Late transition metal complexes bearing nitrogen-containing ligands have many applications in biotechnology or industrial catalysis. Imidazole is one of the most common biofunctional ligands to play critical roles in meta1loenzymes, since the imidazole moiety of the histidyl residues often constitutes all or part of the binding sites of various transition metal ions. We use the newly synthesized tetradentate ligand containing the imidazolyl and pyridyl functional group to react with zinc, copper, nickel, and iron ions in order to carry out biomimetic studies. We have obtained two crystal structures via different methods of crystallization. One of them is a mononuclear complex while the other is a polymeric structure. The polymeric structure has demonstrated the spontaneous deprotonation on the imidazolyl nitrogen on binding to the metal ion followed by the intermolecular self-assembly process.We believe that the imidazolate -bridged complexes undergo the pH-dependent interconversions between mononuclear (protonated ligand) and self-assembled oligomer (deprotonated ligand). In addition, we have measured the titration curves of the tetradentate ligand and its corresponding metal complexes to determine the preferential binding sites at varying pH. From the titration processes, we got the protonation constant of ligand and stability constants of its corresponding metal complexes.