Hydrolysis reactions of transition metal fluorides in liquid hydrogen fluoride: Oxonium salts with Nb,Ta and W

The hydrolysis reactions of the hexafluorides of molybdenum and tungsten, the pentafluorides of niobium and tantalum and the tetrafluorides of zirconium and hafnium have been studied in liquid hydrogen fluoride. The following new compounds have been isolated and characterized: H₃O⁺WOF^-₅, H₃O⁺NbF^-₆ and H₃O⁺TaF^-₆. Hydrolysis of MoF₆ leads to MoOF₄, but in HF solution there is evidence for the existence of MoOF^-₅ ion.     

Silicium-verbindungen mit starken intramolekularen sterischen wechselwirkungen : VI. Darstellung und eigenschaften des tri-t-butylsilans und der tri-t-butylhalogensilane

Tri-t-butylsilane has been prepared by treatment of t-butyllithium with HSiCl₃ or HSiF₃. Reactions of this compound with the halogens Cl₂, Br₂, I₂, and the pentafluorides PF₅ or SbF₅ gave the expected tri-t-butylhalosilanes. With SO₃ bis(tri-t-butylsilyl) sulfate is obtained via tri-t-butylsilanole. Reaction with dihalocarbenes obtained from phenyl(trihalomethyl)mercury compounds or the system haloform/base leads to the corresponding tri-t-butyl(dihalomethyl)silanes. The reactions with nucleophiles proceed much less readily. Until now only the reaction of tri-t-butylhalosilanes with LiAlD₄ and with KOH giving tri-t-butylsilane-d₁ and tri-t-butylsilanole could be carried out.The attempted preparation of long-living tri-butylsilyl-radicals as well as the direct observation of tri-t-butylsilicenium ions was unsuccessful. In the first case intermolecular hydrogen abstraction by the radical leads to the hydrosilane, and in the second case the experimental results are better explained by Lewis-acid—base interactions than by silicenium ion formation.     

Fluorination of perfluoroalkylsulfenyl chlorides,perfluorodialkyl disulfides and perfluorodialkyl sulfides with chlorine monofluoride

In reactions with perfluoroalkylsulfenyl chlorides (R_fSCl; R_f = F₃, C₂F₅, n-C₃F₇, n-C₄F₉) and perfluoroalkyl disulfides (R_fSSR_f′; R_f = R_f′ = CF₃, R_f = CF₃, R_f′ = C₂F₅) at 25°, chlorine monofluoride acts primarily as a chlorinating and fluorinating reagent to give the corresponding perfluoroalkylsulfur chloride tetrafluorides, R_fSF₄Cl, in good yields. However, small amounts of perfluoroalkylsulfur pentafluorides, R_fSF₅, are also obtained. A mixture of the cis and trans isomers of bis(trifluoromethyl)sulfur tetrafluoride and of trifluoromethyl pentafluoroethylsulfur tetrafluoride has been formed by the reaction of the corresponding bis(perfluoroalkyl) sulfides and chlorine monofluoride. The new perfluoroalkylsulfur chloride tetrafluorides are colorless, unpleasant smelling liquids. The infrared, mass and ¹⁹F NMR spectral data, as well as thermodynamic and elementary analysis data, are given for the new compounds.     

The preparation of copper(II) and copper(I) salts in acetonitrile using group VA and VB pentafluorides

Copper(II) fluorine reacts with the pentafluorides, TaF₅, PF₅, and AsF₅, in acetonitrile to give solvated Cu^II, hexafluoroanion salts. These react with copper metal to give the corresponding Cu^I compounds. Similar reactions occur between AsF₅ and silver(I) or thallium(I) fluorides, but silver(II) fluoride reacts with MeCN, and Ag^I hexafluoroarsenate is formed. PF₅ oxidises Cu slowly in MeCN to give Cu^I hexafluorophosphate, but AsF₅ has no oxidising ability towards metals in MeCN. Spectroscopic data for Cu(MF₆)₂·5MeCN and Cu(MF₆)·4MeCN (M = Ta or P) are discussed.     

Synthesis and Characterization of 2‐Pyridylsulfur Pentafluorides

Current approaches to prepare SF₅‐substituted heterocycles during the synthesis of targeted heterocyclic compounds require the use of SF₅‐functionalized aryl or alkyne reagents or SF₅Cl as a source of the SF₅ functional group. Herein we report that excess oxidative fluorination of 2,2′‐dipyridyl disulfide with a KF/Cl₂/MeCN system leads to the formation of thirteen new 2‐pyridylsulfur chlorotetrafluorides (2‐SF₄Cl‐pyridines). These molecules are found to undergo further chlorine–fluorine exchange reactions by treatment with silver(I) fluoride enabling ready access to a series of ten new substituted 2‐pyridylsulfur pentafluorides (2‐SF₅‐pyridines). This is the first preparatively simple and readily scalable example of the transformation of an existing heterocyclic sulfur functionality to prepare SF₅‐substituted heterocycles.     

Complex formation of polymeric niobium and tantalum pentafluorides in non-aqueous solvents

¹⁹F NMR and i.r. spectroscopy were employed to study complex formation of niobium and tantalum pentafluorides with triphenylphosphine oxide, ethyl diphenylphosphinate and S-ethyl diphenylthiophosphinate in methylene chloride and in acetonitrile. In methylene chloride solution MF₅L, M₂F_IOL, MF₄L₂⁺ and M₂F_II^? complexes were found (M=Nb, Ta;L- phosphoryl-containing Ligand). I.r. frequencies are assigned. Solvent properties (electric conductivity and donor capacity) affect the relative stability of complexes. The dependence of ¹⁹F NMR parameters on the donor capacity of the ligands is discussed.     

Crystal structures of layered zirconium pentafluorides of methylammonium,glycinium, and β-alanine

For the first time, new hybrid organic-inorganic layered zirconium pentafluorides of methylammonium, glycinium, and β-alanine with the composition (CH₃NH₃)ZrF₅·0.5H₂O, (H₃NCH₂COOH)ZrF₅·2H₂O, and (H₃N(CH₂)₂COOH)ZrF₅ are synthesized and their structures are analyzed. In the studied compounds, CN of the Zr atom is 8, and its coordination polyhedron represents a dodecahedron sharing its 6 vertex with three neighboring Zr polyhedra. The Zr dodecahedra are joined with each other in planar netlike anion layers of the composition _∞²[ZrF₅]⁻. The anion layers are hydrogen bonded into a three-dimensional structure by H₂O cations and molecules.     

Re‐evaluation of the X‐ray Crystal Structure of [Ta4F20] and the Synthesis and Characterization of a Series of Mixed‐Metal Pentafluorides of Niobium and Tantalum

The direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [Nb_xTa_4‐xF₂₀] (x = 1 2 , 2 3 , 3 4 ) as discreet species isostructural with tantalum pentafluoride (x = 0 1 ). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐F_terminal, and 2 Ta‐F_bridging distances. The angles at the bridging fluorine atoms are 172.9(5)°.     

Quasirelativistic energy-consistent 5f-in-core pseudopotentials for pentavalent and hexavalent actinide elements

Quasirelativistic energy-consistent 5f-in-core pseudopotentials modeling pentavalent (5f ^n?2 occupation with n = 2–6 for Pa–Am) and hexavalent (5f ^n?3 occupation with n = 3–6 for U–Am) actinides have been adjusted. Energy-optimized (6s5p4d) and (7s6p5d) valence basis sets contracted to polarized double- to quadruple-zeta quality as well as 2f1g correlation functions have been derived. Corresponding smaller basis sets (4s4p3d) and (5s5p4d) suitable for calculations on actinide(V) and actinide(VI) ions in crystalline solids form subsets of these basis sets designed for calculations on neutral molecules. Calculations using the Hartree–Fock and the coupled-cluster method with single and double excitation operators and a perturbative estimate of triple excitations for actinide pentafluorides show satisfactory agreement with calculations using 5f-in-valence pseudopotentials and experimental data, respectively. However, in the hexavalent case the 5f-in-core approximation seems to reach its limitations except for hexavalent uranium (5f⁰), where results for both uranium hexafluoride and the uranyl ion deviate only slightly from the 5f-in-valence reference data.     

The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds

Some of the transition metal hexafluorides demonstrate an astonishing oxidizing power. In particular may be mentioned PtF₆, which is capable of oxidizing molecular oxygen or xenon, a process requiring an electron affinity, E(PtF₆), > ?156 kcal·mole^?1. From a comparative study of all of the hexafluorides of the third transition series the electron affinity is seen to increase regularly in the sequence WF₆ < ReF₆ < OsF₆ < IrF₆ < PtF₆. The increase in E with unit increase in atomic number of M appears to be ≈ ?20 kcal·mole^?1. On the other hand the ability of the hexafluorides to accept F^? decreases along this series. This effect enables IrF₆ to be more effective than PtF₆ in the generation of nitrogen oxide trifluoride, ONF₃, by the oxidative fluorination of nitrosyl fluoride, ONF. Both PtF₆ and IrF₆ interact spontaneously with ONF or O₂NF to generate fluorine, at or below room temperature. The decrease in F^? -acceptor ability along the series, which stands in sharp contrast to the increase in electron affinity, suggests that ligand crowding increases sharply across the series from WF₆ to PtF₆. This accords with the observed decrease in molecular volume along the series, both in the hexafluorides and in the MF₆^? salts. It is clear from this comparison that the species IrF₆ and PtF₆ are close to a minimum volume for this series. The oxide pentafluorides ReOF₅ and OsOF₅ are similar in oxidizing ability to their respective hexafluorides but are poorer F^? acceptors. Evidently the ligand crowding in MOF₅ molecules is greater than in MF₆.     

The structure type of Re2Te5, a new [M6X14] cluster compound

Re₂Te₅ crystallizes in a new structure type, having space group Pbca (No. 61) with a = 13.003(5), b = 12.935(7), c = 14.212(5) Å, Z = 12. All atoms are in the general positions 8(c), apart from one Te atom which occupies the special position 4(a) in a center of symmetry. The Re atoms are arranged in octahedral [Re₆] clusters and all the atoms in general positions can be grouped as {[Re₆Te₈]Te₆} complexes. The centers of these units and the Te atom in 4(a) are arranged like a slightly distorted rock salt structure. The Te atoms can be replaced by Se atoms up to at least 40%. Re₂Te₅ and Re₂Se₂Te₃ reveal a semiconductor-like electric behavior which is accounted for by the chemical bonding.     

Preparation of a continuous series of solid solutions in the Ta2O5Nb2O5 system

A continuous series of Ta₂O₅Nb₂O₅ solid solutions was obtained by anodically dissolving calculated amounts of tantalum and niobium in a saturated solution of NH₄Cl in methanol (at room temperature), evaporation of the solvent, and thermal decomposition of the product at temperatures not exceeding 750–800°C. X-ray diffraction analysis showed that at all Ta:Nb ratios the product was isomorphic with β-Ta₂O₅ (γ-Nb₂O₅); all reflections could be indexed in an orthorhombic cell, with a increasing linearly from 6.170 to 6.192 Å and c decreasing linearly from 3.935 to 3.885 Å as Ta was substituted for Nb. The changes in parameter b as a function of composition were less pronounced and its values were between 3.657 and 3.662 Å. The method may be used for the preparation of various mixed oxides that are difficult to prepare by other techniques.     

The Three-Center, Four-Electron Bond in Hexacoordinated AB6-Type Main Group Molecules: An Alternative Model of Bonding without d-Orbital Participation in the Central Atom

The hexacoordinated AB₆-type main group molecules have long been thought to have sp³d² hybridization on the central atom, accounting for their molecular geometry (octahedral). However, the s-p-d hybridization does not explain how an energetically unfavorable np nd excitation in an atom of nonmetallic elements, such as sulfur and phosphorus, can be achieved. In this article, the author has re-examined bonding in SF₆ and PF₆^– (O_h symmetry) and proposed that the linear F—S—F and F—P—F bonds in both species are formed via the overlap of the 3p orbital on the central atom with terminal ligand orbitals, resulting in a three-center, four-electron bond. This alternative model, which does not involve d orbitals in bonding, is supported by a partial charge analysis using Allens electronegativity approach. SF₆ or PF₆^– can be characterized by several ionic resonance structures containing a postulated SF₄²⁺ or PF₄⁺ cation (octet on sulfur or phosphorus). The three-center, four-electron bond model can also be used to study bonding in hexacoordinated AB₅E (e.g., halogen pentafluorides) and AB₄E₂ (e.g., xenon tetrafluoride) explaining well the molecular geometry. The author believes that all the results will be useful in updating chemistry texts.     

Hydrogen in polar intermetallics: Syntheses and structures of the ternary Ca5Bi3D0.93, Yb5Bi3Hx, and Sm5Bi3H∼1 by powder neutron or single crystal X-ray diffraction

The syntheses of the title compounds are described in detail. Structural characterizations from refinements of single crystal X-ray diffraction data for Yb₅Bi₃H_x and Sm₅Bi₃H_∼1 and of powder neutron diffraction data for Ca₅Bi₃D_0.93(3) are reported. These confirm that all three crystallize with the heavy atom structure type of β-Yb₅Sb₃, and the third gives the first proof that the deuterium lies in the center of nominal calcium tetrahedra, isostructural with the Ca₅Sb₃F-type structure. These Ca and Yb phases are particularly stable with respect to dissociation to Mn₅Si₃-type product plus H₂. Some contradictions in the literature regarding Yb₅Sb₃ and Yb₅Sb₃H_x phases are considered in terms of adventitious hydrogen impurities that are generated during reactions in fused silica containers at elevated temperatures.     

The crystal structure of 1,1-bis(η5-cyclopentadienyl)-2,3,4,5-tetraphenylzirconole

The crystal and molecular structure of (η⁵-C₅H₅)₂Zr[C₄(C₆H₅)₄] has been determined by single crystal X-ray diffraction methods. The compound is isostructural with its titanium and hafnium analogues, and crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 13.790(5), b = 11.136(5), c = 18.692(7) », β = 92.82(4)°, and ?_calc = 1.34 g cm^?3 for Z = 4. Full-matrix least-squares refinement converged with a conventional R value of 0.049 for 2986 observed reflections. The metallocyclic ring is planar to within 0.05 », and the π-electron density is largely localized. The two independent ZrC(σ) bond lengths are 2.250(5) and 2.265(6) ». The ZrC(η⁵) distances range from 2.482(6) to 2.546(7) », and average 2.521(20) ». A comparison of zirconium- and hafnium-carbon bonds based on the data available shows that for M = Hf the MC bonds are shorter for all cases: C(sp), C(sp²), C(sp³), C(η⁵).     

Synthesis, structures and magnetic properties of pseudo-hollandite chromium sulfides

The pseudo-hollandite chromium sulfides, ACr₅S₈ (A=K, Rb, Cs) and A′_0.5Cr₅S₈ (A′=Sr, Ba), have been synthesized and investigated in structural and magnetic properties. All the compounds crystallize in the isostructure with a monoclinic C2/m. Its crystal structure has triangular lattices and double chains made of Cr³⁺ (d³; S=3/2) triangles. The magnetic susceptibilities of all compounds behave as Curie-Weiss types in high temperature region. From magnetic susceptibility and specific heat measurements, all the compounds have antiferromagnetic ground states. The Néel temperatures are rather low compared to Weiss temperatures, reflecting magnetic frustration in the triangular lattices and double chains. The magnetic transitions in KCr₅S₈ and Ba_0.5Cr₅S₈ are a two-step transition around 50 and 60 K, respectively, while RbCr₅S₈ shows a sharp magnetic transition at 42 K, accompanied by magnetoelastic behavior. CsCr₅S₈ shows a structural transition around 100 K, followed by a magnetic transition at 10 K. In Sr_0.5Cr₅S₈, ferromagnetic interaction develops below 100 K and then a three-dimensional antiferromagnetic order takes place at 30 K. These magnetic properties are discussed from A-cation dependences of local structures and a model of magnetic structure for RbCr₅S₈ is proposed on the basis of the arguments of magnetic interactions and neutron diffraction data. It is different from the known magnetic structure of TlCr₅Se₈.     

EPR studies on some polyamine copper(II) complexes in various solvents

EPR studies have been carried out on a series of copper(IIcomplexes with the general formula CuL(NCS)_xY_2-x[L = N,N,N',N″,N″-pentamethyldiethylenetriamine (Me₅den); x = 1 or 2; and Y = ClO₄, NO₃ or B?₄], dissolved in different solvents. These studies have revealed that the symmetry around copper(II) in [Cu(Me₅den)(NCS)₂] and [Cu(Me₅,den)-NCS]NO₃ is not trigonal-bipyramidal as predicted by IR, conductivity and optical data. The 4s contribution to the ground state is found to influence the isotropic contact term and bond parameters. The hyperfine line-widths observed for the copper(II) ion in solutions of these complexes dissolved in pyridine at room temperature are explained using the theory of Wilson and Kivelson. The isotropic spin—rotational relaxation contribution to the residual line-width is found to be smaller for all the complexes when they are dissolved in pyridine.     

Strain energy due to {001} crystallographic shear planes in materials possessing the ReO3 structure

The elastic strain energy in a structure of the ReO₃ type containing ordered arrays of {001} CS planes has been calculated. The values obtained are for the elastic strain energy of the matrix between CS planes and also the relaxation energy of the ions in the CS planes themselves. Interactions from all the CS planes in the crystal are summed and not just those from nearest neighbors. The extent to which the CS planes can be considered to transmit the forces which strain the crystal is considered by including a variable parameter, α, in the calculations, which is related to the type of chemical bonding present in the CS planes. The results are compared with experimental observations in the WO₃Nb₂O₅ and NbO₂F systems. It is concluded that the value of α is high for WO₃ doped with Nb₂O₅ and low for NbO₂F in accord with the expectations of chemical bonding. The results also support the view that elastic strain energy is important in influencing the microstructures observed in crystals containing CS planes.     

Crystal structures, unusual magnetic properties and electronic band structures of Cr5−xTixTe8

The effect of substitution of the cation Cr by Ti in Cr₅Te₈ has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr_5−xTi_xTe₈ (x=0, 0.5, 1, 1.5, 1.85, 2, 3, 4, 5) were synthesized at elevated temperatures followed by slow cooling the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method. Three structural modifications are identified: monoclinic with space group F2/m for Cr_5−xTi_xTe₈ (x=0, 0.5, 1, 1.5, 1.85), trigonal supercell with space group P-3m1 for Cr_5−xTi_xTe₈ (x=2, 3), and trigonal basic cell with space group P-3m1 for Cr_5−xTi_xTe₈ (x=4, 5). The structures of all these phases are related to the NiAs structure with full and deficient metal layers stacking alternatively along the c-axis.The irreversibility in the field-cooled/zero-field-cooled magnetization with low field depends strongly on the Ti concentration x. Four types of magnetic states are distinguished: re-entrant ferromagnet for m-Cr₅Te₈, cluster-glass for m-Cr_4.5Ti_0.5Te₈ and m-Cr₄TiTe₈, antiferromagnetic for m-Cr_3.5Ti_1.5Te₈, and spin-glass for tr-Cr₃Ti₂Te₈, tr-Cr₂Ti₃Te₈, and Cr_0.25TiTe₂.Accompanying spin polarized scalar-relativistic Korringa-Kohn-Rostoker band-structure calculations strongly support the observation that the crystallographic sites in the full metal layers are preferentially occupied and predict that Ti atoms have the preference to occupy the full metal layers. These compounds are predicted metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented.     

Metal-insulator transition in VnO2n−1

Research on phase relationships and structure studies by electron diffraction confirm V_nO_2n?1 (n = 3–9) phases between V₂O₃ and VO₂. Metal-insulator phase transitions have been found in all phases but V₃O₅ and V₇O₁₃. Electrical, magnetic and thermodynamic properties associated with the transitions are reported for sintered samples or for single crystals prepared by a vapor-transport method. The results are collated and reviewed in summarized form.