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T10TeF5(mes)2]2 and [Tl(mes)2+][B(OTeF5)4'] are in harmony with the molecular structures for these compounds. There are mutually exclusive IR and Raman v(TeO) bands for [TIO-TeF5(mes)2]2, consistent with the nearly centrosymmetric structure of this dimer. The average v(TeO) value of 823 cm'1 is between the low value for HOTeF5 (733 cm"1) and the high value for [N(«-Bu)4+][OTeF5'] (867 cm'1) and correlates well with the Te-0 distances and for this compound (Table VIII). The compound T10TeF5 also exhibits mutually exclusive IR and Raman v(TeO) bands. While little is known about the structure of this compound, the vibrational data indicate that it probably Controlled Hydrolysis of the Hexafluorides of Molybdenum, Tungsten, and Rhenium: Structure of Oxonium (ju-Fluoro)bis(tetrafluorooxotungstate(VI)

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Silicon tetrafluoride has been used as a fluoridating agent to extract titanium, as TiF4, from ilmenite at temperatures above 700 "C. Although the reaction is thermodynamically unfavorable, good conversions are obtained by disturbing the equilibrium of the system through the removal of the TiF4 from the reaction zone using a desublimation technique. The TiF4 is then converted by hydrolysis to Ti02 in the anatase form. All of the reagents can be recycled back into the process and the spent residue, which contains a small level of fluoride, requires only minor treatment before disposal.