Massenspektrometrische Beobachtungen und chemische Transportexperimente mit den Systemen VCl3/Al2Cl6 und VCl2/Al2Cl6 |
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Authors: | Harald Schfer Ulrich Flrke Marita Trenkel |
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Institution: | Harald Schäfer,Ulrich Flörke,Marita Trenkel |
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Abstract: | Mass Spectroscopic Observations and Chemical Transport Experiments with the Systems VCl3/Al2Cl6 and VCl2/Al2Cl6 By mass spectrometry the equilibrium VCl3,s + 0.5 Al2Cl6,g ? VAlCl6,g has been determined: ΔH°(298) = 25.6(±0.5) kcal; ΔS°(298) = 23.0(±3) cal/K, ΔCp (assumed) = ?4 cal/K. This is approximately in agreement with results determined by ligand field spectroscopy by ANUNDSKÅS and ØYE (A. and Ø.). For the dimerization of VCl3,g values for ΔH and ΔS have been derived. The molecule VAl2Cl9 assumed by A. and Ø. could not been observed by mass spectrometry. For the VCl2/Al2Cl6 complex, observed by chemical transport, A. and Ø. give the formula VAl3Cl11. This molecule could not been observed by mass spectrometry. This suggests a smaller concentration, compared with the results of A. and Ø. Stabilization of VCl2,s (by metal-nietal-bonds) shifts the reaction to the left, whith explains the lower complex concentration as well as the larger molecular weight of the complex. With chlorides stabilized by stronger metal-metal bonds (MoCl3, MoCl2, Nb3Cl8) AlCl3 complexes are not formed in observable concentrations. The chemical transport of VCl2 with Al2Cl6 needs relatively high temperatures (973 → 873 K). In this case the addition of SiCl4 hinders the attack of the quartz ampoule by Al2Cl6. Using a VCl3 + VCl2 mixture, VCl3 is transported by Al2Cl6 (673 → 623 K) into the colder region. If afterwords the ampoule is reversed, VCl3 again moves into the colder region, but the thermal decomposition of VCl3 at the same time causes that a VCl2-residue remains in the hot region. |
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