Di- and poly-nuclear zinc(II) Schiff base complexes: synthesis, structuralstudies and reaction with an alpha-amino acid

In order to model peptide hydrolysis by dimetallic aminopeptidases, the din uclear zinc(II) Schiff base complex [Zn2L1(CH3CO2)(2)]ClO4 1a [HL1=2,6-bis{ N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol] has been prepared an d characterised by X-ray crystallography. The zinc ions are bridged by the deprotonated phenolic oxygen of L-1 and two acetate groups, the Zn ... Zn d istance being 3.234(1) Angstrom. Complex 1a was shown to promote hydrolysis of glycine ethyl ester under mild conditions. Reaction of the hydrolysis p roduct glycine with 1a led to the conversion of the ligand into L-2 (H3L2=c orresponding Schiff base derived from glycine). The X-ray analysis of the r esulting zinc complex 2 revealed the novel pentanuclear complex [{Zn2L2(CH3 CO2)(2)}(2)Zn(H2O)(4)]. 4.5H(2)O, and the crystal structure of polymeric {[ Zn(HL2)]. 3H(2)O}(infinity) was determined. Complex 2 is built up of two di nuclear acetate-bridged Zn-2/ligand moieties that are linked through bridgi ng carboxylate functions of the ligand to the fifth Zn atom. In the polymer one co-ordination site of the binucleating ligand is occupied by a Zn, whi le the second one is protonated.