SYNTHESIS AND MOLECULAR-STRUCTURE OF [SM4TI(MU-5-O)(MU-3-OR)2(MU-OR)6(OR)6] (R=PR(I)) - A NOVEL FRAMEWORK FOR HETERONUCLEAR ALKOXIDES WITH A 1 4 STOICHIOMETRY/

The mixed-metal species [SM4Ti(mu5-O)(mu3-OR)2(mu-OR)6(OR)6] (R = Pr(i )) has been obtained by metathesis reaction between SmI2 and [NaTi(OPr i)5]infinity, as well as by Lewis acid-base reactions between SM5O(OPr i)13 and Ti(OPri)4. It has been characterized by an X-ray structure de termination. The molecular structure corresponds to a pentanuclear oxo aggregate with an encapsulated mu5-oxo ligand. The metals form a trig onal bipyramidal polyhedron in which the samarium(III) atoms are six-c oordinate while titanium, which occupies an equatorial position, is on ly five-coordinate. The Sm-O bond lengths range from 2.04(2) to 2.699( 4) angstrom, the order of variation being Sm-ORt < SM-mu2-OR almost-eq ual-to Sm-mu3-OR < Sm-mu5-O; the Ti-O bond distances are shorter [1.81 (2)-1.98(2) angstrom]. The mixed-metal samarium-titanium oxoalkoxide r epresents a novel framework for heteronuclear alkoxides displaying a 1 : 4 stoichiometry.