Ligands-definition-examples-types in co-ordination chemistry .

KAKALI GHOSH , Teacher,blogger. M.Sc chemistry.

4 min readApr 18, 2020

Ligand Definition In Co-Ordination Chemistry

In co-ordination chemistry , the cation to which one or more neutral molecules or ions are co-ordinated is called central metal cation , while the molecules or ions so attached are called Ligand .

For examples , CN– , Cl– , CO , H2O NH2–NH2 etc .

Ligand examples in co-ordination chemistry

There are three types of ligands depending on the nature of charge are known . Such as cationic Ligand , anionic Ligand and neutral Ligand .

Ligand types in co-ordination chemistry

There are different types of ligands are known depending on their function in co-ordination with the central metal ion in co-ordination chemistry .

Such as ambident ligands , flexidentate ligands , classical ligands, non-classical ligands , chelating ligand , π-acid ligand etc .

Ambident ligands.

There are few ligands which contain more than one donor atom , but they can use only one donor atom at once in the formation of complex compound, these type of ligands are called Ambident ligands .

There are two types of ambident ligand, namely , mono dentate ambident ligand and bidentate ambident ligand .

When a mono dentate ambident ligand ( such as nitrite ion ) ,is attached with different central metal ion , it uses either ’N’ atom or ‘ O ‘ atom as a donor atom .

Similarly, when a bi-dentate ambident ligand ( such as dithio oxalate ion ) ,is attached with different central metal ion, it uses either both the ‘O’ atom or both the ‘S ‘ atom together as a donor atom.

Flexidentate ligands :

There are few ligands in co-ordination chemistry which have two or more donor atoms .

But ,they do not use their entire donor atom at once in the formation of co-ordination compound that is in co-ordination with central metal ion .

They use their different donor atom with different metal ion to form co-ordinate bond . Such types of ligands are called flexi dentate ligands.

For example, Cysteine , a tri dentate ligand with three different donor atoms ( S, N, O ) act as a didentate ligand in three different way [ when it uses S,N , N,O and S,O atom separately ]

So, Cysteine is a flexi dentate ligand .

Similarly, there are many other poly dentate ligands those are behaved as a flexi dentate ligand.

Such as , EDTA , a poly dentate ligand , but in some cases it uses as a penta dentate or tetra dentate ligand . so , EDTA is also a flexi dentate ligand .

There are another two types of ligands are known which are , classical ligands and non-classical ligands .

( I ) Classical ligands : Classical ligands are those ligands which can co-ordinate with the central metal ion by using their lone pair of electrons .

For examples CO , CN — , F –, Cl — , OH –, H2O , NH3 etc .

(II ) Non-classical ligands : There are few ligands which uses their electron-pair of pi bond in the formation of co-ordinate bond with the central metal ion , these type of ligands are called Non-classical ligands .