Bipyridine Ligand

2,2'-Bipyridine is a bidentate ligand, and it forms stable tris-complexes with the transition metal ions such as Fe(II) and Ru(II). However, 1 having amino groups at 6,6'-position of 2,2'-bipyridine is coordinated to form only 1 : 1 complex with the bivalent transition metal ions except for Zn(II) due to the steric hindrance of amino groups.¹⁾ This mono-complex is sensitive to the changes in pH-values, and it releases metal ions easily at lower pH region.²⁾ Furthermore, novel compounds with different functions can emerge by replacing the amino groups with other functions. For example, the incorporation abilities of metal ions into organic solvent have been seen improved by the introduction of dodecyl group at the amino groups. 1 can also be utilized for transporting metal ions through liquid membranes,³⁾ and it is regarded as a useful fluorescent material.⁴⁾