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

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)(mu-OMe)](2)[Na(H2O)](2) 2a 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)(mu-OMe)](2)[K(H2O)](2) 2b and [V(O)(oda)-(mu-OMe)](2)[HL](2) 2c-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.