Neue zwitterionische λ51‐Spirosilicate: Synthesen, Einkristall‐Röntgenstrukturanalysen und Festkörper‐NMR‐Untersuchungen

Abstract

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.