The syntheses, solid state, spectroscopic and potentiometric solution characterizations of VO(acac-NH2)2 (acac-NH2 = acetylacetamido) and VO(acac-NMe2)2 (acac-NMe2 = N, N-dimethylacetylacetamido) have been investigated. In VO(acac-NMe2)2 the vanadium ion exhibits a distorted square pyramidal coordination environment. Crystals of VO(acac-NMe2)2 are monoclinic and structural studies were carried out. EPR and UV-visible spectroscopic and potentiometric methods were used to characterize the speciation, complex stability and structures in both aqueous and organic solutions. VO(acac-NH2)2 and VO(acac-NMe2)2 each form two species in solution: a 1:2 and a 1:1 metal:ligand complex. The complexes formed from VO(acac-NH2)2 are slightly more stable than those of VO(acac-NMe2)2; however, VO(acac)2 forms more stable complexes. In non-coordinating solvents the 1:2 complexes maintain a five-coordinate vanadium atom, whereas in coordinating solvents such as water and pyridine the complexes become six-coordinate. Based on the similarity of the EPR parameters of VO(acac-NH2)2 with those of the VO(acac)2 complex, it is likely these species contain the coordinating solvent added trans to the V=O bond. These new VO(acac)2 derivatives are improved with respect to water solubility. Although the solution stability is not as good as that of VO(acac)2, it is higher than that of VO(acac-R)2 (R = CH3 or C2H5). Thus, should the stability of the 1:1 complex be important for the compound's efficacy, both of these new complexes would be predicted to be less effective than VO(acac)2 but more effective than VO(acac-Et)2 (acac-Et = 3-ethylacetylacetonate) in lowering glucose levels in streptozotocin-induced diabetic rats.
|Number of pages||9|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - Jan 1 2001|
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