Polarographic study of Eu(III)-hydroxamic acid complexes

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PreC. In~4ian Acad. Sci. (Chem. Sci.), Vol. 91, Number 5, October 1982, pp. 40~-413.

~) Printed in India.

Polarographic study of Eu(IlI)-hydroxamic acid complexes

P K B H A N S A L I and B I N E M A D E *

Department of Chemistry, University of Bombay, Vidyanagari, Bombay 400098, India

MS received 10 April 1982 ; revised 23 August 1982

.Abstract.

Com31exes of europium(II[) ion with two hydroxamic acids have been investigated by polarographic method of analysis at 30 4- 0" 1 ~ C and t~ = 0" 5 M (KNOs). In both hydroxamie acids phenylaeetohydroxamic acid (PAHA) and acetohydroxamic acid (AI~A), the electrode reaction was found to be quasireversible in nature, hence Gelling's method was used for evaluation of reversible half-wave potential and kinetic parameters. Formation of Eu(III)-hydroxamic acid complex was observed with metal ligand ratio 1 : 2 in aqueous solution.

Keywords. PhenylacetohyAroxamic acid ; acetohydroxamic acid ; polarographic method ; quasireversible.

1. Introduction

In different non-complexing media (Vleck 1955, 1959 ; Gierst and Cornelissen 1960) the reduction o f Eu 3+ + Eu z+ is o f irreversible to quasireversible nature.

Literature survey revealed that there has been no study of the europium hydroxamic acid system by polarographic technique. Hence the present work has been undertaken.

2. Experimental

The current potential curves were recorded on a manual set-up using dropping mercury electrode (dme) and saturated calomel electrode (scE) as reference electrode. The ionic strength was maintained at 0"5 with the help o f potassium nitrate. Gelatin 0 " 0 0 2 ~ was used as a maximum suppressor. All measurements were carried out at 30 ~ 0" 1 ~ C. The capillary had the following characteristics, m = 1"94 mg/sec and t = 4"0 sec in supporting electrolyte potassium nitrate in open circuit. The p H of the solution was measured with an expanded scale p H meter (Electronic Corporation of India Limited, Hyderabad, Model pH 821 B).

* To whom correspondent. ~ should be made.

409

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410

P K Bhansali and B I Nemade

The pH of the experimental solution was adjusted with freshly prepared N a O H or dilute perchloric acid solutions.

PAHA was synthesised by the method given by Blatt (1964). A~IA was pre- pared as described by Fishbein

et al

(1969). The pK values of PAHA and AHA determined by pH titration technique of Irving and Rossotti (1954) were found to be 9"20 and 9"40 respectively (Bhansali and Nemade 1982). Europium solu- tion was prepared by dissolving europium oxide (Koch-light Lab. 99 "9~o pure) in perchloric acid and was standardised as described by Vogel.

3. Results and discussion 3.1. Europium-PAHA system

Well defined polarogram was obtained for Eu(IIl) in 0" 5 M potassium nitrate with half-wave potential at --0"670V

versus

SCE which is in good agreement with the reported values (Chandrasekaran 1970). Above pH = 5"2 formation of precipi- tate took place hence studies were restricted to a pH range of 4"0 to 5"0. With increase in hydroxamate ion concentrations the half-wave potentials shifted to more negative values indicating complexation. The half-wave potentials were determined from the plots of log

i/id-i versus E

(log-plots) and the slopes of the log-plots were of the order 60-90 InV. The reversible half-wave potential and kinetic parameters,

viz, ~

and /(8 were evaluated by Gelling's method (Gelling 1962) (figure 1). The plot of

E;v, versus

pA (data in table 1) resulted in a smooth curve which showed presence of more than one species whose stabili- ties do not differ appreciably. The data were analysed by DeFord and Hume's (DeFord and Hume 1951) method for evaluation of stability constants. The function F0 (A) was calculated from shift in the half-wave potential obtained from the smooth curve of a plot of

Elp. vs

pA using method of DeFord and Hume (1951).

E nF (E1/o.(,) -- E1/2(,~) +

log I39Ls~q

F 0 (A) = Antilog 0.4343 R--T I~o~ /

= 1 + 131 [.4] + flz [A]" + f13 [A] 3 + . . . . ft, [A]" (1) where,

E~/zc,)

and E1/.~c) refer to the half-wave potential of the uncomplexed and complexed ions respectively and I~,~ and I<c) are the corresponding diffusion cur- rents, fl's refer to the overall stability constants, and [.4] is the concentration of the ligand. Values of Fj functions obtained at different l i g a n d concentrations [.4] are given in table 1. The values of the stability constants obtained are

fll = 2 " 0 • 10 7 and f l . : 2 " 7 • 1014

3.2. Europium-AriA system

In the case of Aria the formation of precipitate was observed at pI-I > 5 "8. The

studies were therefore made at pH below 5"8. The slopes of the log-plots are

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Polarographic study of Eu (111)

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p .(A)--~

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~r

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a~ &

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& gl & ~ & ~ ,:,, ,:.1

b~ tq ~ & & ,:.,I ~ ,q ,;-, b~

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412 P K Bhansali and B I Nema~,

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2~olarographic study o f Eu (III) 413

0 . 7 7

~T __c

1

0.70

Gellin~j's method :

(11 6.68 (41 5,15 [21 6.54 (5) 5'05 (3) 6-30 (6) 4-97

2

1 I

O,2 1.0

( i )

[+)O RAIH.A.

A A . H A .

7 N

O +) i . _ i

O. 02 - 0.02

( r

, E- Ev2 ) Figure 1.

f o u n d in the r a n g e 6 0 - 8 7 mV. T h e r e v e r s i b l e h a l f - w a v e p o t e n t i a l s a n d k i n e t i c p a r a m e t e r s were e v a l u a t e d using G e l l i n g ' s m e t h o d (figure 1 a n d t a b l e 2). T w o c o m p l e x e s were identified w i t h s t a b i l i t y ,

fl, = 1"8 • 105 a n d ,f12 = 1"6 • 10 n .

Results s h o w e d t h a t c o m p l e x e s f o r m e d b y PAHA are s t r o n g e r t h a n t h o s e o f

O H

I1 1

AHA the hydroxamic acid functional g r o u p s - - C - - N - - O H acts as bidentate ligand, and chelation usually occurs (Agrawal 1977), by the substitution of hydrogen atom of hydroxylamine by metal atom and ring closure by carbonyl

o x y g e n a t o m .

References

Agrawal Y K 1977 Bull. Sac. Chim. Belgs. 86 (8)

Bhansali P K and Nemade B I 1982 Paper presented in Symposium on ' Fundamental and, Applied Electrochemistry', held. at Bombay in March 12-13

Blatt A H 1964 Organic synthesis (2nd. edn) (New York : John Wiley and. Sons, Inc.) Vol. 2, p. 67

Chgnd.rasekaran V R 1970 Study of electrode Processes by polarography M.Sc. Thesis, a~mc, Bombay

DeFord D D and Hume D N 1951 J. Chem. Soc. 73 5321

Fishbein W N, Daly J and Streeter C L 1969 Analytical biochemistry 28 13-24

Gelling P J Z. Electrochem Bet, Bunsengesellschaft Phys. Chem. 1962, pp. 66, 477, 481,499 ; 1963, 61, 167

Gierst L and Cornelissen P 1960 Collec. Czech. Chem. Communs. 25 3004 Irving H M and Rossctti H S 1954 J. Chem. Soc. p. 2904

Vleck A H 1955 Collec. Czech. Chem. Communs. 20, 1057, 24, 181 Vleek A H 1955 Chem. Listy. 49 p. 565

Vogel A I Quantitative inorganic analysis (3rd. edn), English L~nguagr Book Society and Longman