Co-ordination properties of N-protected amino acids. Solution and solid state behavior of bis(benzyloxycarbonyl-L-tryptophanato)nickel(II) and its mixed complexes

Polarographic measurements show that nickel(II) ion and benzyloxycarbonyl-L-tryptophan (Z-L-tryptophan) form complexes in methanol with 1 : 2 and 1 : 4 metal-to-ligand ratios, depending on the ligand concentration. A complete scheme of the reactions which take place in solution and at the electrode is proposed. The 1 : 2 complex [NiL2]·2H2O and some amine adducts have been obtained in the solid state. In the solids the amino-acid is co-ordinated only through the carboxylate group.