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Thermodynamic stability constants of beryllium(ii) and p-substituted N-phenyl benzohydroxamic acid complexes
ANALYTICAL DATA Table 3. Stabilization parameters and stability constants for the ternary complexes of copper(H) and 2,2’-bipyridyl with maleic and phthalic acids, and for other systems already studied
OX MAL sue CPRD PHT MALE
13.50 13.44 11~10 IS.52 I.86 II.89
I
O-70 0.26 0.30 I.38 0.49 O-36
4.90 565 ~ 7.78 4.60 4-52
I
24 2.50 2.37 0.94 1.32
Ox, MAL, Sue and CPRD arc abbreviations malonic, succinic and cyclopropane-l,I-dicarboxylic
11 ;, 4 this work ..,,
for oxalic, acids.
255
K is of the same order of magnitude. As in our systems A’log K ranges from 0.9 to 2.5, the use of Alog K is a more realiable means of evaluating the stabilization of ternary complexes. This agrees with the opinion of others.13 The final conclusions are: (a) ternary complexes with fivemembered chelate rings are stabilized more than those with six- and seven-membered rings which have similar stabilizing power; (b) a ligand with conjugating and delocalizing properties increases the chelating effect, both with six- and seven-membered rings. Acknowledgements-We thank the “Consiglio delle Ricerche” for financial support.
Nazionale
REFERENCES these complexes are more stable than would be expected on statistical grounds (log K, > 0.6) and show good discriminating properties (namely the complex Cubip*+ prefers to give the species CubipL rather than the cation in fact’,* Alog Ii > 0). Because these systems Cubip:+, have the same co-ordination number and type,” they can be used to assess the influence of the chelate-ring size and the ligand characteristics on the stability of the mixed complexes. Thus the complexes with five-membered rings are more stable than those with six-membered rings, which, in turn, are more stable than those with seven-membered ones; in contrast, the system CubipCPRD showed a different behaviour, as the conjugating effect of the alicyclic increased the chelation effect. Recently, Sigel ligand “,” and co-workers,” examining ternary complexes with fiveor six-membered rings, and also with one five- and one six-membered ring, pointed out that great care is necessary in choosing the parameters for correct comparison of systems. In particular, the mixing constant log K,, because it is strongly influenced by A’log K, can be used as a stabilization index only for series of systems in which A’log
1. H. Sigel, P. R. Huber, R. Griesser and B. Prijs, Inorg. Chem., 1973, 12. 1198. 2. R. Griesser and H. Sigel, ibid., 1970, 9. 1238. 3. R. P. Bonomo, S. Musumeci, E. Rizzarelli and S. Sammartano, Inorg. Chim. Acta, 1975, 14, 251. 4. Idem., J. Inorg. Nucl. Chem., submitted for publication. 5. Idem., work in progress. 6. H. Irving and D. H. Mellor, J. Chem. Sot., 1962, 5222. 7. R. Maggiore, S. Musumeci and S. Sammartano, Talanra, 1975. 22. 43. 8. H. Sigel, P. R. Huber and R. F. Pasternack, Inorg. Chem., 1971, 10. 2226. 9. G. Ostacoli, private communication. 10. S. Musumeci, E. Rizzarelli, S. Sammartano and A. Seminara, VII Convegno Nazionale di Chimica Inorganica, Pesaro, Italy, 1974. Il. A. R. Mochel, J. E. Boggs and P. N. Skancke, J. Molecular Structure, 1973, 15. 93. 12. H. Sigel, R. Caraco and B. Prijs, ibid., 1974, 13. 462. 13. R. B. Martin and R. Prados, J. Inorg. Nucl. Chem., 1974, 36. 1665.
Summary-The stability constants of ternary copper(I1) complexes with 2,2’-bipyridyl and a dicarboxylic acid (maleic and phthalic) have been determined by means of pH-titrations at 25 f 0.1” and an ionic strength of 0.1 M (Na,H)ClO,. The stabilities of ternary complexes are compared with those of similar complexes and related to the size of the chelate rings and the nature of the dicarboxylic ligands.
Talonto. Vol. 23. pp 255.256. Pergamon Press, 1976 Prmted in Great Britam
THERMODYNAMIC STABILITY CONSTANTS OF BERYLLIUM(I1) AND p-SUBSTITUTED N-PHENYL BENZOHYDROXAMIC ACID COMPLEXES* K. R. GUPTA and Department
of Chemistry,
Government
(Received 19 February
Ravishankar Ravishanlhr
Science
College,
Raipur,
1975. Accepted 10 June
The thermodynamic stepwise formation constants of beryllium(I1) complexes with p-substituted N-phenylbenzohydroxamic acids have been determined at 35” by titrations in 50% v/v aqueous dioxan (as the ligands and complexes are insoluble in water). *From the Ph.D. thesis of K. R. Gupta, University, Raipur, 1975. t Present address: Chemistry Department, University, Raipur, (M.P.) India.
S. G. TANDON? (M.P.) India
1975)
EXPERIMENTAL The procedure was essentially that of Bjerrum and Calvin’*’ and Block and McIntyre3 as modified by Goldberg.4*5 The thermodynamic protonation constants of the acids were determined by pH-titrations in the same medium at 35”.6 The acids were synthesized by the method reported earlier,’ recrystallized from benzene/petroleum ether and dried under vacuum over phosphorus pentoxide. Their
256
ANALYTICAL
purity was confirmed by elemental analysis, m.p., and spectroscopy. The stability constants were calculated as described earlier, and activity coefficient corrections were applied. The concentrations of beryllium(II), ligand and nitric acid in the titration vessel were generally around 0.001, 0.01 and OX01 M respectively. The nitric acid was added in the preparation of the beryllium nitrate solutions, to minimize hydrolysis.
DATA
It was found that the Hammett equation is applicable to the K, values for the beryllium complexes; a plot of log K, us. CTbeing linear: log K, = 8.66 - 1.225 c. The values oflog K,, log K2, and pK,, decrease when the substituted acids are arranged in the order CH,OR
> CH,R
where R represents
> HR z CIR > BrR > NOzR
- C,H4.
CO. NOH
C,H,.
Comparison of the metal ionization potentials and K, values RESULTS
AND
DISCUSSION
The thermodynamic stability constants are summarized in Table 1. The maximum scatter in log K, was kO.15. The hydroxamic acids used are bidentate ligands. Beryllium(II) has a co-ordination number of 4 in its hydroxamic acid complexes. ‘3’ The nature of the metal-ligand bond can be assessed from comparison of the pK, of closely related ligands and log K, for the corresponding 1:I beryllium complexes. Correlations between pK, and log Kz are less exact because other factors influence the complex formation. ” This is in agreement with the values given in Table 1. A graph of log K, us. pK, is linear; least squares calculations give the relation log K, = 144 pK, - 6.99. Since the slope is greater than unity the nuclear substitution affects the stability of the complex more than that of the free acid,“~l3 Table
I. Stability
constants
of beryllium(H)
complexes
X
PK,
1% K,
1% K,
OCH, CH, H Cl Br NGz
11.13 10.98* 10.96* 10.68 1@65 IO.15
9.05 8.85 8.68 8.41 8.24 I.76
8.03 7.46 7.15 6.98 6.89 6.48
* Ref. 15. Table 2. Comparison of log K 1 with ionization potential for bivalent metal complexes of N-phenylbenzohydroxamic acid
Ion
CL?+ Be’ + Zn2+ Ni’+ MnZi * This work.
I.P., cV
log K,15
27.92 27.46 27.28 25.76 23.13
10.36 8.68* 7.5 1 7.00 6.02
It is observed that log K 1 of N-phenylbenzohydroxamic acid is linearly related to the ionization potential for Mn, Ni and Zn (Table 2) but the beryllium and copper complexes have higher stability. In the case of copper this may be attributed to the Jahn-Teller effect, and in that of beryllium to the small radius of the beryllium ion. Acknowledgements-The authors are grateful to the Principal, Govt. Science College, Raipur, for facilities and to the Government of Madhya Pradesh and Ravishankar University, Raipur, for granting study leave and a fellowship (to K. R. Gupta). Grateful acknowledgement is made to the Chemical Society, London and van? Hoff Fund, Amsterdam, for partial financial assistance.
REFERENCES
1. J. Bjerrum, Metal Amminr Formation in Aqueous Solutiotl, Hasse, Copenhagen, 1941. 2. M. Calvin and K. W. Wilson, J. Am. Chem. Sot., 1945, 67. 2003. ibid., 1953, 75. 5667. 3. B. P. Block and G. H. McIntyre, 4. D. E. Goldberg, J. Chem. Educ., 1963. 40. 341. and J. L. Rosenstreich, Inorg. Chem., 5. D. E. Goldberg 1965, 4. 909. 6. K. R. Gupta and S. G. Tandon, Talanta, 1974, 31. 249. and S. G. Tandon, J. Chem. Engg. I. U. Priyadarshini Data, 1967, 12. 143. 8. K. R. Gupta and S. G. Tandon, J. Indian Chrm. Sot., 1970, 47. 912. work. 9. S. G. Tandon, unpublished 10. A. E. Martell and M. Calvin, Chemistry of’ the Metal Chelate Compounds, p. 246. Prentice Hall, New York, 1953. 11. J. Hudis and R. W. Dodson, J. Am. Chem. Sot., 1950, 78. 911. 12. L. G. Van Uitert and W. C. Fernelius, ibid., 1954, 76. 379. 13. K. E. Jabalpurwala, Ph.D. Thesis, Bombay University, 1964. 14. J. Lewis and R. C. Wilkins, Modern Coordination Chemistry, p. 53. Interscience, New York, 1960. 15. J. P. Shukla and S. G. Tandon, Talanta, 1972, 19. 71 1.
Summary-The thermodynamic stability constants of beryllium(I1) complexes of p-substituted Nphenylbenzohydroxamic acids have been determined in 50% v/v aqueous dioxan at 35”. The effect of methoxy, methyl, chloro, bromo, and nitro groups as substituents is discussed. There is a linear relationship between log K 1and pK,,, and the Hammett equation is applicable. The beryllium complexes have been compared with those of Cu, Zn, Ni and Mn.
OX MAL sue CPRD PHT MALE
13.50 13.44 11~10 IS.52 I.86 II.89
I
O-70 0.26 0.30 I.38 0.49 O-36
4.90 565 ~ 7.78 4.60 4-52
I
24 2.50 2.37 0.94 1.32
Ox, MAL, Sue and CPRD arc abbreviations malonic, succinic and cyclopropane-l,I-dicarboxylic
11 ;, 4 this work ..,,
for oxalic, acids.
255
K is of the same order of magnitude. As in our systems A’log K ranges from 0.9 to 2.5, the use of Alog K is a more realiable means of evaluating the stabilization of ternary complexes. This agrees with the opinion of others.13 The final conclusions are: (a) ternary complexes with fivemembered chelate rings are stabilized more than those with six- and seven-membered rings which have similar stabilizing power; (b) a ligand with conjugating and delocalizing properties increases the chelating effect, both with six- and seven-membered rings. Acknowledgements-We thank the “Consiglio delle Ricerche” for financial support.
Nazionale
REFERENCES these complexes are more stable than would be expected on statistical grounds (log K, > 0.6) and show good discriminating properties (namely the complex Cubip*+ prefers to give the species CubipL rather than the cation in fact’,* Alog Ii > 0). Because these systems Cubip:+, have the same co-ordination number and type,” they can be used to assess the influence of the chelate-ring size and the ligand characteristics on the stability of the mixed complexes. Thus the complexes with five-membered rings are more stable than those with six-membered rings, which, in turn, are more stable than those with seven-membered ones; in contrast, the system CubipCPRD showed a different behaviour, as the conjugating effect of the alicyclic increased the chelation effect. Recently, Sigel ligand “,” and co-workers,” examining ternary complexes with fiveor six-membered rings, and also with one five- and one six-membered ring, pointed out that great care is necessary in choosing the parameters for correct comparison of systems. In particular, the mixing constant log K,, because it is strongly influenced by A’log K, can be used as a stabilization index only for series of systems in which A’log
1. H. Sigel, P. R. Huber, R. Griesser and B. Prijs, Inorg. Chem., 1973, 12. 1198. 2. R. Griesser and H. Sigel, ibid., 1970, 9. 1238. 3. R. P. Bonomo, S. Musumeci, E. Rizzarelli and S. Sammartano, Inorg. Chim. Acta, 1975, 14, 251. 4. Idem., J. Inorg. Nucl. Chem., submitted for publication. 5. Idem., work in progress. 6. H. Irving and D. H. Mellor, J. Chem. Sot., 1962, 5222. 7. R. Maggiore, S. Musumeci and S. Sammartano, Talanra, 1975. 22. 43. 8. H. Sigel, P. R. Huber and R. F. Pasternack, Inorg. Chem., 1971, 10. 2226. 9. G. Ostacoli, private communication. 10. S. Musumeci, E. Rizzarelli, S. Sammartano and A. Seminara, VII Convegno Nazionale di Chimica Inorganica, Pesaro, Italy, 1974. Il. A. R. Mochel, J. E. Boggs and P. N. Skancke, J. Molecular Structure, 1973, 15. 93. 12. H. Sigel, R. Caraco and B. Prijs, ibid., 1974, 13. 462. 13. R. B. Martin and R. Prados, J. Inorg. Nucl. Chem., 1974, 36. 1665.
Summary-The stability constants of ternary copper(I1) complexes with 2,2’-bipyridyl and a dicarboxylic acid (maleic and phthalic) have been determined by means of pH-titrations at 25 f 0.1” and an ionic strength of 0.1 M (Na,H)ClO,. The stabilities of ternary complexes are compared with those of similar complexes and related to the size of the chelate rings and the nature of the dicarboxylic ligands.
Talonto. Vol. 23. pp 255.256. Pergamon Press, 1976 Prmted in Great Britam
THERMODYNAMIC STABILITY CONSTANTS OF BERYLLIUM(I1) AND p-SUBSTITUTED N-PHENYL BENZOHYDROXAMIC ACID COMPLEXES* K. R. GUPTA and Department
of Chemistry,
Government
(Received 19 February
Ravishankar Ravishanlhr
Science
College,
Raipur,
1975. Accepted 10 June
The thermodynamic stepwise formation constants of beryllium(I1) complexes with p-substituted N-phenylbenzohydroxamic acids have been determined at 35” by titrations in 50% v/v aqueous dioxan (as the ligands and complexes are insoluble in water). *From the Ph.D. thesis of K. R. Gupta, University, Raipur, 1975. t Present address: Chemistry Department, University, Raipur, (M.P.) India.
S. G. TANDON? (M.P.) India
1975)
EXPERIMENTAL The procedure was essentially that of Bjerrum and Calvin’*’ and Block and McIntyre3 as modified by Goldberg.4*5 The thermodynamic protonation constants of the acids were determined by pH-titrations in the same medium at 35”.6 The acids were synthesized by the method reported earlier,’ recrystallized from benzene/petroleum ether and dried under vacuum over phosphorus pentoxide. Their
256
ANALYTICAL
purity was confirmed by elemental analysis, m.p., and spectroscopy. The stability constants were calculated as described earlier, and activity coefficient corrections were applied. The concentrations of beryllium(II), ligand and nitric acid in the titration vessel were generally around 0.001, 0.01 and OX01 M respectively. The nitric acid was added in the preparation of the beryllium nitrate solutions, to minimize hydrolysis.
DATA
It was found that the Hammett equation is applicable to the K, values for the beryllium complexes; a plot of log K, us. CTbeing linear: log K, = 8.66 - 1.225 c. The values oflog K,, log K2, and pK,, decrease when the substituted acids are arranged in the order CH,OR
> CH,R
where R represents
> HR z CIR > BrR > NOzR
- C,H4.
CO. NOH
C,H,.
Comparison of the metal ionization potentials and K, values RESULTS
AND
DISCUSSION
The thermodynamic stability constants are summarized in Table 1. The maximum scatter in log K, was kO.15. The hydroxamic acids used are bidentate ligands. Beryllium(II) has a co-ordination number of 4 in its hydroxamic acid complexes. ‘3’ The nature of the metal-ligand bond can be assessed from comparison of the pK, of closely related ligands and log K, for the corresponding 1:I beryllium complexes. Correlations between pK, and log Kz are less exact because other factors influence the complex formation. ” This is in agreement with the values given in Table 1. A graph of log K, us. pK, is linear; least squares calculations give the relation log K, = 144 pK, - 6.99. Since the slope is greater than unity the nuclear substitution affects the stability of the complex more than that of the free acid,“~l3 Table
I. Stability
constants
of beryllium(H)
complexes
X
PK,
1% K,
1% K,
OCH, CH, H Cl Br NGz
11.13 10.98* 10.96* 10.68 1@65 IO.15
9.05 8.85 8.68 8.41 8.24 I.76
8.03 7.46 7.15 6.98 6.89 6.48
* Ref. 15. Table 2. Comparison of log K 1 with ionization potential for bivalent metal complexes of N-phenylbenzohydroxamic acid
Ion
CL?+ Be’ + Zn2+ Ni’+ MnZi * This work.
I.P., cV
log K,15
27.92 27.46 27.28 25.76 23.13
10.36 8.68* 7.5 1 7.00 6.02
It is observed that log K 1 of N-phenylbenzohydroxamic acid is linearly related to the ionization potential for Mn, Ni and Zn (Table 2) but the beryllium and copper complexes have higher stability. In the case of copper this may be attributed to the Jahn-Teller effect, and in that of beryllium to the small radius of the beryllium ion. Acknowledgements-The authors are grateful to the Principal, Govt. Science College, Raipur, for facilities and to the Government of Madhya Pradesh and Ravishankar University, Raipur, for granting study leave and a fellowship (to K. R. Gupta). Grateful acknowledgement is made to the Chemical Society, London and van? Hoff Fund, Amsterdam, for partial financial assistance.
REFERENCES
1. J. Bjerrum, Metal Amminr Formation in Aqueous Solutiotl, Hasse, Copenhagen, 1941. 2. M. Calvin and K. W. Wilson, J. Am. Chem. Sot., 1945, 67. 2003. ibid., 1953, 75. 5667. 3. B. P. Block and G. H. McIntyre, 4. D. E. Goldberg, J. Chem. Educ., 1963. 40. 341. and J. L. Rosenstreich, Inorg. Chem., 5. D. E. Goldberg 1965, 4. 909. 6. K. R. Gupta and S. G. Tandon, Talanta, 1974, 31. 249. and S. G. Tandon, J. Chem. Engg. I. U. Priyadarshini Data, 1967, 12. 143. 8. K. R. Gupta and S. G. Tandon, J. Indian Chrm. Sot., 1970, 47. 912. work. 9. S. G. Tandon, unpublished 10. A. E. Martell and M. Calvin, Chemistry of’ the Metal Chelate Compounds, p. 246. Prentice Hall, New York, 1953. 11. J. Hudis and R. W. Dodson, J. Am. Chem. Sot., 1950, 78. 911. 12. L. G. Van Uitert and W. C. Fernelius, ibid., 1954, 76. 379. 13. K. E. Jabalpurwala, Ph.D. Thesis, Bombay University, 1964. 14. J. Lewis and R. C. Wilkins, Modern Coordination Chemistry, p. 53. Interscience, New York, 1960. 15. J. P. Shukla and S. G. Tandon, Talanta, 1972, 19. 71 1.
Summary-The thermodynamic stability constants of beryllium(I1) complexes of p-substituted Nphenylbenzohydroxamic acids have been determined in 50% v/v aqueous dioxan at 35”. The effect of methoxy, methyl, chloro, bromo, and nitro groups as substituents is discussed. There is a linear relationship between log K 1and pK,,, and the Hammett equation is applicable. The beryllium complexes have been compared with those of Cu, Zn, Ni and Mn.