CLASSIFICATION OF LIGANDS

 Based on mode of bonding,

1. Chelating ligands
2. Ambidentate ligands
3. Flexidentate ligands

CHELATING LIGANDS_Some multidentate ligands when form bonds with CMI/ CMA, they form ring like structure called chelates and the ligands is called chelating ligands and the phenomenon is called chelation.

CHELATION OR CHELATE EFFECT

# Complexes of chelating ligands are more stable than the complexes of monodentate ligands.

    tris(ethylenediamine)nickel (II) is more stable than hexaamminenickel (II).

#  Therefore, stability of complexes depends upon chelation.

#  Usually the chelating ligands can be five or six membered ring.

        #  Conjugated chelating ligands are more stable due to delocalization of pi electrons.

        #  tris(acetylacetonato)iron (III) is highly stable.

acetylacetonate

    AMBIDENTATE LIGANDS are capable of bonding to a CMA/ CMI via two different atoms however, ligand utilizes only one donor site at a time.

Ambidentate ligands belongs to monodentate ligands.

cyanato & isocyanato

FLEXIDENTATE LIGANDS have variable donor sites. they coordinate with CMI/ CMA through one donor atom forming non-chelated complex or through two donor atoms forming four membered ring.

It belongs to either be monodentate or bidentate ligands.

[Co(NH₃)₄SO₄]_bidentate

[Co(NH₃)₅SO₄]_Monodentate