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Complexes of thallium(I) and thallium(III) with thiosalicylic acid (o-mercaptobenzoic acid) and salicylic acid
1940
Notes
J. inorg,nucl.Chem..197l. Vol.33. pp. 1940to !942. PergamonPress. Printedin Great Britain
Complexes of thallium(I) and thallium(IIl) with thiosalicylic acid (o-mercaptobenzoic acid) and salicylic acid (First received I March 1970; in revised form 20August 1970) CONSIDERABLE interest has been shown in recent years in sulphur ligands and comparisons of the properties of the complexes formed by these ligands with those of the analogous oxygen containing ligands has proved to be a rewarding current interest[l]. The present investigation records an electrometric study of the complexes formed by thallium(I) and thallium(Ill) with o-mercaptobenzoic acid (thiosalicylic acid-H2SA ) and compares them with those of the analogous oxygen containing chelating ligand-o-hydroxy benzoic acid (salicylic acid). Studies of these systems have hitherto not been reported. EXPERIMENTAL AnalaR thallous nitrate, thallic oxide, recrystallised thiosalicylic acid and salicylic acids were used. The concentration of the thallium solutions were checked analytically and diluted accordingly. All other reagents used were of Analar Grade. A Pye model pH meter with combined glass-Ag/AgCI electrode was used. The pH meter was calibrated using 50% aqueous ethanolic buffers of known pH, determined independently from e.m.f. measurements using a quinhydrone electrode. The titrations were carried out in a nitrogen atmosphere at 25°C and at constant ionic strength maintained by the addition of requisite amounts of sodium perchlorate and perchloric acid. Conductance measurements were made using a Type M.C. 1 (Electronic Switchgear Ltd.) conductivity measuring bridge. I.R. spectra were obtained in KBr discs using a Beckmann model I.R.9 spectrophotometer. A Pye model pH meter with combined glass-Ag/AgCl electrode was used. 50% aqueous ethanolic buffers of varying pH between 4.0 and 8.0 were prepared from 0-01M succinic acid-sodium succinate mixtures in 50% aqueous ethanol. The pH of these solutions were determined from e.m.f, measurements using a quinhydrone electrode. These aqueous ethanolic buffers of known pH were then used to calibrate the pH meter before carrying out each of the potentiometric titrations [4]. RESULTS AND DISCUSSION The low solubility of thiosalicylic acid and salicylic acid in water necessitated the use of a 50% aqueous-etbanolic medium in this study. The dissociation constants of these ligand acids corresponding to the ionisation of the carboxyl hydrogens were determined potentiometrically in a 50% aqueousethanolic medium, pkax for salicylic acid was found to be 4.47 and pk~ for thiosalicylic acid was 5.44. The dissociation constant for the sulphydryl hydrogen of thiosalicylic acid in 50% aqueous ethanol is reported to be 9.52[2]. The corresponding pk~ for salicylic acid[3] was corrected for liquid junction potential [4] in 50% aqueous ethanol and calculated to be equal to 13.86. Stoicheiometry. The stoicheiometry of the complex formed during the interaction of Tl(I) with thiosalicylic acid (H2SA) was established from the magnitude of the proton displacement which was determined by titrating solutions containing the ligand against standard alkali in the absence and presence of differing molar quantities of thallium(1). The appearance of an inflection at m = 1 (m represents the moles of NaOH per mole of ligand) corresponds to the neutralization of the carboxyl hydrogen only, and H2SA+OH-~ 1. 2. 3. 4.
HSA-+H20
S. E. Livingstone, Q. Rev. Chem. Soc. 19,386 (1965). A . N . Kumar, H. L. Nigam and T. D. Seth, J. polarograph. Soc. 3.83 (1966). Z. L. Ernest and J. Menashi, Trans. Faraday Soc. 59,230 (1965). R.G. Bates, Determination o f p H , Theory and Practice p. 224. Wiley, New York (1965).
Notes
1941
the absence of an inflection at n l = 2 suggests that the sulphydryl proton is not directly titrable. However, the presence of Tl(l) alters the shape of the free ligand titration curve and this shift of the curve is evidently due to the liberation of protons from the - S H group of thiosalicylic acid indicating the formation of the Tl( I)-S link. The magnitude of this proton displacement corresponds to the formation o f a 1 : 1 metal to ligand Tl(l) chelate: TI ~ + H . 2 S A + 2 O H
---,TI(SA) + 2 H ~ O .
This was further confirmed by the use of mixtures of Tl(l) and H._,SA in different molar ratios as well (Fig. I).
/ /f /
,°i~
/,or
pH
/
i
{
/
,.,,i.,.
s~
l
i
1
1
I
0
2
4
6
8
I0
mL,
0.0,5 M
NaOH
Fig. I. Potentiometric titration curves of thiosalicylic acid (H2SA) in the absence and presence of Thallium with 0.05M N a O H . Curve A, 3 × 10 SM H C I O q + 2 × 10 SM N a C I O ¢ Curve I, 2-5× 10 4M H~SA: Curve lI: 2 . 5 x 10-;M H_,SA+5 x 10-SM Tl(I): Curve 111:2-5 x 10--4M H 2 S ~ + 1 x 10 "M Tl(1): Curve IV; 2.5 x 10 ~M H ~ S A + 2 . 5 x 10 SM Tl(lll): Curve V; 2.5 x 10-4M H 2 S A + 5 × 10 SM Tl(lll). When the above titrations were carried out with the following mixtures: (a) Tl(l) and salicylic acid. (b) Tl(lll) and thiosalicylic acid, and (c) Tl(lll) and salicylic acid, the following results were obtained: (i) FI( 1) is found not to complex with salicylic acid. f ii) Tl( l 11 ) chelates to thiosalicylic acid in the stoichiometric ratio of metal to ligand of I : 3. (iii) Tl( l I 1) chelates to salicylic acid in the stoicheiometric ratio of I : 2. Conductometric titrations of a I : 1 mixture of thiosalicylic acid and Tl(I) against standard alkali indicates two breaks at 1 and 2 moles of alkali/mole of ligand confirming the stoicheiometry obtained from potentiometric data. Similar conductometric titrations with mixtures of (a) thiosalicylic acid and Tl( 111 ): and (b) salicylic acid and Tl( 1! 1); against standard alkali confirmed the stoicheiometry of the respective complexes as obtained potentiometrically.
1942
Notes
Stability constants. Calvin and Melchior's[5] extension of Bjerrum's method[6] was used to calculate the stability constants of the complexes from potentiometric data. The stability constants were computed using the correction term method [7]. The present investigation records the formation of the following: (a) a metal to ligand 1 : 1 complex between TI(1) and thiosalicylic acid with log k of 4.675. (b) a metal to ligand 1:3 complex of TI(III) with thiosalicylic acid with log kl, log k2 and log k.~ of 8.964; 8.647; 5.420 respectively. (c) a metal to ligand 1:2 complex of TI(III) with salicylic acid with log k~ = 12.729 and log kz = 12-013.
Solid thallium(l)-thiosalicylic acid chelate. A white solid was isolated by the addition of excess thallous ions to an alkaline solution of thiosalicylic acid. The i.r. spectra of this complex as compared with that of pure thiosalicylic acid revealed the following features: (i) the presence of a strong band at 840 cm -1 in the complex indicating the presence of coordinated water [8]: (ii) the strong band at 1690 cm -1 in thiosalicylic acid assigned to - - C - - O stretching frequency in unionised - C O O H
is shifted to 1500cm 1 in the complex due to - - C - - O - - - M antisymmetric
stretching vibration [9]; (iii) the bands at 2530 cm -1 in thiosalicylic acid due to the - - S H group were absent in the complex indicating the formation of the TI(I)-S link. The spectral data together with the elemental analysis of the solid complex is in agreement with the following structure for the chelate
~
S~TI~"OH~I C/0/~
TI+
~"OH~ J
Elemental analysis Found: C = 13.86: H = 1.20; S = 5.77; (ionic)Tl = 33.2; (totallTI = 66.32. Calc. for the above structure: C = 13.95; H = 1-33; S = 5.33; (ionic)Tl = 34-0; (total)Tl = 67.95. It is of interest to note from the thermodynamic values of stability constants that whereas TI(I) does not chelate with salicylic acid, it forms a 1 : 1 chelate with the analogous sulphur ligand, thiosalicylic acid. However, TI(II1) is shown to form a more stable complex with salicylic acid than with thiosalicylic acid. This should classify TI(I) as a class (b) acceptor and Tl(lll) as a class (a) acceptor [10].
A c k n o w l e d g e m e n t - T h e authors are grateful to the University of Ceylon, Colombo for providing a research grant. Department o f Chemistry University o f Ceylon Colombo 3 Ceylon 5. 6. 7. 8. 9. 10.
R. S. R A M A K R I S H N A M. E. F E R N A N D O P U L L E
N. Calvin and N. C. Melchoir, J. Am. chem. Soc. 70, 3270 (1948). J. Bjerrum, M e t a l A m m i n e Formation in Aqueous Solutions. Haase, Copenhagen ( 1941 ). H. Irving and H. S. Rossotti,J. chem. Soc. 3397 (1953). I. Gamo, Bull. chem. Soc. Japan 34, 760 ( 1961 ). L.J. Bellamy, Infrared Spectra o f Complex Molecules, Methuen, London ( 1958). S. Ahrland, J. Chatt and N. R. Davies, Q. Rev. chem. Soc. 12,265 (1958).
Notes
J. inorg,nucl.Chem..197l. Vol.33. pp. 1940to !942. PergamonPress. Printedin Great Britain
Complexes of thallium(I) and thallium(IIl) with thiosalicylic acid (o-mercaptobenzoic acid) and salicylic acid (First received I March 1970; in revised form 20August 1970) CONSIDERABLE interest has been shown in recent years in sulphur ligands and comparisons of the properties of the complexes formed by these ligands with those of the analogous oxygen containing ligands has proved to be a rewarding current interest[l]. The present investigation records an electrometric study of the complexes formed by thallium(I) and thallium(Ill) with o-mercaptobenzoic acid (thiosalicylic acid-H2SA ) and compares them with those of the analogous oxygen containing chelating ligand-o-hydroxy benzoic acid (salicylic acid). Studies of these systems have hitherto not been reported. EXPERIMENTAL AnalaR thallous nitrate, thallic oxide, recrystallised thiosalicylic acid and salicylic acids were used. The concentration of the thallium solutions were checked analytically and diluted accordingly. All other reagents used were of Analar Grade. A Pye model pH meter with combined glass-Ag/AgCI electrode was used. The pH meter was calibrated using 50% aqueous ethanolic buffers of known pH, determined independently from e.m.f. measurements using a quinhydrone electrode. The titrations were carried out in a nitrogen atmosphere at 25°C and at constant ionic strength maintained by the addition of requisite amounts of sodium perchlorate and perchloric acid. Conductance measurements were made using a Type M.C. 1 (Electronic Switchgear Ltd.) conductivity measuring bridge. I.R. spectra were obtained in KBr discs using a Beckmann model I.R.9 spectrophotometer. A Pye model pH meter with combined glass-Ag/AgCl electrode was used. 50% aqueous ethanolic buffers of varying pH between 4.0 and 8.0 were prepared from 0-01M succinic acid-sodium succinate mixtures in 50% aqueous ethanol. The pH of these solutions were determined from e.m.f, measurements using a quinhydrone electrode. These aqueous ethanolic buffers of known pH were then used to calibrate the pH meter before carrying out each of the potentiometric titrations [4]. RESULTS AND DISCUSSION The low solubility of thiosalicylic acid and salicylic acid in water necessitated the use of a 50% aqueous-etbanolic medium in this study. The dissociation constants of these ligand acids corresponding to the ionisation of the carboxyl hydrogens were determined potentiometrically in a 50% aqueousethanolic medium, pkax for salicylic acid was found to be 4.47 and pk~ for thiosalicylic acid was 5.44. The dissociation constant for the sulphydryl hydrogen of thiosalicylic acid in 50% aqueous ethanol is reported to be 9.52[2]. The corresponding pk~ for salicylic acid[3] was corrected for liquid junction potential [4] in 50% aqueous ethanol and calculated to be equal to 13.86. Stoicheiometry. The stoicheiometry of the complex formed during the interaction of Tl(I) with thiosalicylic acid (H2SA) was established from the magnitude of the proton displacement which was determined by titrating solutions containing the ligand against standard alkali in the absence and presence of differing molar quantities of thallium(1). The appearance of an inflection at m = 1 (m represents the moles of NaOH per mole of ligand) corresponds to the neutralization of the carboxyl hydrogen only, and H2SA+OH-~ 1. 2. 3. 4.
HSA-+H20
S. E. Livingstone, Q. Rev. Chem. Soc. 19,386 (1965). A . N . Kumar, H. L. Nigam and T. D. Seth, J. polarograph. Soc. 3.83 (1966). Z. L. Ernest and J. Menashi, Trans. Faraday Soc. 59,230 (1965). R.G. Bates, Determination o f p H , Theory and Practice p. 224. Wiley, New York (1965).
Notes
1941
the absence of an inflection at n l = 2 suggests that the sulphydryl proton is not directly titrable. However, the presence of Tl(l) alters the shape of the free ligand titration curve and this shift of the curve is evidently due to the liberation of protons from the - S H group of thiosalicylic acid indicating the formation of the Tl( I)-S link. The magnitude of this proton displacement corresponds to the formation o f a 1 : 1 metal to ligand Tl(l) chelate: TI ~ + H . 2 S A + 2 O H
---,TI(SA) + 2 H ~ O .
This was further confirmed by the use of mixtures of Tl(l) and H._,SA in different molar ratios as well (Fig. I).
/ /f /
,°i~
/,or
pH
/
i
{
/
,.,,i.,.
s~
l
i
1
1
I
0
2
4
6
8
I0
mL,
0.0,5 M
NaOH
Fig. I. Potentiometric titration curves of thiosalicylic acid (H2SA) in the absence and presence of Thallium with 0.05M N a O H . Curve A, 3 × 10 SM H C I O q + 2 × 10 SM N a C I O ¢ Curve I, 2-5× 10 4M H~SA: Curve lI: 2 . 5 x 10-;M H_,SA+5 x 10-SM Tl(I): Curve 111:2-5 x 10--4M H 2 S ~ + 1 x 10 "M Tl(1): Curve IV; 2.5 x 10 ~M H ~ S A + 2 . 5 x 10 SM Tl(lll): Curve V; 2.5 x 10-4M H 2 S A + 5 × 10 SM Tl(lll). When the above titrations were carried out with the following mixtures: (a) Tl(l) and salicylic acid. (b) Tl(lll) and thiosalicylic acid, and (c) Tl(lll) and salicylic acid, the following results were obtained: (i) FI( 1) is found not to complex with salicylic acid. f ii) Tl( l 11 ) chelates to thiosalicylic acid in the stoichiometric ratio of metal to ligand of I : 3. (iii) Tl( l I 1) chelates to salicylic acid in the stoicheiometric ratio of I : 2. Conductometric titrations of a I : 1 mixture of thiosalicylic acid and Tl(I) against standard alkali indicates two breaks at 1 and 2 moles of alkali/mole of ligand confirming the stoicheiometry obtained from potentiometric data. Similar conductometric titrations with mixtures of (a) thiosalicylic acid and Tl( 111 ): and (b) salicylic acid and Tl( 1! 1); against standard alkali confirmed the stoicheiometry of the respective complexes as obtained potentiometrically.
1942
Notes
Stability constants. Calvin and Melchior's[5] extension of Bjerrum's method[6] was used to calculate the stability constants of the complexes from potentiometric data. The stability constants were computed using the correction term method [7]. The present investigation records the formation of the following: (a) a metal to ligand 1 : 1 complex between TI(1) and thiosalicylic acid with log k of 4.675. (b) a metal to ligand 1:3 complex of TI(III) with thiosalicylic acid with log kl, log k2 and log k.~ of 8.964; 8.647; 5.420 respectively. (c) a metal to ligand 1:2 complex of TI(III) with salicylic acid with log k~ = 12.729 and log kz = 12-013.
Solid thallium(l)-thiosalicylic acid chelate. A white solid was isolated by the addition of excess thallous ions to an alkaline solution of thiosalicylic acid. The i.r. spectra of this complex as compared with that of pure thiosalicylic acid revealed the following features: (i) the presence of a strong band at 840 cm -1 in the complex indicating the presence of coordinated water [8]: (ii) the strong band at 1690 cm -1 in thiosalicylic acid assigned to - - C - - O stretching frequency in unionised - C O O H
is shifted to 1500cm 1 in the complex due to - - C - - O - - - M antisymmetric
stretching vibration [9]; (iii) the bands at 2530 cm -1 in thiosalicylic acid due to the - - S H group were absent in the complex indicating the formation of the TI(I)-S link. The spectral data together with the elemental analysis of the solid complex is in agreement with the following structure for the chelate
~
S~TI~"OH~I C/0/~
TI+
~"OH~ J
Elemental analysis Found: C = 13.86: H = 1.20; S = 5.77; (ionic)Tl = 33.2; (totallTI = 66.32. Calc. for the above structure: C = 13.95; H = 1-33; S = 5.33; (ionic)Tl = 34-0; (total)Tl = 67.95. It is of interest to note from the thermodynamic values of stability constants that whereas TI(I) does not chelate with salicylic acid, it forms a 1 : 1 chelate with the analogous sulphur ligand, thiosalicylic acid. However, TI(II1) is shown to form a more stable complex with salicylic acid than with thiosalicylic acid. This should classify TI(I) as a class (b) acceptor and Tl(lll) as a class (a) acceptor [10].
A c k n o w l e d g e m e n t - T h e authors are grateful to the University of Ceylon, Colombo for providing a research grant. Department o f Chemistry University o f Ceylon Colombo 3 Ceylon 5. 6. 7. 8. 9. 10.
R. S. R A M A K R I S H N A M. E. F E R N A N D O P U L L E
N. Calvin and N. C. Melchoir, J. Am. chem. Soc. 70, 3270 (1948). J. Bjerrum, M e t a l A m m i n e Formation in Aqueous Solutions. Haase, Copenhagen ( 1941 ). H. Irving and H. S. Rossotti,J. chem. Soc. 3397 (1953). I. Gamo, Bull. chem. Soc. Japan 34, 760 ( 1961 ). L.J. Bellamy, Infrared Spectra o f Complex Molecules, Methuen, London ( 1958). S. Ahrland, J. Chatt and N. R. Davies, Q. Rev. chem. Soc. 12,265 (1958).