New Chiral Zwitterionic (lambda)5Si-Silicates with an SiO5 or SiO4C Framework: Syntheses, Crystal Structures, and Properties

The syntheses of the zwitterionic (molecular) spirocyclic (lambda)5Si-silicates 7 and 8 (SiO5 skeletons) and 10-12 (SiO4C skeletons) are described. These 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 spacers that connect the ate and onium center of these zwitterions. Compound 7, 8, and 10-12 were studied by single-crystal X-ray diffraction, solution-state (1H, 13C, 29Si) and solid-state (29Si CP/MAS) NMR spectroscopy, and VT 1H-NMR spectroscopy. The experimental investigations were completed by ab initio studies of the related anionic (lambda)5Si-silicate 13.