Synthesis of ZnN-salicylidene-L-aminoacidatos:: X-ray structure of [(N-salicylidene-L-alaninato) (aqua)zinc(II)]•0.25H2O and [(N-salicylidene-L-valinato) (aqua)zinc(II)]

The synthesis in aqueous ethanol solution of eight Zn(II) compounds of salicylaldehyde-amino acid Schiff bases together with their spectral characterisation is reported. Two of the complexes, [ (N-salicylidene-L-alaninato) (aqua)zinc(II) ] . 0.25H(2)O (1) and [ (N-salicylidene-L-valinato) (aqua)zinc(II) ] (2), have been obtained in the form of crystals suitable for X-ray crystallography. The coordination geometry about the zinc in both structures is between distorted trigonal bipyramidal and distorted square pyramidal with the iminic nitrogen N(4) (1=2.020(3) and 2=2.015(7) Angstrom), the phenolic O(8) (1=1.991(2) and 2=1.997(6) Angstrom) and the carboxylic O(1) (1=2.160(2) and 2=2.156(5) Angstrom) of the N-salicylidene-aminoacidato base ligand. Another carboxylic O(1)* of an adjacent unit (1=2.033(2) and 2=2.033(5) Angstrom), curiously shorter than the bond from the ligand itself, and a water molecule (1=2.006(3) and 2=1.999(6) Angstrom) comprise the fourth and fifth coordination positions, The crystals are constituted by polymeric [ (N-salicylidene-L-aminoacidato)zinc(II) ] moieties forming helical arrays about three-fold screw axes. To our knowledge these are the first two structures of binary complexes of the type [ (N-salicylidene-L-aminoacidato) Zn(II) ]. The NMR studies, in DMSO, agree with a,general endo disposition between the side chain of the amino acid and the aromatic ring of the salicylidene moiety. (C) 2000 Elsevier Science Ltd All rights reserved.