The hexacoordinate silicate dianions mer-tris[glycolato(2-)-O(1),O(2)]silicate and fac-tris[benzilato(2-)-O(1),O(2)]silicate: syntheses and structural characterization.
Treatment of tetramethoxysilane with glycolic acid and morpholine (molar ratio 1:3:2) in methanol, followed by crystallization from methanol/tetrahydrofuran, yielded morpholinium mer-tris[glycolato(2-)-O(1),O(2)]silicate (mer-7). Treatment of benzilic acid with sodium hydride, followed by addition of tetrachlorosilane and triethylamine (molar ratio 3:4:1:2), afforded, after crystallization from 1,4-dioxane/acetonitrile/diethyl ether/n-pentane, triethylammonium fac-tris[benzilato(2-)-O(1),O(2)]silicate-hemi-1,4-dioxane (fac-8.(1)/(2)C(4)H(8)O(2)). Single-crystal X-ray diffraction studies showed that the Si-coordination polyhedra of the hexacoordinate silicon(IV) complexes mer-7 and fac-8.(1)/(2)C(4)H(8)O(2) are distorted octahedra. Both compounds were additionally characterized by solid-state VACP/MAS NMR studies ((13)C, (29)Si), and fac-8.(1)/(2)C(4)H(8)O(2) was studied in solution by (1)H, (13)C, and (29)Si NMR experiments. The structural investigations were complemented by computational studies (MP2 studies, TZP level) of the dianions of fac-7 and mer-7.
Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Ingo
I
Richter
Martin
M
Penka
Reinhold
R
Tacke