What is meant by unidentate and ambidentate ligands ? Give two examples for each.

Explanation

Unidentate ligand : When a ligand is bound to a metal ion through a single donor atom, as in `Cl^(-), H_2O` or `NH_3`, the ligand is said to be unidentate.
Bidentate. ligand : When a ligand can bind through two donor atoms as in `H_2NCH_2 CH_2NH_2` (ethane-1, 2-diamine) or `C_2O_4^(2-)` (oxalato), the ligand is said to be bidentate.
Polydentate ligand : When several donor atoms are present in a single ligand as in `N(CH_2CH_2 NH_2)`, the ligand is said to be polydentate.
Ethylenediaminetetraacetate ion (EDTA) is an important hexadentate ligand. It can bind through two nitrogen and four oxygen atoms to a central metal ion.

Ambidentate ligand : Ligand which can ligate through two different atoms is called ambidentate ligand.
Examples of such ligands are the `NO_2^(-)` and `SCN^(-)` ions. `NO_2^(-)` ion can coordinate either through nitrogen or through oxygen to a central metal `"atom"//"ion"`. Similarly, `SCN^(-)` ion can coordinate through the sulphur or nitrogen atom.
`underset("nitrito-O")(M larr O - N = O)" "underset("thiocyanato")(M larr SCN)" "underset("isothiocyanato")(M larr NCS)`