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International Journal of Scientific and Research Publications, Volume 3, Issue 2, February 2013 299
ISSN 2250-3153
For mono basic ligand
For dibasic ligand
Where K 1 andK 2 are the first and second dissociation
constants, CA= Total concentration for ligands, a= number of
moles of alkali added per mole of ligand.
The stability constants (log K MLL’) for ternary mixed
ligand complexes were calculated as suggested by Ramamoorthy
and Santappa (49) for simultaneous complexation of ligand to the
metal ion. The stability constants for the ternary system were
calculated by the following expression
found as Ni(II) ˃Cu(II)>Co(II)>Zn(II) . It can be correlated in
terms of increasing ionic potential (ϕ) of the metal ion (50). It
was reported that (51) the stability of ternary complexes depends
on several factors such as a double bond present in a ligand
increases stability of the complex due to exocyclic conjugation,
the OH group present in the ligand increases stability due to
electron withdrawing nature, if the ring form is bigger, the
stability will be low.
The average (log K MLL’ ) values were used to calculate the
free energy (∆G 0 ), enthalpy (∆H 0 ) and entropy (∆S 0 ) from the
Van’t Hoff’s isotherm., The values of free energy (∆G 0 ),
enthalpy (∆H 0 ) and entropy (∆S 0 ) change of the resulting ternary
complexes are shown in the table-3, the calculated ∆G 0 has been
found to be negative in all the systems indicating spontaneity of
the complex formation. Calculated positive values of entropy
(∆S 0 ) indicate the formation of ternary complexes in the solution.
The negative enthalpy (∆H 0 ) values indicate the exothermic
nature of the reaction.
Where,
Where T M =Total metal ion concentration; K 1 and K 2 =
the first and second dissociation constants of ligand (L’); K 1 = the
dissociation constant of the ligand (L)
The calculated values of stability constants are
summarised in Table-2. The relative order of stability has been
IV. CONCLUSION
On the basis of above study the stability of various
ternary complexes has been found in the following order Ni (II)
˃Cu (II)>Co (II)>Zn (II). The observed order of stability of
complexes may be correlated in terms of increasing polarisability
of metal ion due to their decrease in size and increase in ionic
potential (ϕ).
TABLE: 1 Dissociation Constants of PDA and HBAA at experimental temperatures
Ligand PK 1 PK 2
298.15K 313.15K 298.15K 313.15K
PDA 2.57 2.63 4.33 4.38
HBAA 4.37 4.77 8.36 8.45
TABLE:2 Stability Constants for M(II)-PDA-HBAA, Ternary System[µ=0.1 mol dm -3 (KNO 3 ), KOH=0.1M] at temperatures
298.15 and 313.15K
S.No. m Cu(II)-PDA-HBAA Ni(II)-PDA-HBAA Zn(II)-PDA-HBAA Co(II)-PDA-HBAA
298.15K 313.15K 298.15K 313.15K 298.15K 313.15K 298.15K 313.15K
1 0.2 11.92 11.65 12.05 11.92 11.11 11.03 11.13 11.05
2 0.3 11.63 11.56 11.68 11.63 10.74 10.74 10.77 10.69
3 0.4 11.51 11.35 11.47 11.42 10.53 10.53 10.56 10.48
4 0.5 11.42 11.12 11.24 11.19 10.30 10.30 10.33 10.25
5 0.6 11.21 10.89 11.02 10.97 10.08 10.08 10.11 10.03
6 0.7 10.97 10.81 10.93 10.88 9.99 9.99 10.02 9.98
TABLE: 3 Free energy (∆G 0 ), Enthalpy (∆H 0 ) and Entropy (∆S 0 ) changes of ternary complexes [µ=0.1 moldm -3 (KNO 3 )] at
temperatures 298.15 and 313.15K
+∆S
Systems, Mean Value logK
S.No.
MLL’ -∆H -∆G (k.cal/Mole)
(Cal/Mole/degree)
1:1:1
(k.cal/Mole)
298.15K 313.15K 298.15K 313.15K 298.15K 313.15K
Cu(II)-
1
10.82 10.61 5.97 14.75 15.19 29.46 29.45
PDA-
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