Question

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

Answer 1

Hint:Ligands are those species which have donating species of electrons, atoms through which the central metal atom forms a co-ordinate bond with the ligands. The monodentate,bidentate and tridentate ligands are the different classifications of ligands.

Complete step-by-step answer:In the question, it is asked to comment on the unidentate ligand, bidentate ligand, and ambidentate ligands. Before going into these terms let's have a basic idea of the coordinate bond, central metal atom, and ligands.
Coordination compounds are the compounds that are formed by the coordinate bonding between a central metal atom and the ligand.
A coordinate bond is a type of bond in which a bond is formed by the sharing of electrons from an atom i.e. the two electrons present in a bond will be completely contributed by an atom or molecule. The atoms of molecules that donate their electrons are called the ligands and the species to which the ligand donates the electrons are called the central metal atom.
The central metal atom will be an electron-deficient species and the ligands will be electron-rich species.
The ligands are classified into many based on the number of donor atoms present in a ligand.
The various types of ligands are unidentate, bidentate, tridentate.
Unidentate is the species that has the potential to form a coordinate bond through one donor atom. The unidentate ligands will have only one donating site available in them.
Examples for unidentate ligands are, $C{l}_2$,$N{H}_3$etc.
Bidentate ligands: These are ligand species that have two donating sites available in them to coordinate with the central metal atom and form the coordinate bond. These are also known as bidentate ligands.
Example of bidentate ligands: oxalate ion and Ethylenediamine
Ambidentate ligand: These are ligand species in which the donor species have the tendency to coordinate with the central metal atom through two different sites.
Example for ambidentate ligand SCN and $N{O}_2$
In SCN when S acts as a donor atom it is thiocyanate ligand and in isothiocyanate, N is the donor atom.
In$N{O}_2$, nitro group N is the donor atom, and in the nitrito group, O acts as the donor atom.

Note:The unidentate ligand is also called the monodentate ligand.
The molecules like water, O has two lone pairs so it could donate two pairs of electrons but it is not the condition for being a bidentate ligand, two atoms should be there or two different coordinating sites should be available, so water is a monodentate ligand.
Many get confused between the number of lone pairs available and the number of donating sites available, hence the concept should be studied properly to avoid these types of confusions.