THE INTRIGUING STRUCTURAL CHARACTERISTICS OF THE HETEROSILOXANE MOLECULE NA4[SB2O(OSIME3)8]

Treatment of Sb(OSiMe3)3 with NaOSiMe3 in the molar ratio 1:2 in hexane at ambient temperature leads to the formation of Me3SiOSiMe3 and a crystalline complex of the formula Na4[Sb2O(OSiMe3)8] in ca. 35% yield. The composition of the product has been confirmed by elemental analysis and negative-ion CI mass spectrometry. The single crystal X-ray structure analysis (rhombohedral, space group R3cBAR, Z = 6) resulted in a disorder model for the complex with pseudo-cubic symmetry owing to virtually random distribution of sodium and antimony atoms over the vertices of an oxygen-centered octahedron with the eight silyloxy groups capping the faces. Low solubility in non-coordinating solvents prevented solution NMR studies, but solid-state NMR investigations using cross polarization and magic-angle spinning techniques (C-13, Si-29) allowed the assignment of a point group C2v structure with the Sb(III) atoms in cis position relative to the oxo center of the complex.