Vanadium : Part XVI. Oxo-Vanadium (IV) Schiff Base Complexes

The paper describes the syntheses and characterisation of a group of oxo-vanadium (IV) complexes of (a) bidenate, monobasic Schiff bases and of (b) quadridentate, dibasic Schiff bases. The complexes are 5 co-ordinate, paramagnetic (1.54-1.85 B.M.) and show vanadyl stretching frequency at 989\(\pm\)39 cm^-1 and coordinated C = N stretching at 1617\(\pm\)17 cm^-1. Bidentate Schiff bases derived from arylamines provide a weaker ligand field than those of the alkyldmines. Square pyramidal structure is indicated in solid state and in chloroform. In pyridine all bands move to higher energy. The d-orbital ordering \(d\)_\(xy\) < \(d\)_\(xz\), \(d\)_\(yz\) < \(d\)_\(x\)2__\(y\)2 < \(d\)_\(z\)2 has been preferred to an alternative \(d\)_\(xy\) < \(d\)_\(x\)2__\(y\)2 < \(d\)_\(xz\), \(d\)_\(yz\) < \(d\)_x². The complexes of the quadridentate Schiff bases give comparable spectra in solid state, in chloroform and in pyridine. This failure to add^, a sixth ligand has been interpreted as the result of saturation in the acceptor ability of oxo-vanadium (IV) due to strong a-donation by the equatorial ligands.