Tripodal ligand

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Motifs for complexation of tri- and tetradentate tripodal ligands TripodCoordModes.png
Motifs for complexation of tri- and tetradentate tripodal ligands

Tripodal ligands are tri- and tetradentate ligands. They are popular in research in the areas of coordination chemistry and homogeneous catalysis. Because the ligands are polydentate, they do not readily dissociate from the metal centre. Many tripodal ligands have C3 symmetry.

Coordination chemistry

In their coordination complexes with an octahedral molecular geometry the tridentate tripod ligands occupy one face, leading to a fixed facial (or fac) geometry. The tetradentate tripodal ligands occupy four contiguous sites, leaving two cis positions available on the octahedral metal center. When bound to four- and five-coordinate metal centres, these ligands impose C3 symmetry, which can lead to uncommon ligand field splitting patterns. Tripodal ligands are often able to coordinately saturate metal ions with lower coordination numbers.

One tripodal ligand of commercial significance is nitrilotriacetate, N(CH2CO2)3 because it is cheaply produced and has a high affinity for divalent metal ions. Other tripodal triamine ligands include tren (N(CH2CH2NH2)3) and cis-1,3,5-triaminocyclohexane. [1] Certain triphosphines such as RC(CH2PPh2)3 are also tripodal. Many kinds of donor groups have been incorporated into the arms of tripodal ligands, including amido (R2N), [2] and N-heterocyclic carbenes.

Structure of [Ni(TACH)(H2O)3] (color code: blue = nitrogen, red = oxygen, dark blue = nickel). BAVNAN01.png
Structure of [Ni(TACH)(H2O)3] (color code: blue = nitrogen, red = oxygen, dark blue = nickel).

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Scorpionate ligand

The term scorpionate ligand refers to a tridentate ligand which would bind to a metal in a fac manner. The most popular class of scorpionates are the hydrotris(pyrazolyl)borates or Tp ligands. These were also the first to become popular. These ligands first appeared in journals in 1966 from the then little-known DuPont chemist of Ukrainian descent, Swiatoslaw Trofimenko. Trofimenko called this discovery "a new and fertile field of remarkable scope".

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Denticity refers to the number of donor groups in a single ligand that bind to a central atom in a coordination complex. In many cases, only one atom in the ligand binds to the metal, so the denticity equals one, and the ligand is said to be monodentate. Ligands with more than one bonded atom are called polydentate or multidentate. The word denticity is derived from dentis, the Latin word for tooth. The ligand is thought of as biting the metal at one or more linkage points. The denticity of a ligand is described with the Greek letter κ ('kappa'). For example, κ6-EDTA describes an EDTA ligand that coordinates through 6 non-contiguous atoms.

Iron tetracarbonyl dihydride Chemical compound

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Dichlorotris(triphenylphosphine)ruthenium(II) Chemical compound

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in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).


Trisoxazolines are a class of tridentate, chiral ligands composed of three oxazoline rings. Despite being neutral they are able to form stable complexes with high oxidation state metals, such as rare earths, due to the chelate effect. The ligands have been investigated for molecular recognition and their complexes are used in asymmetric catalysts and polymerisation.


Tris(oxazolinyl)borate compounds are a class of tridentate ligands; often abbreviated ToR, where R is the substituent on the oxazoline ring. Most commonly the substituent is either a methyl, propyl, tert-butyl or hydrogen. The formation of anionic boron backbone with addition of a phenyl group on boron allows the ligand to strongly bind to the metal center. It results in a more robust complex.


In chemistry, hexahydro-1,3,5-triazine is a class of heterocyclic compounds with the formula (CH2NR)3. They are reduced derivatives of 1,3,5-triazine, which have the formula (CHN)3, a family of aromatic heterocycles. They are often called triazacyclohexanes or TACH's but this acronym is also applied to cis,cis-1,3,5-triaminocyclohexane

Tetradentate ligands are ligands that bind four donor atoms to a central atom to form a coordination complex. This number of donor atoms that bind is called denticity and is a way to classify ligands. Tetradentate ligands are common in nature in the form of chlorophyll which has a core ligand called chlorin, and heme with a core ligand called porphyrin. They add much of the colour seen in plants and humans. Phthalocyanine is an artificial macrocyclic tetradentate ligand that is used to make blue and green pigments.

In homogeneous catalysis, C2-symmetric ligands refer to ligands that lack mirror symmetry but have C2 symmetry. Such ligands are usually bidentate and are valuable in catalysis. The C2 symmetry of ligands limits the number of possible reaction pathways and thereby increases enantioselectivity, relative to asymmetrical analogues. C2-symmetric ligands are a subset of chiral ligands. Chiral ligands, including C2-symmetric ligands, combine with metals or other groups to form chiral catalysts. These catalysts engage in enantioselective chemical synthesis, in which chirality in the catalyst yields chirality in the reaction product.

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<i>cis</i>,<i>cis</i>-1,3,5-Triaminocyclohexane Chemical compound

cis,cis-1,3,5-Triaminocyclohexane is an organic compound with the formula (CH2CHNH2)3. It is a triamine. Of the many isomers possible for triaminocyclohexane, the cis,cis-1,3,5-derivative has attracted attention because it is a common tripodal ligand, abbreviated as tach. It is a colorless oil. It is a popular tridentate ligand in coordination chemistry.

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Transition metal dithiocarbamate complexes are coordination complexes containing one or more dithiocarbamate ligand, which are typically abbreviated R2dtc. Many complexes are known. Several homoleptic derivatives have the formula M(R2dtc)n where n = 2 and 3.

1,1,1-Tris(diphenylphosphinomethyl)ethane Chemical compound

1,1,1-Tris(diphenylphosphinomethyl)ethane, also called Triphos, is an organophosphorus compound with the formula CH3C[CH2PPh2]3. An air-sensitive white solid, it is a tripodal ligand ("three-legged") of idealized C3v symmetry. It was originally prepared by the reaction of sodium diphenylphosphide and CH3C(CH2Cl)3:


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