Bond cleavage, Si - C
Solid-state NMR, 29Si and 15N
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
New Zwitterionic λ51-Spirosilicates: Syntheses, Single-Crystal X-Ray Structure Analyses, and Solid-State NMR StudiesThe zwitterionic spirocyclic λ51-silicates bis[3,4,5,6-tetrabromo-1,2-benzenediolato(2-)][2-(pyrrolidinio)ethyl]silicate (5; and its monohydrate 5 · H2O) and bis[1,2-benzenediolato(2-)]1-[(dimethylammonio)methyl]silicate (6) were synthesized by various methods including Si - C bond cleavage reactions. The crystal structures of 5, 5·H2O, and 6 were investigated by X-ray diffarction. Furthermore, 5, 5·H2O, 6, and the related zwitterionic λ51-spirosilicates 1·1/4 CH3CN, 2·CH3CN, 3·CH3CN, and 4 were characterized by solid-state NMR spectroscopy (29Si and 15N CP/MAS). The pentacoordinate silicon atoms of 5, 5·H2O (two cystallographically independent zwitterions and two crystallographically independent water molecules), and 6 (two crystallographically independent zwitterions) are surrounded by four oxygen atoms and one carbon atom. The coordination polyhedrons around the silicon atoms of 5 and 6 can be described as distorted (5) or nearly ideal (6) trigonal bipyramids, the carbon atoms being in equatorial positions. 5 forms intramolecular and 6 intermolecular (→ for-mation of dimeric units) N - H…O hydrogen bonds. The co-ordination polyhedrons around the two crystallographically independent silicon atoms of 5·H2O can be described as a nearly ideal and slightly distorted square pyramid, respectively, the carbon atoms being in the apical positions. In the crystal lattice of 5·H2O, intermolecular N - H…O O - H…O hydrogen bonds between the zwitterions and water molecules are observed. The results obtained by X-ray diffraction and solid-state NMR spectroscopy are consistent for each compound studied.
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