ZWITTERIONIC BIS[VIC-ARENEDIOLATO(2-)][(MORPHOLINIO)ALKYL]SILICATE - SYNTHESIS AND STRUCTURAL CHARACTERIZATION IN SOLUTION AND IN THE CRYSTAL

The zwitterionic lambda(5)-spirosilicates bis[1,2-benzenediolato(2-)][(morpholinio)methyl]silicate (1), bis[2,3-naphthalenediolato(2-)][(morpholinio)methyl]silicate (2; isolated as 2.CH3CN), bis [1,2-benzenediolato(2-)][3-(morpholinio)propyl]silicate (3) and bis-[2,3-naphthalenediolato(2 -)][3-(morpholinio)propyl] silicate (4; isolated as 4.1/2 CH3CN) have been synthesized by various methods including Si-C bond leavage reactions. The crystal structures of 2.CH3CN and 4.1/2CH(3)CN have been determined. 1,2.CH3CN, 3 and 4.1/2CH(3)CN have also been characterized by solution-state (H-1, C-13, Si-29) and solid-state NMR spectroscopy (Si-29 CP/MAS). The pentacoordinate silicon atoms of the zwitterions 1-4 are surrounded by four oxygen atoms and one carbon atom. In the crystal, the coordination polyhedra around the silicon atoms of 2.CH3CN (two crystallograpically independent zwitterions and two crystallographically independent acetonitrile molecules) can be described as nearly ideal trigonal bipyramids, with the carbon atoms occupying equatorial sites. The crystal structure of 2.CH3CN is considerably influenced by intermolecular N-H...N hydrogen bonds between the zwitterions and the acetonitrile molecules. The coordination polyhedron observed for the silicon atom in the crystal of 4.1/2 CH3CN can be described as a distorted square pyramid, with the carbon atom in the apical position. The crystal structure of 4.1/2 CH3CN is considerably governed by intermolecular N-H...O hydrogen bonds between the zwitterions which form infinite chains in the crystal. The Si-29 chemical shifts (delta = -75,5 to -85,8) observed for 1, 2.CH3CN, 3 and 4.1/2 CH3CN in solution ([D-6]DMSO) and in the crystal are typical of pentacoordinate silicon of the type SiO4C. For all compounds very similar Si-29 chemical shifts have been observed for the solution and solid state [Delta(delta(29)Si)less than or equal to 0,9] indicating that the zwitterions 1-4 do also exist in solution.