J. Sperlich et al., ZWITTERIONIC BIS [VIC-ARENEDIOLATO(2-)][( MORPHOLINIO)ALKYL]SILICATES- SYNTHESIS AND STRUCTURAL CHARACTERIZATION IN SOLUTION AND IN THE CRYSTAL, Zeitschrift fur Naturforschung. B, A journal of chemical sciences, 48(12), 1993, pp. 1693-1706
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.