Crystal and molecular structure of [V2O3(sal-L-val)2(H2O)](sal-L-val =N-salicylidene-L-valinate) and spectroscopic properties of related complexes

The dinuclear vanadium(v) complex [V2O3(sal-L-val)2(H2O)]1(sal-L-val =N-salicylidene-L-valinate) has been prepared and characterized and its crystal structure determined. The compound contains a double bridge by O (oxo) and O (carboxylate) and is one of the rare examples where the two VO groups make an angle near 90°. There are two independent molecules, A and B, in the asymmetric unit which are similar and each consists of two VO(sal-L-val) groups at nearly right angles to each other. They exhibit a distorted-octahedral geometry, involving in the equatorial plane the O,N,O atoms of the Schiff-base ligand and the bridging O (oxo) group and in the axial positions a carboxyl oxygen of the second VO(sal-L-val) group and a water molecule. The bridging V–O(oxo) bond lengths range between 1.787 and 1.823 Å, and are significantly shorter than the bridging V–O(carboxylate), ranging between ≈1.93–1.94 Å for equatorial and ≈2.40–2.43 Å for axial. Several known [VO(sal-L-aa)(H2O)] and new [VO(sal-L-aa)(bipy)](sal-L-aa =N-salicylidene-L-amino acidate, bipy = 2,2′-bipyridine) complexes were also prepared and their spectroscopic (ESR, UV and CD) properties studied. A correlation observed between the CD intensities and the size of the amino acid side groups is discussed.