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 (r_a) for CCl (SiMe₃)₃, with estimated standard deviations in parentheses, are r(C–Cl) 182.3 (15) pm, r(Si–C_inner) 193.9(6) pm, r(Si–C_outer) 188.2(2) pm, and angles Cl–C–Si 102.7(5)° and C_outer–Si–C_outer 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–C_inner) 195.4(15) pm, r(Si–C_outer) 187.7(3) pm, Br–C–Si 106.5(6)° and C_outer–Si–C_outer 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.