**5.4 Electron spin resonance study**

ESR spectrum of VO(II) complexes was recorded at room temperature as polycrystalline sample, on *x*-band at 9.1 GHz, under the magnetic field strength 3000 G using TCNE as marker. The value of g|| and g┴ is shown in **Table 5**. Paramagnetism of vanadyl ion arises from the single unpaired electron, its paramagnetism is due to spin angular momentum and VO2+is most stable diatomic cation. In V(IV) complexes value of g is below value of free electron. The trend 2.0023 > g┴ > g||, observed for the complexes. The EPR signal are split into eight lines suggested that V(IV) complexes are mononuclear [29]. The oxovanadium(IV) ion belong to the 3d1 system. Because of strong multiple covalent vanadium oxo-bond, a tetragonal compression occurs and therefore square pyramidal geometry proposed for VO(II) complex. The d orbital split into different level, dx2 -y 2 orbital is least stable as it is face to face with all four equatorial ligands. dxy being most stabilized orbital therefore d1 electron lies in dxy orbital. As G values of present complexes are lower than four indicates, the ligands involve in the complex formation are the strong field ligands.
