A family of mixed-ligand oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands derived from acetylhydrazide and 2-hydroxybenzaldehyde/2-hydroxyacetophenone

Abstract

In the title family the tridentate ONO donor ligands are the fully deprotonated forms of acetylhydrazones of 2-hydroxybenzaldehyde (H2L1) and 2-hydroxyacetophenone (H2L2) (general abbreviation H2L), while bidentate mononegative OO donor ligands are the deprotonated salicylaldehyde (Hsal), vanillin (Hvan) and monodeprotonated 1,2-ethanediol (H2ed) (general abbreviation HB). The reaction of VIVO(acac)2 with H2L and Hsal or Hvan in equimolar ratio in MeOH afforded the complexes of the type [VVO(L)(B)], (1)–(4). The reaction of VIVO(acac)2 with H2L1 (in an equimolar ratio) and an excess of H2ed in MeOH yielded the complex [VVO(L1)(Hed)], (5) but the similar reaction with H2L2 ligand failed to produce such a type of complex. Complexes have been characterized by elemental analyses and by i.r., n.m.r. and u.v.-vis. spectroscopies. All the complexes are diamagnetic and display only LMCT bands. 1H-n.m.r. spectral data indicate that complexes (1)–(4) exist in two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios in CDCI3 solution. Complexes (1)–(4) display a quasi-reversible one electron reduction peak in the −0.06 to +0.05 V versuss.c.e. region in CH2CI2 solution and (5) displays an irreversible reduction peak at −0.46 V versuss.c.e. in DMF solution. The trend in the redox potential values has been correlated with the basicity of both the primary and auxiliary ligands.