Synthesis, Spectral and Electrochemical Studies of Mixed-Ligand Oxovanadium(IV) and Oxovanadium(V) Complexes Incorporating the Tridentate ONO Donor Schiff Base Derived from Acetylacetone and Benzoylhydrazine

• Published in: Transition metal chemistry (Weinheim) 2004-05, Vol.29 (4), p.444-450
• Main Authors: Ghosh, Tapas, Bandyopadhyay, Chandrakanta, Bhattacharya, Sharmila, Mukherjee, Gurunath
• Format: Article
• Language: English
• ISSN: 0340-4285; 1572-901X
• DOI: 10.1023/B:TMCH.0000027457.32094.aa

Mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes with a tridentate dinegative ONO donor Schiff base ligand [viz., 4-(1-hydroxybenzylidenehydrazono)-2-penten-2-ol (H^sub 2^L)] and bidentate NN [viz., 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen): complexes (1) and (2), respectively] or OO^sup -^[viz., ethylene glycol (H^sub 2^gol), salicylaldehyde (Hsal) and vanillin (Hvan): complexes (3)-(5), respectively] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r., n.m.r., and u.v.-vis. spectroscopies. The complexes with NN donor ligands are one electron paramagnetic, displaying axial e.p.r. spectra and exhibiting two ligand-field transitions in the visible region, whereas the complexes with OO^sup -^ donor ligands are diamagnetic and display only LMCT bands. ^sup 1^H n.m.r. spectral data indicate that the pentavalent complexes (4) and (5) exist in two isomeric forms [(4A), (4B) and (5A), (5B) in 1:1 and 4:1 ratios, respectively]. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.67 V while among the vanadyl(V) complexes, (3), displays an irreversible reduction peak near -0.20 V and (4) and (5) display a quasi-reversible one electron reduction peak near +0.25 V versus s.c.e. The trend in redox potential values and the selective stabilization of VO^sup 2+^ and VO^sup 3+^ motifs have been explained on the basis of the basicity of the bidentate auxiliary ligands.[PUBLICATION ABSTRACT]