-hex-2-enopyranosides gave exclusively alkyl 4-azido-6-O-(tert-butyldimethylsilyl)-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides in the presence of Pd₂(dba)₃/PPh₃ as the catalyst and Me₃SiN₃ as the nucleophile. The bis-hydroxylation followed by hydrogenation of ethyl 4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranoside afforded the corresponding 4-amino-α-d-mannopyranoside, when propyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-3-enopyranoside gave the 2-amino-α-d-altropyranoside under the same conditions.     

Infrared spectra of the ammonium ion in ammonium hexavanadate (NH4)2V6O16

The infrared bands of the NH⁺₄ and ND⁺₄ groups in (NH₄)₂V₆O₁₆ and its deuterated analogue can be assigned with a fair amount of certainty at 90 K under the space group P2₁/m(C²_2h). The ND stretching modes of isotopically dilute NH₃D⁺ ions in the crystal are in agreement with the predicted splitting into C_s, C_s and C₁(2) components. The frequencies, shapes and temperature dependence of these modes suggest that both normal and bifurcated hydrogen bonds are formed. The latter closely resembles corresponding bonds in NH₄VO₃, but the normal hydrogen bonds are not as strong as the similar bonds in NH₄VO₃. This can be expected as NH⁺₄ ions are dynamic in character in (NH₄)₂V₆O₁₆ and remain so down to temperatures of 90 K.     

Synthesis and fluorescence properties of covalently linked homo- and hetero-porphyrin dyads containing meso-tolyl porphyrin and meso-furyl porphyrin sub-units

Three porphyrin building blocks with N₄, N₃S and N₂S₂ cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N₄-N₄, N₃S-N₃S, N₂S₂-N₂S₂, N₄-N₃S, N₄-N₂S₂ and N₃S-N₂S₂ containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form.     

Alkali metal and ammonium peroxodiphosphates: Preparation,vibrational and 31P NMR spectra,and the X-ray crystal structure of ammonium peroxodiphosphate dihydrate (NH4)4[P2O8]·2H2O

Improved preparations are reported of M₄[P₂O₈]·nH₂O (M = K, n = 0; M = Na, n = 18; M = Li, n = 4; M = NH₄, n = 2), as well as their ³¹P NMR spectra; the vibrational spectra for Li₄[P₂O₈]·4H₂O are described. The X-ray crystal structure of (NH₄)₄[P₂O₈]·2H₂O has been determined, its unit cell is monoclinic with a = 15.336(2), b = 9.893(2), c = 8.789(1) Å, β = 91.28(2)° (at 20°C), space group C2/c, and Z = 4. The structure has been refined to R = 0.034. The peroxodiphosphate anion consists of two phosphate tetrahedra linked by a peroxide bond.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

Photoelectrochemical properties of MoO2 thin films

Thin MoO₂ films were electrodeposited on a selenium pre-deposited SnO₂|glass plate. The photoelectrochemical properties of MoO₂ films were investigated in 0.1 M Na₂SO₄ solution by the ultraviolet–visible spectrophotometry, linear sweep voltammetry, and altering current impedance measurement techniques. It was found that under illumination with the incident light of λ?=?366 nm, the photo response of the MoO₂|SnO₂|glass electrode resulted from the MoO₂ layer, while the SnO₂ layer served as a sink for photogenerated charge carriers. The MoO₂ film exhibited n-type conductivity. A schematic band structure diagram of MoO₂ in 0.1 M Na₂SO₄ solution was constructed. The flat band potential (E _fb), the donor concentration (N _D), the photogeneration current efficiency depended on MoO₂ film thickness. The [Fe(CN)₆]^4?/3? redox PEC cell with MoO₂|SnO₂|glass plate as a photoanode was constructed. Power output characteristics such as the open circuit voltage (V _OC), short circuit current (I _SC), the fill factor (FF), and the light-to-electrical conversion efficiency (η) were determined. The maximum light-to-electrical conversion efficiency exhibited by the PEC cell was 0.94 %.     

Properties of MgB2 bulks after combined doping with Fe and C by adding Iron(II) lactate (C6H10FeO6)

Bulk MgB₂ doped with C and Fe was prepared by using the solid state sintering method with C₆H₁₀FeO₆ as dopant. The phase composition, microstructure, and superconducting properties were studied. X-ray diffraction (XRD) shows the presence of iron after the doping. The addition of C₆H₁₀FeO₆ increases the a- and c-axis parameters of MgB₂, as evidenced by the shifting of the (100) and (002) peaks to a lower angle on the XRD patterns. Fe atoms were distributed uniformly, as shown by the field emission scanning electron microscope images, while the magnetization of the sample was dominated by the signals from the MgB₂ superconductor, although the iron-containing materials also contributed a minor amount of magnetization. The residual resistivity ratio was decreased as the C₆H₁₀FeO₆ doping level increased. The critical temperature also decreased with increased doping level, as did the critical current density, J_c. The doping also caused decreases in the irreversibility field, H_irr, and the upper critical field, H_c2. The decrease in H_c2 and H_irr, together with the harmful effects from impurity phases such as MgO is the reason for the decrease in J_c.     

Lattice distortions in layered type arsenides LnTAs2 (Ln=La-Nd, Sm, Gd, Tb; T=Ag, Au): Crystal structures, electronic and magnetic properties

The lanthanide coinage-metal diarsenides LnTAs₂ (Ln=La, Ce-Nd, Sm; T=Ag, Au) have been reinvestigated and their structures have been refined from single crystal X-ray data. Two different distortion variants of the HfCuSi₂ type are found: PrAgAs₂, NdAgAs₂, SmAgAs₂, GdAgAs₂, TbAgAs₂, NdAuAs₂ and SmAuAs₂ crystallize as twofold superstructures in space group Pmcn with the As atoms of their planar layers forming zigzag chains, whereas LaAgAs₂, CeAgAs₂ and PrAuAs₂ adopt a fourfold superstructure (space group Pmca) with cis-trans chains of As atoms. The respective atomic positions can be derived from the HfCuSi₂ type by group-subgroup relations. The compounds with zigzag chains of As atoms exhibit metallic behaviour while those with cis-trans chains are semiconducting as measured on powder pellets. The majority of the compounds including 4f elements show antiferromagnetic ordering at T_N<20 K.     

Nickel deficiency in RENi2-xP2 (RE=La, Ce, Pr). Combined crystallographic and physical property studies

Large single crystals from RENi_2-xP₂ (RE=La, Ce, Pr) were synthesized from the pure elements using Sn as a metal flux, and their structures were established by X-ray crystallography. The title compounds were confirmed to crystallize in the body-centered tetragonal ThCr₂Si₂ structure type (space group I4/mmm (No. 139); Pearson's symbol tI10), but with a significant homogeneity range with respect to the transition metal. Systematic synthetic work, coupled with accurate structure refinements indicated strong correlation between the degree of Ni-deficiency and the reaction conditions. According to the temperature dependent dc magnetization measurements, LaNi_2-xP₂ (x=0.30(1)), as expected, is Pauli-like paramagnetic in the studied temperature regime, while the Ce-analog CeNi_2-xP₂ (x=0.28(1)) shows the characteristics of a mixed valent Ce³⁺/Ce⁴⁺ system with a possible Kondo temperature scale on the order of 1000 K. For three different PrNi_2-xP₂ (x?0.5) samples, the temperature and field dependence of the magnetization indicated typical local moment 4f-magnetism and a stable Pr³⁺ ground state, with subtle variations of T_C as a function of the concentration of Ni defects. Field-dependent heat capacity data for CeNi_2-xP₂ (x=0.28(1)) and PrNi_2-xP₂ (x=0.53(1)) are discussed as well.     

Synthesis, structure and reactivity of binuclear metal-metal bonded molybdenum(V) and tungsten(V) thioselenohalides: Molecular structure of Mo2(μ-S2)2Cl6(SeCl2)2 and W2(μ-S2)2Cl6(SeCl2)2

Thioselenohalide complexes Mo₂(μ-S₂)₂Cl₆(SeCl₂)₂ (I), Mo₂(μ-S₂)₂Br₆(SeBr₂)₂ (II), and W₂(μ-S₂)₂Br₆(SeBr₂)₂ (III) were synthesized by the reactions of corresponding metal halides or carbonyls or molybdenum metal with excesses of S₂ X ₂+Se₂ X ₂ mixtures. The complex W₂(μ-S₂)₂Cl₆(SeCl₂)₂ (IV) was obtained by an exchange reaction between (III) and excess of Se₂Cl₂. Coordination of the neutral SeX ₂ ligands to thiohalidesM ₂(μ-S₂)₂ X ₆ results in higher thermal stability, and suggests the possibility to synthesize SeX ₂ complexes of the unstable parent tungsten thiohalides. An unusual oxidative addition reaction of (I) was detected: {fx27-1} Both (I) and (IV) were characterized by X-ray crystal structure analysis. They are isostructural and form discrete molecules. Bridging S ₂ ^2? ligands are coordinated perpendicularly to the metal-metal bond;d(M?M)=2.8066 Å and 2.793 Å for I and IV, respectively. Nonequivalence of chlorine atoms which are bound to the metal atom, relate to nonequivalence of halogen atoms in the complexesM ₂(μ?S₂)₂ X ₈ ^2? . Chlorine atomstrans to SeCl₂ ligands form short bonds with the metal; the corresponding³⁵Cl NQR frequency is increased. The selenium dichloride ligand is ambidentate. The selenium atom binds as a donor to the metal and as an acceptor to two chlorine atoms which are also bound covalently to the same metal atom.     

Studies on the reactions of fluoroalkanesulfonyl azide with aromatic compounds

The thermal decomposition reactions of fluoroalkanesulfonyl azides R_fSO₂N₃ (1) in the presence of various substituted benzene X_nC₆H_6−n [X: CH₃ (n=1, 2, 4, 6), OCH₃ (n=1, 2), C₆H₅CH₂ (n=1), F, Cl, Br] were studied in detail. The N-aryl fluoroalkanesulfonyl amides [R_fSO₂NHC₆H_5−nX_n] were produced as the major products. The ortho/para ratio resembled that of an electrophilic aromatic substituted reaction. An ionic π- or σ-complex was postulated as the intermediate for these reactions.     

[Cu(mim)4]2[α-Mo8O26] – A layer-type octamolybdate framework

By reaction of (NH₄)₆Mo₇O₂₄·4H₂O, Cu(NO₃)₂·2.5H₂O and 1-methylimidazole (mim) under hydrothermal conditions the novel copper molybdate [Cu(mim)₄]₂[α-Mo₈O₂₆] is obtained in the form of blue, rectangular-shaped crystals. The title compound crystallizes with monoclinic lattice symmetry in the space group P2₁/n. The predominant structural feature of the title compound is a two-dimensional framework that is constituted by [α-Mo₈O₂₆]^4?octamolybdate units as framework nods and the copper complex [Cu(mim)₄]²⁺ as a linker. In addition to single-crystal structure analysis [Cu(mim)₄]₂[α-Mo₈O₂₆] is characterized by powder diffraction as well as by FT-IR and UV–vis spectroscopy.     

Synthesis, crystal structure, and magnetic properties of the manganate La2Ca2MnO6(O2) related to the hexagonal perovskite-type structure

The compound La₂Ca₂MnO₆(O₂) has been synthesized from La₂Ca₂MnO₇ heated at 1123 K under high pressure (4 GPa) with KClO₃ as oxygen source. The crystal structure has been refined from X-ray powder data in the space group. The unit-cell parameters are a=5.6335(2) Å and c=17.4879(8) Å. Perpendicular to the c-axis, the structure is built up by the periodic stacking of two close packed [LaO₃] layers separated by a layer of composition [Ca₂O₂] containing (O₂)²⁻ peroxide ions. This oxide belongs to the family of compounds formulated as [A′₂O_2−δ][A_nB_n−1O_3n] for n=2 and δ=0. It is the first member of the series where the thickness of the perovskite slab corresponds to one [BO₆] (B=Mn) octahedron. The structural relationships with La₂Ca₂MnO₇ are discussed and the magnetic properties show that in both phases manganese is tetravalent.