Tripodal ligands are

tri- Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example: * unicycle, bicycle, tricycle (1-cycle, 2-cycle, 3-cyc ...

and

tetradentate In chemistry, 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 method of classifying ligands. Tetradentate ligands ar ...

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

s. They are popular in research in the areas of

coordination chemistry A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

and

homogeneous catalysis In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...

. Because the ligands are polydentate, they do not readily dissociate from the metal centre. Many tripodal ligands have C₃

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

Coordination chemistry

In their

coordination complexes A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

with an

octahedral molecular geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...

the tridentate tripod ligands occupy one face, leading to a fixed

facial A facial is a family of skin care treatments for the face, including steam, exfoliation (physical and chemical), extraction, creams, lotions, facial masks, peels, and massage. They are normally performed in beauty salons, but are also a comm ...

(or ''fac'') geometry. The

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 Ligand field theory (LFT) describes the bonding, orbital arrangement, and other characteristics of coordination complexes. It represents an application of molecular orbital theory to transition metal complexes. A transition metal ion has nine valen ...

splitting patterns. Tripodal ligands are often able to coordinately saturate metal ions with lower

coordination number In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central i ...

s. 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 Tren may mean: *Tris(2-aminoethyl)amine, a coordination chemistry compound *Trenbolone, a veterinary steroid * ''Tren'', a 1978 Yugoslav film See also *train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is ...

(N(CH₂CH₂NH₂)₃) and cis-1,3,5-triaminocyclohexane. 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 , and

N-heterocyclic carbene A persistent carbene (also known as stable carbene) is a type of carbene demonstrating particular stability. The best-known examples and by far largest subgroup are the ''N''-heterocyclic carbenes (NHC) (sometimes called Arduengo carbenes), for ex ...

File:TripodalPhosphine.png, A tripodal triphosphines, X can be CR, SiR, Si⁻, BR⁻, B, N, P etc. File:Tris(pyridylmethyl)amine (structural diagram).png,

Tris(2-pyridylmethyl)amine Tris(2-pyridylmethyl)amine (abbreviated TPMA or TPA) is an organic compound with the formula (C5H4NCH2)3N. It is a tertiary amine with three picolyl substituents. It is a white solid that is soluble in polar organic solvents. It is a ligand in ...

, a tetradentate tripodal ligand popular in

bioinorganic chemistry Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those t ...

. File:LnMTp.png, Structure of a metal complex of trispyrazolylborate, an anionic tridentate tripod ligand.{{cite journal, author=Parkin, G., title=The Bioinorganic Chemistry of Zinc: Synthetic Analogues of Zinc Enzymes that Feature Tripodal Ligands, journal=Chemical Communications, year=2000, issue=20 , page=1971-1985, doi=10.1039/B004816J File:Nitrilotriacetic-acid-2D-skeletal.png, NTA is a commercially important tripodal ligand. Its three carboxylic acid groups undergo deprotonation upon complexation. File:KlauiCmpx.png, The

Kläui ligand The Kläui ligand is the anion −. The ligand, popularized by Wolfgang Kläui, binds metals and metalloids via a facial O3 donor set. Related tridentate and tripodal anionic ligands include trispyrazolylborates. : 160px, General structure o ...

, a dianionic organometallic ligand. File:1,1,1-Tris(aminomethyl)ethane.svg,

1,1,1-Tris(aminomethyl)ethane 1,1,1-Tris(aminomethyl)ethane (TAME) is an organic compound with the formula CHC(CHNH). It is a colorless liquid. It is classified as a polyamine tripodal ligand, i.e., capable of binding to metal ions through three sites and hence is a tridenta ...

File:Cis,cis-1,3,5-triaminocyclohexane.png, cis,cis-1,3,5-triaminocyclohexane File:Zitronensäure - Citric acid.svg,

citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

, when triply deprotonated, is an unsymmetrical tripodal ligand.

Coordination chemistry

References