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

The zwitterionic lambda(5)-spirosilicates 2-benzenediolato(2-)][(morph olinio)methyl]silicate (1), phthalenediolato(2-)][(morpholinio)methyl] silicate (2; isolated as 2.CH3CN), bis benzenediolato(2-)][3-(morpholi nio)propyl]silicate (3) and bis-[2,3-naphthalenediolato(2 -)][3-(morph olinio)propyl] silicate (4; isolated as 4.1/2 CH3CN) have been synthes ized by various methods including Si-C bond leavage reactions. The cry stal 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-sta te (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 surround ed by four oxygen atoms and one carbon atom. In the crystal, the coord ination polyhedra around the silicon atoms of 2.CH3CN (two crystallogr apically independent zwitterions and two crystallographically independ ent acetonitrile molecules) can be described as nearly ideal trigonal bipyramids, with the carbon atoms occupying equatorial sites. The crys tal structure of 2.CH3CN is considerably influenced by intermolecular N-H...N hydrogen bonds between the zwitterions and the acetonitrile mo lecules. The coordination polyhedron observed for the silicon atom in the crystal of 4.1/2 CH3CN can be described as a distorted square pyra mid, with the carbon atom in the apical position. The crystal structur e of 4.1/2 CH3CN is considerably governed by intermolecular N-H...O hy drogen 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 c rystal are typical of pentacoordinate silicon of the type SiO4C. For a ll 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.