NEW ZWITTERIONIC LAMBDA(5)-SPIROSILICATES - SYNTHESES, SINGLE-CRYSTAL X-RAY STRUCTURE ANALYSES, AND SOLID-STATE NMR-STUDIES

The zwitterionic spirocyclic lambda5-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-)]-[(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 diffraction. Furthermore, 5, 5 . H2O, 6, and the related zwitterionic lambda5-spirosilicates 1 - 1/4 CH3CN, 2 - CH3CN, 3 . CH3CN, and 4 were characterized by solid-state NMR spectroscopy (Si-29 and N-15 CP/MAS). The pentacoordinate silicon atoms of 5, 5 . H2O (two crystallographically 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 (--> formation of dimeric units) N - H ... O hydrogen bonds. The coordination 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 and 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.