N-salicylideneamino acidate complexes of oxovanadium(IV). Part 1. Crystal and molecular structures and spectroscopic properties

Abstract

The complex [VO(salgly)(H₂O)] 1 dissolved in pyridine (py) to form brown [VO(salgly)(py)₂]2(salgly =N-salicylideneglycinate). A brown complex [VO(sal-L-ala)(bipy)]3 precipitated on adding 2,2′-bipyridine (bipy) to [VO(sal-L-ala)(H₂O)]4(sal-L-ala =N-salicylidene-L-alaninate) in methanol. The structures of 2 and 3 have been determined by X-ray diffraction analysis. In both the tridentate Schiff-base ligands occupy equatorial positions and the two heterocyclic nitrogen atoms of py or bipy co-ordinate in equatorial and axial positions, completing an octahedral geometry around the vanadium. The circular dichroism spectra of 3 dispersed in Nujol and in methanolic solutions are very similar. This finding together with EPR and thin-layer chromatographic experiments suggests that 3 is relatively stable to hydrolysis and that its structures in the solid state and solution are similar. Complex 2 and [VO(sal-L-ala)(py)_n] are not as stable to hydrolysis as 3 and a solid formulated as [VO(salgly)(py)(H₂O)] was also isolated.