INFRARED MATRIX ISOLATION STUDIES OF PENTACOORDINATE SILICON ANIONS: SiF$5_{^{-}}$ AND ITS CHLORINE ANALOGS
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Date
1978
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Ohio State University
Abstract
The salt/molecule reaction technique, in conjunction with matrix isolation, hag been applied to the synthesis and characterization of nonlinear polyatomic anions. The reaction of alkali fluoride salt molecules with $SiF_{4}$ yielded three moderately intense bands between 800 and $950\, cm^{-1}$ as well as one or more bands below $500\, cm^{-1}$. The upper bands have been assigned to the Si-F stretching vibrations of $SiF_{5}{^{-}}$, while the lower band, or bands, have been assigned to Si-F deformation modes, similar spectra have been obtained for the mixed chlorine/fluorine species, except for the pure chlorine species $SiCl_{5}{^{-}}$ which could not be formed under these conditions. Annealing of the matrix led to two new, intense bands which are in agreement with literature values far $SiF_{6}{^{-}}$. These results have been interpreted to indicate that the $SiF_{6}^{=}$ anion has been formed in a matrixion pair, but the geometry, at best, can be described as a perturbed trigonal bipyramid. The spectra can be accounted for by invoking distortion of the $SiF_{5}{^{-}}$ anion by the ion-paired cation (which could either activate the forbidden Si-F stretching mode, or. split the doubly degenerate Si-F stretching vibration), or by postulating s structure other than a trigonal bipyramid.
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Author Institution: Department of Chemistry, University of Cincinnati