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Tungsten chloride fluorides: the preparation of cis- and trans-tungsten dichloride tetrafluoride and its decomposition into other tungsten fluorides
Abstract
Tungsten dichloride tetrafluoride has been prepared and found to consist of both cis- and trans-forms. The isomers are apparently in equilibrium and have not been separated by physical or chemical techniques. The compound is thermally unstable at room temperature, decomposing to tungsten hexachloride and tungsten hexafluoride. Other chloride fluorides of tungsten(VI) have been identified by 19F n.m.r. spectroscopy. The stability of cis- and trans-tungsten dichloride tetrafluoride is discussed.
... WF 5 Cl) according to earlier work using WF 6 and TiCl 4 . The work by Fraser et al. [14] suggest these compounds are very unstable and will most likely decompose quickly as the reactor temperature is increased. The final consideration was that WF 6 is reacting rapidly and can be depleted quickly. ...
In this work chemical vapor deposited (CVD) coatings of (Tix,W1-x)Ny from TiCl4, WF6, NH3 and Ar were investigated. This coating material has previously been deposited using other vacuum techniques but no publication has so far demonstrated CVD of (Tix,W1-x)Ny. The studied (Tix,W1-x)Ny coatings had a metallic molar ratio (Ti:W) close to 2:1 and 1:1, and were slightly over-stoichiometric with regard to N. The coatings appeared homogeneous and crystallised in a rock salt structure on an α-Al2O3 substrate. The cell parameter varied between 4.16 and 4.23 Å as a function of the deposition conditions, ranging from a pure TiNx to a pure WNx coating. The texture in the normal direction was 〈100〉 for the TiNx and (Tix,W1-x)Ny coatings and 〈111〉 for WNx. Electron backscattered diffraction (EBSD) results showed that a strong correlation to the substrate existed but random in-plane orientation was also present. The microstructure showed columnar grains with well defined facets growing. Adding a mixture of TiCl4 and WF6 to produce (Tix,W1-x)Ny did increase the grain size significantly when compared to the case when only one metal precursor was present. The down-stream thickness profile, using only WF6 and NH3, displayed mass transport control behaviour, with the coating thickness converging to zero within the deposition zone. Using only TiCl4 on the other hand showed a uniform deposition profile, the signs of a surface kinetics controlled process.
The chemistry of the boron trihalides has been extensively studied. These compounds are strong Lewis acids and form a wide range of simple 1 : 1 adducts that have served as model compounds for the study of Lewis acid-base interactions. Many reviews of their coordination chemistry have appeared and these are summarized in the more recent reviews appearing in the mid-1960s. In boron trifluoride adducts, fluorine displacement is relatively difficult, and thus, the widest range of adducts has been prepared for the trifluoride. As fluorine is replaced by successively heavier halogens, the displacement of halogen occurs more readily and secondary reactions of the initially formed donor-acceptor adducts become more important. Whereas the initial formation of a donor acceptor bond is a simple process, the secondary reactions of adducts need not be simple. Many such reactions, and related catalytic activity of donor-acceptor adducts of the boron trihalides, have been reported.
The chapter focuses on the fluorine-19 nuclear magnetic resonance (NMR) spectroscopy. Most of the acyclic olefins and acetylenes have either fluorine or a fluoroalkyl group attached to the multiply-bonded carbon. The chapter elaborates the fluorohydrocarbons, and describes their properties and the results of the studies for their chemical shifts. The chapter also describes the heterocyclic systems, such as nitrogen heterocycles; oxygen, and sulphur heterocycles and some mixed systems. Measurement of line width as a function of the temperature and pressure of gaseous samples has been used to obtain relaxation times for silicon tetrafluoride, tetrafluoromethane, and sulphur hexafluoride comparable with those obtained by pulse techniques. The chapter discusses the fluorinated derivatives of main group elements; transition metal fluorides and their derivatives; and transition metal complexes of the fluorinated molecules.
Enthalpies of formation of the tungsten (VI) compounds WF5Cl, WF4Cl2, WF5(OMe), cis-WF4(OMe)2 and cis-WF2(OMe)4 are reported. Re-distribution and decomposition reactions in the chloride-fluoride and in the methoxide-fluoride series are discussed in the light of the thermochemical results.
The 19F NMR spectra of TaF5 and TaF5-Ta(OC2H5)5 as well as Ta(OC2H5)5-HF dissolved in ethanol and acetonitrile were studied. In these solutions neutral, anionic and cationic complexes were found to be formed. In fluoro-anion with two OC2H5-groups only cis-arrangement was found, while in neutral and cationic complexes with two fluorine atoms both cis- and trans-isomers were present.
The reactions between UF5 and either Me3SiCl or UCl5 in anhydrous acetonitrile yield soluble uranium (V) chloridefluorides. The crystalline complexes UF5·2tppo and UCl2F3·2tppo are obtained in the presence of an excess of triphenylphosphine oxide (tppo).
Fluorine-19 n.m.r. measurements show that UF6 undergoes facile halide exchange with either SiMe3Cl or UCl6 in CFCl3 or CF2Cl2 solution at temperatures below –60 °C. Hence all the uranium (VI) chloride fluorides in the series UFnCl6-n(n= 1–5) have been characterized virtually definitively. The visible and mass spectra of the mixed halides have been investigated also. Unlike UF6 and UCl6, the mixed halides decompose at temperatures above –60 °C liberating chlorine gas and giving halides of uranium(IV) or uranium(V).
High oxidation state transition metal fluorides are selective fluorinating agents for dichloromethane; those with d0; electronic configurations undergo hydrogen–fluorine exchange and metal reduction, while dn species undergo chlorine–fluorine exchange.
Reactions involving 1.1:1 molar ratios of uranium hexafluoride to either trimethylsilylchloride or trimethylsilylbromide in halocarbon solutions yield β-UF5 at room temperature. With 2 mol equivalents of trimethylsilylchloride the product is UF4. The reactions appear to proceed via the intermediate formation of unstable brown uranium(VI) chloride and bromide fluorides. Calculations show that UClF5 and UCl2F4 are thermodynamically unstable with respect to the loss of chlorine at room temperature.
Enthalpies of formation of ReCl5, –86·1 ± 0·8 kcal mol–1, and ReF6, –322·6 ± 2·3 kcal mol–1, have been estimated from hydrolysis measurements. The reaction of rhenium hexafluoride with boron trichloride, under various conditions, has been shown to yield rhenium pentachloride as the only major solid phase; the previously reported hexachloride has not been detected.
The gas-phase composition of the systems C/F2/Y2 and W/C/F2/Y2(Y = Cl, Br) has been calculated using a digital computer on the basis that thermodynamic equilibrium is attained at the gas/solid interface with tungsten and that the rate of reaction is not kinetically controlled.The partial pressures of the various components, i.e. CX, CX2, CX3, CX4, C2X2, C2X4, C2X6 and WX, WX2, WX4, WX5, WX6, together with those of W, X2 and X (where X = F, Cl, Br) have been evaluated as a function of the temperature and of the halogen concentration in the input gas. While compounds of the type CnXm are quite stable in C/F2/Y2 systems, they are relatively unstable in the presence of solid tungsten where the corresponding tungsten compounds are formed.From the temperature dependence of the mass balance of tungsten, the direction of the chemical transport reactions in these systems may be predicted. In W/C/F2/Y2 systems, two points of inversion exist as in the tungsten-fluorine system. At low temperatures, transport proceeds down the temperature gradient, reversing its direction at moderate temperatures and proceding down the temperature gradient once more at high temperatures.
Die Substitution von Fluor durch F5TeO-Gruppen in WF6 mittels B(OTeF5)3 führt zu WFn(OTeF5)6-n. WF5OTeF5 und cis-WF4(OTeF5)2 konnten isoliert werden. Die Verbindungen mit n > 2 wurden durch 19F-NMR identifiziert. Das Ligandenverhalten der F5TeO-Gruppe wird mit OMe und OPh verglichen.Tungsten(VI) Fluoride Pentafluorotellurates(VI): WFn(OTeF5)6-nIn WF6 fluorine can be replaced by F5TeO groups by means of B(OTeF5)3 to form WFn(OTeF5)6-n. Isolation was achieved for WF5OTeF5 and cis-WF4 (OTeF5)2. Compounds with n > 2 have been identified by 19F-nmr spectroscopy. The ligand behaviour of the F5TeO group is compared to OMe and OPh.
The compounds WF6–n(OR)n(R = Me, n= 1–5; R = Ph, n= 1,2), WOF4L [L = Me2O or (MeO)2P(O)Me] and (MeO)3PMe+WOF5– have been studied by use of 19F–{183W}, 19F–{19F}, 1H–{19F}, and 1H–{31P} double-resonance techniques. 183W Chemical shifts are reported and the factors affecting these and the 19F shifts are discussed. By similar techniques WOF4,OS(OMe)2 and the µ-fluoro-bis[oxotetrafluorotungstate(VI)] anion, W2O2F9–, have been identified as products from the reaction of WF5OMe with (MeO)2SO. The coupling constants 2J(FcFt), 1J(FcW), and 1J(FtW)(Fc,Ft, cis and trans respectively to oxygen) all have the same sign in WF5OR and cis-WF4(OMe)2 but 1J(FcW) is of opposite sign to J(FcW) and J(FcFt) in WOF5– and W2O2F9–.
The compound F5UOMe has been prepared by the reaction of UF6 with MeOH in CFCl3 solvent at –90°C and has been characterized by 13C, 1H, and 19F n.m.r. methods.
Uranium(V) chloridefluoride complexes of compositions UClxF5 − x· nMeCN (0 ⩽ x ⩽ 5, n = 1 and 2) and UClxF5 − x·ntppo (0 ⩽ x ⩽ 5, n = 1 and 2, tppo triphenylphosphineoxide) have been prepared and characterized. Visible-near-IR and IR spectra are reported.
Tungsten hexafluoride reacts with trimethylsilyldiethylamine or trimethyl(pentafluorophenoxo)silane at or below ambient temperature with the replacement of F by –NEt2 or –OC6F5 groups. Compounds isolated were monomeric WF2(NEt2)4, polymeric WF4(NEt2)2 and monomeric WF5OC6F5. WF4(OC6F5)2 appears to exist in cis- and trans-forms and undergoes reorganisation to give other members of the series.
The diethylamido-niobium and -tantalum fluorides, MF4NEt2 and MF3(NEt2)2 are formed from the pentafluorides and Me3SiNEt2 at 20 °C. They are weaker Lewis acids than the pentafluorides and are thought to be fluoro-bridged polymers from their i.r. spectra. Niobium pentafluoride reacts with Me3SiCl in Et2O to give labile niobium chlorofluoride species and finally NbCl5, OEt2.
The low temperature 19F n.m.r. spectra of the mixtures TiF62−−TiX62− (X = Cl−, Br−, NCS−, NCO−) in sulfur dioxide solution have been examined. When X = Cl− or Br− rapid fluorine exchange is occurring even at the lowest accessible temperature, but when X = NCS− or NCO− the spectra of the individual mixed species TiF6−xXx2− are observed. In the latter two cases the solutions also contain fluorine-bridged dimers in stable equilibrium. The 19F chemical shifts of TiF6−xXx2− (X = NCS− or NCO−) and of some related mixed complexes are reasonably represented by the equation δ = pC + qT where C and T are constants characteristic of the substituent X and p and q are the number of ligands X cis and trans respectively to the resonating fluorine. The constants T appear to be a measure of the π-donor ability of the ligand X in these complexes, supporting the idea that the chemical shift of a fluorine in fluorotitanates is determined largely by the extent to which fluorine-to-titanium back donation occurs.
The preparation and characterization of compounds of composition Cl6-xW(OCH2CF3)x (x = 1−6) and X4W[OC(CH3) (CF3)2]2 (X = Cl,F) together with 19F NMR spectra are reported. An X-ray structure analysis of Cl4W[OC(CH3)(CF3)2]2 shows a W-O-C angle of 173.6°, which is unusually large for metal alkoxides, and a short W-O distance of 181.9 pm. A discussion on structural aspects and a comparison with related tungsten-nitrogen compounds are presented. Cl4W[OC(CH3) (CF3)2]2 is monoclinic, space group C2/m, with a = 820.3(2), b = 1059.2(2), c = 1071.6(2) pm, β = 99.72(2)°, Z = 2 and was refined to R = 0.031 for 848 observed reflections.
The reactions of chlorine perchlorate and bromine perchlorate with numerous fluoroalkyl halides were examined. In the case of fluorocarbon iodides, these reactions were generally found to produce high yields of the novel fluorocarbon perchlorates CF3ClO4, CF3CF2ClO4, n-C7F15ClO4, O4ClCF2CF2ClO4, and ICF2CF2ClO4. Important insight into the mechanism of formation of these compounds was obtained through the isolation of complex intermediates such as (CF3)2CFI(ClO4)2 and n-C7F15I(ClO4)2. Based on their vibrational spectra, these intermediates have the ionic structure [(Rf)2I]+[I(ClO4)4] -. Fluorocarbon bromides reacted less readily but sometimes did produce perchlorate derivatives such as (O4ClCF2CFBr-)2, CF3CFBrCF2ClO4, and BrCF2CF2ClO4. Neither mono nor di, primary nor secondary chlorine contained in saturated RfCl materials interacted with these halogen perchlorates. These and other related reactions are discussed and characteristic data are given for this new and interesting class of compounds.
The equilibrium Te(OH)6 + nHF ⇌ Te(OH)nF6-n + nH2O has been studied, mainly by 19F nmr spectroscopy. In the solvolysis of Te(OH)6 in HF, products up to n = 3 have been identified, while in the hydrolysis of TeF6 products with n = 0-5 have been observed. The stereochemical configuration of most of the species has been determined. Solvolysis of selenic acid in HF leads to pentafluoroorthoselenic acid and two other products, one of which is probably HSeO3F.
The diethylaminotungsten(VI) fluorides WF5NEt2, WF4(OMe)(NEt2), and WF4(OPh)(NEt2), have been prepared from reactions of trimethylsilyldiethylamine with tungsten hexafluoride, methoxy-, and phenoxytungsten(VI) pentafluorides, respectively. Their i.r. and n.m.r. spectra are reported and compared with those of other substituted tungsten(VI) fluorides. WF5NEt2 and WF5OPh undergo complex reactions with dimethyl sulphite which may be explained in terms of the formation of WF4(X)[OS(O)OMe] and WF4(X)(OMe) (X = NEt2 or OPh).Es wurden die Diäthylaminowolfram(VI)-fluoride WF5NEt2, WF4(OMe)(NEt2) and WF4(OPh)(NEt2) durch Umsetzung von Trimethylsilyldiäthylamin mit WF6, WF5OMe bzw. WF5OPh dargestellt. Ihre IR- und KMR-Spektren werden mit denen anderer substituierter Wolfram(VI)-fluoride verglichen. Mit Dimethylsulfit reagieren WF5NEt2 und WF5POh offenbar jeweils zu einem Gemisch aus WF4(X)[OS(O)OMe] und WF4(X)(OMe) (X = NEt2 oder OPh).
IntroductionStructures of the Halides and OxyhalidesReactions of Metal Halides and Oxyhalides of the Noncluster TypeReactions of Cluster Metal HalidesSome Further Remarks
IntroductionThe Chemistry of W(VI)The Chemistry of W(V)The Chemistry of W(IV)The Chemistry of W(III)The Chemistry of W(II)Complexes of DinitrogenNitrosyl ComplexesHydrido Complexes
Phosphorus and arsenic pentafluorides and arsenic trifluoride form 1:1 complexes with many simple anions. The hexafluoroanion and multiply anion substituted species are frequently formed from the pentafluoride complex. Phosphorus trifluoride reacts with some anions to give PF6− and other species.
Uranium (VI) chloride fluorides were synthesized by the reaction of liquid HCl and solid UF6 between −80 and −114°C. These dark red compounds are unstable above −40 to −60°C. The simplest formulas derived from compositional analysis are UF5Cl and UF4Cl2.
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