MOLECULAR-STRUCTURES OF TITANIUM(IV) AND VANADIUM(IV) AMIDES AND ALKOXIDES

Gas-phase electron diffraction data for Ti(NMe2)4, V(NMe2)4 and V(OBut)4 obtained with nozzle temperatures of 130-156-degrees-C are consistent with molecular models of S4 symmetry. The metal to ligand bond distances (r(a)) are Ti-N 191.7(3), V-N 187.9(4) and V-O 177.9(6) pm, respectively. A set of bonding radii for Ti(IV), V(IV), Cr(IV) and W(VI) for use with the modified Schomaker-Stevensen rule is proposed. The valence angle bisected by the S4 axis in the titanium amide, N-Ti-N 114.2(17)-degrees, indicates that the co-ordination tetrahedron is slightly flattened. The corresponding angles in the vanadium amide and alkoxide are N-V-N 100.6(5)-degrees and O-V-O 115.1(19)-degrees, indicating that the co-ordination polyhedron in the former is significantly elongated, while in the latter it is significantly flattened. The shapes of the co-ordination tetrahedra in these and related molecules are discussed in terms of donation of pi electrons from N or O into low-lying d orbitals on the metal atom.