Synthesis, molecular structure and properties of oxo-vanadium(iv) complexes containing the oxydiacetate ligand

Abstract

The complex [V(O)(oda)(H₂O)₂] 1 [oda = O(CH₂COO⁻)₂] has been obtained by reaction of aqueous solutions of [V(O)(acac)₂] with oxydiacetic acid. The coordination geometry around the vanadium in 1 is distorted octahedral with mutually trans water ligands and a planar conformation of the oda ligand (mer). The relative stability of the experimentally determined structure and that of the alternative isomer with a puckered oda conformation (fac) has been investigated by DFT calculations. The latter confirms that the mer geometry is more stable by 35.6 kJ mol⁻¹. The complex [V(O)(oda)(μ-OMe)]₂[Na(H₂O)]₂2a is obtained by reaction of 1 with NaOH in methanol. The anions feature two V(O)(oda) units symmetrically bridged by methoxy groups in a syn-orthogonal arrangement, while the oda ligands have the fac conformation. Similar complexes [V(O)(oda)(μ-OMe)]₂[K(H₂O)]₂2b and [V(O)(oda)(μ-OMe)]₂[HL]₂2c–2g are obtained from reaction with KOH or with selected N-donor bases (L), respectively. An excess of pyridine, however, causes the simple substitution of the water molecules in 1 and generates the monomer [V(O)(oda)(py)₂] 3. Antiferromagnetic behaviour of binuclear compounds 2a, 2d and 2e is suggested by a variable-temperature study. Finally, the reaction of 1 with bidentate N-donor ligands allows the synthesis of the complexes [V(O)(oda)(N–N)]·H₂O (N–N = 2,2′-bipyridine, 4; o-phenanthroline, 5). X-Ray characterization of 4 shows that the conformation of oda has changed from mer (as in the reactant 1) to fac.