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Polarographic study of mixed ligand complexes: Cadmium-imidazole-malonate system
J. inorg, nucl. Chem. VoL 43. No. I1. pp, 2885-2888, 1981 Printed in Great Britain
0022-1902/81/112885-04502.0010 Pergamon Press Ltd.
POLAROGRAPHIC STUDY OF MIXED LIGAND COMPLEXES: CADMIUM-IMIDAZOLE-MALONATE SYSTEM MADHU SHIVHARE, KRISHNA, NISHA JAIN and MUKHTAR SINGH* Chemical Laboratories, Agra College, Agra 282002, India
(Received 4 December 1980; receivedfor publication 18 May 1981) Abstract--The mixed ligand complexes of imidazole (Im) and malonate (Mal) with Cd(lI) have been studied
polarographically at constant ionic strength, # =2.0 (NaNO3) and pH 8 at 25±0.1°C. The reduction of the complexes at d.m.e, is reversible and diffusion-controlled. Three mixed complexes, [Cd(lm)(Mal)], [Cd(Im)(Mal)2]2and [Cd(Im)2(Mal)J are formed. Their overall stability constants at 25°C are: log,8, =4.0, log /312= 4.4 and log/~21 = 5.9, respectively. INTRODUCTION
Li et al) have studied polarographically the composition and stability constants of simple complexes of Cd(II) with imidazole, a monodentate ligand, L2 in aqueous and alcoholic media. The composition and the stability constants were determined by Lingane's 3 method. Although the plot of E~/2 vs log [Im] was a curve, it was interpreted 4 as a composite of three straight lines. The analysis of these straight lines revealed the formation of three complexes, [Cd(Im)2]z+, [Cd(Im)3] 2+ and [Cd(Im)4] 2+ with stability constants, 1og/32 = 5.0, log/3~ =6.5 and log/34 = 7.5, respectively. However, the method employed by Li et al. for studying the composition and the stability constants of the consecutive complexes of Cd(II) with imidazole was not accurate: It was, therefore, thought worthwhile to undertake the polarographic study of the simple and mixed complexes of Cd(II) with imidazole and malonate ions using DeFord and Hume's method. EXPERIMENTAL
All reagents were analytical grade and their solutions were prepared in conductivity water. The ionic strength was maintained constant at # = 2.0 using NaNO3 as supporting electrolyte. Imidazole and potassium malonate were used as ligands. The concentration of Cd(ll) was maintained at 1 x 10-3 M. Polarograms were obtained by means of a manual polarograph (Toshniwal CL 02) in conjunction with Toshniwal polyflex galvanometer (PL 50). All the measurements were made at 25-+ 0.1°C and pH 8. A saturated calomel electrode (S.C.E.) was used as reference electrode. The d.m.e, had the following characteristics (in 0.I M NaNO3, open circuit): m = 1.5mg/sec, t = 2.75 sec, m2:3t~t6= 1.55 mg2/3 sec-~/2, hcorr= 52 cm. RESULTS AND DISCUSSION
The reduction of Cd(II) in both imidazole and malonate media was found to be reversible and diffusioncontrolled. The same was true for the mixed system. The slopes of linear plots of log ilia- i VS Ea.¢. were of the order of 33 mV and the plots of id vs h~c/o2rrwere linear and passed through the origin. The stability constants of simple complexes of Cd(II) with imidazole and malonate were determined separately prior to the study of mixed ligand system. Identical conditions were maintained in both the simple and mixed systems.
Cd(II)-imidazole system A plot of E~/2 vs log [Im] was a smooth curve, suggesting the formation of successive complexes. DeFord and Hume's method was applied to determine the stability constants of successive complexes. The polarographic characteristics and Fj[X] functions of Cd(II)-imidazole system are listed in Table 1. Four complexes, [Cd(Im)] 2+, [Cd(Im)2]2÷, [Cd(Im)3] 2+ and [Cd(Im)4] 2+ with stability constants, log/3|o = 2.7, log/32o = 4.0, log/330 -- 5.3 and log B4o = 7.0, respectively, are formed.
Cd(II)-malonate system A plot of E~/2 vs log [Mal2 ] was a smooth curve thereby suggesting the formation of successive complexes. DeFord and Hume's method was applied to determine the stability constants of successive complexes. The polarographic characteristics and Fj[X] functions of Cd(II)-malonate system are presented in Table 2. Three complexes, [Cd(Mal)], [Cd(Mal)2] ~- and [Cd(Mal)3]4- with stability constants log/3o~=l.0, log/3o2 = 2.6 and log/3o3 = 3.6, respectively, are formed. The values are nearly the same as reported by Gaur 7 for this system.
Cd(II)-imidazole-malonate-mixed system Imidazole concentration was varied from 0.02 to 0.16 M and that of malonate was kept constant at 0.10 M. The Et/2 values were greater compared to those obtained in the absence of malonate thereby showing the formation of mixed complexes. The system was repeated at another concentration of malonate (0.20 M). The method of Schaap and McMasters 8 was used to determine the values of the stability constants of mixed complexes. The polarographic characteristics and F~[XY] functions of mixed complexes of Cd(II) with imidazole and malonate at fixed [MaF ] (0.10M and 0.20 M) are presented in Tables 3 and 4. The stability constants of the mixed complexes were calculated from the constants s A, B, C and D. Three mixed complexes as noted below are formed: [Cd(Im)(Mal)]; log/3,, = 4.0 [Cd(Im)(Mal)2]2-; log/3,2 = 4.4 [Cd(Im)2(Mal)]; log/32~ = 5.9.
*Author to whom correspondence should be addressed.
The mixing constant KM (equilibrium constant) for the 2885
2886
M. SHIVHARE et aL Table 1. Cd(II~im~azole system: [Cd 2+] = 1 x 10-3 M; ~ = 2.0 (NaNO3); pH 8; temp. 25°C t
,
M
i
V , (S. 3. ~.)
div.
' ,
x10--
t
t
t
~ ×10->
' v10 ,
' ×10-6
I
0.0
O. 605
1 "3
0.02
0.636
110
11.¢9
5.24
O. 04
0.660
110
74.61
I~.~0
35.60
5.87
0.06
0.675
110
740.20
3a.~6
58.10
£.O1
O. 08
0.687
108
622.90
77.73
90. ql
lq.ll
10.15
0.10
0.697
106
1394.00
158.30
15~.30
I~.5~
I0.~5
O. 20
0.730
104
18460.00
9oq.45
459.7~
~2.¢3
In. eq
0.30
0.752
104
87680.00
2o~2.63
079.54
~9.08
1~.02
0.40
0.764
10¢
260600.00
651¢.97
1627.49
40.~5
9.60
0.50
0.776
104
664700.00
13293.98
2657.79
52.95
Iq.50
O. 60
0.784
97
1529410.00
22156.80
5691.q6
61.36
le.O0
Table 2. Cd(II)--malonate system: [Cd2+] = 1 x 10-3 M;/~ = 2.0 (NaNO3); pH 8; temp. 25°C v
r
w
v
v
Fo[X ] , z1[x2 M
V '(S.C.~.)
' ,
I
!
dlv.
'
, x l O -I
0.00
0.605
110
0.05
0.619
100
3.27
4.48
0.10
0.639
99
15.71
14.71
0.15
0.647
98
29.61
19.07
O. 2O
O.656
97
60.26
0.30
0.668
96
155.20
0.40
0.678
95
342.00
0.50
0.685
94
0.60
0.692
93
!
,
F2[x]
,
F3[x)
!
x!O -I
!
xlO - 2
87.15
31.43
29.63
118.15
39.07
51.40
151.33
37.11
85.25
198.12
59.53
595.70
118.94
225.88
57.17
1038.00
172.93
278.05
39.67
Table 3. Cd(II)-imidazole-malonate system: [Cd 2+] = 1 x 10-3 M, [Mal2-] = 0.1 M (fixed);/t = 2.0 (NaNO3); pH 8; temp. = 25°C !
'
V (S.C.~.)
!
'
ld
'
' ,
dlv.
'
!
I
, x10 -3
, x 1 0 -5
Fo[XY] '1o ' x10 -2 T
|
0.00
0.605
110
0.02
0.569
99
63.89
23.94
0.04
0.677
98
306.60
72.65
0.06
0.687
96
682.20
111.03
151.71
8.61
0.08
0.695
96
1273.O0
157.12
171.40
8.92
0.10
0.701
95
2053°00
203.70
187.70
8.7O
0.12
0.707
91
3165.00
262.25
201,87
8.49
0.14
0.711
91
4671.00
332.50
223.21
8.7~
0.16
0.716
89
6696.00
417.50
248.43
9.24
A . 16 , B = 20xi02
C
IO0xi03
D
8.5xi05
131.62
Polarographic study of mixed ligand complexes
2887
Table 4. Cd(II)-imidazole--malonate system: [Cd2+] = 1 x 10-3 M; [Mal2-] = 0.2 M (fixed);/~ temp. = 25°C
%]
, -~I12
M
,(S.C.m..)
, q
2.0 (NaNO3); pH 8;
,1'oo [xY] ,~IO [x~] ,~2o [xq
,~o
'
, x10 -5
V div,
=
,
x10 -2
, xlO -4
[x~]
0.00
0.605
110
0.02
0.665
97
121.60
0.04
0.685
95
590.80
132.50
22.87
0.06
0.695
95
1286.00
204.33
27.21
17.00
0.08
0,702
94
2424.00
295,50
31.81
18.51
0.10
0.709
93
3910.00
385.00
34.40
17.40
0.12
0.714
8B
6101.00
503.41
38.53
17.94
0.14
0.719
87
9114.00
646.71
43.27
17.66
0.16
0.723
87
12450.00
774.37
45.88
18. O0
A
- 60 , B = 41x102 , C = 17x104 , D = 17.5x105
Table 5. Equilibria involved in three mixed complexes and quilibrium constant (K) values Nquilibria
io ~_ K at 25°C
I.
ca 2÷ + I~ ÷ ~ i 2- ".~
2.
~2~
3.
~ . +. 2Im. +. Mal. 2-.
+ Im + ~ I
4.
[Cd(Ira) (:',~l~] +
5.
[o~Ii~]
~- .
Im
~--
+
-" [o~(I~Jm~lJ]
~.o
------" [ c d ( I ~ ( ~ _ ~ l ) ~ ]
~
---
.-
"
i...
2-
4.~
[~d(Im) 2(Mal ~] 2-
5.9
[~d(Ira) 2(Mal)-J
I. 9
- [~(I~(,;~l]
+ ,~-
1.5
9--
+ 2Mal
-
~
~-
reactions: l/2[Cd(Imh] 2+ + U2[Cd(Malh] 2' [Cd(Im)(Mal)] l/2[Cd(Imh] 2÷ + l/2[Cd(Malhl 2. "[Cd(Imh(Mal)]
d(Ira)(Mal)
[~
2-
~-
solution as compared to parent binary complexes. This is given by the following relations 9'1° (1) (2)
indicates the relative stability of mixed complexes in
KM = fll,/X/(fl2oBo2)
(3)
Ku =/32,/X/(B~/3o2).
(4)
These yield +1.4 for reaction (1) and +0.9 for reaction
2888
M. SHIVHARE et al.
(2). The positive values show that the mixed complexes, [Cd(Im)(Mal)] and [Cd(Im)e(Mal)] are somewhat more stabJe than the simple complexes: [Cd(Im)2] 2+, [Cd(Imh] 2+ and [Cd(Mal)2] 2-. Three mixed complexes exist in solution in the equilibria shown in Table 5. The equilibrium constants (log values) are given for each equilibrium. From the equilibrium constant values the tendency of a ligand to add to a complex and to substitute another ligand may be compared. It is seen that Im adds to [Cd(Im)(Mal)] readily. The ligand Im can replace Mal 2in complex [Cd(Mal)3] 4-. Equilibria 10, 11 and 12 favour mixed complexation over the simple ones. The stabilities of three mixed complexes follow the order: [Cd(Im)~(Mal)] > [Cd(Im)(Mal)2] 2- > [Cd(Im)(Mal)]. Acknowledgement--We thank Dr. S. N. Srivastava, Principal, Agra College, Agra for provision of facilities.
REFERENCES 1. N. C. Li, J. M. White and E. Doody, J. Am. Chem. 76, 6219 (1954). 2. D. R. Crow, J. Polarog. Soc. 11, 67 (1967). 3. J. J. Lingane, Chem. Rev. 29, 1 (1941). 4. D. R. Crow, Polarography of Metal Comple~es, p. 63. Academic Press, New York (1969). 5. D. R. Crow, Polarography of Metal Complexes, p. 62. Academic Press, New York (1969). 6. D. D. DeFord and D. N. Hume, J. Am. Chem. Soc. 73, 5321 (1951). 7. R. S. Sharma and J. N. Gaur, Ind. J. Chem. 16A, 509 (1978). 8. W. B. Schaap and D. L. McMasters, J. Am. Chem. Soc. 83, 4699 (1961). 9. R. Sundaresan and A. K. Sundaram, Proc. Ind. Acad. Sci. 79A, 161 (1974). 10. S. L. Jain, J. Kishan and R. C. Kapoor, Ind. J. Chem. 18A, 133 (1979).
0022-1902/81/112885-04502.0010 Pergamon Press Ltd.
POLAROGRAPHIC STUDY OF MIXED LIGAND COMPLEXES: CADMIUM-IMIDAZOLE-MALONATE SYSTEM MADHU SHIVHARE, KRISHNA, NISHA JAIN and MUKHTAR SINGH* Chemical Laboratories, Agra College, Agra 282002, India
(Received 4 December 1980; receivedfor publication 18 May 1981) Abstract--The mixed ligand complexes of imidazole (Im) and malonate (Mal) with Cd(lI) have been studied
polarographically at constant ionic strength, # =2.0 (NaNO3) and pH 8 at 25±0.1°C. The reduction of the complexes at d.m.e, is reversible and diffusion-controlled. Three mixed complexes, [Cd(lm)(Mal)], [Cd(Im)(Mal)2]2and [Cd(Im)2(Mal)J are formed. Their overall stability constants at 25°C are: log,8, =4.0, log /312= 4.4 and log/~21 = 5.9, respectively. INTRODUCTION
Li et al) have studied polarographically the composition and stability constants of simple complexes of Cd(II) with imidazole, a monodentate ligand, L2 in aqueous and alcoholic media. The composition and the stability constants were determined by Lingane's 3 method. Although the plot of E~/2 vs log [Im] was a curve, it was interpreted 4 as a composite of three straight lines. The analysis of these straight lines revealed the formation of three complexes, [Cd(Im)2]z+, [Cd(Im)3] 2+ and [Cd(Im)4] 2+ with stability constants, 1og/32 = 5.0, log/3~ =6.5 and log/34 = 7.5, respectively. However, the method employed by Li et al. for studying the composition and the stability constants of the consecutive complexes of Cd(II) with imidazole was not accurate: It was, therefore, thought worthwhile to undertake the polarographic study of the simple and mixed complexes of Cd(II) with imidazole and malonate ions using DeFord and Hume's method. EXPERIMENTAL
All reagents were analytical grade and their solutions were prepared in conductivity water. The ionic strength was maintained constant at # = 2.0 using NaNO3 as supporting electrolyte. Imidazole and potassium malonate were used as ligands. The concentration of Cd(ll) was maintained at 1 x 10-3 M. Polarograms were obtained by means of a manual polarograph (Toshniwal CL 02) in conjunction with Toshniwal polyflex galvanometer (PL 50). All the measurements were made at 25-+ 0.1°C and pH 8. A saturated calomel electrode (S.C.E.) was used as reference electrode. The d.m.e, had the following characteristics (in 0.I M NaNO3, open circuit): m = 1.5mg/sec, t = 2.75 sec, m2:3t~t6= 1.55 mg2/3 sec-~/2, hcorr= 52 cm. RESULTS AND DISCUSSION
The reduction of Cd(II) in both imidazole and malonate media was found to be reversible and diffusioncontrolled. The same was true for the mixed system. The slopes of linear plots of log ilia- i VS Ea.¢. were of the order of 33 mV and the plots of id vs h~c/o2rrwere linear and passed through the origin. The stability constants of simple complexes of Cd(II) with imidazole and malonate were determined separately prior to the study of mixed ligand system. Identical conditions were maintained in both the simple and mixed systems.
Cd(II)-imidazole system A plot of E~/2 vs log [Im] was a smooth curve, suggesting the formation of successive complexes. DeFord and Hume's method was applied to determine the stability constants of successive complexes. The polarographic characteristics and Fj[X] functions of Cd(II)-imidazole system are listed in Table 1. Four complexes, [Cd(Im)] 2+, [Cd(Im)2]2÷, [Cd(Im)3] 2+ and [Cd(Im)4] 2+ with stability constants, log/3|o = 2.7, log/32o = 4.0, log/330 -- 5.3 and log B4o = 7.0, respectively, are formed.
Cd(II)-malonate system A plot of E~/2 vs log [Mal2 ] was a smooth curve thereby suggesting the formation of successive complexes. DeFord and Hume's method was applied to determine the stability constants of successive complexes. The polarographic characteristics and Fj[X] functions of Cd(II)-malonate system are presented in Table 2. Three complexes, [Cd(Mal)], [Cd(Mal)2] ~- and [Cd(Mal)3]4- with stability constants log/3o~=l.0, log/3o2 = 2.6 and log/3o3 = 3.6, respectively, are formed. The values are nearly the same as reported by Gaur 7 for this system.
Cd(II)-imidazole-malonate-mixed system Imidazole concentration was varied from 0.02 to 0.16 M and that of malonate was kept constant at 0.10 M. The Et/2 values were greater compared to those obtained in the absence of malonate thereby showing the formation of mixed complexes. The system was repeated at another concentration of malonate (0.20 M). The method of Schaap and McMasters 8 was used to determine the values of the stability constants of mixed complexes. The polarographic characteristics and F~[XY] functions of mixed complexes of Cd(II) with imidazole and malonate at fixed [MaF ] (0.10M and 0.20 M) are presented in Tables 3 and 4. The stability constants of the mixed complexes were calculated from the constants s A, B, C and D. Three mixed complexes as noted below are formed: [Cd(Im)(Mal)]; log/3,, = 4.0 [Cd(Im)(Mal)2]2-; log/3,2 = 4.4 [Cd(Im)2(Mal)]; log/32~ = 5.9.
*Author to whom correspondence should be addressed.
The mixing constant KM (equilibrium constant) for the 2885
2886
M. SHIVHARE et aL Table 1. Cd(II~im~azole system: [Cd 2+] = 1 x 10-3 M; ~ = 2.0 (NaNO3); pH 8; temp. 25°C t
,
M
i
V , (S. 3. ~.)
div.
' ,
x10--
t
t
t
~ ×10->
' v10 ,
' ×10-6
I
0.0
O. 605
1 "3
0.02
0.636
110
11.¢9
5.24
O. 04
0.660
110
74.61
I~.~0
35.60
5.87
0.06
0.675
110
740.20
3a.~6
58.10
£.O1
O. 08
0.687
108
622.90
77.73
90. ql
lq.ll
10.15
0.10
0.697
106
1394.00
158.30
15~.30
I~.5~
I0.~5
O. 20
0.730
104
18460.00
9oq.45
459.7~
~2.¢3
In. eq
0.30
0.752
104
87680.00
2o~2.63
079.54
~9.08
1~.02
0.40
0.764
10¢
260600.00
651¢.97
1627.49
40.~5
9.60
0.50
0.776
104
664700.00
13293.98
2657.79
52.95
Iq.50
O. 60
0.784
97
1529410.00
22156.80
5691.q6
61.36
le.O0
Table 2. Cd(II)--malonate system: [Cd2+] = 1 x 10-3 M;/~ = 2.0 (NaNO3); pH 8; temp. 25°C v
r
w
v
v
Fo[X ] , z1[x2 M
V '(S.C.~.)
' ,
I
!
dlv.
'
, x l O -I
0.00
0.605
110
0.05
0.619
100
3.27
4.48
0.10
0.639
99
15.71
14.71
0.15
0.647
98
29.61
19.07
O. 2O
O.656
97
60.26
0.30
0.668
96
155.20
0.40
0.678
95
342.00
0.50
0.685
94
0.60
0.692
93
!
,
F2[x]
,
F3[x)
!
x!O -I
!
xlO - 2
87.15
31.43
29.63
118.15
39.07
51.40
151.33
37.11
85.25
198.12
59.53
595.70
118.94
225.88
57.17
1038.00
172.93
278.05
39.67
Table 3. Cd(II)-imidazole-malonate system: [Cd 2+] = 1 x 10-3 M, [Mal2-] = 0.1 M (fixed);/t = 2.0 (NaNO3); pH 8; temp. = 25°C !
'
V (S.C.~.)
!
'
ld
'
' ,
dlv.
'
!
I
, x10 -3
, x 1 0 -5
Fo[XY] '1o ' x10 -2 T
|
0.00
0.605
110
0.02
0.569
99
63.89
23.94
0.04
0.677
98
306.60
72.65
0.06
0.687
96
682.20
111.03
151.71
8.61
0.08
0.695
96
1273.O0
157.12
171.40
8.92
0.10
0.701
95
2053°00
203.70
187.70
8.7O
0.12
0.707
91
3165.00
262.25
201,87
8.49
0.14
0.711
91
4671.00
332.50
223.21
8.7~
0.16
0.716
89
6696.00
417.50
248.43
9.24
A . 16 , B = 20xi02
C
IO0xi03
D
8.5xi05
131.62
Polarographic study of mixed ligand complexes
2887
Table 4. Cd(II)-imidazole--malonate system: [Cd2+] = 1 x 10-3 M; [Mal2-] = 0.2 M (fixed);/~ temp. = 25°C
%]
, -~I12
M
,(S.C.m..)
, q
2.0 (NaNO3); pH 8;
,1'oo [xY] ,~IO [x~] ,~2o [xq
,~o
'
, x10 -5
V div,
=
,
x10 -2
, xlO -4
[x~]
0.00
0.605
110
0.02
0.665
97
121.60
0.04
0.685
95
590.80
132.50
22.87
0.06
0.695
95
1286.00
204.33
27.21
17.00
0.08
0,702
94
2424.00
295,50
31.81
18.51
0.10
0.709
93
3910.00
385.00
34.40
17.40
0.12
0.714
8B
6101.00
503.41
38.53
17.94
0.14
0.719
87
9114.00
646.71
43.27
17.66
0.16
0.723
87
12450.00
774.37
45.88
18. O0
A
- 60 , B = 41x102 , C = 17x104 , D = 17.5x105
Table 5. Equilibria involved in three mixed complexes and quilibrium constant (K) values Nquilibria
io ~_ K at 25°C
I.
ca 2÷ + I~ ÷ ~ i 2- ".~
2.
~2~
3.
~ . +. 2Im. +. Mal. 2-.
+ Im + ~ I
4.
[Cd(Ira) (:',~l~] +
5.
[o~Ii~]
~- .
Im
~--
+
-" [o~(I~Jm~lJ]
~.o
------" [ c d ( I ~ ( ~ _ ~ l ) ~ ]
~
---
.-
"
i...
2-
4.~
[~d(Im) 2(Mal ~] 2-
5.9
[~d(Ira) 2(Mal)-J
I. 9
- [~(I~(,;~l]
+ ,~-
1.5
9--
+ 2Mal
-
~
~-
reactions: l/2[Cd(Imh] 2+ + U2[Cd(Malh] 2' [Cd(Im)(Mal)] l/2[Cd(Imh] 2÷ + l/2[Cd(Malhl 2. "[Cd(Imh(Mal)]
d(Ira)(Mal)
[~
2-
~-
solution as compared to parent binary complexes. This is given by the following relations 9'1° (1) (2)
indicates the relative stability of mixed complexes in
KM = fll,/X/(fl2oBo2)
(3)
Ku =/32,/X/(B~/3o2).
(4)
These yield +1.4 for reaction (1) and +0.9 for reaction
2888
M. SHIVHARE et al.
(2). The positive values show that the mixed complexes, [Cd(Im)(Mal)] and [Cd(Im)e(Mal)] are somewhat more stabJe than the simple complexes: [Cd(Im)2] 2+, [Cd(Imh] 2+ and [Cd(Mal)2] 2-. Three mixed complexes exist in solution in the equilibria shown in Table 5. The equilibrium constants (log values) are given for each equilibrium. From the equilibrium constant values the tendency of a ligand to add to a complex and to substitute another ligand may be compared. It is seen that Im adds to [Cd(Im)(Mal)] readily. The ligand Im can replace Mal 2in complex [Cd(Mal)3] 4-. Equilibria 10, 11 and 12 favour mixed complexation over the simple ones. The stabilities of three mixed complexes follow the order: [Cd(Im)~(Mal)] > [Cd(Im)(Mal)2] 2- > [Cd(Im)(Mal)]. Acknowledgement--We thank Dr. S. N. Srivastava, Principal, Agra College, Agra for provision of facilities.
REFERENCES 1. N. C. Li, J. M. White and E. Doody, J. Am. Chem. 76, 6219 (1954). 2. D. R. Crow, J. Polarog. Soc. 11, 67 (1967). 3. J. J. Lingane, Chem. Rev. 29, 1 (1941). 4. D. R. Crow, Polarography of Metal Comple~es, p. 63. Academic Press, New York (1969). 5. D. R. Crow, Polarography of Metal Complexes, p. 62. Academic Press, New York (1969). 6. D. D. DeFord and D. N. Hume, J. Am. Chem. Soc. 73, 5321 (1951). 7. R. S. Sharma and J. N. Gaur, Ind. J. Chem. 16A, 509 (1978). 8. W. B. Schaap and D. L. McMasters, J. Am. Chem. Soc. 83, 4699 (1961). 9. R. Sundaresan and A. K. Sundaram, Proc. Ind. Acad. Sci. 79A, 161 (1974). 10. S. L. Jain, J. Kishan and R. C. Kapoor, Ind. J. Chem. 18A, 133 (1979).