Determination by electron diffraction of the molecular structures of chloro- and bromo-tri(trimethylsilyl)methane in the gas phase

Abstract

The molecular structures of chloro- and bromo-tris (trimethylsilyl)methane in the gas phase have been determined by electron diffraction. Both molecules have inner Si–C bonds which are longer than normal and wide Si–C–Si angles. Principal parameters (ra) for CCl (SiMe3)3, with estimated standard deviations in parentheses, are r(C–Cl) 182.3 (15) pm, r(Si–Cinner) 193.9(6) pm, r(Si–Couter) 188.2(2) pm, and angles Cl–C–Si 102.7(5)° and Couter–Si–Couter 109.6(4)°. The three trimethylsilyl groups are twisted 14.6(7)° from the staggered positions, and tilted 1.3(6)° away from the molecular three-fold axis. For CBr(SiMe3)3 the major parameters are r(C–Br) 191.1(35) pm, r(Si–Cinner) 195.4(15) pm, r(Si–Couter) 187.7(3) pm, Br–C–Si 106.5(6)° and Couter–Si–Couter 109.3(5)°. The trimethylsilyl groupos are twisted 13.5(7)° from the stagtgered positions, but the tilt angle of these groups could not be determinded.