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CH COO:CH CH N::OOCCH :OOCCH COO::NCH COMPLEXES

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CHELATE COMPLEXES

Among the complexes, the most important ones are the chelate complexes. They are complexes formed by the ligand being attached to the central atom from more than one place and ringed by the ring closure (Greek also means khele claw). The most important chelating agent is EDTA (Ethylene Diamine Tetra Acetic Acid): it is made of hexa dentate (6 teeth)

CH2COOH CH2COOH NCH2CH2N

HOOCCH2 HOOCCH2

CH2COO:

CH2COO:

:NCH2CH2N:

:OOCCH2 :OOCCH2

HEXA DENTATE STRUCTURE

COMPLEXES

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WATER-İNSOLUBLE CHELATES:

N OH N OH H3C

C C H3C

N OH

N O

OH

Dimethyl glyoxime 8-Hydroxy quinoline

-nitroso -naftol

COMPLEXES

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POLINUCLEAR CHELATS

Chelate complexes are mostly mononuclear. Complexes with more than one center atom in their structure are called poly nuclear chelates.

CH

2

NH

2

Ag

+

NH

2

CH

2

Ag

+

NH

2

CH

2

CH

2

NH

2

COMPLEXES

(4)

EDTA MAKES A 1: 1 COMPLEX. EDTA'S DISODIUM SALT IS USED IN CHEMICAL PROCEDURE

TRADE NAMES: COMPLEKSON III; CALSOL; CHALATON, EDTA TETRA PROTIC ACID.

NTA (NITRILOTRIACETIC ACID)

COMPLEXES

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Fraction of EDTA in the form Y 4-

COMPLEXES

   

   

 

H Y

       

H Y HY Y HY Y

EDTA

Y CT Y

2- 3- 4-

2 3

4

4 4

4

Y4

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Steps of Complex formation:

Cu+2 + NH3  Cu(NH3)+2 (1)

Cu(NH3)+2 + NH3  Cu(NH3)2+2 (2) Cu(NH3)2+2 + NH3  Cu(NH3)3+2 (3)

Cu(NH3)3+2 + NH3  Cu(NH3)4+2 (4)

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1. Formation constant for the EDTA reaction :

Q

2

= K

2 formation

=

Q

3

= K

3 formation

= Q

4

= K

4 formation

= Q

1

= K

1 formation

=

COMPLEXES

 

3 2



3

2 2 3

) (

) (

NH NH

Cu

NH Cu

 

2



3

3) 2

(

NH Cu

NH Cu

 

 

3

2 2 3

2 3 3

) (

) (

NH NH

Cu

NH Cu

 

 

3

2 3 3

2 4 3

) (

) (

NH NH

Cu

NH Cu

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Ionization of complexes is denoted by Kion or Qd. Ag(NH3)2+ : Ag(NH3)2+  Ag+ + 2NH3

Kion = Qd=

In the chemical calculations in complex

equilibria, both decomposition and formation constants can be used.

COMPLEXES

  

3 2

2 3

) Ag(NH

NH

Ag

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EDTA can be showed in the form of H4Y. Their ionization constants can be expressed in the following format:

H4Y  H3Y- + H+ Qd1=

H3Y-  H2Y= + H+ Qd2=

H2Y=  HY-3 + H+ Qd3=

HY-3  Y-4 + H+ Qd4=

COMPLEXES

Y H

Y H H

4

3

Y H

Y H H

3 2 2

2 2

3

Y H

Y H H

3 4

HY Y H

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