EDTA

 

EthyleneDiamineTetraAceticacid

[H4*EDTA]
Bidentate ligand
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[H3*EDTA]-
Tridentate ligand
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DISODIUM EDTA

[H2*EDTA]2-
Tetradentate ligand

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[H*EDTA]3-
Pentadentate ligand
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[EDTA]4-

Hexadentate ligand

[EDTA]4-

Chelating ligand

TETRASODIUM EDTA

CALCIUM DISODIUM EDTA

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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

CLASSIFICATION OF LIGANDS

 

Based on number of donor sites,

1. Monodentate ligands contains only one donating atom.

   a) Neutral monodentate ligands:

NAME OF THE LIGAND	STRUCTURE SHOWING DONOR ATOM
ammine
aqua
carbonyl
nitrosyl

    b)Positive/ cationic monodentate ligand:

NAME OF THE LIGAND	STRUCTURE SHOWING DONOR ATOM
nitronium
nitrosyelium
hydronium
ammonium

   c) Negative/ anionic monodentate ligand:

NAME OF THE LIGAND	STRUCTURE SHOWING DONOR ATOM
halo	x-
cyno
thiocyanate
amido

 

^{2. Polydentate ligands contains more than one donating atom.}

• Bidentate ligand has two donor atoms.

  

  ethylenediaminetetraacetic acid (edta)

  
  

oxalato (ox)

glycinato (gly)

ethylenediamine (en)

• Tridentate ligand has three donor atoms.

  

  diethylenetriamine (dien)

  
  
  
  
• Tetradentate ligand has four donor atoms.

triethylenetetramine (trien)

• Pentadentate ligand has five donor atoms.

ethylenediaminetriacetato 

• Hexadentate ligand has six donor atoms.

  

  ethylenediaminetetraacetato (edta^4-)

  
  

trans-dichlorobisethylenediamineplatinum (II)

[Pt(en)₂Cl₂]

cis-dichlorobisethylenediamineplatinum (II)

[Pt(en)₂Cl₂]

cis-diamminedichloroplatinum (II) or cisplatin

[Pt(NH₃)₂Cl₂]

trans-diamminedichloroplatinum (II) or transplatin

[Pt(NH₃)₂Cl₂]