NEW COMPOUNDS IN THE CHEMISTRY OF GROUP-4 TRANSITION-METAL ALKOXIDES .4. SYNTHESIS AND MOLECULAR-STRUCTURES OF 2 POLYMORPHS OF [TI16O16(OET)32] AND REFINEMENT OF THE STRUCTURE OF [TI7O4(OET)20]

Two polymorphs of the condensed species [Ti16(mu-4-O)4(mu-3-O)8(mu-O)4(mu-OEt)16(OEt)16] have been obtained: a monoclinic form prepared in absolute ethanol and a tetragonal one obtained from 5% aqueous ethanol. The monoclinic form (compound 1) crystallizes in the space group C2/c with a = 23.392(7), b = 19.627(8), c = 24.130(14) angstrom and beta = 96.4(4)-degrees. The tetragonal variety (compound 2) crystallizes in the space group P4(2)/n with a = 14.642(2) and c = 25.972(7) angstrom. Both structures have been solved by direct methods and refined to R = 0.078 for 5766 independent reflections (compound 1) and to R = 0.053 for 3130 independent reflections (compound 2). They are built from different packings of the same hexadecanuclear molecule. Both molecules show slight differences in the titanium-oxygen network and in the orientations of the ethoxy groups. The initial hydrolysis product of tetraethyltitanium(IV), [Ti7O4(OEt)20] 3 has been obtained by a new route. Its structure has been solved by direct methods and refined to R = 0.069 for 6293 independent reflections. This redetermination resulted in location of all the ethyl groups.