Preparation of [VO(sal-L-Trp)(H₂O)] (sal-L-Trp = N-salicylidene-L-tryptophanate) and characterisation of an unusual product obtained from its solutions in water-pyridine

A vanadium(IV) complex [VO(sal-L-Trp)(H₂O)] 1 (sal-L-Trp = N-salicylidene-L-tryptophanate) has been isolated from solutions containing oxovanadium(IV), L-tryptophan and salicylaldehyde. From solutions also containing quinolin-8-ol (Hhquin) a similar oxovanadium(IV) complex VO(sal-L-Trp)·Hhquin·2H₂O 2 was isolated. From solutions of 1 in water-pyridine, orange-brown crystals of [HPy⁺]₄[C₁₄H₁₃N₂ ⁺]₂[V₁₀O₂₈^6-] 3 were isolated and characterised by X-ray diffraction. The mechanism proposed for this reaction involves the attack of a pyridine molecule at the β-carbon atom of the tryptophan residue in 1.