Tridentate ligand

A tridentate ligand (or terdentate ligand) is a ligand that has three atoms that can function as donor atoms in a coordination complex.[1]

The iminodiacetic anion is a tridentate ligand forming a complex with a metal labelled "M"

Well-known tridentate ligands include diethylenetriamine with three nitrogen donor atoms, and the iminodiacetate anion which consists of one deprotonated amine nitrogen and a pair of carboxylate groups.[1]

An octahedrally coordinated atom has six positions around it. Two tridentate ligands may form a complex with such an atom. There are two possible arrangements for such a complex: fac where the coordination is in a triangle on one face of the octahedron, and mer where the coordinating atoms are in an arc around the central atom, with two atoms of the ligand opposite each other. Fac tridentate ligands are termed scorpionate ligands, especially in reference to polypyrazolylborates.[2]

If the tridentate ligand is not symmetrical, then in the fac complexes in octahedral coordination there are three possible isomers. In the mer complexes there are two enantiomers, mirror images of each other.

List
name abbreviation formula CAS shape type charge central atoms pic
1,4,7-trioxonane 9-Crown-3 (C2H4O)3 27725-91-3 ring OOO 0 Li
methyl Tm ligandTmMetripodS31−Li Na K
TrispyrazolylborateTp−tripodN31−K Ru U
Tris(4,4-dimethyl-2-oxazolinyl)phenyl borateToMtripodN31−
Tris(4S-isopropyl-2-oxazolinyl)phenylborateToPtripodN31−
N,N,N′,N′′,N′′-pentamethyldiethylenetriaminePMDTA[(CH3)2NCH2CH2]2NCH33030-47-5linearNNN0 or +1Li AlH2
Bis(diphenylphosphinoethyl)phenylphosphineTriphos23582-02-7linearPPP0transition metals
1,4,7-Trithiacyclononane9-ane-S3(CH2CH2S)36573-11-1ringSSS0Fe Cu
1,4,7-Trimethyl-1,4,7-triazacyclononaneMe3TACN(CH2CH2N(CH3))396556-05-7RingNNN0Re Mn Ru Cu Fe
1,4,7-TriazacyclononaneTACN(CH2CH2NH)34730-54-5RingNNN0Mo
cis,cis-1,3,5-Triaminocyclohexanetach(CH2CHNH2)326150-46-9tripodN30Ni Mn
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References
  1. Cotton, F. Albert; Wilkinson, Geoffrey (1966). Advanced Inorganic Chemistry. John Wiley. pp. 140–141.
  2. Trofimenko, Swiatoslaw (1999). Scorpionates: the coordination chemistry of polypyrazolborate ligands (Reprinted. ed.). River Edge, NJ: Imperial College Press. pp. 3–5. ISBN 1860941729.

See also
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