1. Review dealing with zwitterionic λ5Si-silicates: Tacke, R.; Pülm, M.; Wagner, B.Adv. Organomet. Chem.1999,44, 221−273, and references therein.
2. Pentacoordination of Silicon by Four Covalent Si−S Bonds and One Covalent Si−C Bond
3. The hydrogen-bonding systems were analyzed by using the program system PLATON: Spek, A. L. PLATON; University of Utrecht: Utrecht, The Netherlands, 1998. In this context, see also: Jeffrey, G. A.; Saenger, W.Hydrogen Bonding in Biological Structures; Springer-Verlag: Berlin, Germany, 1991; pp 15−24.