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
WATER-İNSOLUBLE CHELATES:
N OH N OH H3C
C C H3C
N OH
N O
OH
Dimethyl glyoxime 8-Hydroxy quinoline
-nitroso -naftol
COMPLEXES
POLINUCLEAR CHELATS
Chelate complexes are mostly mononuclear. Complexes with more than one center atom in their structure are called poly nuclear chelates.
CH
2NH
2Ag
+NH
2CH
2Ag
+NH
2CH
2CH
2NH
2COMPLEXES
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
Fraction of EDTA in the form Y 4-
COMPLEXES
H Y
H Y HY Y HY YEDTA
Y CT Y
2- 3- 4-
2 3
4
4 4
4
Y4
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)
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
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
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