Munshi, K. N.

Sarin, R.

English

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indian Journal of ChemistryVol. 15A, April 1977, pp. 327-329Stepwise Stability Constants & Thermodynamic Functions of In (III)Complexes with Some Substituted Derivatives of Quinoline & Pyridin eR. SARIN & K. N. MUNSHIDepartment of Chemistry, New University Campus, NagpurReceived 3 February 1976; accepted 22 July 1976Stability constants of indium (III) complexes with 8-hydroxyquinoline, 8-hydroxy-2-methyl quinoline (in SO~~aq, dioxane) and with 8-hydroxyquinoline-S-sulphonic acid, 8-hydroxy-7-iodoquinoline-S-sulphonic acid, pyridine-2-carboxylic acid and pyridine-2,6-di~arboxylic acid(in aq. medium) have been determined ustng Calvin-Bjerrum pH-titration technique as modi-fied by Ir-ving and Rossotti. The log K. values have been refined employing various computationalmethods. The stepwise changes in the free energy, enthalpy and entropy values for complexa-tion reactions have been evaluated at three different temperatures.COMPLEXES of In(III) with 8-hydroxyqui-noli.ie and some of its derivatives have beenstudied using spectrophotometrict-s. solubilitv''and solvent extraction methods+ However, thestability constants of the complexes have not beenreported. We report here the stepwise metal-ligandstability constants of indium(III) complexes with8-hydroxyquinoline (OX), 8-hydroxy-2-methylqui-noline (MeOX) , 8-hydroxyquinoline-S-sulphonic acid(OXSA), 8-hydroxy-7-iodoquinoline-S-sulphonic acid(OXISA) , pyridine-2-carboxylic acid (PA) and pyri-dine-2,6-dicarboxylic acid (DPA). The stepwise freeenergy (~G), enthalpy (AH) and entropy (~S)changes accompanying the complexation reactionshave also been evaluated.Materials and MethodsA stock solution (O·OlM) of In(N03)3.SH20(Schuchardt, Munich) was prepared in a calculatedquantity of perchloric acid to prevent the hydrolysis.The In (III) content was determined gravimetrically5.8-Hydroxyquinoline (Analalc, BDH) and 8-hydroxy-2-methylquinoline (Eastman-Kodak) were recrystal-lized from aq. ethanol and the stock solutions(O'OlSM) prepared in purified dioxane'', 8-Hydroxy-quinolinc-Svsulpho.ric acid (Merck) and 8-hydroxy-7-iodoquinoline-S-sulphonic acid (BDH) were driedat 100° and their stock solutions (0'004M) preparedin doubly distilled water. These solutions werestandardized by determining the equivalent weightsof the acids. Stock solutions (0'02SM) of pyridine-2-carboxylic acid (Koch-Light) and pyridine-2,6-dicarboxylic acid (Fluka) were prepared in doublydistilled water and standardized potentiometrically.A pH-meter (Beckman model H-2) with a glass-calomel electrode assembly connected through agarbridge saturated with KN03 was used for pHmeasurements. Temperature was maintained usinga thermostat having an accuracy of ± 0'2°. Thetitration cell was so designed that it enabled PH-measurements in an atmosphere of nitrogen.Procedure - Bjerrum-Calvin pH-titration tech-nique7,8 was employed for which the following threemixtures were prepared: (A) perchloric acid: (B)perchloric acid + ligand solution; (C) perchloricacid + ligand solution + metal salt solution. Theconcentrations of the common ingredients wereidentical in different mixtures. An appropriateamount of neutral sodium perchlorate (l'OM) wasadded to maintain the desired ionic strength. Thesemixtures were titrated against standard carbonate-free sodium hydroxide (l'OM) standardized poten-tiometrically against potassium hydrogen phthalatet,A graph between PH meter reading B and thevolume of alkali added was plotted. The threetitration curves obtained were referred to as acidtitration curve (A), ligand titration curve (B), andcomplex titration curve (C).Proton-ligand and metal-ligand stability constants- The proton-ligand stability constants were com-puted as follows: The values of iiA at various PH(-?) v~lues were calc.ulat,ed from the acid and ligandtltratlO~ curves uSI~g the formula of Irving and~ossOttll0. Calculation of the "practical" proton-ligand stability constants. was carried out byplottIng a graph of iiA against PH (B) and thenapplying various computational methodsu.The stepwise stability constants of the metalcomplexes were determined by analysing the for-~atlOn curves (ii versus PL) using various cornputa-tional methods-'. The values of ii, the averagenumber of Iigands attached per metal ion, and thefree ligand exponent pL were calculated from ligandand complex titration curves using the formula ofIrving and Rossottiw.Thermodynamic parameters - The values of theoverall changes in free energy (IlG) , enthalpy (~H),and entropy (AS) for In (III) complexes have beencalculated using the temperature coefficient andGibbs-Helmholtz equationw,Results"Practical'.' proton-ligand stability constants - Thecurves obtained from the function iiA (B) wereextended between 0 and 2 in the iiA scale for OXand MeOX. This showed that the dissociation of327INDIAN J. CHEM., VOL. 15A, APRIL 1977H2U (where L = OX or MeOX) takes place asfollows:K2 tc,H2L+~HL+H+~L-+H+The curves obtained from the function nA (PH) wereextended between 0 and 2 in the nA scale for OXSAand OXISA showing the complete dissociation of-S03H group present in both the ligands. Thusthe dissociation of H2L (where L = OXSA andOXISA) can be represented as follows:K2 s,H3L+-+H2L~HL-+H+~L2-+H+The curves obtained from the function nA (PH) wereextended from 0 to 1 for PA and from 0 to 2 forDPA. The results showed that pyridyl nitrogenin both the cases gets deprotonated at a very lowPH value. This is in agreement with the resultsreported earlier for PAI3 and DPA14. Thus, thedissociation of H2U (where L = PA) and H3L+(where L = DPA) can be represented as follows:KlH2U-+HL~L-+H+ (where L = PA)K2 KlH3U-+H2L~HL-~V-+Hr (where L = DPA)The values of stepwise proton-ligand stabilityconstants at various temperatures obtained by themethod of interpolation at various nA values--are summarized in Table l.Metal-ligand stability constants - The nature ofthe formation curves (Fig. 1) for In(III)-OX,In(III)-MeOX, In(III)-OXSA. In(III)-OXISA andIn(III)-PA shows the stepwise formation of threechelates. The values of log K1, log K2 and log K3were obtained from the formation curves at n = 0'5,1·5 and 2·5 respectively. But this method did notgive reliable values as log Kl/K2 and log K2/Ka <3·0. Therefore, the values obtained by trois methodhave been refined by (i) correction term method,(ii) grapilical method and (iii) least-squares method-t.The mean values of stability constants at varioustemperatures having error limit of ± 0·05 aresummarized in Table 1.The formation curves for In(III)-DPA show thestepwise formation of two chelates. The valuesof log Kl and log K2 for these chelates are summa-rized in Table 1.',01(){) 11·0 12.(J 13-04·0 5-0Fig. 1 - Formation curves of In (III) complexes withOX. MeOX, OX5A, PA and DPAThermodynamic parameters - Values of the step-wise changes in the free energy (AG), enthalpy (Mi)and entropy (Ll.S) , calculated at three differenttemperatures, have been summarized in Table 2.ConstantsTABLE 1 -" PRACTICAL" PROTON-LIGANDAND METAL-LIGAND STABILITYCONSTANTSlog K~log K~10·77~'53TemperatureOX10·694·4710·875·018·113·856·742·47PA5·184·392·0312·5512·0410·0812·2210·408·739·709·517·708·207·776·67log K,log K2log K.In(III)-PA5'56 5·445'14 5·013·82 3·74In(IlI)-DPA45°10·604·4110·764·958·003·806·662·445·054·292·0012·4211·899·8812·1210·278·609·619·417·608·127·706·595·344·903-645·635·01328MeOXlog K~log K;r10·975·08OX5Alog K~log K.H8·213·90OXISAlog K~log K;r6·822·50log K~ 5·30DPAlog Krlog K~4·482·06In(IIl)-OXlog K,log K.log K.12·6612·1710·26In (I1I)-MeOXlog K,log K,log K.12·3010·518·86In(III)-OXSAlog K,log K,log K.9·809·607·82In (III) -OXISAlog K,log K,log K.8·277·856·85log K,log K,5·825·215·735·10S.\RI~ & :\1U:\SHI: STABILITY CONSTANTS OF In(III) COMPLEXESTABLE 2 - YALUES OF THER)IODY:-f.UHC PAR.HIETERSReaction ~G (kcaljmole) at /),.H /),.Sstep (kcalj (e.u.)25° 35° 45° mole) atat 35°35°n=111=211=311=111=211-=3n=1n=211=311=111=211=3n=1n=2n=3n=1n=2In(IIl)-OX-17'26 -17·69 -18'16-16·60 -16,97 -17·30-13·99 -14·21 -14·37In(III)-:\IeOX-16·77 -17·23 -17·64-14·33 -14·66 -14·95-12,08 -12-30 -12'51In(III)-OXSA-13·36 -13·66 -13·98-13,08 -13·40 -13·69-10,65 -10·85 -11·06In(III)-OXISA-11·28 -11-55 -11,81-10·70 -10·95 -11,20-9'20 -9040 -9·60In(III)-PA-7·57 -7·66 -7·77-7·01 -7·06 -7,13-5,21 -5·27 -5,30In(III)-DPA-7·93-7·10-8·08-7·19-8·19-7·29-4·9-5·7-7·7-3·7-4·9-5·3-3·6-4'5-5·3-2,8-3·2-3·2-4·5-4·9-3·7-3,7-4·1+42+36+21+44+32+26+33+29+18+28+25+20+10+7+5+14+10The precision of !l.G values is ± 0'8 kcal mole-I,AH values ± 1·0 kcal mole'< and !l.S values is± 2·0 cal deg! mole+,DiscussionIt is clear from Table 1 that In(Ill)-OX complexesare more stable than In(UI)-MeOX complexes,though on the basis of basicity considerations alone,MeOX complexes should have been more stable.This anomaly may be due to steric hindrance causedby the methyl group.In(III)-OXISA complexes are less stable thanIn(UI)-OXSA due to lower basicity of OXISA asa result of electron-withdrawing iodo group.The greater stability of In(llJ)-DPA complexesas compared with that of In(III)-PA complexes isdue to the fact that DPA arts as a tridentateligand and thus forms two stepwise chelates whereasPA acts as a bidentate ligand and forms threestepwise chelates with indium (III).AcknowledgementWe thank Prof. R. H. Sahasrabudhey, Head ofthe Deoartrnent for providing facilities and UGC,New Delh for the award of a research fellowshipto one of us (R.S.).References1. MOELLER. T. & COHEN, A. J.. J. Am. chem. Soc .• 72 (1950).3546.2. JOHNSON. J. E.. LAVINE. :\f. C. & ROSENBERG. Analyt.Chem .• 30 (1958).2055.3. PYSTNITSKII. 1. V. & KOSTISHINA. A. P .• Ukrain khim,Zhur .• 23 (1957).1957.4. STRAY. J.. Analyt. cu,« Acta. 28 (1963). 132.S. ERDEY. LASZLO. Gravimetric analysis. Vol. 7 in inter-national series of monographs on analytical chemistry(Pergamon Press. London). 1965. 598.6. VOGEL. A.!.. Practical organic chemistry (LongrnansGreen. London). 1971. 177.7. BJERRU)I. J .. Metal ammine formation on aqueous solu-tion (Haase. Copenhagen), 1941. 298.8. CALVIN. M. & WILSO:-l. K. W .• J. Am. chem, Soc .• 67(1945).2903.9. VOGEL. A.!,. Quantitative inorganic analysis (LongmansGreen. London). 1961. 241.10. IRVING. H. & ROSSOTTI. H. S .• J. chem. Soc .• (1954).2904.11. IRVING. H. & ROSSOTTI. H. 5.. j. chem, Soc .• (1953).3397.12.YATSIMIRSKII. K. B. & VAsl·L·Ev. V. P., Instabilityconstants of complex compounds (D. Van Nostrand. NewYork). 1960. 63.13. LUMME. P.O .• Suomen. Kem, 31 (1958). 250; Chern.Abstr .. 53 (1959).3848.14. ANDEREGG. G .• Helo, chim. Acta. 43 (1960).414./329

Stepwise Stability Constants & Thermodynamic Functions of In (III) Complexes with Some Substituted Derivatives of Quinoline & Pyridine

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Stepwise Stability Constants & Thermodynamic Functions of In (III) Complexes with Some Substituted Derivatives of Quinoline & Pyridine

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