STRUCTURAL STUDIES OF TRIS(DIALKYLAMINO)SULFONIUM (TAS) FLUOROSILICATES

The crystal structures of two pentavalent silicon anions are discussed . The structure of [SiMe3F2]- 1 shows a trigonal bipyramidal structure with the fluorines in apical positions. The Si-F bond distances are t he longest known of this type. The crystal structure of fluorosilicate 2 rifluoromethyl]-1,3-dihydro-2,1-benzoxasi-lole[ion 1-]) is distorte d toward a rectangular structure along the Berry pseudorotation coordi nate. The lone Si-F bond distance in 2 is much shorter than that in 1. The ab initio calculations on a variety of pentavalent fluorinated si licon anions are reported, and good agreement with the experimental da ta are found. Fluoride affinities for the fluorosilanes are reported a nd are in reasonable agreement with the experimental values where know n. The fluoride affinity of the tetra-coordinated species is related t o the length of the Si-F bond in the pentavalent anion.