Hexacoordinate Silicon(IV) Complexes with Si O 6 Skeletons and Multidentate Ligands Derived from Citric Acid or Malic Acid

Morpholinium meso ‐bis[citrato(3‐)‐ O 1 , O 3 , O 6 ]silicate ( meso ‐ 5 ) and racemic morpholinium bis[citrato(4‐)‐ O 1 , O 3 , O 6 ]silicate ( rac ‐ 6 ) were synthesized by treatment of tetramethoxysilane with citric acid and morpholine (molar ratio 1:2:2 and 1:2:4, respectively). Treatment of tetramethoxysilane with ( S )‐malic acid and tri( n ‐propyl)amine or tri( n ‐butyl)amine (molar ratio 1:3:2) yielded tri( n ‐propyl)ammonium ( Λ , S , S , S )‐ mer ‐tris[malato(2‐)‐ O 1 , O 2 ]silicate (( Λ , S , S , S )‐ mer ‐ 7 ) and tri( n ‐butyl)ammonium ( Λ , S , S , S )‐ mer ‐tris[malato(2‐)‐ O 1 , O 2 ]silicate (( Λ , S , S , S )‐ mer ‐ 8 ). The hexacoordinate silicon compounds meso ‐ 5 ·2MeOH, rac ‐ 6 ·1.73MeOH, ( Λ , S , S , S )‐ mer ‐ 7 , and ( Λ , S , S , S )‐ mer ‐ 8 ·2MeCN were structurally characterized in the solid state by single‐crystal X‐ray diffraction and VACP/MAS NMR spectroscopy ( 13 C, 15 N, 29 Si). Upon dissolution in water at 20 °C, spontaneous hydrolysis of the λ 6 Si ‐silicate anions was observed.