As 2,2'-biimidazole (H2biim) is a bidentate chelating with multi-proton donor sites, it is able to coordinate to a transition metal with three reversible types of protonated and deprotonated modes: neutral (H2biim), mono-deprotonated (monoanion, Hbiim-), and di-deprotonated (dianion, biim2-) types. The imidazole group of protein histidyl residues has been demonstrated as an important binding site for a wide variety of metalloprotein. Since the coordination ability of this ligand has profound eff...