Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the hydroximato(2-) type: Syntheses and structural characterization in the solid state

Reaction of Si(OMe)(4) with acetohydroxamic acid or benzohydroxamic acid and HNMe2 (molar ratio 1:3:2) in MeCN yielded dimethylammonium fac-tris[acetohydroximato(2-)]silicate (fac-5) and N,N-dimethylacetamidinium fac-tris-[benzohydroximato(2-)]silicate (fac-8), respectively. Reaction of Si(OMe)4 with benzohydroxamic acid and HNMe2 (molar ratio 1:3:2) or ethane-1,2-diamine (molar ratio 1:3:1) in MeOH gave dimethylammonium fac-tris[benzohydroximato(2-)]silicate-methanol (fac-6.MeOH) and ethane-1,2-diammonium mer-tris[benzohydroximato(2-)]silicate-dimethanol (mer-9.2MeOH), respectively. Reaction of Ge(OMe)4 with benzohydroxamic acid and HNMe2 (molar ratio 1:3:2) in MeOH resulted in the formation of dimethylammonium fac-tris[benzohydroximato(2-)]germanate-methanol (fac-7.MeOH). Single-crystal X-ray diffraction studies showed that the Si (Ge)-coordination polyhedra of the racemic hexacoordinate silicon (germanium) compounds fac-5, fac-6.MeOH, fac-7.MeOH, fac-8, and mer-9.2MeOH are distorted octahedra, All compounds were additionally characterized by solid-state VACP/MAS NMR studies (C-13, N-15, Si-29). The structural investigations were complemented by computational studies of the dianions of fac-5 and mer-5.