New chiral zwitterionic lambda Si-5-silicates with an SiO5 or SiO4C frame work: Syntheses, crystal structures, and properties

The syntheses of the zwitterionic (molecular) spirocyclic lambda(5)Si-silic ates 7 and 8 (SiO5 skeletons) and 10-12 (SiO4C skeletons) are described. Th ese chiral compounds contain a pentacoordinate (formally negatively charged ) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. The pairs 7/11 and 8/12 are isoelectronic O/CH2 analogues and 10-12 represent a series of homologous compounds containing different alkylene sp acers that ray diffraction, solution-state (H-1, C-13, Si-29) and solid-sta te (Si-29 CP/MAS) NMR spectroscopy, and VT H-1-NMR spectroscopy. The experi mental investigations were completed by ab initio studies of the related an ionic lambda(5)Si-silicate 13.