Chemistry of mononuclear and mixed valence binuclear oxovanadium chelates incorporating ONO-hydrazone ligands

Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata-700 032, India
E-mail : panda_bikas@rediffmail.com
Manuscript received 24 December 2004, accepted 5 July 2005

The dark coloured complex of type [V^v₂O₃(L)₂] has been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H₂L in the presence of air in acetone. In presence of small amount of water [V^vO₂(HL)] is isolated. Electronic and IR spectra as well as the metal reduction potentials of the complexes are reported. In crystalline [V^vO₂(HL¹)] the vanadium(v) has a distorted square-pyramidal geometry where the ligands bind as a tridentate monoionised form. The C-N and C-O bond lengths around the chelate rings are consistent with the ketonic description of the ligand. The O-V-O bond angle is greater than 107° which is a characteristic feature of the VO⁺₂ complexes with pentacoordinate vanadium. In the crystal lattice the [V^vO₂(HL¹)] molecule forms a dimer via intermolecular N....O hydrogen bonding. The green coloured complex Et₄N[V₂O₃(L)₂] has been synthesized in almost quantitative yields by one electron reduction of [V^v₂O₃(L)₂] ( at ~0.0 V vs SCE) in dichloromethane solution containing tetraethylammonium perchlorate. The complex Et₄N[V₂O₃(L)₂] is characterized by electronic, IR and EPR spectroscopic methods. The isotropic solution spectra of the complex consists of 15 lines (A ~50 G; and g ~1.950) revealing the delocalization of the unpaired electron over the two equivalent metal centers. The EPR spectra in the frozen state is consistent with the localization of the unpaired electron in one center (A_‖ ~174 G; A_ꓕ ~74 G; g_‖ ~1.950 g_ꓕ~1.960).