Bipyridine Ligands, Terpyridine Ligands

Bipyridine Ligands, Terpyridine Ligands

A ligand formed by combining a plurality of pyridyl groups is referred to as a bipyridine ligand. A terpyridine ligand refers to a ligand formed by a combination of three pyridyl groups. From a structural point of view, bipyridine ligands have a plurality of nitrogen atoms with strong coordination ability, have intramolecular conjugated bonds, electron donating ability and electron accepting ability, and have good intramolecular electron transport and energy transfer properties. Therefore, bipyridine ligands can form stable complexes with various metal ions and are widely used as chelate ligands in modern coordination chemistry.

Figure 1. Bipyridine ligand

Figure 2. Triple pyridine ligand

Figure 3. Tetrapyridine ligand

Applications

Bipyridine ligands and terpyridine ligands have good chelating ability, are easy to form complexes with most metal ions, and are structurally stable, so they are widely used in molecular catalysis, colorimetric analysis, molecular recognition, self-assembly and anti-tumor drugs and other fields.

• Supramolecular chemistry: Some bipyridine ligands (such as bistriphenyl pyridine ligands) can form metal ions as cross-molecular two-dimensional polymers in the form of cross-links. Due to the introduction of metal ions, the structure is diversified, giving the polymer an unusual property. Materials with excellent electrical, optical, magnetic and other properties can be obtained.
• Luminous materials: A bipyridyl ligand containing a chromophoric group, after coordinating with a rare earth metal, absorbs energy and transfers energy to the cation as much as possible. At the same time, the reaction between the complex and the solvent can be inhibited, thereby suppressing the quenching of the rare earth fluorescence by the solvent and greatly improving the luminous efficiency. Therefore, it can be used for the preparation of a fluorescent material such as a light emitting diode. Some terpyridines can also be used to make special devices such as molecular optical "switches" and solar cells.
• Catalyst: The complex formed by the terpyridine ligand and the high-valent transition metal has good catalytic performance and is sufficient to increase the selectivity of the reaction. Therefore, a terpyridine complex is also widely used as a catalyst, and it can catalyze various reactions such as an oxidation reaction, a carbonylation reaction, and a hydroformylation reaction.
• Energy transfer: The functionalized terpyridine ligand can be modified on a variety of metal surfaces to provide an energy transfer process such as modification on the surface of titanium dioxide, silicon-titania and gold to form a single layer structure or semiconductor. Dendritic bipyridine ligands can serve as molecular devices for light capture at the molecular level, exploiting their advantages in energy transfer and electron transfer.
• Gas adsorbent: The topological network configuration complex formed by chelation of bipyridine ligand with Zn²⁺ has certain adsorption capacity for N₂, H₂, CH₄, CO₂ and other gases. Therefore, bipyridine ligands can act as adsorbents and function in the fields of gas storage and transportation, environmental protection, and climate warming.
• Other applications: Some terpyridines, when coordinating with lanthanide metals to form supramolecules, can effectively combine the characteristics (the excited state energy level transition of the rare earth metal, the broad absorption band of the ligand, and the effective transferability) of the two. The desired illuminant is used in biological and chemical fields such as biodetectors, markers, or sensing elements. The terpyridine complex is also biologically active, and its interaction with DNA can inhibit tumor proliferation, and thus can also be used in the medical field.

References

1. Bar, Manoranjan. (2017). “Ru-Os dyads based on a mixed bipyridine-terpyridine bridging ligand: modulation of the rate of energy transfer and pH-induced luminescence switching in the infrared domain.” Dalton Transactions 46(38), 12950-12963.
2. Schmollinger. (2017). “Synthesis of ruthenium and palladium complexes from glycosylated 2,2'-bipyridine and terpyridine ligands.” Tetrahedron Letters 58(37), 3643-3645.
3. Mongal, Binitendra Naath. (2016). “A novel ruthenium sensitizer with-OMe substituted phenyl-terpyridine ligand for dye sensitized solar cells.” Solar Energy 134,107-118.