Structure and chemistry of sulfur tetrafluoride

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Goettel, James T.
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Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry, c2013
Sulfur tetrafluoride was shown to be a useful reagent in preparing salts of ReVIIO2F4−, IVOF4−, and IVIIO2F4−. Sulfur tetrafluoride reacts with oxo-anions in acetonitrile or anhydrous HF (aHF) via fluoride-oxide exchange reactions to quantitatively form oxide fluoride salts, as observed by Raman and 19F NMR spectroscopy. Pure Ag[ReO2F4] as well as the new CH3CN coordination compounds [Ag(CH3CN)2][ReO2F4] and [Ag(CH3CN)4][ReO2F4]•CH3CN were prepared. The latter was characterized by single-crystal X-ray diffraction. The reaction of [N(CH3)4]IO3 with SF4 in acetonitrile gave the new [N(CH3)4][IOF4] salt. Sulfur tetrafluoride forms Lewis acid-base adducts with pyridine and its derivatives, i.e., 2,6-dimethylpyridine, 4-methylpyridine and 4-dimethylaminopyridine, which have recently been identified in our lab. In the presence of HF, the nitrogen base in the SF4 base reaction systems is protonated, which can formally be viewed as solvolysis of the SF4•base adducts by HF. The resulting salts have been studied by Raman spectroscopy and X-ray crystallography. Crystal structures were obtained for pyridinium salts: [HNC5H5+]F−•SF4, [HNC5H5+]F−[HF2−]•2SF4; 4-methylpyridinium salt: [HNC5H4(CH3)+]F−•SF4, [HNC5H4(CH3)+][HF2−]; 2,6-dimethylpyridinium salt: [HNC5H3(CH3)2+]2[SF5−]F−•SF4; 4-dimethylaminopyridinium salts: [HNC5H4N(CH3)2+]2[SF5−]F−•CH2Cl2, [NC5H4N(CH3)2+][HF2−]•2SF4; and the 4,4’-bipyridinium salts: [HNH4C5−C5H4N+]F−•2SF4, [HNH4C5−C5H4NH2+]2F−•4SF4. These structures exhibit a surprising range of bonding modalities between SF4 and fluoride and provide an extensive view of SF4 in the solid state. For the first time, the solid-state structure of SF4 was elucidated by single-crystal X-ray diffraction. The structure can best be described as a network with weak intermolecular S---F contacts formed exclusively by the axial fluorines that exhibit more ionic character. A similar structural motif was found in the novel [HNC5H3(CH3)2+]2[SF5−]F−•4SF4 salt which contains layers of SF4. Adduct formation of SF4 with oxygen-bases was observed for the first time. These SF4•O-base adducts (SF4•OC4H8, SF4•(OC4H8)2, SF4•(CH3OCH2)2, SF4•(O=C5H8)2) were synthesized, isolated, and characterized at low temperatures. The structures were elucidated by X-ray crystallography and Raman spectroscopy. The characterization of the SF4•ketone adduct (SF4•O=C5H4) is of great significance, since SF4 can serve as a fluorinating agent towards carbonyl groups. These adducts offer the first extensive view of dative O---S(IV) bonds.
xviii, 177 leaves : ill. ; 29 cm
Sulfur tetrafluoride -- Structure , Sulfur tetrafluoride -- Analysis