Dc. Crans et al., 6-CO-ORDINATED VANADIUM-(IV) AND VANADIUM-(V) COMPLEXES OF BENZIMIDAZOLE AND PYRIDYL CONTAINING LIGANDS, Journal of the Chemical Society. Dalton transactions, (16), 1997, pp. 2799-2812
A new series of vanadium-(IV) and -(V) complexes with ligands containi
ng functionalities including hydroxyethyl, carboxylate, amine, pyridyl
and benzimidazole have been prepared. The crystal structures of three
complexes have been determined. All the vanadium atoms are six-co-ord
inate even though previous complexes of the diethanolamine type have c
ontained five-co-ordinate vanadium. The V-N (amine) bonds of the benzi
midazole complexes are significantly longer than those of pyridyl comp
lexes. An empirical relationship between pK(a) value of the protonated
ligand and the V-N (amine) bond length (trans to an oxo group) of the
corresponding vanadium-(IV), -(V) and -(IV/V) complexes was observed.
Spectroscopic studies (NMR, ESR and UV/VIS) showed that the complexes
remain intact in aqueous solution. In general, the hydroxyethyl subst
ituted vanadium complexes are less stable than corresponding acetate s
ubstituted ones and the benzimidazole complexes are less stable than c
orresponding pyridyl complexes. The combined knowledge concerning the
properties of all these complexes provides an excellent platform to de
sign new vanadium complexes pertinent to biological applications.