Knowledge Bank

The structure and dipole moment of the Lewis acid-base adduct $(CH3)3N-SO3$ have been determined by microwave spectroscopy. Analysis yields an N-S bond length of $1.914(33)\backslash AA$ and an NSO angle of $100.0(4)\circ$. These data indicate that the formation of the N-S dative bond is nearly (but not entirely) complete in the gas phase. Comparison with previous work on the closely related system $H3N-SO3$ indicates that the increased basicity of the $(CH3)3N$ relative to that of $H3N$ is effective at driving the dative bond further towards completion. Analysis of nuclear hyperfine structure indicates that about 0.6 electrons are transferred from the nitrogen to the $SO3$ upon formation of the complex. This is significantly larger than that observed in $H3N-SO3$. The dipole moment, obtained from Stark effect measurements, of 7.111(7)D, arises from a combination of charge transfer, out-of-plane distortion of the $SO3$ and the intrinsic moment of $(CH3)3N$.