EDTA

 

EthyleneDiamineTetraAceticacid

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

DISODIUM EDTA

[H2*EDTA]2-
Tetradentate ligand

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

[EDTA]4-

Hexadentate ligand

[EDTA]4-

Chelating ligand

TETRASODIUM EDTA

CALCIUM DISODIUM EDTA

🏆🏆🏆🏆🏆

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]

 

INTRODUCTION

• What are coordination compounds?
• Types
• Terminologies 

LIGANDS	CENTRAL METAL ION/ ATOM
😊Species having at least one lone pair of electron and donate its lone pair of electron to the central metal cation.     😊Electron rich site and hence called as Lewis base/ nucleophile.	😊They do accept that lone pair of electron.     😊Electron deficit site and hence called as Lewis acid/ electrophile.

So when a group of ligands donate its lone pair of electron i.e., one donor atom of a ligand donates one pair of electron to the metal cation/ atom, coordinate bonds are formed and the result is called complex ion.

A compound with that complex ion is called as coordination compound.

NEUTRAL COMPLEX COMPOUNDS	IONIC COMPLEX COMPOUNDS
[Pt(NH3)2Cl2] [Co(NH3)3Cl3]	CATIONIC COMPLEX ANIONIC COMPLEX BOTH [Co(NH3)6]Cl3 K4[Fe(CN)6] [Pt(NH3)4][PtCl4]

[Pt(NH₃)₂Cl₂]👉❌DISSOCIATE

Diamminedichloroplatinum(II)

[Co(NH₃)₃Cl₃]👉❌DISSOCIATE

Triamminetrichlorocobalt(III)

*NOTE: The above complexes in aqueous medium does not dissociate into its constituent ions.

[Co(NH₃)₆]Cl₃ 👉 [Co(NH₃)₆]³⁺ + 3Cl^-          

Hexamminecobalt(III) chloride                    

K₄[Fe(CN)₆]👉4K⁺ + [Fe(CN)₆]^4-

Potassium hexacyanoferrate(II)

[Pt(NH₃)₄][PtCl₄]👉[Pt(NH₃)₄]²⁺ + [PtCl₄]^2-

Tetrammineplatinium(II) tetrachloroplatinate(II)

*NOTE: The above complexes in aqueous medium undergoes partial dissociation.

Unlike double salts coordination compounds do not loose their identity and do not give positive test for all their constituent ions!

IONISATION SPHERE ←K₄[Fe(CN)₆]→COORDINATION SPHERE

                       ↙       ↘

         CENTRAL METAL ION          LIGANDS

• The central metal ion bonded to the ligand via coordinate covalent bond is always written within the square bracket is called as coordination sphere.
• The cation/ anion outside the coordination sphere is called as ionization sphere or counter ion.
• The atom in the ligand which is directly attached to the central metal ion is called as donor atom.
• The number of donor atoms attached to the CMI is called as coordination number.