Structures and Properties of NbOF3 and TaOF3 — with a Remark to the O/F Ordering in the SnF4 Type Structure

Powder samples of NbOF₃ und TaOF₃ were prepared by heating mixtures of NbO₂F and NbF₅ or TaO₂F and TaF₅, respectively, in the corresponding stoichiometric ratio in platinum crucibles under argon atmosphere (180—220 °C). Both oxide fluorides are coulourless with a slight greyish tinge. They are sensitive to moisture and decompose in air at room temperature within hours. Both, NbOF₃ and TaOF₃ crystallize as a variant of the SnF₄ type structure, space group I4/mmm. The structures have been refined from X‐ray powder diffraction data using the Rietveld method (a = 3.9675(1) Å, c = 8.4033(1) Å, R_B = 3.60 %, R_p = 4.58 % for NbOF₃ and a = 3.9448(1) Å, c = 8.4860(1) Å, R_B = 2.07 %, R_p = 2.44 % for TaOF₃). Characteristic building units are sheets of corner sharing MX₆ octahedra which are stacked via van der Waals interactions to a three dimensional framework. The occupancy of the two crystallographic sites for the anions by O and F is discussed on the basis of structure refinements, bond order summations, IR and NMR data and calculations of the Madelung parts of the lattice energy.     

Phase diagrams of the KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript> and KF-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> systems

The phase diagrams of the systems KF-K₂TaF₇ and KF-Ta₂O₅ were determined using the thermal analysis method. The phase diagrams were described by suitable thermodynamic model. In the system KF-K₂TaF₇ eutectic points at x _KF=0.716 and t=725.4°C and at x _KF=0.214 and t=712.2°C has been calculated. It was suggested that K₂TaF₇ melts incongruently at around 743°C forming two immiscible liquids. The system KF-Ta₂O₅ have been measured up to 8 mol% of Ta₂O₅. The eutectic point was estimated to be at x _KF∼0.9 and t∼816°C. The formation of KTaO₃ and K₃TaO₂F₄ compounds has been observed in the solidified samples.     

Niobium,tantalum, and titanium fluoride solutions

Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO₂F, TaO₂F, Ta₃O₇F, and TiOF₂. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH₄NbOF₄ and (NH₄)₃Nb₂OF₁₁.     

Die relative Unterkühlung an Quarzglasoberflächen und anderen Substraten beim chemischen Transport fester Stoffe über die Gasphase

The Relative Undercooling on Silica Glass Surfaces and other Substrates during the Chemical Transport of Solids via the Vapor-phase . The relative undercooling on etched surfaces of silica glass at the chemical transport of ZnS in a stream of gaseous iodine at 652–854°C is found to be ΔT = 37–43°. Scrapers on silica glass lead to a substantial smaller undercooling. During the deposition of ZnS (made from “pure” components) in a temperature gradient one finds a remarkable fractionation. In closed (etched) silica glass ampoules the relative undercooling is determined for the systems ZnS/I₂, ZnSe/I₂, ZnS/HCl; ZnS/H₂, CdS/I₂, CdSe/I₂, Al₂S₃/I₂ and Nb₂O₅/NbCl₅ using a special furnace, The region free of nuclei (or crystals) for instance at T₂ ≈ 800°C depending on the system (and T₂) is ΔT ≈ 13–45°. The variation of the substrates showed: for fire polished silica surfaces for ZnS/I₂ is ΔT ≈ 56°; for the different quartz-faces and ZnS/I₂ is ΔT ≈ 13–35°. Generally, on different substrates (broken pieces, fragments) one finds for ZnS/I₂ ΔT ≈ 20–28°. Using another way for the systems MoO₃/Cl₂, MoO₃/Cl₂, Ar, MoO₃/Cl₂, O₂ and MoO₃/HgCl₂ with T₂ a strongly decreasing value of ΔT is found.     

Determination of dissociation degrees of K3NbF8 and K3TaF8 by thermodynamic analysis of subsystems of the KF-K2NbF7 and KF-K2TaF7 systems

A special form of the LeChatelier-Shreder equation describing the equilibrium between the crystalline phase and the melt in system A-AB in which the substance AB partially dissociates upon melting was applied to systems KF-K₃NbF₈, K₂NbF₇-K₃NbF₈ and to KF-K₃TaF₈, K₂TaF₇-K₃TaF₈ subsystems of the binary systems KF-K₂NbF₇ and KF-K₂TaF₇ in which the additive compounds K₃NbF₈ and K₃TaF₈ are formed. Using the phase diagram of the system KF-K₂NbF₇ determined by McCawley and Barclay (1971) and the values of the fusion enthalpy of K₃NbF₈ taken from literature, the intervals of the dissociation degree values of K₃NbF₈ for both branches of the liquidus curve of K₃NbF₈ were calculated. The calculated values of the dissociation degree depend on the coordinates of the liquidus curve of K₃NbF₈ of the pertinent phase diagram, on its used branch and section, and on the value of the fusion enthalpy of K₃NbF₈. For the measured fusion enthalpy of K₃NbF₈ (57 kJ mol⁻¹), a common interval of the dissociation degree values of K₃NbF₈ for both branches of the liquidus curve of K₃NbF₈ is 0.71–0.72. Similarly, intervals of the dissociation degree values of K₃TaF₈ for both branches of the liquidus curve of K₃TaF₈ were calculated using the phase diagram of the system KF-K₂TaF₇ determined by Boča et al. (2007) and the measured fusion enthalpy of K₃TaF₈ ((52 ± 2) kJ mol⁻¹). The error of the determination of the fusion enthalpy of K₃TaF₈, the common interval of the dissociation degree values of K₃TaF₈ for both branches of the liquidus curve of K₃TaF₈ is 0.68–0.69.     

Unit cell dimensions of some oxofluorometallates of transition metals

Unit cell dimensions of seven oxofluorometallates of transition metals were investigated by powder X-ray diffraction method. The compounds K₃NbO₂F₄ and K₃TaO₂F₄ were found to be isomorphous with cubic (FCC) structure and having lattice parameters 8.885 and 8.942 Å respectively. Similarly, the compounds K₂NbOF₅ (a = 8.367 Å, c = 13.038 Å) and K₂TaOF₅ (a = 8.463 Å, c = 13.139 Å) were also found to be isomorphous with a tetragonal structure. The compound K₃Zr₂O₂F₇ (a = 9.367 Å) was found to possess a cubic (FCC) structure. Both K₂V₂O₅F₂ (a = 6.739 Å, c = 10.635 Å) and K₂VO₃F (a = 5.984 Å, c = 10.914 Å) have a hexagonal structure.     

Nano particles of iron oxides in SiO<Subscript>2</Subscript> glass prepared by ion implantation

Quartz (SiO₂) glass was implanted with 5 × 10^{16 57}Fe ions/cm² at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mössbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO₂ glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe³⁺ and Fe²⁺ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe²⁺ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic ε-Fe₂O₃ precipitated in SiO₂ matrix. Small amounts of α-Fe₂O₃ were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible.     

Low temperature synthesis of Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite using a modified sol–gel method

The paper presents a study on the preparation of Co₂SiO₄/SiO₂ nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC₂H₅)₄), cobalt nitrate Co(NO₃)₂·6H₂O and some diols: ethylene glycol (C₂H₆O₂), 1,2propanediol (C₃H₈O₂) and 1,3propanediol (C₃H₈O₂), for a final composition: 30% CoO/70% SiO₂. During the heating of the gels at 140 °C, a redox reaction takes place between NO₃ ⁻ ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co₃O₄ inside the matrices pores. When CoO results, it reacts with SiO₂ at low temperature leading to Co₂SiO₄, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co₂SiO₄ (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co₂SiO₄ nanoparticles are homogenously dispersed inside the silica matrix.     

Features of the ion mobility and phase transitions in hexafluoro complex compounds of tantalum(V), niobium(V), and titanium(IV) with the tetramethylammonium cation

¹⁹F, ¹H NMR and DSC methods are used to study the ion mobility and phase transitions in hexafluoro complex compounds of tantalum(V), niobium(V), and titanium(IV) with the tetramethylammonium cation. A transformation of the NMR spectra observed in a temperature range 77(130)-450 K is found to be associated with a change in the type of ion motions in the anion and cation sublattices of the studied compounds. In a temperature range 170-450 K the main types of ion motions are isotropic reorientations of TaF₆, NbF₆, TiF₆ octahedra and tetramethylammonium ions. Two endothermic effects with the maxima at 232.5 K and 256.5 K for [N(CH₃)₄]TaF₆ and 235 K and 250 K for [N(CH₃)₄]NbF₆, which are observed in the DSC curve in the range 170-400 K correspond to phase transitions that have almost no effect on the NMR spectral parameters the a temperature range 230-260 K. For the [N(CH₃)₄]₂TiF₆ compound, an endothermic effect at 422 K is observed, corresponding to the phase transition from the rhombohedral to the cubic modification.     

Eu5F[SiO4]3 und Yb5S[SiO4]3: Gemischtvalente Lanthanoid‐Silicate mit Apatit‐Struktur

Eu₅F[SiO₄]₃ and Yb₅S[SiO₄]₃: Mixed‐Valent Lanthanoid Silicates with Apatite‐Type of Structure By the reaction of Eu, EuF₃, Eu₂O₃ with SiO₂ in evacuated gold ampoules, using NaF as flux, at a temperature of 1000 °C for ten hours, dark‐red, platelet‐shaped single crystals of Eu₅F[SiO₄]₃ are obtained. Similarly dark‐red, but pillar‐shaped single crystals of Yb₅S[SiO₄]₃ are obtained by the reaction of Yb, Yb₂O₃ and S with SiO₂ in the presence CsBr as flux in evacuated silica ampoules at 850 °C and an annealing time of seven days. Both compounds crystallize hexagonally (P6₃/m, Z = 2; Eu₅F[SiO₄]₃: a = 954.79(9), c = 704.16(6) pm; Yb₅S[SiO₄]₃: a = 972.36(9), c = 648.49(6) pm) in the case of Eu₅F[SiO₄]₃ analogous to the mineral fluorapatite and for Yb₅S[SiO₄]₃ as a bromapatite—type variety. The crystal structure containing isolated [SiO₄]^4— tetrahedra distinguishes two rare‐earth cation positions with coordination numbers of nine (M1) and seven (M2), in which the position M1 of the europium fluoride silicate is almost exclusively occupied by Eu²⁺ cations, whereas in ytterbium sulfide silicate it contains di‐ and trivalent Yb cations in the ratio 1 : 1. In both cases, however, the M2 position is only populated with M³⁺.     

Derivate des Flußspat-Typs: [Fe(NH3)6][TaF6]2 und [Ni(NH3)6][TaF6]2

Derivatives of the Fluorite Type: [Fe(NH₃)₆][TaF₆]₂ and [Ni(NH₃)₆][TaF₆]₂ Light blue single crystals of [Fe(NH₃)₆][TaF₆]₂ and [Ni(NH₃)₆][TaF₆]₂ are obtained from 36 : 1 : 6 molar mixtures of (NH₄)F, iron/nickel and tantalum powders, respectively, in sealed Monel metal ampoules at 400 °C. They both crystallize isotypic with [Co(NH₃)₆][PF₆]₂ (cubic, Fm-3m, Z = 4, a = 1259.0(2)/1260.4(2) pm) in a structure that can be derived from the basic fluorite-type of structure according to [Ca][F]₂≡[Fe(NH₃)₆][TaF₆]₂, for example.     

Neues zu Oxidchloriden der Seltenen Erden mit Vanadium und Rhenium

New Oxychlorides of the Rare-Earth Metals with Vanadium and Rhenium i) New compounds Ln_12.33V₆O₂₃(OH)Cl₂₀ (Ln = La, Ce) were prepared by heating mixtures of LnCl₃, LnOCl and V₂O₅ (4 : 8 : 3) in evacuated, sealed silica ampoules (850 °C, 4 d). Single crystals could be obtained by chemical vapor transport (T₂ → T₁, T₂ = 900 °C, T₁ = 800 °C, 14 d, p(Cl₂, 298 K) ≈ 70 mbar). The single-crystal study of the lanthanum compound [a = 17.8818(25) Å, c = 4.0567(7) Å, Z = 1, 1035 independent I₀, 70 parameters, R1 = 3.52%] showed that vanadium has CN = 4 (tetrahedrally) and lanthanum has CN = 9 (threefold capped trigonal prismatic). A strong relationship to the structures of the Pr₃NbO₄Cl₆- and the La₂TaO₄Cl₃-type could be discussed. ii) Further we obtained dark red powder of La₃ReO₆Cl₃ by heating (740 °C, 5 d) a mixture of ReO₃ and LaOCl (1 : 3) in sealed silica ampoules under argon atmosphere (p{Ar, 298 K} = 1 atm). This new rhenium-compound crystallizes in the hexagonal space group P6₃/m (No. 176) [a = 9.4164(6) Å, c = 5.4248(4) Å] and is isostructural to La₃WO₆Cl₃.     

Preparation of FexOy/SiO2 nanocomposites by thermal decomposition of some carboxylate precursors formed inside the silica matrix

In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in the redox reaction between Fe(NO₃)₃ and diol. We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO₃)₃·9H₂O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe₂O₃/50% SiO₂. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO₃)₃-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors took place up to 300°C.     

Reaction of perfluoro-1-methylindan with SiO2-SbF5

The reaction of perfluoro-1-methylindan with SiO₂-SbF₅ depending on the amount of SiO₂ led to the formation after hydrolysis of the reaction mixture of perfluoro-3-methylindan-1-one, perfluoro-4-methylisochromen-1-one, 6-(1-carboxy-2,2,2-trifluoro-ethyl)-2,3,4,5-tetrafluoro-benzoic and 6-(carboxymethyl)-2,3,4,5-tetrafluorobenzoic acids. Heating in the SbF₅ medium perfluoro-1-methylindan in a glass ampoule at 130°C, or perfluoro-3-methylindan-1-one at 70°C provided a solution of a perfluoro-4-methylisochromenium salt that on treating with anhydrous HF was converted into perfluoro-4-methyl-1H-isochromen, and on hydrolysis, into perfluoro-4-methylisochromen-1-one.     

Er2(CO3)2(C2O4)(H2O)2 — Synthese,Kristallstruktur und thermischer Abbau eines Carbonat‐Oxalat‐Hydrates des Erbiums

Er₂(CO₃)₂(C₂O₄)(H₂O)₂ — Synthesis, Crystal Structure and the Thermal Decomposition of a Carbonate‐Oxalate‐Hydrate of Erbium The hydrothermal reaction of an equimolar ratio of Er₂O₃ with the aminoacid L‐cysteine in evacuated glass ampoules in H₂O at 130 °C gave transparent, pink crystals of the formula Er₂(CO₃)₂(C₂O₄)(H₂O)₂. It crystallises in the monoclinic space group Cm (Z = 2, a = 777.3(2) pm, b = 1492.0(3) pm, c = 473.09(8) pm, b = 90.12(9)°). The thermal decomposition of Er₂(CO₃)₂(C₂O₄)(H₂O)₂ was investigated.     

Complex Formation of [Ph2P(O)I2 C=CH2 and [Ph2 P(O) I2 C=PPh3 with Phosphorus and Tantalum Pentafluorides

Abstract

Reactions of PF₅ and TaF₅ with [Ph₂P(O)]₂ C=CH₂ (I) and [Ph₂P(O)]₂ C=PPh₃ (II) in MeCN and CH₂Cl₂ were studied by means of ¹⁹F, ³¹P, ¹H and ¹³C NMR spectroscopy. It has become evident, that one or two phosphoryl groups in (I) and (II), as well as in cis- and trans-Ph₂P(O)CH=CHP(O)Ph₂, are involved in complex formation. The formation of tetra-fluoro cations PFL and PF₄L along with pentafluorocom-plexes PF₅L and TaF₅L was found. Ligands are coordinated with central ions of complexes as chelates. The trans-atoms F₁ of TaF ₅L are nonequivalent because of nonsymmetric position to the Ph3P-group. The F₁-atoms in PF₄L are supposed to be symmetric to the Ph₃P-group. The formation of tri-fluorocomplexes TaOF₃L was also observed. Since the position of ¹⁹F NMR resonance lines of TaOF₃L is near to that of pentafluorocomplexes, it can be supposed that either the change of Ta coordination number takes place, either oxygen atom comes into complex with inner sphere in the reaction with ligand or during hydrolysis.     

SiO2/SnO2 and Sn/Sb-oxide/SiO2 gel-derived composites. Part 2: Thermal evolution and phase analysis

The thermal behaviour of samples with nominal composition 80/20=SiO₂/SnO₂, class B, 76.8/19.2/4.0=SiO₂/SnO₂/Sb₂O₅, class C₁, and 76.8/19.2/2.0/2.0=SiO₂/SnO₂/Sb₂O₅/Sb₂O₃, class C₂, is studied in the interval 25–1050°C by various instrumental methods. Results on these classes of samples, obtained from alkoxide precursors, are compared themselves and with samples of class A obtained from Si(OEt)₄ and SnCl₄. The segregation and crystallization of SnO₂ occurs at 400°C in the presence of microdomains of SnO₂·nH₂O in the SiO₂ gel matrix (class A), whereas it is observed at 700°C for samples B and C composed of Sn and Sb cations homogeneously dispersed in SiO₂. This fact implies different mechanisms of SnO₂ nucleation and growth. The crystallization of SiO₂ is observed at 1200°C for samples A, at 1050°C for B and at 800°C for C. For this latter, the presence of Sb-oxide/ SiO₂ reactive glass is invoked to the low-temperature crystallization of SiO₂. G. Carturan, R. Ceccato, R. Campostrini, G. Principi, and U. Russo, submitted to J. Sol-Gel Sci. Tech.     

Structure of Dibenzocrown Ethers and their H-bonded Adducts. 3. Isolation of Oxonium Ions by Biphenyl-20-crown-6 and [1.5]Dibenzo-18-Crown-6 in Complexes with [NbF6]− and [TaF6]−

The reaction of Nb₂O₅ and Ta₂O₅ with an aqueous solution of hydrofluoric acid, HF in the presence of biphenyl-20-crown-6 (BP20C6, L¹) or [1.5]dibenzo-18-crown-6 ([1.5]DB18C6, L²) results in the complexes [L¹·(H₃O)][NbF₆] (1), [L¹ (H₃O)][TaF₆] (2), [2L²·(H₇O₃)][NbF₆] (3) and [2L²·(H₇O₃)][TaF₆] (4). Complexes 1–4 were identified by the elemental and X-ray structural analysis and IR spectroscopy. Complexes 1 and 2 are isostructural, with the H₃O⁺ oxonium ion embedded in one crown molecule via OH···O hydrogen bonds. Complexes 3 and 4 represent the supramolecular isomers distinctive by the crown conformations and crystal packing, with the (H₇O₃)⁺ cation enclosed in the cage of two crown molecules. Being poor H-bond acceptors, NbF₆⁻ and TaF₆⁻ anions do not compete with the crown oxygen atoms for the oxonium hydrogen atoms, but are involved in the numerous C–H···F short contacts responsible for the extended supramolecular architectures in all cases. A change of crown ethers’ conformation in complexes 1–4 and a correlation between the degree of proton hydration and an accessibility of the crown ether oxygen atoms is observed. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

New Compounds in the IMb2O6(Ta2O5)-V2O6 Systems

Tetraphenyl Imidodiphosphate as Ligand in Fluoro Complexes. 3. Fluoro Complexes of Niobium, Tantalum, and Antimony Tetraphenyl imidodiphosphate forms with NbF₅, TaF₅, and SbF₅ the addition complexes MF₅ · LH and (MF₅)₂(μ-LH). The imidodiphosphate acts in the latter as bidentately bridging ligand. Furtheron, it reacts with NbF₅ and TaF₅ by replacing fluoride forming tetrafloro and trifluoro complexes: [MF₄(μ-L)]₂ and MF₃(η²-L)(OPh) or μ-O[MF₃(η²-L)]₂, resp., (M ? Nb, Ta). SbF₅ does not form substitution complexes. The constitution and conformation of the complexes have been concluded from n.m.r. spectroscopic data.     

Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method

Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm⁻¹, attributed to NH₄ ⁺. TG and FTIR analyses show that the NH₄ ⁺ decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ is thus TaO _x (OH)_5-x (NH₄) _x . This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic acid at room temperature. The NH₄ ⁺ in tantalum hydroxide can be exchanged completely in aqueous HNO₃ solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH₄ ⁺ can also be exchanged completely with aqueous H₂SO₄ solution; however, SO₄ ²⁻ is weakly absorbed on the tantalum hydroxide. Finally, the NH₄ ⁺ can be exchanged partially with aqueous H₃PO₄ solution; however, PO₄ ³⁻ is strongly absorbed on the tantalum hydroxide.