ZWITTERIONIC S[CITRATO(2-)-O-3,O-4](MORPHOLINIOMETHYL)GERMANATE HYDRATE AND ITS SILICON ANALOG - SYNTHESES AND CRYSTAL-STRUCTURE ANALYSES

The zwitterionic spirocyclic lambda(5)Ge-germanate s[citrato(2-)-O-3,O -4](morpholiniomethyl)germanate (2) and its silicon analogue is[citrat o(2-)-O-3,O-4](morpholiniomethyl)silicate (3) were synthesized by reac tion of citric acid with trimethoxy(morpholinomethyl)germane (4) and t rimethoxy(morpholinomethyl)silane (5), respectively. Both reactions we re carried out at room temperature in acetonitrile and the products is olated, after crystallization from water, as the hydrates 2.H2O and 3. H2O. In addition to NMR spectroscopic (solution-state H-1, C-13, and S i-29 NMR; solid-state Si-29 CP/MAS NMR) and mass spectrometric (FAB MS ) characterization of 2, 2.H2O, 3, and 3.H2O, the hydrates were struct urally characterized by single-crystal X-ray diffraction. The zwitteri ons 2 and 3 contain a pentacoordinate (formally negatively charged) ge rmanium and silicon atom, respectively, and a tetracoordinate (formall y positively charged) nitrogen atom. The central atom of 2 (Ge) and 3 (Si) is surrounded by four oxygen atoms and one carbon atom. In the cr ystal of 2.H2O and 3.H2O, the coordination polyhedra around the german ium and silicon atom can be best described as distorted trigonal bipyr amids, the carboxylate oxygen atoms occupying the axial sites. In term s of the Berry pseudorotation coordinate, the geometries are displaced by 14.0% (2.H2O) and 13.4% (3.H2O) from the ideal trigonal bipyramid toward the ideal square pyramid. According to NMR spectroscopic studie s, the zwitterions 2 and 3 also exist in solution ([D-6]DMSO).