Pandeya, K. B.

Sindhu, R. S.

Singh, R. P.

English

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for Mn2+, Cu2+ and Zn2+ complexes are 12'04, 15·81and 15·45 kcal/mole respectively.The E, (Mn-Zn) valle found to be 50·5 is of thesame order as observed in the case of many otherligands which are bonded to two nitrogen atoms andone oxygen atom ar d having two five-memberedrings as in structure (I).One of the authors (A.K.R.) is thankful to CSIR,New Delhi, for awarding junior research fellowship.References1. RISHI, A. K., Metal chelaies of 1-(2-pyridylazo)-2-phenan-throl, Ph.D. Thesis, University of Delhi, Delhi, 1972.2. CHISWELL, B., LIONS, F. & TOMLINSON,M. L., J. inorg.Chem., 3 (1964), 392.3. IRVING, H. M. & ROSSOTTI,H. S., J. chem, Soc., (1954),2904.4. IRVING, H. M. & ROSSOTTI, H. S., J. chem, Soc., (1953),3397.5. BJERRUM, J., Metal ammine formation in aqueous solution. (P. Haase & Sons, Copenhagen), 1941.6. IRVING, H. & WILLIAMS, R. J. P., J. chem, Soc., (1953),3192.7. MALEY, L. & MELLOR, D. P., Nature, Lond., 159 (1947),370.8. GEARY,W. J., NICKLESS,G. & POLLAND,F. H., Analyticachim. Acta, 27 (1962). 71.9. GEORGE. P. & MCCLURE, D. S.. Progress in inorganicchemistry. Vol. I (Interscience, New York). 1959, 428.Polarographic Studies of Cd(II) & Pb(I1)Complexes with 2,3-DihydroxypyridineR. S. SINDHU. K. B. PANDEYA & R. P. SINGHDepartment of Chemistry. University of DelhiDelhi 110007Received 24 October 1975; accepted 24 February 19762,3-Dihydroxypyridine (DHP) form both 1 : 1 and 1: 2(metal: li~and) complexes· with Cd(II) and Pb(II).For Cd(II). lit = 14·0 x 10' and Ih = 23·4 x 1011and forPb(II). Pl = 21·5 X 107 and PI = 19·3 X 1010. As ex-pected the proportion of bi~her species increases withincreasin~ [li~and].DlHYDROXYPYRIDlNE (DHP) is a biologi-cally- important compound and its complexationbehaviour has been studied earlier>" using poten-tiometric and spectrophotometric techniques. Thepresent note describes polarographic studies oncomplex formation of DHP with Cd(II) andPb(II). The ligand exists in the tautometric formsIa and lb.(~OH ~=N)-OH(Ia)('t0H".N/- 0J(Ib)NOTESA d.c. manual polaragraph with a scalamp galvano-meter acting as a current recorder was used. Allpotential measurements were made with respectto SCE. The d.m.e. had the characteristics m =1·99 mg/sec and t = 6·0 sec. Deoxygenation ofsolutions. was done by bubbling purified nitrogenfor 15 rmn. All the measurements were carried outat 35° ± 0·1 °C temperature.All the reagents used were of AR grade andtheir solutions were prepared in conductivity water.~otassium chloride (0·1M~ was used as the support-mg electrolyte and gelatin (0·005%) as maximumsuopressor. NH3-NH4Cl buffer was used to main-tain pH.The reduction of Cd2+ and Pb2+ in DHPinvariably gave a single well-defined reduction wave.The slopes=32 ± l.mV of the plots of log (iji-i) ver-sus Ea.e. coupled With the constancy of the ia/fheff)tvalues indicate that the reversible two-ele~tronreduction is entirely diffusion-controlled. E values.for Cd(II) and Pb(II) are 0·60 and 0·386 V respec-tively. Ei values of the systems Cd(II)-DHP andPb(II)-DHP at different [ligand] are given in Table LThe cathodic shift in Ei on increasing [ligand] atfixed [metal ion] indicates the formation of comPlexspecies. The plots of Et versus log C", (where C", is.the total ligand concentration) in both cases aresmooth curves (not linear), showing, therefore theformation of two or more complex species in equili-brium. The classical method due to Lingane, there-fore. cannot be used for the determination offormation constants. Deford and Humes treatmentas modified by Irving-? has been applied.The formation constants of the complexes formedare obtained by plotting Fo_;[xJ functions against[ligand] followed by graphical extrapolation. Theresults are given below:~l ~aCd2+ 14x 108 23·4x 1011Pb2+ 21·5 X 107 19·3 X 1010Th: plots of Fa[x] were horizontal t.o x-axis, indi-eating that only two complexes were involved, Thefirst stepwise formation constant is greater thanthe second. This is in agreement with the generaltrend of the stepwise formation constant values;KN being greater than KN+l owing to the steric and.statistical considerations.TABLE 1- Et VALUES (VS SCE) OF Cd(II)-DHP ANDPb(II)-DHP SYSTEMSAT DIFFERENT LIGANDCONCENTRATIONS{[Metal ion] = 5 X 10-lM; [KCl] = O'lM}Cd(II)-DHP system (PH 10) Pb(II)-DHP system (pH 9·5>[Ligand] Ei [Ligand] EtmM V mM V2·0 0·810 2'0 0'5562·5 0·812 2'5 0·5723·0 0·814 3·0 0'5753·5 0·817 3-5 0'5784·0 0'820 4·00 0'5814·5 0·823 +SO 0'583S'O 0'826 5'00 0'5869UINDIAN J. CHEM., VOL. 14A, NOVEMBER 1976co -~~'" )( )(S2'160x24120804000... "C> C>Tx x21.120 F2[X]600801.002008t. Ol(4 62 4 6[Li90ncU mMFig. 1 - Plots of FJ[x] versus ligand concentration {(A)Cd(II)-DHP system; (B) Pb(II)-DHP system}120CdL2 101;f- 80 ~(bl(f)•.••,Ir PbL2WU 1.0 ••••. PbLilla.. ~_(bl(f) CdL 10100 2 I. 6[Ligand] ,mMFig. 2 - Plots of percentage distribution of species versusligand concentration {(a) Cd(II)-DHP system; (b) Pb-DHP system}The proportions of the uncornplexed metal ionand the various complex species as a function of the[ligand] can be calculated by means of Eqs, (1) and (2)M 1eM = Fo[x]MJe; ~jLx]jc;;= Fo[x]where M denotes the concentration of the uncom-plexed metal ions, MXj is the concentration of jthcomplex and C is the [total metal ion] added to thesystem. Percentage distribution of Cd2+ and Pb2+in various forms as a function of the [ligand] areplotted in Fig. 2. As expected, the proportion ofhigher species increases with increasing [ligand].For both the metal ions reduction at the eJectrodeis reversible which makes it impossible .to determine•.. (1)... (2)914which of the species actually reacts with the elec-trode in the electron transfer process.One of the authors (R.S.S.) is thankful to CSIR,New Delhi, for awarding a junior research fellowship.References1. MOUGHTON,C., WRIGHT,K. A. & CAIN,R. B., Biochem,J., 106 (1968), 51.2. KATYAL,M., GOEL,D. P. & SINGH,R. P., T'alanta, 15(1968), 711.3. CURTIS,K. E. & ATKINSON,G. F., Can. J. Chem., 50(1972), 1649.4. GOEL,D. P., DUTT,Y. & SINGH,R. P., J. inorg, llucl.css«, 32 (1970), 3119.5. CURTIS,K. E., THOMSON,J. A. & ATKINSON,G. F.,A nalytica chim. Acta, 49 (1970), 351.6. KUSHWAHA,V., SINGH,R. P. & KATYAL,M., Mikrochirn.Acta, (1972), 807.7. GOEL,D. P. & SINGH,R. P., Analyst, 96 (1971), 123.8. LINGANE,J. J., Chern. Rev., 29 (1940), 1.9. DEFORD,D. D. & HUME, D. N., J. Am. chem, Soc., 73(1951), 5221.10. IRVING,H., Adv. Polarog., 1 (1960), 42.Complexes of La(III), Pr(III) & Nd(III) withNitrilotriacetic Acid as Primary Ligand &Hydroxy Acids as Secondary LigandsH. s. RANA& J. P. TANDONDepartment of Chemistry, University of Rajasthan, JaipurReceived 27 September 1975; accepted 21 APf'il 1976The formation constants of mixed Ilgand complexesof La(III), Pr(III) and Nd(III) with nitrilotriacetic acidas primary Hiland and pyrocatechol, disodium salts of1,2-dihydroxybenzene-3,5-disulphonic acid and 1,8-dihydroxynaphtha1ene-3,6-disulphonic acid as secon-dary lil1ands have been evaluated p.H-metrically at30° ± 1° and J1 = O·lM (KNOa). These values are lowerthan the corresponding KM.NTA values. The diffe-rences have been explained on the basis of electrostaticattraction and the basicity of the 11l1and involved. Thevalues of KM.NTA.L follows the order: La -cPr <Nd.NITRILOTRIACETIC acid is known to formquite stable complexes with a number of metalions1-a even at higher' pH. In the present note,K::~i~.L values, where M= La, Pr or Nd, NTA =nitrilotriacetic acid, L = pyrocatechol (PY) ordisodium salts of 1,2-dihydroxybenzene-3,5-disul-phonic acid (Tiron) or 1,8-dihydroxyna-pthalene-3,6-disulphonic acid (CS) have been determinedusing Thompson and Loraas method at 30° ± 10,which are not reported earlier in the literature.The chemicals used were of AR grade. The rare-earth oxides were of spectral grade and a stocksolution was prepared and standardized as describedearlier+ The dipotassium salt of NTA (Koch Light,England) was prepared by dissolving its knownamount in the required volume of 0·1M potassiumhydroxide. The solutions of PY (E. Merck), Tiron(E. Merck) and CS (Fluka) were prepared by dis-solving their calculated amounts in doubly distilledwater and standardized potentiometrically.The following solutions (total vol. 50 ml) weretitrated pH-metrically for Ln-NTA-PY (where Ln =La, Pr or Nd) system at 30° ± 10 under oxygen-free

Polarographic Studies of Cd(II) & Pb(II) Complexes with 2,3-Dihydroxypyridine

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Polarographic Studies of Cd(II) & Pb(II) Complexes with 2,3-Dihydroxypyridine

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