- Spectroscopic Studies on Matrix Isolated Tungsten Chlorides and Bromides
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Tungsten pentachloride has been heated in high vacuum, and the vapour species isolated in inert matrices at ca. 12 K.Subsequent i.r. spectra showed intense features at 410 and 365 cm-1 which are assigned as the A2'' and E' stretching modes respectively of monomeric D3hWCl5.Corresponding studies on the hexachloride showed that monomeric WCl6 could similarly be isolated, and for this species, the u.v.-visible spectrum was also obtained and analysed in detail.The vaporisation of tungsten bromide samples of typical stoicheiometry WBr5.3 yielded a new spectroscopic feature in the matrix i.r. spectrum at ca. 305 cm-1 which is assigned to molecular WBr6.At higher temperatures, the vaporisation of the solid pentabromide resulted in bands at 280 and 245 cm-1 which are assigned as the A2'' and E' stretching modes in D3hWBr5.
- Brisdon, Alan K.,Hope, Eric G.,Levason, William,Ogden, J. Steven
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- Gas-phase electron-diffraction studies of the molecular structures of tetrachlorosulfidotungsten(VI), WSCl4, and tetrachloroselenotungsten(VI), WSeCl4
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The molecular structures of WSCl4 and WSeCl4 have been studied by gas-phase electron diffraction at average nozzle temperatures of 200 and 220°C, respectively. The experimental data for both species are fitted by square-pyramidal models of C4v symmetry in which the tungsten atom is slightly above the plane of the four chlorine atoms. The following principal distances (ra), angles, and root-mean-square amplitudes of vibration (l) with estimated uncertainties of 2σ were obtained. WSCl4: r(W=S) = 2.086 (6) A?, r(W-Cl) = 2.277 (3) A?, ∠SWCl = 104.2 (5)°, ∠ClWCl = 86.5 (2)°, l(W=S) = 0.031 (6) A?, l(W-Cl) = 0.058 (4) A?, l(S·Cl) = 0.147 (17) A?, l(Cl·Cl) = 0.114 (10) A?, l(Cl··Cl) = 0.120 (25) A?. WSeCl4: r(W=Se) = 2.203 (4) A?, r(W-Cl) = 2.284 (3) A?, ∠SeWCl = 104.4 (3)°, ∠ClWCl = 86.5 (2)°, l(W=Se) = 0.055 (4) A?, l(W-Cl) = 0.060 (3)A?, l(Se·Cl) = 0.147 (9) A?, l(Cl·Cl) = 0.116 (8) A?, l(Cl··Cl) = 0.116 (19) A?. The similarities and differences of these structures, together with that of WOCl4 available in the literature, are interpreted in terms of relative bond orders and nonbond repulsions.
- Page, Elizabeth M.,Rice, David A.,Hagen, Kolbj?rn,Hedberg, Lise,Hedberg, Kenneth
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- Kinetic study of Hubnerite (MnWO4) chlorination
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The kinetics of Argentinean Hubnerite (MnWO4) chlorination using gaseous chlorine as chlorination agent was studied between 750 and 950 °C. The relative mass change during the chlorination reaction was continuously monitored using a high resolution thermogravimetric system. The starting temperature for the reaction of the manganese tungstate with chlorine was determined at about 650°C. The influence of gaseous flow rate, sample mass, chlorine partial pressure, and temperature on the reaction rate was analyzed. The dependence of the reaction rate with sample mass clearly indicates that the reaction is not occurring under chemical control, so the reaction proceeds under mixed control for sample masses greater than 0.5 mg. In those conditions, an apparent activation energy of 198 ± 9 kJ mol-1 was obtained with an isoconversional method. Concerning the influence of chlorine partial pressure, it was determined that pressures greater than 35 kPa do not modify the kinetic regime. For the experiment at 850°C, it was found that the chlorination rate was proportional to a potential function of the partial pressure of chlorine whose exponent is around 0.85. Finally, a global rate equation that includes these parameters was developed.
- Fouga,Taddeo,Bosco,Bohé
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- μ-Nitrido Complexes of Tungsten(VI). The Crystal Structure of PPh4
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W2NCl9 was obtained as a brilliant red crystal powder from tungsten hexachloride and tris(trimethylsilyl)amine.According to its IR spectrum it has dimeric molecules 2 with bridging chlorine atoms.Its reaction with tetraphenylphosphonium chloride yields PPh4, and with phosphorus oxide chloride W2NCl9*OPCl3 is obtained; both are soluble in dichloromethane.The crystal structure of PPh4 was determined by X-ray diffraction (2521 observed reflexions, R = 0.065).Crystal data: triclinic, space group P, Z = 2, a = 1125.7, b = 1278.2, c = 1347.8 pm, α = 110.08, β = 94.55, γ = 111.55 deg.The structure consists of PPh4(+) ions which are arranged to (PPh4(+))2 pairs about inversion centres, and of (-) anions.The latter possess an almost linear WNW group (173 deg) with slightly different WN bond lengths of 179 and 188 pm corresponding to double bonds.Each tungsten atom has an octahedral coordination.The WCl bonds trans to the nitrido ligand are about 9 pm longer than the bonds in the cis positions. - Key words: μ-Nitrido Complexes, Synthesis, IR Spectra, Crystal Structure
- Godemeyer, Thomas,Berg, Alexander,Gross, Hans-Dieter,Mueller, Ulrich,Dehnicke, Kurt
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p. 999 - 1004
(2007/10/02)
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