Polypyridine complex
Encyclopedia
Polypyridine complexes are compounds in which a polypyridine, such as 2,2'-bipyridine
, 1,10-phenanthroline
, or 2,2';6'2"-terpyridine
, coordinates to a metal ion.
Polypyridine compounds are multidentate ligand
s which have characteristic properties, such as photosensitization. The complexes are very stable to light, electricity, and heat because the bonds between the central metal ion and polypyridine ligands are usually very strong; furthermore, the polypyridine itself is generally very stable. The compounds have peculiar optical, electrochemical, and magnetic properties. Some complexes exhibit a strong absorption band in the visible light region, which is called metal-to-ligand charge transfer (MLCT) or ligand-to-metal charge transfer (LMCT). The properties of the complexes can be tuned easily by introducing substituents, for example, electron donation, electron withdrawal, and π-conjugating groups, to the polypyridine moiety. The MLCT absorption band can be shifted, the emission wavelength can be changed, and the emission lifetime can be extended.
A well-known example of a polypyridine complex is rutheniumtris(bipyridine), Ru[(bpy)3]2+. This complex exhibits intense luminescence
at room temperature in aqueous solution. Another example is a platinum-bipyridine-dithiolate complex, Pt(bpy)(bdt), in which bdt denotes a 1,2-benzenedithiolate anion
. This complex also exhibits photoluminescence
at room temperature, and its wavelength and lifetime can be tuned by substitution of either bipyridine or dithiolate moieties. Structural control is easier than for ruthenium
complexes due to the square planar structure of the platinum
complex.
2,2'-Bipyridine
2,2'-Bipyridine is a organic compound with the formula . This colorless solid, commonly abbreviated bipy or bpy , is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals...
, 1,10-phenanthroline
Phenanthroline
Phenanthroline is a heterocyclic organic compound. As a bidentate ligand in coordination chemistry, it forms strong complexes with most metal ions...
, or 2,2';6'2"-terpyridine
Terpyridine
Terpyridine is a heterocyclic compound derived from pyridine. This colourless solid is used as a ligand in coordination chemistry.-Synthesis:...
, coordinates to a metal ion.
Polypyridine compounds are multidentate ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s which have characteristic properties, such as photosensitization. The complexes are very stable to light, electricity, and heat because the bonds between the central metal ion and polypyridine ligands are usually very strong; furthermore, the polypyridine itself is generally very stable. The compounds have peculiar optical, electrochemical, and magnetic properties. Some complexes exhibit a strong absorption band in the visible light region, which is called metal-to-ligand charge transfer (MLCT) or ligand-to-metal charge transfer (LMCT). The properties of the complexes can be tuned easily by introducing substituents, for example, electron donation, electron withdrawal, and π-conjugating groups, to the polypyridine moiety. The MLCT absorption band can be shifted, the emission wavelength can be changed, and the emission lifetime can be extended.
A well-known example of a polypyridine complex is rutheniumtris(bipyridine), Ru[(bpy)3]2+. This complex exhibits intense luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
at room temperature in aqueous solution. Another example is a platinum-bipyridine-dithiolate complex, Pt(bpy)(bdt), in which bdt denotes a 1,2-benzenedithiolate anion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
. This complex also exhibits photoluminescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
at room temperature, and its wavelength and lifetime can be tuned by substitution of either bipyridine or dithiolate moieties. Structural control is easier than for ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
complexes due to the square planar structure of the platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
complex.