The denticity of a ligand is the number of donor groups from that ligand attached to the same central atom.
Bidentate ligands are attached to the central metal through two donor groups.
Ethane-1,2-diamine (H2NCH2CH2NH2) is a common example of a bidentate ligand. This ligand was formerly known as ethylenediamine. It is commonly shown in formulae for complexes as en.
Ethanedioate (–O2CCO2–) is also a bidentate ligand. This ligand was formerly known as oxalate. It is commonly shown in formulae for complexes as ox.
Bidentate ligands coordinate to the metal at adjacent sites (see diagrams).
For both of the ox and en ligands, this results in a five-membered ring including the central metal atom. The two-carbon bridge between the donor atoms is not sufficient for coordination at sites oppposite to one another.
The hexadentate ligand at the right has six donor atoms, each pair separated by a two-carbon bridge.
The coordination number for a complex is equal to the number of atoms coordinated to the central atom.
Thus the number of bidentate ligands in the formula is multiplied by two to assess the coordination number.
Chelation is formation of more than one bond between a ligand and the central metal atom.
Complexes that have one or more polydentate ligands such as the two given above are known as chelates.
en ligand
ox ligand
Ethane-1,2-diamine (H2NCH2CH2NH2) is a common example of a bidentate ligand. This ligand was formerly known as ethylenediamine. It is commonly shown in formulae for complexes as en.
Ethanedioate (–O2CCO2–) is also a bidentate ligand. This ligand was formerly known as oxalate. It is commonly shown in formulae for complexes as ox.
Bidentate ligands coordinate to the metal at adjacent sites (see diagrams).
For both of the ox and en ligands, this results in a five-membered ring including the central metal atom. The two-carbon bridge between the donor atoms is not sufficient for coordination at sites oppposite to one another.
edta ligand
The hexadentate ligand at the right has six donor atoms, each pair separated by a two-carbon bridge.
This tetra-anion was formerly known as ethylenediaminetetraacetate*. Thus the tetraanion is commonly shown in complex formulae as edta.
The systematic name of the anion is 2,2',2",2'"-(ethane-1,2-diyldinitrilo)tetraacetate.
The systematic name of the anion is 2,2',2",2'"-(ethane-1,2-diyldinitrilo)tetraacetate.
The coordination number for a complex is equal to the number of atoms coordinated to the central atom.
Thus the number of bidentate ligands in the formula is multiplied by two to assess the coordination number.
Examples:
The [Co(en)3]3+ and [Mg(edta)]2– complexes both have a coordination numbers of 6.
The [Co(en)3]3+ and [Mg(edta)]2– complexes both have a coordination numbers of 6.
Chelation is formation of more than one bond between a ligand and the central metal atom.
Complexes that have one or more polydentate ligands such as the two given above are known as chelates.