A comparison of the adsorption of KF and NH4F onto silica gel

Silica gel has been fluorinated with KF, Na₂SiF₆, NH₄F and (NH₄)₂SiF₆, and the resulting reagents have been analysed by ¹⁹F and ²⁹Si magic angle spinning NMR and infrared spectroscopy. Fluorination with NH₄F and (NH₄)₂SiF₆ results in the formation of (SiO)₃SiF groups at the surface, where F has replaced OH, whereas the anion SiF²⁻₆ is formed when silica is fluorinated with KF.     

Dynamisch thermische analyse der Zersetzung von K2SiF6

Thermal decomposition of K₂SiF₆ is a complicated process depending on several parameters, the combination of which cause difficulty in comparing the results obtained from different methods. An experimental method for the study of small quantities of material is described. This allows direct comparison with thermoanalytical results. The influence of experimental conditions is discussed. The decomposition of K₂SiF₆ is a model for other complexes which produce easily hydrolysed products during thermal reaction. The course of thermal decomposition of K₂SiF₆ is described up to complete vaporisation of the products at 1200°C.     

Zum Einfluß der Gasphase auf die thermische Zersetzung von K2[SiF6]

Effect of the Gas Phase on the Thermal Decomposition of K₂[SiF₆] K₂SiF₆ produced in usual ways is contaminated by traces of oxygen and protons. These and traces of water fed by gas atmosphere influence the thermal decomposition reaction. To study the influence of the gas phase definite amounts of H₂O and HF were added. The formation of SiF₄ was determined. The development of a SiO₂ phase in presence of H₂O and other experimental results suggest the construction of a layer on the K₂SiF₆ surface, which hinders further SiF₄ being developped. Temperature and linear velocity of the gas influence the length of a zone of decomposition migrating through the solid. This is explained by sorption and reaction behavior of intermediately formed fluorosiloxanes.     

强离子键体系电子相关能简捷计算方案的应用

The calculation results of electron correlation energies of KF and （KF）2 were reported. The transferability of 1s^2 K , 1s^2 F and the inner core correlation effects of K and F in both K, K^＋, KF and F, F^-, KF systems were investigated respectively. The correlation energy contributions of K and F component to KF system were calculated. By applying the simple estimation scheme to the calculation of the correlation energy of the strong ionic compound KF and （KF）2, it was shown that such a powerful scheme could not only reach the chemical accuracy but also need little computational work.     

Phasenbeziehungen und Natriumionenleitung im quasi-binären System Na2SiF6/Na3AlF6

Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na₂SiF₆/Na₂AIF₆ . The phase diagram of the Na₂SiF₆/Na₃AlF₆ system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na₃AlF₆ accomodates up to 73 mol.-% Na₂SiF₆ maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na₃AlF₆ with Na₂SiF₆.     

Interaction between hydrofluorosilicic acid and 1,10-phenanthroline: Hydrolytic stability of chelate complexes of silicon tetrafluoride with bidentate N-donors

Hexafluorosilicate (LH₂)SiF₆ and the cis-[SiF₄(L)] chelate complex characterized by ¹⁹F NMR are products of reaction between hydrofluorosilicic acid and 1,10-phenanthroline (L). XRD findings show that the structure of (LH₂)SiF₆ is stabilized by NH···F hydrogen bonds (N···F 2.618(4), 2.676(4) Å) and CH···F contacts. The relative resistance of the cis-[SiF₄(L)] complex to hydrolysis is associated with the chelate effect.     

Hydrogen‐bonded frameworks of bis(2‐carboxypyridinium) hexafluorosilicate and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate

In bis(2‐carboxypyridinium) hexafluorosilicate, 2C₆H₆NO₂⁺·SiF₆²⁻, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C₁₀H₈NO₂⁺·SiF₆²⁻·2H₂O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF₆]²⁻ anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF₆]²⁻ anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å].     

Solid state reactions of hexafluorosilicates

At beginning thermal decomposition K₂[SiF₆] loses SiF₄-planes from [SiF₆]^2?-octahedrons, which has been proved by x-ray-diffraction [1], [2]. Analogous disorder structures are supposed to be present with all solids having complex ions including carbonates, sulfates and others. The result is a high reactivity at this spots. Another reactive form in hexefluorosilicates is represented by mobile SiF-species, perhaps SiF₃⁺. The reactivity is shown by heterogenous reactions with CHCl₃ and by solid-solid reactions for instance with halides, oxides etc. As an example corundum (α-Al₂O₃) reacts at 600°C giving K₃ AlF₆ and KAlSiO₄ [3].     

Crystal structure of bis(3-carboxypyridinium) hexafluorosilicate

Complex [3-HO(O)CC₅H₄NH]₂SiF₆ is synthesized, and its structure is determined by single-crystal X-ray diffraction. In its ionic structure, the centrosymmetric SiF ₆ ^2? anions (the Si-F bond lengths are 1.6658(15)–1.7033(17) Å) and [3-HO(O)CC₅H₄NH]⁺ cations are linked through interionic H-bonds NH…F, NH…O, and OH…F (the N…F, N…O, and O…F distances are 2.752(3), 2.935(3), and 2.596(2) Å, respectively).     

Crystal structure of <Emphasis Type="Italic">ortho</Emphasis>-toluidinium hexafluorosilicate

The structure of the complex (o-CH₃C₆H₄NH₃)₂SiF₆ was determined by X-ray diffraction. In the ionic structure of the complex, the SiF ₆ ^2? anions (Si-F, 1.595(9)-1.683(17)Å) and the o-CH₃C₆H₄NH ₃ ⁺ cations are combined by NH?F hydrogen bonds (N?F 2.757(10)-3.25(2) Å). The components of the structure are combined into a layer whose central part is formed by the SiF ₆ ^2? anions and the outer hydrophobic surfaces are formed by the aromatic rings of the cations.     

Hydrodechlorination of chlorophenols over Pd catalysts supported on zeolite Y,MCM-41 and graphene

Hydrodechlorination (HDC) reaction of chlorophenols was carried out using Pd catalysts supported over zeolite Y, MCM-41 or graphene. Pd-MCM-41 and Pd-Y zeolite were prepared by impregnation and ion-exchange method, respectively. Pd-graphene (Pd-G) was prepared by hydrazine hydrate reduction of palladium ion dispersed on graphene oxide. The catalysts were characterized by several analytical tools such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). These catalysts were subjected to HDC reaction of chlorophenols, such as 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP) and 3,4-dichlorophenol (3,4-DCP). The reaction rate of HDC of chlorophenols catalyzed by Pd catalysts with various solid bases, such as KF/Al₂O₃ (alumina), sodium acetate (NaOAc) and K₂CO₃ was compared. First, Pd-MCM-41 and Pd-Y catalysts were compared. 2,4- and 3,4-DCPs were completely decomposed within 6 h, in the case of Pd-MCM-41 with NaOAc. Using Pd-Y instead of Pd-MCM-41 with NaOAc, much faster decomposition was observed. Faster decomposition of 4-CP and DCPs was observed with NaOAc base than K₂CO₃ or KF/Al₂O₃ under the same condition. In the case of Pd-Y with KF/Al₂O₃, slower decomposition of 4-CP and DCPs was observed. These base effects were interpreted using the solubility of NaCl and KCl in alcohol and the basic sites of KF/Al₂O₃. Because the solubility of NaCl is known to be larger than KCl solubility in alcohol, byproduct NaCl could be easily dissolved and ionized in solvents. For Pd-Y with KF/Al₂O₃, the small pore size of Y zeolite can interfere with the diffusion of HCl to KF/Al₂O₃ basic site. Second, three catalysts, including Pd-graphene, were compared. 2,4-DCP was decomposed within 2 h using Pd-G with either K₂CO₃, NaOAc or KF/Al₂O₃. Pd-G catalyst showed the highest catalytic activity among Pd-G, Pd-MCM-41 and Pd-Y catalysts. The high activity and stability of the Pd-G could be attributed to the strong metal–support interaction with an electron-deficient site and a critical Pd particle size (ca. 3.5 nm) of Pd-G nanocatalyst with a stronger resistance to the deactivation and good affinity toward aromatic organic molecules, especially phenols. The progress of HDC reaction was monitored by gas chromatography with flame ionization detection (GC/FID), and a feasible degradation process could be explained by analyzing the degradation products such as phenol, cyclohexanone and cyclohexanol from resulting GC chromatograms. The effect of reaction temperature on HDC in Pd-G catalyst was also discussed. In conclusion, Pd-G is an efficient catalyst for decomposition of chlorophenols and can be applied to remediation of chlorophenol-contaminated water under mild conditions.     

Crystal structure of p-nitroanilinium hexafluorosilicate

Complex (p-O₂NC₆H₄NH₃)₂SiF₆ (I) is prepared by reacting fluorostlicic acid with p-nitroaniline in methanol and structurally studied using single-crystal X-ray diffraction. In the ionic structure of this complex, SiF ₆ ^2? centrosymmetrical anions (avg. Si-F, 1.671(3) Å) and O₂NC₆H₄NH ₃ ⁺ cations are linked through NH…F interionic H-bonds (N…F 2.823(5)-3.205(7) Å). The thermochemical features of complex I are discussed in light of the structure data.     

Untersuchungen zur Reaktion zwischen Alkalihexafluorosilicaten und einigen oxidischen Niobverbindungen

Investigations of the Reaction between Alkalihexafluorosilicates and Some Oxidic Niobium Compounds The reactions of Na₂SiF₆ with M-Nb₂O₅ or NaNbO₃ always produce Na₂Nb₂O₅F₂ and the thermolysis product is NaNbO₃. On the other hand various reactions of K₂SiF₆. exist. Initially with M-Nb₂O₅ an intermediate phase of a bronzestructure type is formed, like α-K_0,25NbO_2,25F_0,75, being converted into K₃NbO₂F₄ and another amorphous niobium phase. Moreover K₂NbO₃F crystallizes in a long time reaction. However first of all K₂NaNbO₂F₄ is formed by the reaction of K₂SiF₆ with NaNbO₃ and only if there is an excess of K₂SiF₆ this substance is changed slowly into K₃NbO₂F₄. The thermolysis of K₃NbO₂F₄ can produce such compounds as K₆Nb₂O₇F₂.     

A novel mononuclear gold(I) complex: Synthesis and x-ray structure of [Au{P(C6H5)3}3][SiF5] · 1.5 CH2Cl2

Tris(triphenylphosphine)gold(I)-pentafluorosilicate(IV) ([Au{P(C₆H₅)₃}₃][SiF₅]) was prepared and the structure was determined by single crystal x-ray diffraction. The complex crystallizes in the triclinic space group P1 (No. 2). The lattice constants are a = 14.634(2) Å, b = 17.180(2) Å, c = 22.212(3) Å, α = 86.48(1)°, β = 78.95(1)°, γ = 83.99(1)°. Number of molecules per cell: Z = 4. The gold atoms are coordinated to three triphenylphosphine ligands to form the trigonal planar cation [Au{P(C₆H₅)₃}₃]⁺. Separated from the cation is the [SiF₅]^? anion which is regular trigonal bipyramidal coordinated. No interactions between the fluorine atoms and the gold atoms were observed.     

Synthesis and crystal structure of <Emphasis Type="Italic">N,N</Emphasis>-dimethylbiguanidinium hexafluorosilicate

The complex [(CH₃)₂NC(NH₂)NHC(NH₂)NH₂]SiF₆ (I) was synthesized and its structure was determined by X-ray crystallography. The crystals are monoclinic: a = 7.4346(10) Å, b = 12.7628(10) Å, c = 11.0828(10) Å, β 104.080(10)°, V = 1020.01(18) ų, ρ_calc = 1.780 g/cm³, μ(MoK _α) = 0.302 mm^?1, Z = 4, space group P2₁/c. The crystals of I are composed of SiF ₆ ^2? anions (Si-F, 1.657(2)–1.699(2) Å) and N,N-dimethylbiguanidinium (H₂L²⁺) cations combined in a framework by interionic H-bonds NH···F. In the cations, protonation sites are the terminal imide groups.     

Quantenchemische Modellrechnungen zur Baugruppenwanderung in Hexafluorosilicaten

Quantum Chemical Model Calculations on the Migration of Si? F Groups in Hexafluorosilicates The transport of different Si? F species was simulated using two [SiF₆]^2? octahedra as example. Activation barriers and charge distributions were calculated with the EHT method. Bearing in mind the structure of cubic hexafluorosilicates calculations were carried out on the migration both along an edge and along a (110) face of the elementary cell. At first [SiF₂]²⁺ and SiF₄ groups were removed from an [Si₂F₁₂]^4? unit to produce a surface vacancy. During a second step planar SiF₄ groups were moved to the neighbouring lattice position. A diffusion of planar SiF₄ is favoured, if the electrostatic interaction between moved and fixed fluorine atoms is as small as possible.     

Phase equilibria in the fluorosilicic acid-o-phenylenediamine-water system at 25°C: The crystal structure of o-phenylenediammonium hexafluorosilicate

The interactions in the H₂SiF₆-o-phenylenediamine-H₂O (FSA-PDA-H₂O) system at 25°C is studied using the isothermal solubility method. The solid phases existing in the system are o-PDA (0-23.70 wt % H₂SiF₆) and hexafluorosilicate formulated as (o-PDAH₂)SiF₆ (23.70–44.60 wt % H₂SiF₆). The structure for the latter is solved in single-crystal X-ray diffraction experiments. In the ionic structure of the complex, o-PDAH ₂ ²⁺ cations and SiF ₆ ² anions are linked through H-bonds NH-F((N-F 2.865(2)-2.967(2) Å) into a two-dimensional net. The Si-F bond lengths are 1.6709(12)-1.6958(12) Å.     

Synthesis,Structure, and Properties of Nonlinear Optical Crystal Na2SiF6

Nonlinear optical crystals of fluosilicate Na₂SiF₆ are synthesized via hydrothermal method and its structure is determined by single‐crystal X‐ray diffraction (XRD). The space group of Na₂SiF₆ is P321 with cell parameters a = 8.8715(3) Å, c = 5.0484(5) Å, Z = 3, V = 344.09(4) ų. The properties of the crystal are measured by powder XRD, infrared (IR) spectroscopy, ultraviolet/visible (UV/Vis) near‐infrared (NIR) diffuse reflectance spectroscopy, thermogravimetric (TG), and differential scanning calorimetry (DSC) analysis. The bandgap calculated using CASTEP is 7.41 eV, indicating that the cut‐off edge of the Na₂SiF₆ crystal can be down to deep‐UV energy region. The first‐principles studies were performed to elucidate the structure/property relationship of Na₂SiF₆.     

Bis(2-alkyl-4-thiocarbamoyl-4-pyridinium) hexafluorosilicates

The reaction of 45% silicahydrofluoric acid with 2-ethyl-4-thiocarbamoyl-4-pyridine (L¹) and 2-propyl-4-thiocarbamoyl-4-pyridine (L²) yields (L¹H)₂SiF₆ and (L₂H)₂SiF₆ hexafluorosilicates. These hexafluorosilicates are characterized by the data of IR spectroscopy, mass spectrometry, potentiometry, and solubility. The structure of (L¹H)₂SiF₆ is determined by X-ray diffraction. In the ionic structure of the complex, the L¹H⁺ cations (the protonation center is the pyridinic N atom) and SiF ₆ ^2? anions (Si-F 1.657(2)–1.699(2) Å) are joined by a system of interionic hydrogen bonds NH?F. Correlation between the characteristics of the interionic hydrogen bonds and the solubility of the hexafluorosilicates is discussed.