Synthesis and characterisation of oxovanadium(IV) complexes with tridentate ONO donor azo ligands

Department of Chemistry, Victoria Institution (College), 78/B, A.P.C. Road, Calcutta-700 009, India

Department of Chemistry, R. K. Mission V. C. College, Rahara-743 186, 24-Parganas (N), West Bengal, India

Manuscript received 10 December 1998, revised 30 March 1999, accepted 9 April 1999

Reaction of VOSO₄ with three tridentate dibasic ONO donor azo ligands (H₂L^1-3, 1) separately in aqueous alcoholic me­dium produces complexes 2-4 of the type [VO(L)(H₂O)x]y, where x = 1, y = 1 for H₂L¹ : complex 2; x = 0, y = 2 for H₂L² and H₂L³ : complexes 3 and 4 respectively. Complex 2 shows normal magnetic moment for a d¹ system while 3 and 4 show subnormal behaviour. This behaviour is explained in terms of metal-metal bonding, and the magnetic moment order, 2 > 3 > 4 is correlated with the basicity of the donor atoms. One bonded water molecule is present only in complex 2. Among the three complexes only 2 shows two ligand field transitions. All the three complexes exhibit one LMCT transition and two intra­ligand transitions characteristic for azo group. They display either irreversible or quasireversible one-electron oxidation peaks in DMF. The electrochemical behaviour has been rationalised on the basis of basicity of the coordinating atoms.