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.