PUB - Publikationen an der Universität Bielefeld

(N,N-Dimethylaminoxy)trifluorosilane, F3SiONMe2 (1), was prepared by the reaction of LiONMe2 with SiF4 in Me2O at -96 degrees C as a colorless, air-sensitive liquid, which was identified by gas-phase IR spectroscopy and NMR spectroscopy of the nuclei H-1, C-13, N-15, O-17,F-19, and Si-29. The gas-phase geometry of 1, as determined by electron diffraction analysis refined in C-s symmetry, is influenced by weak attractive interactions between Si and N: Si ... N 2.273(17) Angstrom, Si-O-N 94.3(9)degrees, [Si-O 1.619(8) Angstrom, N-O 1.479(7) Angstrom, O-Si-Fin-plane 104.1(10)degrees, O-Si-Fout-of-plane 111.8(10)degrees]. X-ray diffraction analysis of 1 reveals that intramolecular Si N interactions are much stronger in the solid state than in the gas phase: Si ... N 1.963(1) Angstrom, Si-O-N 77.1(1)degrees [Si-O 1.639(1) Angstrom, N-O 1.508(1) Angstrom, O-Si-Fin-plane 102.5(1)degrees, O-Si-Fout-of-plane 118.0(1)degrees and 120. 1(1)degrees]. Using measured NMR chemical shifts in C6D6 solution, the geometry of 1 in solution was determined with the NMR/ab initio/DFT-IGLO method to fall between that of the gas-phase geometry and the geometry in the solid state. MP2 and DFT calculations reveal that electrostatic interactions between 1 and the surrounding medium increase with the dielectric constant epsilon since mutual charge polarization enhances the molecular dipole moment from 4 to more than 6 D, which implies a compression of the Si-O-N angle and the Si N distance. Since electrostatic attraction between N and Si supports these changes, the increase in molecular energy upon reduction of the Si ... N distance is small and compensated by the gain of stabilizing intermolecular interactions. The analysis of the calculated electron density distribution shows that the main aspects of bonding in 1 are not changed in the solid state and that the Si ... N attraction is not of covalent nature, but rather due to strong electrostatic and dipole interactions.