polypyridyl

Polypyridyl refers to a class of multidentate ligands that contain two or more pyridine rings connected through a spacer. The nitrogen atoms in the pyridine rings serve as coordinating sites for metal centers, enabling the formation of chelate or polynuclear complexes. Depending on the arrangement, polypyridyl ligands can be bidentate, tridentate, or higher denticity, and their rigidity and extended π-conjugation can strongly influence the geometry and electronic properties of the resulting metal complexes.

The best-known examples are bipyridyl and terpyridyl ligands: 2,2'-bipyridine coordinates through its two nitrogens; 2,2':6',2''-terpyridine coordinates through three nitrogens. More extended polypyridyls include quadrapyridyl, hexapyridyl, and related conjugated systems. They are widely used with transition metals such as ruthenium, iridium, iron, copper, and zinc. Because of their rigid, planar structures and strong σ-donor/π-acceptor character, polypyridyl ligands modulate redox and photophysical properties, enabling applications in catalysis, electrochemistry, and light harvesting.

In materials chemistry, polypyridyl ligands are employed in coordination polymers and metal-organic frameworks as linkers or building blocks. They are also used in dye-sensitized solar cells and in molecular electronics and sensing. Synthesis typically involves linking pyridine units via carbon–carbon or carbon–nitrogen bonds with appropriate spacers, allowing tuning of distance and orientation between coordinating sites.