Microwave spectrum and structure of difluoro(trifluorosilyl)borane, SiF3BF2

Abstract
The microwave spectrum of 28SiF3 11BF2 has been thoroughly examined in the region 24–40 GHz. Transitions have been assigned within the five lowest-lying torsional states and the earlier analysis of the spectrum refined. An improved value for the barrier to internal rotation about the Si—B bond has been determined as V6= 2.178 ± 0.005 cal mol–1(9.11 ± 0.02 J mol–1). The spectra of the isotopic species 28SiF3 10BF2 and 29SiF3 11BF2 have also been assigned allowing the zero-point average Si—B bond length to be determined as 2.027 ± 0.005 Å, significantly longer than that expected for a single bond. The remaining rz structural parameters are determined to be: Si—F = 1.567 ± 0.005 Å, B—F = 1.312 ± 0.005 Å, ∠FBF = 118.5 ± 0.5°, ∠FSiB = 110.9 ± 0.2°. The structure and bonding of SiF3BF2 are compared with those of related molecules.

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