Ni(II), Cu(II) and Zn(II) complexes of a bifunctional bis(picolyl)amine (bpa) ligand derived from glycine

The reactions of the tripodal ligand bpaAc–Gly–OEt (1a) (bpaAc–Gly–OEt=(N,N-bispicolylamino)acylglycine ethyl ester) with three different transition metal dihalides MCl2 (M=Ni, Cu, Zn) have been studied. 1a is a typical member of a new family of quadridentate amino acid derived ligands developed in our laboratories. X-ray crystal structures of the products [(bpaAc–Gly–OEt)NiCl2] (2), [(bpaAc–Gly–OEt)CuCl]2[(H2O)CuCl3]Cl·3H2O (32[(H2O)CuCl3]Cl), and [(bpaAc–Gly–OEt)ZnCl]2[ZnCl4] (42[ZnCl4]) were obtained. The formation of octahedral (2), square-pyramidal (3), and trigonal-bipyramidal (4) coordination geometries demonstrates the flexibility of the quadridentate N3O ligand framework. A comparison with literature data reveals some general trends in the chemistry of our amino acid ligands with different metal ions. The ligands are designed as building blocks for larger molecular and supramolecular assemblies. This report is part of our effort to study their basic coordination chemistry in order to gain insight in structural properties of aggregates based on synthetic metallopeptides.