Molecular structures of titanium(IV) and vanadium(IV) amides and alkoxides

Abstract

Gas-phase electron diffraction data for Ti(NMe₂)₄, V(NMe₂)₄ and V(OBu^t)₄ obtained with nozzle temperatures of 130–156 °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)°, 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)° and O–V–O 115.1(19)°, 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 π electrons from N or O into low-lying d orbitals on the metal atom.