The zwitterionic λ5 Si-organofluorosilicates F4SiCH2NMe2H (5) and F3MeSiCH2NMe2H (7; crystallographic modifications 7a and 7b) were synthesized by reaction of the silanes (MeO)3SiCH2NMe2 (11) and (MeO)2MeSiCH2NMe2 (13), respectively, with HF in a mixture of ethanol and hydrofluoric acid at 0 °C. The related zwitterionic λ5 Si-organofluorosilicates F4SiCH2NMe3 (6) and F3MeSiCH2NMe3 (8) were obtained analogously by reaction of HF with the ammonium iodides [(MeO)3SiCH2NMe3]I (12) and [(MeO)2MeSiCH2NMe3]I (14), respectively. Reaction of the silanes (MeO)3SiCH2NR2 (16) and (MeO)2 tBuSiCH2NR2 (17) (NR2 = 2,2,6,6-tetramethylpiperidino) with HF gave the zwitterionic λ5 Si-organofluorosilicates F4SiCH2NR2H (9) and F3 tBuSiCH2NR2H (10), respectively. The crystal structures of compounds 5, 6, 7a,b, and 8−10 were determined by single-crystal X-ray diffraction studies. Compounds 5−10 were studied by solution-state 1H, 13C, 19F, and 29Si NMR experiments at room temperature (solvent CD3CN). These studies indicate a rapid fluorine exchange at room temperature. As shown by temperature-dependent 19F NMR experiments with 10 (solvent CD2Cl2), this ligand exchange can be reduced on cooling. According to line-shape analyses, the dynamic behavior of 10 can be described by two different processes. For compounds 5−8 and related model species ab initio studies at the SCF/SVP and MP2/TZP levels were performed. Calculated and experimental (crystal structures) geometric data were compared, and the influence of intermolecular interactions (packing effects) in the solid state and intramolecular interactions between the charged centers in the calculated zwitterions were studied. Furthermore, the dynamic behavior of the title compounds was investigated by ab initio studies of the related model species F4SiCH2NH3 (19) and F3MeSiCH2NH3 (20).

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are surrounded by four oxygen atom s and one carbon atom. In the crystal, the coordination polyhedra around the silicon atom s of 2 -C H 3CN (two crystallographically independent zwitterions and two crystallographically independent acetonitrile molecules) can be describ ed as nearly ideal trigonal bipyram ids, with the carbon atom s occupying equatorial sites. Verlag der Zeitschrift für Naturforschung,

On the Existence of Zwitterionic λ5‐(Ammonioorganyl)tetrafluorosilicates: Synthesis and Crystal and Molecular Structure of Tetrafluoro(pyrrolidiniomethyl)silicate The zwitterionic tetrafluoro(pyrrolidiniomethyl)silicate (6) was synthesized by the reaction of trimethoxy(pyrrolidinomethyl)silane (7) with hydrogen fluoride in ethanol/hydro‐fluoric acid (yield 83%). 6 crystallizes in the space group P1/c with two crystallographically distinct molecules in the asymmetric unit. In both molecules the pentacoordinate silicon atom is surrounded by four fluorine atoms and one carbon atom, the latter being in an equatorial position. The coordination polyhedron of the silicon atoms can be described as a slightly distorted trigonal bipyramid. The zwitterionic structure was also proved for dissolved 6 (solution in CD3CN, NMR‐spectroscopic studies).

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