INDIAN J. CHEM., VOL. 18A, JULY 1979

3. SCHAAP,W. B. & McMAsTERS, D. L., J. Am. chem. Soc.,83 (1961), 4699. TABLE 1 - VALUESOF EIII ANDid FOREu(UI)-AcRYLIC ACID

4. DEFoRD, D. D. & HUME, D. N., J. Am. chern. Soc., 73 Eu(III)-CROTONIC ACID SYSTEMS(1951), 5321.

5. GELUNGS, P. J., Z. Electrochem. Bes. Bunsengs, 66 (1962),477, 481, 799; 67 (1963), 1.67.

6. LEDEN, I «, Z. phys. Chem., A-188 (1941), 60.

Compositions and formation constants of .Eu(lll) complexeswith acrylic acid and crotonic acid have been studied polaro-graphically. The reductions are reversible and diffusion-controlled.The plot of ElIl versus -log Cx is linear in the case of Eu(lll)-aicrylic acid systlm. The change in number of Iigands bound toeuropium during reduction was found to be =1 and ratio of _dissociation constants of Eu(lll) and Eu(l1) was found to be40.76xlO-I• In the case of Eu(lll)-crotonic acid system, c~m-position and formation constants have been calculated by themethod of Deford and Hume. Crotonic acid forms two complexspecies with europium (~I' 60; ~a, 4.2x 10+2). The percentagedistribution of various complex species as a function of ligandconcentration has been calculated in the case of Eu(lll)-crotnoicacid system. A polarographic method for the determination ofmicro amounts of Eu(lll) in the presence of diverse ions has beendeveloped. Under optimum condltlons Eu(llI) in the concentra-tion range 4x lO-'-2x lO-IM can be successfully determinedin various mixtures.

Polarographic Determination of Stability Constants ••of Eu(lll) Complexes with Acrylic Acid & Crotonic

Acid

A. L. J. RAO* & MAKHAN SINGH

Department of Chemistry, Punjabi University, Patiala 147 002

Received 13 September 1978; accepted 22 January 1979

ELECTRO-REDUCTION of Eu(III) at the drop-ping mercury electrode has been studied in

various supporting electrolytes'r". But so far nostudy has been made using acrylic acid or crotonicacid as the supporting electrolyte. The present notereports the polarographic studies of Eu(III). in acrylicacid and crotonic acid media.

All the chemicals used were of reagent grade purity.A O.OlM solution of EU203 was prepared by dissolv-ing it in the minimum amount of perchloric acidand diluting with distilled water. Crotonic acid servedas the complexing agent. Ionic strength was main-tained at 1.0 by sodium perchlorate. All the polaro-grams were recorded at 25 ± 0.10 with a manualpolarograph. .A saturated calomel electrode wasused as the reference and was connected to thepolarographic cell by a potassium chloride-agarbridge. Oxygen was expell~d by passing a str~am ofnitrogen through the solution before recording thepolarograms. Doubly distilled mercury was usedand the values of m and t were 2.08 mg/sec and 3.1 seerespectively in distilled water and in open circuit.

Solutions containing 0.5 mM metal ionand varyingconcentrations of crotonic acid and acrylic acid wereprepared. The pH of the solutions were measuredwith a Philips pH meter.

A single well-defined reduction wave appeared inall the solutions. The plots of id versus "'h- and laversus C were linear and passed through the origin.

86

I

(

([Eu(lIl)] =- 0.5 mM}

[Acid] EIII (-V) id «(.'A) Fo[X)M

Acrylic acid system

0.0 0.706 1.3060.1 0.745 0.940.2 0.773 0.940.3 0.783 0.940.4 0.794 0.9170.5 0.801 0.869

Crotonic acid system

0.0 0.706 1.3060.02 0.720 0.964 2.3610.04 0.735 0.964 4.2480.08 0.753 0.964 8.5540.20 0.777 0.869 24.4200.30 0.800 0.840 61.510.40 0.815 0.775 120.00.80 0.840 0.775 321.7

The plots of log .L;versus Ed,e were also linear withId-l

slopes of the order of 0.06 ± 0.002 in agreement withthe theoretical value of one electron transfer processindicating the reversibility of the electrode reactions.The values ofid and -Ell 2 for different ligand concen-tration (Cx) are given in Table 1 and 2. A number ofpolarograms were recorded in the pH range 2-5.4.As the pH of the solution increases E1/2 increases.Above pH 5.5 precipitation occurs. So all thepolarograms are recorded at a pH of 2 as there is noneed of adjustment of pH.

Eu(III) is not reversibly reduced at the d.m.e. inthe absence of acrylic acid and crotonic acid. Thevalue of standard rate constant was found to be7.2 X 10-( cm2/sec (in the absence of acrylic andcrotonic acid) which shows the quasi-reversibilityof the electrode reduction. So E{,2 was calculated byGelling's method" for the study of complex formation.

In the case of europium-acrylic acid system theplot of Ell2 versus -log Cx (Cx= ligand concentration)is linear which indicates the formation of one com-plex only. As the oxidised and reduced forms ofeuropium are both in solution Lingane's method forthe study of complex formation was applied usingEq. 1

RT I ~Olt- " Ell 2 = -- og --cs nF ~red

RT+ (p - q) nF log Cx ... (1)

where p and q are the number of ligands attached toEu(III) and Eu(II) respectively and ~Olt and ~red arethe dissociation constants of Eu(III) and Eu(II)complexes respectively. The plot of -Ell 2 versus -logCx is linear the slope of which gives the change in thenumber of ligands bound to europium (p-q). Itwas found to be ~ 1. The intercept of the plotgives the ratio of the dissociation constants which wasfound to be (40.76 x 10-2).

eo

60..!!oco 40..'iiio0.

~ 20CJ

MO~---L----~--~~--~2-0 '·5 ',0 0'50

-log ex

Fig. 1- Distribution diagram for Eu(IlI)-crotonic acid system

o

In the case of europium-crotonic acid system, acurvature obtained in the plot of Ell 2 versus -log Cxshowed the formation of successive complexes. TheDeford and Hume treatment as modified by Irvingwas applied and Eu(lIl) was found to form 1:1 and1:2 complexes with crotonic acid with stability cons-tant values of 60 and 4.2 x 10+2 respectively. From theknown stability constant data, values of the degreeof formation (Fig. 1) for each complex in a systemhave been calculated using Eq.2 (ref. 10).

... (2)

Stability constant data show that the complexes ofEu(lIl) with crotonic acid are more stable than thatwith acrylic acid.

The reduction equilibrium for the formation ofsuccessive complexes reported above may be repre-sented by Eqs 3 and 4 :

Eu3+ + HX ~ [Eu(X)]2+ + H+ (3)[EuX]2+ + HX ~ [EU(X)2]++ H+ (4)

The percentage distribution of various complexspecies as a function of ligand concentration has beencalculated in the case of Eu(III)-crotonic acid system.Based on this a polarographic method for the deter-mination of microamounts of Eu(lll) has beendeveloped. Under optimum conditions Eu(lll) inthe range 4x 10-4-2 x 1O-3M can be successfullydetermined in presence of different ions. Theaverage percentage recovery of Eu(llI) in the presenceof various ions has been found to be 99.99 % with astandard deviation of 0.192.

Metal ions like Ag(I), Au(lIl) and Te(IV) are preci-pitated. Metal ions like Se(VI), W(VI), Se(IV),Ti(IV) and Zn(lV) do not undergo reduction. Te(VI),Cr(VI), Sb(lll) Cr(III), As(III), Pb(II), Tl(I), U(VI),Cu(II), Yb(III), Mn(II), Co(II), Ni(IJ) and Zn(IJ)undergo reduction at different potentials than thatof Eu(III). Only Mo(VI), V(V), Cd(lI) and In(III)interfere in the determination of Eu(IIJ).

References1. MACERO, D. J., ANDERSON, L. B. & MACHESKY, P., J. electro-

onalyt . Chem., ]0 (1965), 76.2. MACERO, D. J., HERMAN, H. R. & DUKAT, A. J., Analyt.

Chem., 37 (1965), 675.3. ZUTSHI, K., Res. Polaroqr. Japan., ]4 (1967), 294.4. IDE, Y., Bull. chem. Soc. Japan, 40 (1967), 2981.

(

NOTES

5. LAL, S., Bull. chem. Soc. Japan, 46 (1973), 2232.6. LAL, S., Aust. J. Chem., 25 (1972), 1571.7. HOLLECK, L., Z. Naturforsch., 26 (1947), 81.8. GELLINGS, P. J., Z. Elektrochem., 66 (1962), 477; 67 (1963),

1679. DEFORD, D. D. & HUME, D. N., J. Am. chem. Soc., 73

(1951), 5321.10. CRow, D. R., Polarography of metal complexes (Academic

Press, London), 1969. 5.

Formation Constants of Dioxouranium (VI), Cu (11),Ni(II), Zn (II), Co(II) & Mn(1I) Complexes of

Peonoloxime

V. SURESH BABU, D. UGANDHAR R.Aru & R. RAGHAVA NAIDU·Department of Chemistry, Sri Venkateswara University.

Tirupati 517502

Received 22 August 1978; accepted 27 January 1979

The metal-ligand stability constants log K, and log K. and theproton-ligand stability constant log KL have been determined in50% (vrv) dloxan-water, acetone-water. and 2-ethoxyethanol-water mixtures using the Bjerrum-Calvin pH titration techniqueas modified by Irving and Rossotti. The stability constants arein fair agreement with Irving-Williams rule. The results obtainedare compared with the data available in the literature for struc-turally similar ligand complexes. Amongst the solvents usedacetone-water shows abnormal behaviour •

IN view of the analytical applications- of peono-Ioxime (2-hydroxy-4-methoxyacetophenoneoxime),

it is of interest to know the physico-chemicalproperties such as absorption spectral characteristics,thermal properties, magnetic susceptibility and stabi-lities of its metal complexes. Hence the authorshave undertaken these studies and the present investi-gation deals with the determination of the stabilityconstants of the complexes of U022i' , Cu2+, Ni2i',Zn2+, C02+ and Mn2+ with peonoloxime by Calvin-Bjerrum titration techniques+ as modified byIrving and Rossetti", Since the chelates were inso-luble in water (except cobalt, zinc, and uranium)the study was carried out at 28° in 50% (v/v)dioxane-water, acetone-water and 2-ethoxyethanol-water mixtures.

Peonoloxime was prepared according to literaturemethods" and its solution (O.IM) was prepared inthe respective organic solvents. The metal nitratesolutions were prepared in doubly distilled waterand star.dardised .. Dioxan", acetone" and 2-ethoxy-ethanol'? were purified l::efore use.

Elico (Ll-IOA) pH meter was used for pH measure-ments.

Procedure - The experimental procedure involvedthe titration of the following carl::onate-free solutions(total volume 50 mI) against standard sodium hy-droxide (0.1025M) :

(a) 5 mI of(O.OIM) nitric acid + 25 ml of organicsolvent + 20 ml of water.

(b) 1 mI of (O.IM) ligand in pure organic solvent+ 5 mI of (O.OIM) nitric acid + 24 mI oforganic solvent + 20 mI of water.

(c) 0.5 mI of (O.OIM) metal solution + 1 mI of(O.IM) ligand + 5 mI of (O.OIM) nitric acid+ 24 mI of organic solvent + 19.5 ml ofwater.

87

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