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D. L. FIACCO, M. E. OTT AND K. R. LEOPOLD, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455; A. TORO, Pontifical Catholic University of Puerto Rico, Ponce, PR 00731-6382.
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) Å 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.