- Email: [email protected]
Polarographic behaviour of complexes of gluconate ions with Zn(II), In(III) and Eu(III)
179
Journal of the Less-Common Metals, 60 (1978) 179 - 184 @ Elsevier Sequoia S.A., Lausanne -Printed in the Netherlands
POLAROGRAPHIC IONS WITH Zn(II),
OM PARKASH*,
BEHAVIOUR OF COMPLEXES In(II1) AND Eu(II1)
OF GLUCONATE
S. K. BHASIN* and D. S. JAIN
Chemical Laboratories, Rajasthan University, Jaipur-302004 (Received October 4,1977;
(India)
in revised form January 30, 1978)
Summary The reductions of Zn(II), In(II1) and Eu(II1) at a dropping mercury electrode have been studied in sodium gluconate solutions at 30 “C (p = 1.0). The reduction is diffusion controlled but is reversible only in the presence of gluconate ion with Eu(II1). The kinetic parameters K, and OLhave been calculated by Gelling’s method. K, was found to be of the order of lop3 cm S- ’ showing that the reduction is a completely quasi-reversible process for Zn(I1) and In(II1). The stability constants and composition have been calculated by DeFord and Hume’s method as modified by Irving. Mihailov’s mathematical method and Lingane’s method were used to calculate the stability constants of the Eu(III)-gluconate system. Zn(I1) and In(II1) form five complexes each; Eu(II1) forms only two complexes.
1. Introduction The interaction of gluconate ions with Pb(I1) and Cd(I1) has been studied by Peasok and Juvet [l, 21; the formation of a single complex was shown. Complex formation with Zn(I1) has been studied poientiometrically by Cannon and Kibrick [3] who also reported the formation of a single complex. The present study compares the polarographic behaviour of complexes formed by gluconate ions with Zn(II), In(II1) and Eu(II1).
2. Experimental Solutions containing 1.0 mM of Zn(I1) and 0.5 mM of In(II1) and Eu(II1) with various concentrations of gluconate ions were prepared at p = 1.0 by adding the requisite amounts of sodium perchlorate (pH 6.5). The dropping mercury electrode had the characteristics m = 1.7645 mg s-l and t, = 3.64 s (open circuit). All the measurements were carried out at *Present address: M.L.N. College, Yamuna Nagar, Haryana, India.
180
30 + 0.01 “C; this temperature was maintained by a Haake-type ultrathermostat. Purified nitrogen gas was bubbled through for about 20 - 25 mm to deaerate the solutions. An H-type cell with an agar-agar plug saturated with sodium chloride was used as the electrolytic vessel. 3. Results and discussion In each case, a single well-defined reduction wave was obtained. The plots of i, uersus v/h (h is the effective height of the mercury column) and i, uersus CM (CM is the metal ion concentration) are linear and pass through the origin, showing that the reduction process is diffusion controlled. The plots of log i/(ia - i) versus E d.e. are linear in all cases but, wherever the slope is higher than the slope of the reversible reduction process, the analysis of the curves has been carried out by Gelling’s [4] theoretical method. 3.1. Zn(II) glucona te system The plots of log i/(id - i) uersus I&.,. are linear but the slopes are much higher than the slope of a two-electron reversible reduction. The reversible half-wave potentials E ff2 have been calculated by Gelling’s method and the kinetic parameters for the electrode reaction have been calculated by plotting (E&, - E) uersus log (2 - 1). The method has been discussed in detail earlier [ 51 . The plots of Ef,, uersus -log Cx (Cx, gluconate ion concentration) is a smooth curve. The value of the coordination numberp calculated from the equation A&,, A log Cx
=-_
0.06~
n
is about 5. A modified DeFord and Hume’s [6] method has been applied to calculate the Fj ([X ] ) values; this shows the formation of five complexes: [ Zn(gluconate)]+, fZn(gluconate)2 J , [ Zn(gluconate)s]-, [ Zn(gluconate),] 2and [Zn(gluconate)5] 3-, with PI. Ps, Ps, 04 and 0s equal to 50,40,70,110 and 1020, respectively. The experimentally determined polarographic characteristics, Fj ([Xl ) functions and kinetic parameters are presented in Table 1 and the d~tribution of the various complex species is shown in Fig. 1.
3.2. In(III) gluconate system Here also the plots of log i/(id - ij uersus Edae. are linear but the slopes are higher than the slope of a three-electron reversible reduction. The reversible half-wave potentials have been calculated by Gelling’s 141 method as described earlier; the kinetic parameters were obtained by plotting (E&s E) uersus log (2 - 1). The plot of E;,z uersus --log Cx (C, is the gluconate ion concentration) is a smooth curve~which indicates the presence of two or more com-
181 TABLE 1 Pola~~aphie characteristics, F’([X] ) values and kinetic parameters of the Zn( II) gluconate system at 30 “C (Zn(I1) = 1.0 mM;@ = 1.0)
cx
id
(moi)
MA)
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
7.735 7.462 7.189 7.098 7.007 6.916 6.825 6.643 6.370
El/2
Eli2
F()([X])
(- V us. SCE) 0.9995 1.0390 1.0370 1.0420 1.0505 1.0530 1.0630 1.0690 1.0750
0.9920
-
1.0180 1.0285 1.0360 1.0420 1.0490 1.0560 1.0640 1.7000
7.30 17.72 31.93 51.25 82.24 154.00 281.40 483.00
Fig. 1. Plots of the percentage distribution us. -log
KsX103 (cm s-l)
cY
1.39
4.88 -
0.21
3.27 3.23 3.19
1.30 1.18 1.13 -
4.24 3.82 3.60 -
0.21 0.52 0.50 -
3.11 3.02 2.90
1.18 1.29 1.42
3.89 3.92 4.12
0.52 0.47 0.47
D”2x
lo3
h
(cm2 s-l)
(s-“~)
3.52
Cx for various species.
plexes in equilibrium. The value of the coordination number p is again 5. The stability constants have been calculated by a modified DeFord and Hume’s method which shows the formation of five complex species: [In(gluconate)] *, [In(gluconate)2]‘, [In(gluconate)3], [Infgluconate), ]- and [In(gluconate)s] 2-, when pl. oz. f13, 64 and P5 are 2 X 10’ 2 X 106, 30 X 106, 4 X 10’ and 210 X lo’, respectively. The experimentally determined polarographic characteristics, Fi( [Xl ) values and kinetic parameters are presented in Table 2 and the distribution of the various complex species is shown in Fig. 2.
182 TABLE 2 Polarographic characteristics, Fj( [Xl) values and kinetic parameters of the In(II1) gluconate system at 30 “C (In(II1) = 0.5 mM; /J = 1.0) cX
id
(moi)
(CIA)
0.00 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.50
3.913 3.822 3.822 3.822 3.913 3.822 3.640 3.640
5.369
El/Z (-V
E&2
us. SCE)
0.5260 0.6210 0.6340 0.6480 0.6570 0.6700 0.677 5 0.6820 0.6915
-1ogc,
0.524 0.619 0.631 0.642 0.650 0.658 0.663 0.669 0.678
Fo([X])
x 10-b
0.77 3.14 11.16 28.03 68.77 125.20 262.20 739.10
lo3 (cm2 s-l)
A (s-l12)
K,x103 (cm s-l)
cr
3.26 2.37 2.32 2.32 2.32 2.37 1.32 2.21 2.21
2.36 1.71 1.87 1.56 1.08 0.57 0.36 0.45 0.44
7.68 4.05 4.34 3.61 2.50 1.34 0.83 0.99 0.97
0.51 0.29 0.46 0.29 0.29 0.29 0.49 0.45 0.47
D112X
-
Fig. 2. Plots of the percentage distribution us. -log
CX for various species.
3.3. Eu(III) gluconate system In this case the plots of log i/id - i uersus Ed.,. are again linear but the slope for the simple metal ion in 1 .OM sodium perchlorate is 90 mV. However, the slope is of the order of 62 f 1 mV in the presence of gluconate ion, indicating that the electrode reaction is reversible for a one-electron reduction in the presence of the ligand. The reversible half-wave potential Eilz for the simple metal ion has been calculated by Gelling’s method as described earlier. The plot of E,,, uersus -log Cx is a straight line and the value of the coordination number p is about two. DeFord and Hume’s method has been
183
used to calculate the stability constants. The plot of F. ([Xl ) uersus Cx is a smooth curve which indicates the formation of more than one complex. This suggests that the linear plot of E1,a uersus -log Cx is not the only criterion for the formation of a single complex; the plot of F,( [X] ) uersus C, should also be a straight line. The plot of F1 ([Xl ) uersus C, is a straight line with a slope and that of F, ([Xl ) versus Cx is a straight line parallel to the X axis, indicating the formation of two complex species, [Eu(gluconate)12’ and [Eu(gluconate)2]‘. The values of the stability constants have also been calculated by Mihailov’s [7] mathematical method which does not involve graphical extrapolation. The values of Mihailov’s constant a for various ligand concentrations have been obtained and the average value of a has been calculated, neglecting the values of a which are furthest from the mean. This average value of a was used to calculate the values of A at different ligand concentrations. The average values of a and A are then used to calculate the overall formation constants of the complexes using the relation:
The values of a for various combinations of ligand concentrations and of A at various ligand concentrations are obtained. The values of the stability constants are : Pl
DeFord and Hume Mihailov
P2
700 649.33
9000 8850.41
These are in good agreement, indicating the validity of the graphical method of DeFord and Hume. The value,of f12 by Lingane’s method is 6979. The polarographic characteristics and the F, ([Xl ) values are presented in Table 3; the distribution of the various species is shown in Fig. 3. TABLE
3
Polarographic (Eu(II1)
characteristics
= 0.5 mM;p
and Fj( [Xl)
values of the Eu(II1) gluconate
cx
id
(mol)
(divs.)
-Q/2 (-V us. SCE)
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
67.5 55.0 54.0 52.0 52.0 51.5 50.5 50.5 50.5
0.6840a 0.8080 0.8400 0.8580 0.8710 0.8820 0.8905 0.8975 0.9030
aE l/2
=
e;,.
system
at 30 “C
= 1.0)
Fo([Xl)
143.1 497.6 1031.0 1697.0 2621.0 3797.0 4837.0 5973.0
184
0
M I .o
A
I
0% -togcx
I 0.6 -
1
I
0.4
I
I 0.2
4
Fig. 3. Plots of the percentage distribution us. -log
Cx for various species.
The value of K, for Eu(II1) in 1 .O M sodium perchlorate is 2.94 X lo- 3 cm s-l andcz = 0.44. A survey of the values of kinetic parameters shows that the value of K, is of the order of lo- 3 cm s- ’ in all cases. Therefore the electrode reactions are quasi-reversible for Zn(I1) gluconate and In(II1) gluconate systems. However, in the case of the Eu(II1) system only the electrode reduction of the simple metal ion in 1.0 M sodium perchlorate is quasi-reversible. Similarly a survey of the stability constants shows that In(II1) forms the strongest and Zn(I1) forms the weakest complexes with gluconate ions. Since all the reduction processes are diffusion controlled, these metals can be estimated polarographically in the presence of gluconate ions.
Acknowledgments The authors wish to express their thanks to Professor J. N. Gaur, Head of the Chemistry Department, Rajasthan University, Jaipur, for the provision of research facilities. References 1 2 3 4
R. L. Peasok and R. S. Juvet, J. Am. Chem. Sot., 77 (1955) 202. R. L. Peasok and R. S. Juvet, J. Am. Chem. Sot., 78 (1958) 3967. P. K. Cannon and A. Kibrick, J. Am. Chem. Sot., 60 (1938) 2314. P. J. Gellings, 2. Electrochem. Ber. Bunsenges. Phys. Chem., 66 (1962) 477, 481, 799; 67 (1963) 167. 5 D. S. Jain and J. N. Gaur, Rev. Polarogr. Sot., Jpn, 14 (1967) 206. 6 H. Irving, in I. S. Longmuir (ed.), Advances in Polarography, Pergamon Press, Oxford, 1960, Vol. 1, p. 42. 7 M. H. Mihailov, J. Inorg. Nucl. Chem., 36 (1974) 107,114.
Journal of the Less-Common Metals, 60 (1978) 179 - 184 @ Elsevier Sequoia S.A., Lausanne -Printed in the Netherlands
POLAROGRAPHIC IONS WITH Zn(II),
OM PARKASH*,
BEHAVIOUR OF COMPLEXES In(II1) AND Eu(II1)
OF GLUCONATE
S. K. BHASIN* and D. S. JAIN
Chemical Laboratories, Rajasthan University, Jaipur-302004 (Received October 4,1977;
(India)
in revised form January 30, 1978)
Summary The reductions of Zn(II), In(II1) and Eu(II1) at a dropping mercury electrode have been studied in sodium gluconate solutions at 30 “C (p = 1.0). The reduction is diffusion controlled but is reversible only in the presence of gluconate ion with Eu(II1). The kinetic parameters K, and OLhave been calculated by Gelling’s method. K, was found to be of the order of lop3 cm S- ’ showing that the reduction is a completely quasi-reversible process for Zn(I1) and In(II1). The stability constants and composition have been calculated by DeFord and Hume’s method as modified by Irving. Mihailov’s mathematical method and Lingane’s method were used to calculate the stability constants of the Eu(III)-gluconate system. Zn(I1) and In(II1) form five complexes each; Eu(II1) forms only two complexes.
1. Introduction The interaction of gluconate ions with Pb(I1) and Cd(I1) has been studied by Peasok and Juvet [l, 21; the formation of a single complex was shown. Complex formation with Zn(I1) has been studied poientiometrically by Cannon and Kibrick [3] who also reported the formation of a single complex. The present study compares the polarographic behaviour of complexes formed by gluconate ions with Zn(II), In(II1) and Eu(II1).
2. Experimental Solutions containing 1.0 mM of Zn(I1) and 0.5 mM of In(II1) and Eu(II1) with various concentrations of gluconate ions were prepared at p = 1.0 by adding the requisite amounts of sodium perchlorate (pH 6.5). The dropping mercury electrode had the characteristics m = 1.7645 mg s-l and t, = 3.64 s (open circuit). All the measurements were carried out at *Present address: M.L.N. College, Yamuna Nagar, Haryana, India.
180
30 + 0.01 “C; this temperature was maintained by a Haake-type ultrathermostat. Purified nitrogen gas was bubbled through for about 20 - 25 mm to deaerate the solutions. An H-type cell with an agar-agar plug saturated with sodium chloride was used as the electrolytic vessel. 3. Results and discussion In each case, a single well-defined reduction wave was obtained. The plots of i, uersus v/h (h is the effective height of the mercury column) and i, uersus CM (CM is the metal ion concentration) are linear and pass through the origin, showing that the reduction process is diffusion controlled. The plots of log i/(ia - i) versus E d.e. are linear in all cases but, wherever the slope is higher than the slope of the reversible reduction process, the analysis of the curves has been carried out by Gelling’s [4] theoretical method. 3.1. Zn(II) glucona te system The plots of log i/(id - i) uersus I&.,. are linear but the slopes are much higher than the slope of a two-electron reversible reduction. The reversible half-wave potentials E ff2 have been calculated by Gelling’s method and the kinetic parameters for the electrode reaction have been calculated by plotting (E&, - E) uersus log (2 - 1). The method has been discussed in detail earlier [ 51 . The plots of Ef,, uersus -log Cx (Cx, gluconate ion concentration) is a smooth curve. The value of the coordination numberp calculated from the equation A&,, A log Cx
=-_
0.06~
n
is about 5. A modified DeFord and Hume’s [6] method has been applied to calculate the Fj ([X ] ) values; this shows the formation of five complexes: [ Zn(gluconate)]+, fZn(gluconate)2 J , [ Zn(gluconate)s]-, [ Zn(gluconate),] 2and [Zn(gluconate)5] 3-, with PI. Ps, Ps, 04 and 0s equal to 50,40,70,110 and 1020, respectively. The experimentally determined polarographic characteristics, Fj ([Xl ) functions and kinetic parameters are presented in Table 1 and the d~tribution of the various complex species is shown in Fig. 1.
3.2. In(III) gluconate system Here also the plots of log i/(id - ij uersus Edae. are linear but the slopes are higher than the slope of a three-electron reversible reduction. The reversible half-wave potentials have been calculated by Gelling’s 141 method as described earlier; the kinetic parameters were obtained by plotting (E&s E) uersus log (2 - 1). The plot of E;,z uersus --log Cx (C, is the gluconate ion concentration) is a smooth curve~which indicates the presence of two or more com-
181 TABLE 1 Pola~~aphie characteristics, F’([X] ) values and kinetic parameters of the Zn( II) gluconate system at 30 “C (Zn(I1) = 1.0 mM;@ = 1.0)
cx
id
(moi)
MA)
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
7.735 7.462 7.189 7.098 7.007 6.916 6.825 6.643 6.370
El/2
Eli2
F()([X])
(- V us. SCE) 0.9995 1.0390 1.0370 1.0420 1.0505 1.0530 1.0630 1.0690 1.0750
0.9920
-
1.0180 1.0285 1.0360 1.0420 1.0490 1.0560 1.0640 1.7000
7.30 17.72 31.93 51.25 82.24 154.00 281.40 483.00
Fig. 1. Plots of the percentage distribution us. -log
KsX103 (cm s-l)
cY
1.39
4.88 -
0.21
3.27 3.23 3.19
1.30 1.18 1.13 -
4.24 3.82 3.60 -
0.21 0.52 0.50 -
3.11 3.02 2.90
1.18 1.29 1.42
3.89 3.92 4.12
0.52 0.47 0.47
D”2x
lo3
h
(cm2 s-l)
(s-“~)
3.52
Cx for various species.
plexes in equilibrium. The value of the coordination number p is again 5. The stability constants have been calculated by a modified DeFord and Hume’s method which shows the formation of five complex species: [In(gluconate)] *, [In(gluconate)2]‘, [In(gluconate)3], [Infgluconate), ]- and [In(gluconate)s] 2-, when pl. oz. f13, 64 and P5 are 2 X 10’ 2 X 106, 30 X 106, 4 X 10’ and 210 X lo’, respectively. The experimentally determined polarographic characteristics, Fi( [Xl ) values and kinetic parameters are presented in Table 2 and the distribution of the various complex species is shown in Fig. 2.
182 TABLE 2 Polarographic characteristics, Fj( [Xl) values and kinetic parameters of the In(II1) gluconate system at 30 “C (In(II1) = 0.5 mM; /J = 1.0) cX
id
(moi)
(CIA)
0.00 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.50
3.913 3.822 3.822 3.822 3.913 3.822 3.640 3.640
5.369
El/Z (-V
E&2
us. SCE)
0.5260 0.6210 0.6340 0.6480 0.6570 0.6700 0.677 5 0.6820 0.6915
-1ogc,
0.524 0.619 0.631 0.642 0.650 0.658 0.663 0.669 0.678
Fo([X])
x 10-b
0.77 3.14 11.16 28.03 68.77 125.20 262.20 739.10
lo3 (cm2 s-l)
A (s-l12)
K,x103 (cm s-l)
cr
3.26 2.37 2.32 2.32 2.32 2.37 1.32 2.21 2.21
2.36 1.71 1.87 1.56 1.08 0.57 0.36 0.45 0.44
7.68 4.05 4.34 3.61 2.50 1.34 0.83 0.99 0.97
0.51 0.29 0.46 0.29 0.29 0.29 0.49 0.45 0.47
D112X
-
Fig. 2. Plots of the percentage distribution us. -log
CX for various species.
3.3. Eu(III) gluconate system In this case the plots of log i/id - i uersus Ed.,. are again linear but the slope for the simple metal ion in 1 .OM sodium perchlorate is 90 mV. However, the slope is of the order of 62 f 1 mV in the presence of gluconate ion, indicating that the electrode reaction is reversible for a one-electron reduction in the presence of the ligand. The reversible half-wave potential Eilz for the simple metal ion has been calculated by Gelling’s method as described earlier. The plot of E,,, uersus -log Cx is a straight line and the value of the coordination number p is about two. DeFord and Hume’s method has been
183
used to calculate the stability constants. The plot of F. ([Xl ) uersus Cx is a smooth curve which indicates the formation of more than one complex. This suggests that the linear plot of E1,a uersus -log Cx is not the only criterion for the formation of a single complex; the plot of F,( [X] ) uersus C, should also be a straight line. The plot of F1 ([Xl ) uersus C, is a straight line with a slope and that of F, ([Xl ) versus Cx is a straight line parallel to the X axis, indicating the formation of two complex species, [Eu(gluconate)12’ and [Eu(gluconate)2]‘. The values of the stability constants have also been calculated by Mihailov’s [7] mathematical method which does not involve graphical extrapolation. The values of Mihailov’s constant a for various ligand concentrations have been obtained and the average value of a has been calculated, neglecting the values of a which are furthest from the mean. This average value of a was used to calculate the values of A at different ligand concentrations. The average values of a and A are then used to calculate the overall formation constants of the complexes using the relation:
The values of a for various combinations of ligand concentrations and of A at various ligand concentrations are obtained. The values of the stability constants are : Pl
DeFord and Hume Mihailov
P2
700 649.33
9000 8850.41
These are in good agreement, indicating the validity of the graphical method of DeFord and Hume. The value,of f12 by Lingane’s method is 6979. The polarographic characteristics and the F, ([Xl ) values are presented in Table 3; the distribution of the various species is shown in Fig. 3. TABLE
3
Polarographic (Eu(II1)
characteristics
= 0.5 mM;p
and Fj( [Xl)
values of the Eu(II1) gluconate
cx
id
(mol)
(divs.)
-Q/2 (-V us. SCE)
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
67.5 55.0 54.0 52.0 52.0 51.5 50.5 50.5 50.5
0.6840a 0.8080 0.8400 0.8580 0.8710 0.8820 0.8905 0.8975 0.9030
aE l/2
=
e;,.
system
at 30 “C
= 1.0)
Fo([Xl)
143.1 497.6 1031.0 1697.0 2621.0 3797.0 4837.0 5973.0
184
0
M I .o
A
I
0% -togcx
I 0.6 -
1
I
0.4
I
I 0.2
4
Fig. 3. Plots of the percentage distribution us. -log
Cx for various species.
The value of K, for Eu(II1) in 1 .O M sodium perchlorate is 2.94 X lo- 3 cm s-l andcz = 0.44. A survey of the values of kinetic parameters shows that the value of K, is of the order of lo- 3 cm s- ’ in all cases. Therefore the electrode reactions are quasi-reversible for Zn(I1) gluconate and In(II1) gluconate systems. However, in the case of the Eu(II1) system only the electrode reduction of the simple metal ion in 1.0 M sodium perchlorate is quasi-reversible. Similarly a survey of the stability constants shows that In(II1) forms the strongest and Zn(I1) forms the weakest complexes with gluconate ions. Since all the reduction processes are diffusion controlled, these metals can be estimated polarographically in the presence of gluconate ions.
Acknowledgments The authors wish to express their thanks to Professor J. N. Gaur, Head of the Chemistry Department, Rajasthan University, Jaipur, for the provision of research facilities. References 1 2 3 4
R. L. Peasok and R. S. Juvet, J. Am. Chem. Sot., 77 (1955) 202. R. L. Peasok and R. S. Juvet, J. Am. Chem. Sot., 78 (1958) 3967. P. K. Cannon and A. Kibrick, J. Am. Chem. Sot., 60 (1938) 2314. P. J. Gellings, 2. Electrochem. Ber. Bunsenges. Phys. Chem., 66 (1962) 477, 481, 799; 67 (1963) 167. 5 D. S. Jain and J. N. Gaur, Rev. Polarogr. Sot., Jpn, 14 (1967) 206. 6 H. Irving, in I. S. Longmuir (ed.), Advances in Polarography, Pergamon Press, Oxford, 1960, Vol. 1, p. 42. 7 M. H. Mihailov, J. Inorg. Nucl. Chem., 36 (1974) 107,114.