Spectroscopic properties of K5Li2UF10

A new uranium (III) fluoro-complex of the formula K₅Li₂UF₁₀ has been synthesised and characterised by X-ray powder diffraction and electronic absorption spectra measurements. The compound crystallises in the orthorhombic system, space group Pnma, with a = 20.723, b = 7.809, c = 6.932 Å, V = 1121.89 ų, Z = 4 and is isostructural with its K₅Li₂NdF₁₀ and K₅Li₂LaF₁₀ analogous. The absorption spectrum of a polycrystalline sample of K₅Li₂UF₁₀ was recorded at 4.2 K in the 3500–45,000 cm⁻¹ range and is discussed. The observed crystal-field levels were assigned and fitted to parameters of the simplified angular overlap model (AOM) and next to those of a semi-empirical Hamiltonian, which was representing the combined atomic and one-electron crystal-field interactions. The starting values of the AOM parameters were obtained from ab initio calculations. The analysis of the spectra enabled the assignment of 71 crystal-field levels of U³⁺ with a relatively small r.m.s. deviation of 37 cm⁻¹. The total splitting of 714 cm⁻¹ was calculated for the ⁴I_9/2 ground multiplet.     

A theoretical investigation of C5

Large-scale CEPA-1 calculations have been carried out for linear C₅, a molecule of substantial interest to combustion processes and astrochemistry. The equilibrium bond lengths are predicted to be 1.289 Å (outer CC bond) and 1.283 Å (inner CC bond), with an accuracy of 0.002 Å. The calculated ν₃ band origins of 2161 cm⁻¹ (105 CGTO basis) and 2137 cm⁻¹ (150 CGTO basis) are in good agreement with the experimental value of 2169 cm⁻¹. This band has an extremely large transition moment of 0.74 D. The less intense stretching fundamental ν₄ (μ=0.18 D) is predicted to occur at 1478 ± 10 cm⁻¹. Predictions for the totally symmetric stretching and the bending vibrational frequencies (in cm⁻¹) are 2008 (1σ_g⁺), 792 (2σ_g⁺), 570 (1π_u), 209 (1π_g) and 119 (2π_u).     

Synthesis and crystal structures of La3MgBi5 and LaLiBi2

Two new ternary bismuthides, La₃MgBi₅ and LaLiBi₂, have been prepared by solid-state reactions of the corresponding pure metals in welded niobium tubes at high temperature. Their structures have been established by single-crystal X-ray diffraction studies. La₃MgBi₅ crystallizes in the hexagonal space group P6₃/mcm (No.193) with cell parameters of , , , and Z=2. LaLiBi₂ belongs to tetragonal space group P4/nmm (No.129) with cell parameters of , ,, and Z=2. The structure of La₃MgBi₅ is of the ‘‘anti’’ Hf₅Sn₃Cu type, and features 1D linear Bi⁻ anionic chains and face-sharing [MgBi_6/2]⁷⁻ octahedral chains. The structure of LaLiBi₂ is isotypic with HfCuSi₂, and is composed of 2D Bi⁻ square sheets and 2D LiBi layers with La³⁺ ions as spacers. Band calculations indicate that both compounds are metallic.     

V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。     

The crystal structure of Sc2Ru5B4

The crystal structure of Sc₂Ru₅B₄ has been determined by single-crystal X-ray analysis. Sc₂Ru₅B₄ crystallizes in the primitive monoclinic space group $\text{P2}\text{m}$ with a = 9.983(6), b = 8.486(4), c = 3.0001(3)Å, γ = 90.01(7)°, Z = 2. Deviations from the orthorhombic space group Pbam-D⁹_2h are small but significant. Intensity measurements were obtained from a four-circle diffractometer. The structure was solved by Patterson methods and refined by full matrix least-squares calculation. $\text{R =}\text{∑|ΔF|}\text{∑|F}{}_0\text{|}\text{= 0.036}$ for an asymmetric set of 863 independent reflections (|F₀|>2σ(F₀)). The crystal structure is characterized by two different types of boron atoms: (a) isolated borons B(1) and B(3) in distorted trigonal Ru-prisms with tetrakaidekahedral metal coordination: 6Ru + 3Sc, and (b) boron atoms B(2) and B(4) with a pronounced tendency to form boron pairs (B(2)-B(2) = 1.86 Å, B(4)-B(4) = 1.89 Å); the metal coordination of these boron atoms is 6Ru + 2Sc. Sc atoms have a coordination number of 17 consisting of 10Ru + 2Sc + 5B. The crystal structure of Sc₂Ru₅B₄ is a pentagon layer structure (Ru, B atoms) with a 4.3.4.3²-secondary layer of Sc atoms. The structure is furthermore related to the structure types of Ti₃Co₅B₂ and CeCo₃B₂. From powder photographs Sc₂Os₅B₄ is isotypic. No superconductivity was observed for Sc₂(Ru, Os)₅B₄ down to 1.5 K.     

Twinned crystal structure and compressibility of TlTeVO5

The high-pressure behavior of TlTeVO₅ has been investigated in situ using single-crystal X-ray diffraction in a diamond anvil cell. This material is structurally stable at least to 7.11 GPa, the highest pressure reached in this study. TlTeVO₅ is twinned both at ambient and high pressures (Pna2₁, Z=4). The twinning law relating the two individuals is equivalent to a rotation of approximately 3° around the direction. Within errors, no changes in the orientation of the two individuals are observed as a function of pressure. The refined twin volume fractions do not change within estimated standard deviations, either.The material is the most and the least compressible along the c and a axes, respectively. The P-V data could be fitted by a Murnaghan equation of state with B₀=32(1) GPa, V₀=504.4(4) Å³, and B′=7.97(43). The most important effect of pressure is the increase of the coordination numbers for the Tl and Te atoms. The Tl-O distance nearly parallel to the [001] direction is the most sensitive structural feature to pressure, resulting in the anisotropic compressibility. The long Te-O distances decrease, while the short ones are constant or even become slightly longer. Such a pressure-induced change of the coordination is interpreted as due to increasing uniformity of the oxygen atoms surrounding the cations and to decreasing activity of the electron lone pairs. The change is accompanied by an increase of the pseudosymmetry of the structure with respect to the centrosymmetric space group Pnna.     

Preparation and characterization of mono-cyclopentadienylvanadium dihalide bis-phosphine complexes; crystal structure of (η5-C5H5)VCL2(PMe3)2

Mono-cyclopentadienyl complexes CpVX₂(PR₃)₂ and Cp′VX₂ (PR₃)₂ (Cp = η⁵- C₅H₅; Cp′ = η⁵-C₅H₄Me; R = Me, Et; X = Cl, Br) have been prepared by reaction of VX₃(PR₃)₂ with CpM (M = Na, T1, SnBuⁿ3, 1/2 Mg) or Cp′Na. Attempts to prepare analogous complexes with other phosphine ligands, PPh₃, PPh₂ Me, PPhMe₂, Pcy₃, DMPE and DPPE failed. Reduction of CpVCl₂(PEt₃)₂ with zinc or aluminium under CO (1 bar) offers a simple method for the preparation of CpV(CO)₃(PEt₃). The crystal structure of the trimethylphosphine complex CpVCl₂(PMe₃)₂ is reported.     

Spectroscopic studies of the AlCl3 · NH3 complex

A normal coordinate analysis for the AlCl₃ · NH₃ complex is performed. Calculations for a hypothetical complex with a planar AlCl₃ ligand are included. A deviation from planarity is found in the realistic complex. Force fields for free NH₃ and AlCl₃ molecules are employed in the construction of an initial approximate force field. The theory of kinematic coupling is used to study the frequency shifts from free to complexed ligands. A final force field is developed so as to reproduce exactly a set of observed frequencies from the literature. Calculations on mean amplitudes and perpendicular amplitude correction coefficients are reported.     

The crystal structure of the cation-disordered phase (Tl0.75Pb0.25)4Cl5

The 3 : 1 compound in the TlClPbCl₂ system crystallizes in the noncentrosymmetric space group P4₁2₁2 (D₄⁴) or its enantiomorph P4₃2₁2 D₄⁶). Lattice constants are a = 8.450(1)Å and c = 14.927(1)Å. Single-crystal X-ray diffraction data were collected using AgKα radiation. The structure was determined by analysis of Patterson and difference Fourier syntheses. Least-squares refinement of 41 parameters with 402 unique data converged with R_w = 0.036. In the structure the 12 Tl(I) and 4 Pb(II) ions are disordered over two eightfold sites. The formula is therefore appropriately written as (Tl_0.75Pb_0.25)₄Cl₅. A difference in size of the two positions suggests a preferential concentration of Pb(II) in the smaller site. The disordering of aliovalent cations together with a three-dimensional network of face-sharing polyhedra of cations surrounding the anions of the structure suggests (Tl_0.75Pb_0.25)₄Cl₅ as a particularly favorable case for enhancement of chloride ion conductivity by doping with TlCl. Irregularities in the coordination polyhedra about the cations can be explained by the presence of stereochemically active lone-pair electrons of the cations. The structure of (Tl_0.75Pb_0.25)₄Cl₅ is similar to that of the alloy Zr₅Si₄.     

Enthalpies of polymerisation of SbF5, NbF5 and TaF5

The enthalpies of polymerisation of SbF_5(g), NbF_5(g) and TaF_5(g) have been estimated from molecular weight data to be ?18.5, ?25.9 and ?25.7 kJ mol^?1 respectively assuming mixtures of monomer and tetramer. Estimates of the entropy changes have also been made.     

The crystal chemistry of L-Ta2O5 and related structures

Single crystals of a new form of L-Ta₂O₅ with a 19×b superstructure have been synthesised by flux growth. The phase is most likely stabilised by the incorporation of a small amount of lithium (0.14 wt% Li) from the flux. The phase has C-centred monoclinic symmetry with , (), , γ=90.00(1)°. The structure was refined in space group C112/m to R₁=0.044 for 814 unique reflections with F>4σ(F). The structure can be described as comprising chains of edge-shared TaO₇ pentagonal bipyramids that are regularly folded at (010) planes to give sinusoidal chains along [010]. These chains are interconnected along [100] and [001] by corner sharing, creating inter-chain regions that are occupied by isolated TaO₆ octahedra and pairs of corner-shared octahedra. A comparison with published data for high-quality refinements of related structures has led to the development of a general model that can explain the structural chemistry variations in the known L-Ta₂O₅-related structures. A shorthand notation is presented for representing the structures, based on the sequence along [010] of the interchain octahedra.     

Synthesis and crystal structure of [CODRh(SC6F5)]2

The metathetical reaction of Pb(SC₆F₅)₂ with the halogen bridged compounds [L RhCl]₂ where L are chelating dienes, afforded the chalcogen bridged analogs. Subsequent reactions with a variety of ligands including phosphines, arsines, sulfides and selenides, have shown important differences between sulphur and halogen bridged complexes, attributable to the fluorinated moiety. Some of these reactions will be discussed and the crystal structure of [COD Rh(SC₆F₅)]₂ will be described.     

Synthesis and crystal structure of the novel Pb5Sb2MnO11 compound

The new Pb₅Sb₂MnO₁₁ compound was synthesized using a solid-state reaction in an evacuated sealed silica tube at 650°C. The crystal structure was determined ab initio using a combination of X-ray powder diffraction, electron diffraction and high-resolution electron microscopy (a=9.0660(8)Å, b=11.489(1)Å, c=10.9426(9)Å, S.G. Cmcm, R_I=0.045, R_P=0.059). The Pb₅Sb₂MnO₁₁ crystal structure represents a new structure type and it can be considered as quasi-one-dimensional, built up of chains running along the c-axis and consisting of alternating Mn⁺²O₇ capped trigonal prisms and Sb₂O₁₀ pairs of edge sharing Sb⁺⁵O₆ octahedra. The chains are joined together by Pb atoms located between the chains. The Pb⁺² cations have virtually identical coordination environments with a clear influence of the lone electron pair occupying one vertex of the PbO₅E octahedra. Electronic structure calculations and electron localization function distribution analysis were performed to define the nature of the structural peculiarities. Pb₅Sb₂MnO₁₁ exhibits paramagnetic behavior down to T=5 K with Weiss constant being nearly equal to zero that implies lack of cooperative magnetic interactions.     

Structure of ten-layer orthorhombic Ba5Fe5O14 (BaFeO2.8) determined from single crystal X-ray diffraction

The structure of the mixed-valent Ba₅Fe₅O₁₄ (BaFeO_2.8), prepared using a molten KOH-Ba(OH)₂ flux, has been determined using single crystal X-ray diffraction. Ba₅Fe₅O₁₄ forms twinned crystals with the orthorhombic space group Cmcm, a=5.7615(8), b=9.9792(14) and c=24.347(3) Å, Z=4. The structure, which is closely related to the 10H BaFeO_2.65 perovskite, is composed of two oxygen-deficient BaO₂ layers and eight BaO₃ layers with a (hchhc)₂ stacking sequence, where h and c denote hexagonal or cubic layers. A displacement of barium and oxygen atoms in the BaO₂ layers from hexagonal special positions lowers the symmetry from hexagonal to orthorhombic. This combination of stacking and vacancies creates trimers of face-sharing FeO₆ octahedra pillared by dimers of corner-sharing FeO₄ tetrahedra. The Fe⁴⁺ atoms are located in the center of the trimer and in the tetrahedral sites. The magnetism of Ba₅Fe₅O₁₄, investigated using SQUID magnetometry, is characteristic of a strongly coupled antiferromagnet.     

High-pressure synthesis and crystal structure of the lithium borate HP-LiB3O5

The new lithium borate HP-LiB₃O₅ was synthesized under high-pressure/high-temperature conditions of 6 GPa and 1050 °C in a multianvil press with a Walker-type module. The compound crystallizes in the space group Pnma (no. 62) with the lattice parameters a=829.7(2), b=759.6(2), and c=1726.8(4) pm (Z=16). The high-pressure compound HP-LiB₃O₅ is built up from a three-dimensional network of BO₄ tetrahedra and BO₃ groups, which incorporates Li⁺ ions in channels along the b-axis. Band assignments of measured IR- and Raman spectra were done via quantum-mechanical calculations. Additionally, the thermal behavior of HP-LiB₃O₅ was investigated.     

Spectroscopic studies of polymorphs of AlPO4 and SiO2

IR spectra of basic polymorphic forms of AlPO₄, measured at different temperatures, are presented. Diffuse reflectance spectroscopy has been used for high temperature measurements. According to the crystal structures of different AlPO₄ forms by means of factor group analysis, a number of modes and their activities have been determined. An attempt to assign bands to specific normal vibrational modes has been undertaken, comparing spectra of subsequent forms of AlPO₄ with each other. The obtained results have been discussed with regard to data referring to various isomorphous polymorphic forms of SiO₂, comparing, respectively, cristobalite with phosphocristobalite, berlinite with quartz, and phosphotridymite with tridymite (M. Handke and W. Mozgawa, Vib. Spectrosc. 5 (1993) 75; M. Handke, W. Mozgawa and M. Rokita, Michrochim. Acta [Suppl] 14 (1997) 511). Differences and similarities have been shown for the spectroscopic data and thus for structures of AlPO₄ and SiO₂.     

Phase diagram and infrared-spectral investigation of the 2TeO2 · V2O5-Na2O · V2O5 · 2TeO2 system

The phase diagram of the 2TeO₂ · V₂O₅-Na₂O · V₂O₅ · 2TeO₂ system is studied by X-ray diffraction, ir spectroscopy, and DTA. A new compound with a composition of Na₂O · 3V₂O₅ · 6TeO₂ is established. The ir spectra of the alkaline trivanadates are interpreted. They are considered as structural analogs of the new phase. As a result of this comparison, the postulate is made that the main structural units in the Na₂O · 3V₂O₅ · 6TeO₂ compound are V₂O₈ groups, while tellurium is present both in the TeO₃ and TeO₄ groups. Contrary to the crystal phases, in glasses the transition from VO₅ toward VO₄ does not proceed through the formation of new structural units of vanadium; but rather a gradual transition of the structure is observed with a change in the composition from 2TeO₂ · V₂O₅ to Na₂O · V₂O₅ · 2TeO₂.     

Synthesis of SF5benzene (SF5C6H5) by the SF5halide method

Several significant and useful syntheses of pentafluorothiobenzene (SF₅C₆H₅) from SF₅halides (SF₅X, X=Cl, Br) and cyclohexene or derivatives of cyclohexene are presented.     

Synthesis and crystal structure determination of yttrium ultraphosphate YP5O14

The crystal structure of monoclinic YP₅O₁₄ (space group C2/c, a=12.919(2) Å, b=12.796(4) Å, c=12.457(2) Å, β=91.30(1)°, Z=8) has been refined from single-crystal X-ray diffraction data. Full-matrix least-squares refinement on F² using 2249 independent reflections for 183 refinable parameters results in a final R value of 0.027 (ωR=0.069). The structure is isotypic with HoP₅O₁₄. This structure is built up from infinite layers of PO₄ tetrahedra linked through isolated YO₈ polyhedra. The three-dimensional cohesion of the framework results from Y-O-P bridges. This crystal structure refinement leads to the calculated X-ray diffraction powder pattern of this monoclinic polymorph, which has been the starting point of a thorough study of the solid-state synthesis of this ultraphosphate. This investigation further leads to a better outstanding of features observed during the synthesis of powdered samples. The thermal behavior of this ultraphosphate has been studied by DTA and TGA analyses. The infrared and Raman spectroscopic characterizations have been carried out on polycrystalline samples. The luminescence properties of the Eu³⁺ ion incorporated in the monoclinic C2/c polymorph of YP₅O₁₄ as local structural probe show that in YP₅O₁₄: 5% Eu³⁺ sample, the Eu³⁺ ions are distributed over the two Y³⁺ crystallographic sites of C₂ symmetry of this structure.     

The Na2O-SrO-B2O3 diagram in the B-rich part and the crystal structure of NaSrB5O9

The subsolidus phase relations in the B-rich part of the ternary system, Na₂O-SrO-B₂O₃, are investigated by the powder X-ray diffraction method. Four ternary compounds: NaSrBO₃, NaSr₄B₃O₉, Na₃SrB₅O₁₀ and NaSrB₅O₉ were found in it, the two lasts are new. NaSrB₅O₉ crystallizes in the monoclinic space group P2₁/c, with the lattice parameters a=6.4963(1) Å, b=13.9703(2) Å, c=8.0515(1) Å, β=106.900(1)°. Na₃SrB₅O₉ is also monoclinic, space group C2, a=7.290(1) Å, b=13.442(2) Å, c=9.792(1) Å, β=109.60(1). NaSrB₅O₉ is isostructural with another pentaborate NaCaB₅O₉, and its structure was refined by Rietveld method based on the structural model of NaCaB₅O₉. The fundamental building units are [B₅O₉]³⁻ anionic groups, forming complex thick anionic sheets, extending parallel to the ac plane. The Na and Sr atoms are all eight-coordinated with O atoms, forming trigonal dodecahedra. The [NaO₈] polyhedra are distributed between the B-O sheets, while the [SrO₈] polyhedra located in the sheets and connect with each other by edges to form infinite chains along the c-axis.