1DETERMINATION OF FORMATION CONSTANT OF ACIDS & AMINO ACIDS WITH TRANSITION AND INNER TRANSITION METALS BY PH – METRY Suresh D. Dhage and Gopal V. Mane Email:
[email protected] Department of Chemistry, SSJES, Arts ,Commerce & Science College, Gangakhed-431514 Dist. Parbhani.(M.S.)India Department of Chemistry, Mahatma Phule College, Ahmedpur- 413515 Dist. Latur(M.S.) India ABSTRACT The present work deals with the study of proton - ligands and metal- ligands of malic acid,maleic acid and Glycine with Mn(II), Cu(II), Fe(III), Ni(II) and UO 2 (II). More over the Binary chelate of carboxylic acids and amino acids have been studied with Lanthanides. The metal ligands stability constant of Binary and ternary complexes were evaluated using Irving– Rossotti titration technique. Key words : pH-metry , determination, binary, ternary, formation constants, Cu(II), Mn(II), Fe(III), Ni(II) and UO 2 (II), complexes. INTRODUCTION Recently there has been considerable interest in the study of binary ternary and quaternary complexes by pH – metric method 1-4 . The study of formation constants of metal-methionine and metal-methionine NTA (Nitrilotriacetic acid) (binary and mixed) Complexes have been investigated by Praveen P.Singh etal. 5 2 The study of Kinetic parameter and formation constants of ( Mn- antibiotics cefoperazone) complexes Vis-à-vis Kinetics of electrode reaction have been investigated by Farid Khan & Rakhi Agrawal .6 The mixed ligand complexes of transition metals are comparatively less studied than inner transition elements 7 . Ternary complexes of Ni (II) with glycine and glycinamide as primary ligands and imidazole, histamine and L – histidine as secondary ligands have been investigated by Nair and Neelkantan 9 , Nair et al 10 . The ternary complexes of Ni (II) and Cu (II) with Nicotinic acid as primary ligand and imidazole, benzimidazole, histamine and L – histidine as secondary ligands have been studied potentiometrically 8 . The study of stability constans of Mn (II) , Co (II) , Ni (II) , Cu (II) and Zn (II) with nitrilotriacetic acid (NTA) and iminodiacetic acid (IMDA) as primary ligands and pyridoxine hydrochloride (PHC) and ethambutol hydrochloride (EHC) as secondary ligands was reported by Patil etal 7 . The stability constants of Mn (II) , Cu (II) , Ni (II) , Fe (III) and UO 2 have not reported in literature. It was therefore of interest to study the stability constant of binary and ternary complexes of these metal ions with ligands have studied using Irving–Rossotti pH – metric titration teachique in aqueous medium in the present work. EXPERIMENTAL All the ligands was obtained from AR grade. NaClO 4 was used from fluka chemical. NaOH was standardized by standard KHP from AR grade 12 . All other Solution were prepared in doubly distilled water. The pH–metry measurement work carried out by using ELICO digital model LI – 120 pH–meter with glass calomel electrode with an accuracy of ± 0.01 of pH unit at 30 ± 0.5 0 C was standardized against 0.05M KHP (4 pH) 0.01M borax solution (9.18 pH) for the determination of proton–ligand stability constant of the secondary ligands and metal-ligands 3 stability constants of the binary and ternary complexes the following sets of solution were prepared and titrated against stand. alkali solution. Binary System 1] 2 × 10 –1 M HClO 4 2] 2 × 10 –1 M HClO 4 + 1 × 10 –2 M secondary ligands. 3] 2 × 10 –1 M HClO 4 + 1 × 10 –2 M secondary ligands + 1 × 10 –2 M metal ions. Ternary System 1] 2 × 10 –1 M HClO 4 2] 2 × 10 –1 M HClO 4 + 1 × 10 –2 M secondary ligands. 3] 2 × 10 –1 M HClO 4 + 1 × 10 –2 M primary ligands + 1 × 10 –2 M metal ions. 4] 2 × 10 –1 M HClO 4 + 1 × 10 –2 M primary ligands + 1 × 10 –2 M secondary ligands + 1 × 10 –2 M metal ions. The ionic strength was mentioned constant by adding of (1M) NaClO 4 . The ratio of metal (M) : Secondary ligand (L) was maintained at 1 : 5 in each of the Binary system and ratio of metal : Primary ligands (A) : Secondary ligand (L) was maintained at 1 : 5 : 5 in each of the ternary systems. RESULTS AND DISCUSSION Proton–Ligand stability constants. The plots of volume of alkali (NaOH) against pH – meter readings were used to evaluate the proton–ligand stability constants of malonic acid and oxalic acid. The deviation between free acid titration curve & secondary ligand titration curve was used to evaluate the formation functions A n . 4 The proton–ligand formation curves were then obtained by plotting the values of A n Vs pH-meter readings. From the graphs the values of log H 1 K and log H 2 K were evaluated by half-integral method and pointwise calculation method and presented in Table – 1. Table I PROTON – LIGAND STABILITY CONSTANTS. Temperature = 30 ± 0.5 0 C. (µ=0.1M NaClO 4 ) Ligands log H 1 K log H 2 K Malonic acid Malic acid 9.519 8.828 11.360 11.873 Maleic acid 8.550 11.934 Metal – Ligand stability constants of Binary complexes. The metal ligand stability constants of binary complexes were evaluated assuming that the formation of hydrolysed products, polynuclear complexes, hydrogen and hydroxyl bearing complexes were absent. An examination of titration curves indicated that ternary complex formation has taken place in solution on the following grounds. 5 1] The metal titration curves showed displacement with respect to the ligand titration curves along the volume axis. This indicated the affinity of ligand with metal ions which released Protons and produced the volume difference (V 3 – V 2 ). 2] The colour change of the ligand was in presence of metal ions appeared showing the formation of new species. 3] The hydrolysis of metal ions was suppressed due to complex formation and the precipitation did not appear during the titrations. From the ligand and metal titration curves the values of n and from that the values of pL were obtained. The formation curves obtained were used to evaluate the metal. Ligand stability constants by methods are presented in Table-II. The variation of n was found to be 0 to 2 which indicated that the composition of complexes was 1:5 in solution from table - II, it is obvious that the metal – ligand stability 6 constants of Malonic acid were greater than with repect to oxalic acid in every metal. The Irving – Williams order 13,14 of stability constants was followed by both ligands. Table – II METAL – LIGAND STABILITY CONSTANTS OF BINARY COMPLEXES. Ligand Stability constant log M 1 K Fe (III) UO 2(II) Ni (II) Cu (II) Mn (II) Malonic acid 7.455 7.589 12.552 3.361 9.250 Malic acid 8.083 4.200 8.099 4.628 6.472 Maleic acid 5.151 5.264 6.081 4.892 6.386 Metal – ligand stability constants of ternary complexes. The metal ligand stability constants of the ternary complexes were evaluated assuming that the formation of hydroxyl products, Polynuclear complexes hydrogen and hydroxyl bearing complexes was absent. An examination of the titration curves indicated that ternary complex formation has taken place in solution on the following grounds. 1] The ternary complex titration curves show displacement with primary complex titration curves. The horizontal distance was measured between acid curves and the secondary ligand curves (V 2 – V 1 ) and subtracted through the horizontal distance between ternary complex curves and primary complex titration curves (V 3 – V 2 ) show a positive difference which proves the earlier release of protons in the formation of ternary complexes. 2] The hydrolysis of metal ions was suppressed and precipitation did not occur. The values of n vary from 0 to 1, thus confirming the formation of 1 : 5 : 5 mixed ligand complexes. The values of and have been evaluated from the formation curves ( ) 0.5 n At . PL Vs n = in the formation curve, PL = log K. The log K values were also evaluated by pointwise calculation method. The metal–ligand stability constant ic 7 of maleic acid and Maleic acid as secondary ligands and Glycine as primary ligands are presented in Table – 3. TABLE – 4 METAL – LIGAND STABILITY CONSTANTS Metal Stability Constant Ligands Glycine Alanine Malic acid Maleic acid Malonic acid La (III) M 1 K log 5.32 5.30 5.47 6.30 5.34 Ce (III) M 1 K log 5.40 5.42 5.76 6.61 5.72 Pr (III) M 1 K log 5.54 5.56 6.18 6.62 5.92 Nd (III) M 1 K log 5.64 5.66 6.75 6.78 6.01 Sm (III) M 1 K log 5.75 5.76 6.77 6.84 6.12 Eu (III) M 1 K log 5.80 5.82 6.82 6.98 6.10 Gd (III) M 1 K log 5.72 5.70 6.72 6.80 5.94 Tb (III) M 1 K log 5.92 5.93 6.92 7.10 6.26 Dy (III) M 1 K log 6.10 6.08 7.20 7.22 6.32 The Irving Williams – natural order 13, 14 was observed in case of binary as well as ternary complexes which is. Mn (II) < Fe (III) < Ni (II) < Cu (II) < UO 2(II) The aim of the study was to know the effects of binary and ternary ligands on metal complexes. Malonic acid and oxalic acid are the efficient chelating agents for heavy metals & 8 Glycine is functions as antidote against heavy metals ions by forming stable co-ordination compounds. The higher protonation values ( ) H 1 K log was assigned to the–OH group. Glycine and Alanine are ligands of novel type bearing –NH 2 – and –COOH groups. However, pH titration curves of this ligand show two well separated steps of neutralisation and hence two protonation constants are calculated. The ionization of Glycine and Alanine may be represented by the following equations: ( ) ( ) H 1 H L 2 HL 2 2 K 2 2 CH COOH CH COO | | NH NH ÷ ÷ ÷ ÷ ÷÷÷ ( ) ( ) 2 2 L 2 3 HL CH COO CH CH COO | | NH NH | H H K ÷ ÷ ÷ ÷ ÷ ÷ ÷÷÷ ÷ ÷ ( ) ( ) H 1 H L 2 HL 3 3 K 2 2 CH COOH CH COOH CH CH | | NH NH ÷ ÷ ÷ ÷ ÷ ÷÷÷ ( ) ( ) 2 2 L 3 3 HL CH CH COO CH CH COO | | NH NH | H H K ÷ ÷ ÷ ÷ ÷ ÷ ÷ ÷÷÷ ÷ ÷ 9 TABLE – 4 STABILITY CONSTANTS OF MIXED LIGAND COMPLEXES Metal ion Mixed ligand system MXY logK logK A La (III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.226 13.942 13.017 1.564 -2.322 -2.357 Ce (III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.463 14.181 15.585 1.697 -2.171 -2.690 Pr (III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 10.030 14.245 14.155 1.690 -2.085 -2.695 Nd (III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 09.084 15.175 14.816 3.306 -2.755 -2.505 Sm (III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.848 15.530 14.937 2.672 -4.465 -3.067 10 The proton Ligand stability constants determined in this work were used through out the calculations of Metal – ligand stability constants as the latter were determined in an identical experimental conditions to those for the former ones. The M 1 K log values are discussed at the appropriate place. The present investigation was undertaken with a view to studying the stability constants of mixed ligand complexes of the present ligand with rare earth metal ion by maintaining Metal : Primary ligand : Secondary ligand ratio as 1 : 5 : 5 (M ≠ X = Y). The stability constants of the mixed ligand Complexes have been computed by adopting an appropriate method proposed for such a condition. The relative order of stability of ternary chelates in terms of the metal ions as found in this work is La < Ce < Pr < Nd < Sm < Eu < Gd < Tb < Dy which may be attributed to the decreasing size and increasing charge / radius ratio of metal ions. It is an important observation in the present work that the calculation of log K MXY a) in the slightly lower pH range ( ) MXY log K' = b) in the slightly higher pH range ( ) MXY log K'' = c) in the middle (chosen) pH range ( ) MXY K log = that MXY MXY MXY log K' log K'' log K 2 + This method proved to be an additional check on the selection of the pH range chosen for calculating an accurate stability constant of a mixed ligand complex species. 11 REFERENCES 1] A.E. Martell, “Stability constants”, Vol. 17 and 25. The chemical society, London (1964 and 1971). 2] A.E. Martell and R.M. Smith, “Critical Stability Constants” Amino acids, NY (1974). 3] H. Sigel, “Metal Ions in Biological systems–2”, Marcell – Dekker, Ino., NY (1973). 4] M.T. Beck, “Chemistry of complex equilibria”, Van Nostand, NY, (1970) P. 174. 5] P. P. Singh, J. Ind. Chem. Soc., 86,100 (2009) 6] F. Khan and R. Agrawal, J.Ind. Soc.,Chem., 86,83(2009) 7] A.B. Patil and T.H. Mhaske, Asian J. Chem., 14(1), 125(2002) 8] M.S. Nair and N. Kantan, Ind. J. Chem., 34 A, 576 (1998). 9] M.S. Nair and N. Kantan, Ind. J. Chem., 37 A, 1084 (1998) 10] M.S. Nair and N. Kantan, Ind. J. Chem., 38 A, 1307 (1999) 11] H. Irving and H.S. Rossotti, J. Chem. Soc., 76, 2904 (1954) 12] A. I. Vogel, “A Test Book of quantitative Analysis”, London (1961) P. 241. 13] H. Irving and R. J. P. Williams, Nature, 162, 746 (1948). 14] H. Irving and R. J. P. Williams, J. Chem. Soc., 3192 (1953) Fe(III) and UO2 have not reported in literature. The pH–metry measurement work carried out by using ELICO digital model LI – 120 pH–meter with glass calomel electrode with an accuracy of ± 0. histamine and L – histidine as secondary ligands have been investigated by Nair and Neelkantan9. The study of stability constans of Mn(II). The ternary complexes of Ni(II) and Cu(II) with Nicotinic acid as primary ligand and imidazole. pH – EXPERIMENTAL All the ligands was obtained from AR grade.50C was standardized against 0. Cu(II).The study of Kinetic parameter and formation constants of ( Mn. Ternary complexes of Ni(II) with glycine and glycinamide as primary ligands and imidazole.18 pH) for the determination of proton–ligand stability constant of the secondary ligands and metal-ligands 2 . NaClO4 was used from fluka chemical. The stability constants of Mn(II). Ni(II). Cu(II) and Zn(II) with nitrilotriacetic acid (NTA) and iminodiacetic acid (IMDA) as primary ligands and pyridoxine hydrochloride (PHC) and ethambutol hydrochloride (EHC) as secondary ligands was reported by Patil etal7.6 The mixed ligand complexes of transition metals are comparatively less studied than inner transition elements7. benzimidazole. Ni(II).antibiotics cefoperazone) complexes Vis-à-vis Kinetics of electrode reaction have been investigated by Farid Khan & Rakhi Agrawal.05M KHP (4 pH) 0.01 of pH unit at 30 ± 0. It was therefore of interest to study the stability constant of binary and ternary complexes of these metal ions with ligands have studied using Irving–Rossotti metric titration teachique in aqueous medium in the present work. histamine and L – histidine as secondary ligands have been studied potentiometrically8. NaOH was standardized by standard KHP from AR grade12. Co(II).01M borax solution (9. All other Solution were prepared in doubly distilled water. Nair et al10. 3 . The ratio of metal (M) : Secondary ligand (L) was maintained at 1 : 5 in each of the Binary system and ratio of metal : Primary ligands (A) : Secondary ligand (L) was maintained at 1 : 5 : 5 in each of the ternary systems. 2 × 10–1 M HClO4 + 1 × 10–2 M primary ligands + 1 × 10–2 M secondary ligands + 1 × 10–2 M metal ions. Ternary System 1] 2] 3] 4] 2 × 10–1 M HClO4 2 × 10–1 M HClO4 + 1 × 10–2 M secondary ligands. The plots of volume of alkali (NaOH) against pH – meter readings were used to evaluate the proton–ligand stability constants of malonic acid and oxalic acid. 2 × 10–1 M HClO4 + 1 × 10–2 M primary ligands + 1 × 10–2 M metal ions. RESULTS AND DISCUSSION Proton–Ligand stability constants.stability constants of the binary and ternary complexes the following sets of solution were prepared and titrated against stand. The ionic strength was mentioned constant by adding of (1M) NaClO4. 2 × 10–1 M HClO4 + 1 × 10–2 M secondary ligands + 1 × 10–2 M metal ions. alkali solution. The deviation between free acid titration curve & secondary ligand titration curve was used to evaluate the formation functions n A . Binary System 1] 2] 3] 2 × 10–1 M HClO4 2 × 10–1 M HClO4 + 1 × 10–2 M secondary ligands. Temperature = 30 ± 0.360 11. hydrogen and hydroxyl bearing complexes were absent.550 H log K 2 H 11.873 11. An examination of titration curves indicated that ternary complex formation has taken place in solution on the following grounds.934 Metal – Ligand stability constants of Binary complexes.50C.1M NaClO4) Ligands Malonic acid Malic acid Maleic acid log K1 9.828 8. polynuclear complexes. (=0.519 8. 4 . From the graphs the values of log K1 and log K H were evaluated by 2 half-integral method and pointwise calculation method and presented in Table – 1.The proton–ligand formation curves were then obtained by plotting the values of H n A Vs pH-meter readings. Table I PROTON – LIGAND STABILITY CONSTANTS. The metal ligand stability constants of binary complexes were evaluated assuming that the formation of hydrolysed products. it is obvious that the metal – ligand stability 5 . The formation curves obtained were used to evaluate the metal.II. This indicated the affinity of ligand with metal ions which released Protons and produced the volume difference (V3 – V2).1] The metal titration curves showed displacement with respect to the ligand titration curves along the volume axis. Ligand stability constants by methods are presented in Table-II. 3] The hydrolysis of metal ions was suppressed due to complex formation and the precipitation did not appear during the titrations. 2] The colour change of the ligand was in presence of metal ions appeared showing the formation of new species. From the ligand and metal titration curves the values of n and from that the values of pL were obtained. The variation of n was found to be 0 to 2 which indicated that the composition of complexes was 1:5 in solution from table . 455 8. Table – II METAL – LIGAND STABILITY CONSTANTS OF BINARY COMPLEXES.472 6.14 of stability constants was followed by both ligands. The values of n vary from 0 to 1. Ligand Fe(III) Malonic acid Malic acid Maleic acid 7. At n 0.250 6.151 UO2(II) 7. 1] The ternary complex titration curves show displacement with primary complex titration curves. thus confirming the formation of 1 : 5 : 5 mixed ic ligand complexes.264 Stability constant log K1 Ni(II) 12.5 in the formation curve.200 5.628 4.099 6.386 Metal – ligand stability constants of ternary complexes. The horizontal distance was measured between acid curves and the secondary ligand curves (V2 – V1) and subtracted through the horizontal distance between ternary complex curves and primary complex titration curves (V3 – V2) show a positive difference which proves the earlier release of protons in the formation of ternary complexes. PL = log K. The metal ligand stability constants of the ternary complexes were evaluated assuming that the formation of hydroxyl products.361 4. Polynuclear complexes hydrogen and hydroxyl bearing complexes was absent.892 Mn(II) 9.083 5. The values of and have been evaluated from the formation curves n Vs PL . An examination of the titration curves indicated that ternary complex formation has taken place in solution on the following grounds. The Irving – Williams order 13. The log K values were also evaluated by pointwise calculation method. 2] The hydrolysis of metal ions was suppressed and precipitation did not occur.constants of Malonic acid were greater than with repect to oxalic acid in every metal.589 4. The metal–ligand stability constant 6 .552 8.081 M Cu(II) 3. 30 6.18 6.64 5.40 5.61 6.08 5. Malonic acid and oxalic acid are the efficient chelating agents for heavy metals & 7 .76 6. TABLE – 4 METAL – LIGAND STABILITY CONSTANTS Ligands Stability Metal Constant acid La(III) Ce(III) Pr(III) Nd(III) Sm(III) Eu(III) Gd(III) Tb(III) Dy(III) M log K1 Glycine Alanine Malic Maleic acid 6.22 Malonic acid 5.30 5.32 5. Mn(II) < Fe(III) < Ni(II) < Cu(II) < UO2(II) The aim of the study was to know the effects of binary and ternary ligands on metal complexes.20 M log K1 M log K1 M log K1 M log K1 M log K1 M log K1 M log K1 M log K1 The Irving Williams – natural order 13.72 5.56 5.80 7.98 6.10 5.01 6.32 5.66 5.92 6.47 5.84 6.70 5.75 6.82 6.42 5.78 6.94 6.93 6.12 6.62 6.34 5.76 5.10 5.10 7.75 5.92 7.92 6.26 6.72 6. 14 was observed in case of binary as well as ternary complexes which is.of maleic acid and Maleic acid as secondary ligands and Glycine as primary ligands are presented in Table – 3.80 5.77 6.72 5.82 5.54 5. Glycine is functions as antidote against heavy metals ions by forming stable compounds. However. pH titration curves of this ligand show two well separated steps of neutralisation and hence two protonation constants are calculated. novel type bearing –NH2– and –COOH groups. The ionization of Glycine and Alanine may be represented by the following equations: CH 2 COOH | NH 2 H L 2 CH 2 COO | NH 2 HL H K1 H 2 K CH 2 COO CH 3 CH COO | | NH NH | H HL L2 CH 3 CH COOH CH 3 CH COOH K | | NH 2 NH 2 H 1 H2 L HL K CH3 CH COO CH 3 CH COO | | NH NH | H HL H 2 L2 8 . The higher protonation values log K1 Glycine and Alanine are ligands of co-ordination H was assigned to the–OH group. 085 -2.690 -2.690 Pr(III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 10.175 14.357 Ce(III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.937 2.226 13.463 14.530 14.672 -4.067 9 .181 15.245 14.171 -2.697 -2.322 -2.695 Nd(III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 09.585 1.755 -2.816 3.155 1.942 13.017 1.306 -2.TABLE – 4 STABILITY CONSTANTS OF MIXED LIGAND COMPLEXES Metal ion Mixed ligand system logK logK MXY La(III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.465 -3.030 14.505 Sm(III) Glycine – Malic acid Glycine – Maleic acid Glycine – Malonic acid 9.564 -2.848 15.084 15. The present investigation was undertaken with a view to studying the stability constants of mixed ligand complexes of the present ligand with rare earth metal ion by maintaining Metal : Primary ligand : Secondary ligand ratio as 1 : 5 : 5 (M ≠ X = Y). It is an important observation in the present work that the calculation of log KMXY a) b) c) in the slightly lower pH range log K'MXY in the slightly higher pH range log K''MXY in the middle (chosen) pH range log K MXY that M log K MXY log K'MXY log K''MXY 2 This method proved to be an additional check on the selection of the pH range chosen for calculating an accurate stability constant of a mixed ligand complex species. The relative order of stability of ternary chelates in terms of the metal ions as found in this work is La < Ce < Pr < Nd < Sm < Eu < Gd < Tb < Dy which may be attributed to the decreasing size and increasing charge / radius ratio of metal ions. 10 . The stability constants of the mixed ligand Complexes have been computed by adopting an appropriate method proposed for such a condition. The log K1 values are discussed at the appropriate place.The proton Ligand stability constants determined in this work were used through out the calculations of Metal – ligand stability constants as the latter were determined in an identical experimental conditions to those for the former ones. Mhaske.T. J. 14(1). 4] M. Sigel. 86. NY (1974). NY (1973). 2] A..Ind.. Asian J. London (1964 and 1971). Nature. J. (1970) P. J. Kantan.. Chem. 241. Irving and H. NY.REFERENCES 1] A. Irving and R. Kantan.. Soc. P. Martell. Smith. 174. P. Chem. J. Ind.S.. “Metal Ions in Biological systems–2”. Nair and N. 746 (1948). Khan and R. Kantan. 34 A. Ind. Ind. Chem. Patil and T.H.Chem. Nair and N. “Critical Stability Constants” Amino acids. Singh.. 3192 (1953) 11 . “Chemistry of complex equilibria”. Nair and N. Beck. J. Chem. 1307 (1999) 11] H. Agrawal. 162. 37 A. Marcell – Dekker. Van Nostand. 3] H. Rossotti.83(2009) A. London (1961) P. J. Soc.E. Irving and R. Soc. I.. Soc.. 5] 6] 7] 8] 9] P. 38 A. Vogel. J. 76. Chem. J. Williams. Chem. M. 17 and 25.B.. Vol.E. Williams.100 (2009) F. 13] H. J. “Stability constants”.S. The chemical society. 576 (1998). 1084 (1998) 10] M. 14] H. 2904 (1954) 12] A.S..M. Martell and R. Ino. 125(2002) M. Chem. Ind. “A Test Book of quantitative Analysis”. 86. P.S.