Conformational analysis of n-perfluoroalkanes: n-C4F10 and n-C6F14

The vibrational spectra of n-C₄ F₁₀ and n-C₆F₁₄ were investigated in the vapour, liquid and solid phases and the equilibrium conformations of these molecules were determined. Different solid-phase spectra were recorded by changing deposition and/or annealing conditions.     

Syntesis and Crystal Structure of Cs2Nb6Br5F12: A Nb6 Cluster Compound with a One-Dimensional Nb6Br5F7F6 Unit Connection

The synthesis and the crystal structure of Cs₂Nb₆Br₅F₁₂ containing octahedral niobium clusters are presented in this work. This bromofluoride is based on a Nb₆Lⁱ₁₂F^a₆ (L=Br and F) unit and crystallizes in the orthorhombic system (space group, Cccm; Z=4; a=9.2446(2) Å, b=13.6256(3) Å, and c=17.1665(4) Å; R=0.0241). Fluorine and bromine are randomly distributed on the inner ligand positions, Lⁱ, that edge-bridge the Nb₆ cluster whereas fluorine fully occupies the apical positions (L^a). The units are linked to each other by apical ligands leading to an original one-dimensional unit connection. The cesium atoms are statistically distributed on several sites that describe parallel channels along the [1 0 0] direction. The influence of fluorine ligands upon the stabilization of this structure type as well as the structural relationships with Ba₂Zr₆Cl₁₇(B), Nb₆F₁₅, and NaMo₆Cl₁₃ will be evidenced and discussed.     

NH_4Y_3F_(10)多孔纳米晶的制备及其在MALDI-TOF-MS中的应用(英文)

利用水热法合成出NH4Y3F10多孔纳米晶。由于Y3+离子的激发态能量可以转移给具有较高振动能的有机分子,因此这些多孔纳米晶可以作为基质辅助激光解析电离飞行时间质谱的基体材料,用于检测小分子和聚乙二醇。通过与商品化的基体材料(CHCA、DHB)对比,证明NH4Y3F10多孔纳米晶是一种性能优异的基体材料。这种新型基体材料已经成功应用于有机分子、小肽、C60、缺氧诱导因子(HIFs)和聚乙二醇的分子量的检测,显示出这种基体材料具有广泛的应用前景。     

Tieftemperatur-flüssigphase-fluorierung von (C6F5)2Te: Bildung von (C6F5)2TeF2, (C6F5)2TeF4 und (C6F11)2TeF4 [1]

(C₆F₅)₂Te reacts with elemental fluorine step by step to form the tellurium fluorides (C₆F₅)₂TeF₂, (C₆F₅)₂TeF₄ and (C₆F₁₁)₂TeF₄, which can be isolated in pure states. The intermediates (C₆F_11?2n)₂TeF₄ (n = 1,2) are detected spectroscopically. (C₆F₅)₂TeF₂ is also formed from the reaction of (C₆F₅)₂Te with XeF₂. The preparations, properties and ¹⁹F n.m.r. spectra of these new compounds are discussed, the mass and vibrational spectra are described.     

A widely varying range of products in reactions of C6F5BrF2, C6F5IF2, and C6F5IF4 with Lewis acids of different strength

The relative fluoride donor ability: C₆F₅BrF₂ > C₆F₅IF₂ > C₆F₅IF₄ was outlined from reactions with Lewis acids of graduated strength in different solvents. Fluoride abstraction from C₆F₅HalF₂ with BF₃·NCCH₃ in acetonitrile (donor solvent) led to [C₆F₅HalF·(NCCH₃)_n][BF₄]. The attempted generation of [C₆F₅BrF]⁺ from C₆F₅BrF₂ and anhydrous HF or BF₃ in weakly coordinating SO₂ClF gave C₆F₅Br besides bromoperfluorocycloalkenes C₆BrF₇ and 1-BrC₆F₉. In reactions of C₆F₅IF₂ with SbF₅ in SO₂ClF the primary observed intermediate (¹⁹F NMR, below 0 °C) was the 4-iodo-1,1,2,3,5,6-hexafluorobenzenium cation, which converted into C₆F₅I and 1-IC₆F₉ at 20 °C. The reaction of C₆F₅IF₄ with SbF₅ in SO₂ClF below −20 °C gave the cation [C₆F₅IF₃]⁺ which decomposed at 20 °C to C₆F₅I, 1-iodoperfluorocyclohexene, and iodoperfluorocyclohexane. Principally, the related perfluoroalkyl compound C₆F₁₃IF₄ showed a different type of products in the fast reaction with AsF₅ in CCl₃F (−60 °C) which resulted in C₆F₁₄. Intermediate and final products of C₆F₅HalF_n−1 (n = 3, 5) with Lewis acids were characterized by NMR in solution. Stable solid products were isolated and analytically characterized.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Dehalogenative aromatization of perchlorofluoroalicyclic compounds C6Cl6F6, C10Cl8F8 and C5Cl4F5N in the vapour phase or in solution

Dehalogenation of perhalogenated cyclohexanes C₆Cl₆F₆, 1-azacyclohexenes C₅Cl₄F₅N and bicyclo[4.4.0]dec-1(6)-enes C₁₀Cl₈F₈ in the vapour phase over iron filings at 350-500 °C and in solution with Zn and additivities (Cu, NiCl₂·6H₂O + bpy) at 80 °C (heterogeneous reaction) or with P(NEt₂)₃ at 20 °C (homogeneous reaction) was studied. In all cases, perfluoroarenes, chloroperfluoroarenes and dichloroperfluoroarenes (benzenes, naphthalenes and pyridines) were obtained in good overall yield.     

Preparation and characterization of Bi0.75Er0.25O1.5 and Bi0.75Er0.125Y0.125O1.5 nanocrystalline ceramics by SPS

Nanopowders of Bi_0.75Er_0.25O_1.5 and Bi_0.75Er_0.125Y_0.125O_1.5 were prepared by a reverse titration chemical coprecipitation method under controlled pH conditions. After calcination at 500 °C for 3 h, powders with grain size in the order of 10 nm were obtained. In order to keep the nanosize of grains, these powders were densified by spark plasma sintering. Samples with relative density higher than 96% were prepared in only 10 min up to 500 °C with an average grain size of 15 and 11 nm for Bi_0.75Er_0.25O_1.5 and Bi_0.75Er_0.125Y_0.125O_1.5, respectively. Impedance spectroscopy revealed slightly higher conductivity for the Bi_0.75Er_0.125Y_0.125O_1.5 composition compared to Bi_0.75Er_0.25O_1.5 nanoceramic, but performances remained lower than the corresponding Bi_0.75Er_0.25O_1.5 microcrystalline sample. However, mechanical properties of both nanocrystalline ceramics are improved when compared to microcrystalline samples.     

Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6

The synthesis, structure, and basic magnetic properties of Na₂Co₂TeO₆ and Na₃Co₂SbO₆ are reported. The crystal structures were determined by neutron powder diffraction. Na₂Co₂TeO₆ has a two-layer hexagonal structure (space group P6₃22) while Na₃Co₂SbO₆ has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co²⁺ and Te⁶⁺/Sb⁵⁺ ions in the ab plane such that the Co²⁺ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na₂Co₂TeO₆ and Na₃Co₂SbO₆ display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na₃Co₂SbO₆.     

Synthesis and characterization of sodium titanates Na2Ti3O7 and Na2Ti6O13

Na₂Ti₃O₇ and Na₂Ti₆O₁₃ were synthesized by sol-gel method in order to obtain pure phases. Different heat-treatments were applied on powders and pellets of these materials. The effects were studied by XRD, dilatometry, TGA-DTA, SEM and electrochemical impedance spectroscopy. Pure Na₂Ti₃O₇ was obtained at 973 K. Sintering at 1373 K caused a partial decomposition into Na₂Ti₆O₁₃. The Na₂Ti₃O₇ powder sintered at 1273 K showed polygonal microstructure. Na₂Ti₃O₇ pellets sintered at 1323 K for 10 h exhibited large structures. This latter microstructure decreased the electrical conductivity of Na₂Ti₃O₇. Pure Na₂Ti₆O₁₃ was obtained at 873 K. Sintering at 1073 K caused a partial decomposition into TiO₂ (rutile). Na₂Ti₆O₁₃ pellets sintered at 1323 K for 10 h exhibited common shrinkage behavior. This shrinkage process increased the electrical conductivity of this material. The presence of TiO₂ resulted in a oxygen partial pressure dependence of the electrical conductivity.     

The novel Cs4Nb6F8.5I3.5I6 octahedral niobium cluster fluoro-iodide: a step towards the Nb6F12 cluster core excision

The solid state synthesis of Cs₄Nb₆Fⁱ_8.5Iⁱ_3.5I^a₆ starting from Nb₆F₁₅ binary fluoride, as well as its crystal structure determined by X-ray single crystal diffraction, are presented in this work. This novel cluster compound is based on a Nb₆Iⁱ₃Fⁱ₆Lⁱ₃I^a₆ (L=F, I) discrete unit and crystallizes in the monoclinic system (space group C2/m; Z=4 ; a=10.4363(4) Å, b=18.1227(7) Å, c=19.5102(9) Å β=101.223(1)°, V=3619.5(3) Å³, R₁=0.057; wR₂=0.159). This halide is the first octahedral niobium cluster compound containing unshared terminal I^a ligands together with ordered μ₂-Iⁱ and μ₂-Fⁱ ligands on nine inner positions whilst the three last ones (Lⁱ) are slightly affected by a I/F random occupancy. The structural findings are discussed and compared with those of Nb₆F₁₅, Nb₆I₁₁, CsNb₆I₁₁ and the fluorochlorides and fluorobromides recently reported.     

A new efficient visible-light-driven photocatalyst Na0.5Bi1.5VMoO8 for oxygen evolution

A new visible-light-driven photocatalyst Na_0.5Bi_1.5VMoO₈ was developed by making a solid solution of BiVO₄ and (NaBi)_0.5MoO₄. The prepared powders were confirmed crystallizing in the tetragonal scheelite crystal structure by the XRD patterns and Raman spectra. Different from that of the tetragonal BiVO₄, Na_0.5Bi_1.5VMoO₈ showed a high activity for photocatalytic O₂ evolution under visible light irradiation, which is even better than that of monoclinic BiVO₄, a well-known efficient visible-light-driven photocatalyst. The mechanism of the improved activity of Na_0.5Bi_1.5VMoO₈ was discussed.     

Vibrational and calorimetric study of phase transitions in n-C6F14 and n-C8F18 crystals

Heat capacities of n-perfluorohexane and n-perfluorooctane were measured from 4.2 K to room temperature. One solid—solid transition is found for n-C₆H₁₄,two for n-C₈F₁₈. Spectra show that the molecules have the same conformations in the two forms of n-C₆F₁₄. Several isomers are present in the high-temperature forms of n-C₈F₁₈;thus transitions in this compound have order—disorder character.     

The crystal structure of Ca6Eu2Na2(PO4)6F2

The crystal structure of Ca₆Eu₂Na₂(PO₄)₆F₂ has been determined by single crystal X-ray diffraction. The unit cell constants are $\text{a = 9.385(2), c = 6.893(3)}\text{A}\text{?}$ and the space group is $\text{P6}{}_3\text{m}$. The structure was refined by normal full matrix least squares techniques. The final value of the refinement indicator is R = 0.065, based on 419 reflections.The structure of Ca₆Eu₂Na₂(PO₄)₆F₂ contains disordered cations in both the triangle and column positions. The occupation of the six triangle sites is $\text{1}\text{4}\text{Eu}$ and $\text{3}\text{4}\text{Ca}$ and of the four column sites $\text{1}\text{2}\text{Na}\text{,}\text{4}\text{10}\text{Ca}$, and $\text{1}\text{10}\text{Eu}$.     

Synthesis, structure and magnetic properties of Na6Co2O6

Na₆Co₂O₆ was synthesized via the azide/nitrate route by reaction between NaN₃, NaNO₃ and Co₃O₄. Stoichiometric mixtures of the starting materials were heated in a special regime up to 500°C and annealed at this temperature for 50 h in silver crucibles. Single crystals have been grown by subsequent annealing of the reaction product at 500°C for 500 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X-ray analysis of the crystal structure (, Z=1, a=5.7345(3), b=5.8903(3), c=6.3503(3) Å, α=64.538(2), β=89.279(2), γ=85.233(2)°, 1006 independent reflections, R₁=8.34% (all data)), cobalt is tetrahedrally coordinated by oxygen. Each two CoO₄ tetrahedra are linked through a common edge forming Co₂O₆^6- anions. Cobalt ions within the dimers, being in a high spin state (S=2), are ferromagnetically coupled (J=17 cm^-1). An intercluster spin exchange (zJ′=−4.8 cm^-1) plays a significant role below 150 K and leads to an antiferromagnetically ordered state below 30 K. Heat capacity exhibits a λ-type anomaly at this temperature and yields a value of 19.5 J/mol K for the transition entropy, which is in good agreement with the theoretical value calculated for the ordering of the ferromagnetic-coupled dimers. In order to construct a model for the spin interactions in Na₆Co₂O₆, the magnetic properties of Na₅CoO₄ have been measured. This compound features isolated CoO₄ tetrahedra and shows a Curie-Weiss behavior (μ=5.14 μ_B, Θ=−20 K) down to 15 K. An antiferromagmetic ordering is observed in this compound below 10 K.     

Perfluororganozink-verbindungen: darstellung und eigenschaften von (Rf)2Zn-komplexen (Rf = CF3, C2F5, C3F7, C6F5) [1]

A new method for the preparation of bis(perfluoroorgano) zinc compounds is described: CF₃I and C₆F₅I react with dialkylzinc in the presence of a Lewis base quantitatively to give (CF₃)₂Zn and (C₆F₅)₂Zn complexes, while the analogous reactions with C₂F₅I and iC₃F₇I do not yield the pure compounds. ¹H, ¹⁹F n.m.r, i.r. and Raman spectra are presented.     

Compressibilities of disordered fluoride pyrochlores NaCdZn2F7 and NaCaMg2F7

The compressibilities of disordered pyrochlores NaCaMg₂F₇ and NaCdZn₂F₇ (both , Z=8) have been studied with X-ray single-crystal and powder diffraction using diamond anvil cells to 6.5 and 9.0 GPa at room temperature, respectively. The compressibility data are fitted with the Murnaghan equations of state. The zero-pressure bulk modulus B₀ and the unit-cell volume at ambient pressure V₀ (for the fixed first pressure derivative of the bulk modulus B′=4.00) are equal to 83(2) GPa and 1107.12(1.33) Å³ for NaCdZn₂F₇ and to 83(5) GPa and 1079.29(2.62) Å³ for NaCaMg₂F₇. Upon decreasing the unit-cell volume, the positional x parameter of the F(2) atom increases in NaCdZn₂F₇ but is constant in NaCaMg₂F₇. In both cases, the (Na,Cd)F₈ and (Na,Ca)F₈ cubes become more regular and are softer than the ZnF₆ and MgF₆ octahedra, respectively. Both materials are structurally stable at least to the respective highest pressures reached in this study. These observations are compared to the high-pressure behavior of oxide pyrochlores.     

Composition of gas hydrates of CHClF2, CCl2F2 and SF6

Gas hydrates are forms of ice stabilized by the presence of molecules of gas occupying cavities in the solid water lattice. There are two common forms: structure I and structure II. The mean free diameters of the two types of cavities in structure I are about 5.0 and 5.8 angstroms. Very small gas molecules such as Xe or H₂S can occupy both. In the past it has been considered that gas molecules of larger diameter than 5.0 angstroms could not occupy the smaller cavities. It has now been shown through measurement of hydration numbers of CHClF₂ (diameter about 5.4 angstroms) under various pressures at 0°, that some of the small cavities are filled. This state of affairs also exists for CH₃Br. In structure II, the mean diameters of the two types of cavities are about 5.0 and 6.6 angstroms. Hydration numbers of SF₆ (diameter about 5.8 angstroms) and CCl₂F₂ (about 6.2 angstromsm) show that nearly all of the large cavities but essentially none of the small cavities are occupied.     

Xα scattered wave calculations of the ionisation energies of N3P3F6 and N4P4F8

Ionisation energies have been calculated for N₃P₃F₆ and N₄P₄F₈ with the overlapping sphere version of the Xα scattered wave method and with the inclusion of a vacacy sphere for the interior of each PN ring. Experimental energies are calculated to within 1 eV on average for both sets of calculations, but the spacings of the levels are reproduced better with the vacancy sphere model.     

Synthesis and molecular structures of heptafluoropropylated fullerenes: C70(n-C3F7)8, C70(n-C3F7)6O, and C70(C3F7)4

Ampoule reactions of C₇₀ with n- and i-C₃F₇I were carried out at 250-310 °C. Two step HPLC separations allowed the isolation of several C₇₀(n-C₃F₇)_4-8 and C₇₀(i-C₃F₇)₄ compounds. Crystal and molecular structures of C₇₀(n-C₃F₇)₈-V, C₇₀(n-C₃F₇)₆O, C₇₀(n-C₃F₇)₄, and three isomers of C₇₀(i-C₃F₇)₄ have been determined by X-ray crystallography using synchrotron radiation. Molecular structures of the new compounds were compared with the known examples and discussed in terms of addition patterns and relative energies of their formation.