Determination of U02 (II), Th(IV) and Ce(III) complexes formed with halogen and nitro derivatives of 8-hydroxyquinoline

DETERMINATION OF U 0 2 (II), Th(IV) AND Ce(III) COMPLEXES FORMED W ITH HALOGEN AND NITRO DERIVATIVES OF 8-HYDROXY QUIN OLINE

Serap TEKSOZ. Perihan UNAK

Ege University, Institute o f Nuclear Sciences, Department o f Nuclear Applications 35100 Bornova Izmir Turkey

ABSTRACT

Proton-ligand stability constants for some iodo and nitro derivatives of 8-hydroxyquinoline were determined by Calvin Bjerrum potantiometrical method. The stability constants of the corresponding chelates with U 0 2 (II), Th(IV) and Ce(III) were studied potentiometrically at 25 °C by applying Irving-Rossotti computing method. The complexes of the nitro-substituted ligands were less stable than the corresponding complexes of the unsubstituted ligands. The stability constants of metal-ligands depend on the ionic radii and ionic charge of metals and also they decrease with steric repulsions of the nitro groups.

INTRODUCTION

8-Hydroxyquinoline and derivatives are known as chelate forming agents for many metal ions. Complex formation stability constants of some metal ions with derivatives of 8-hydroxyquinoline have been investigated by many workers [1, 6-11], Most of these studies have been carried out according to potantiometrical Irving- Rossotti method. Irving-Rossotti has still been the most common used method to compute stability constants by potantiometrically. On the other hand actinide and lanthanide complexes of 8-hydroxyquinoline have been a source of interest by many years [1,3,6,7-10,12-14],The aim of this study is to determine proton-ligand stability constants of iodo and nitro derivatives of 8-hydroxyquinoline and stability constants of corresponding ligands with U 0 2 (II), Th(IV) and Ce(III).

Synthesis of ligand and complex compounds: 5-Cl-7-N02-8-0HQ (5-chloro-7-nitro- 8-hydroxyquinoline): 5-Chloro-8-hydroxyquinoline was nitrated under the same conditions as earlier [1], Crude product was recrystallized from ethyl alcohol. Yield was 60% and the melting point was 197 °C.

5-I-8-OHQ (5-iodo-8-hydroxyquinoline): Similar procedure was applied under the same conditions as Gershon [2], 0.36 g 8-OHQ was dissolved in 50 mL CHC13 and 0.57 g NIS (n-iodosuccinimide) was added little by little by stirring for 30 minutes at room temperature. Stirring was continued for 3 hours. It was washed firstly 5% sodium acetate solution then procedure was repeated with 5 % sodium bisulfide solution after the reaction ended. CHC13 was evaporated by air flow and crude product was recrystallized from ethyl alcohol. Yield was 62% and the melting point was 124 °C.

5-I-7-NO2-8-OHQ (5-iodo-7-nitro-8-hydroxyquinoline): Similar procedure was applied as Gershon [2]. Crude product of 5-I-8-OHQ was dissolved in 100 mL acetic acid at 5 °C and 0.8 mL of concentrated HNO3 was added drop by drop. The reaction was stopped by pouring in 200 mL water after 2 hours and stirring was continued. After a while it was filtered, washed by distilled water and dried at 70 °C. Yield was 66% and the melting point was 220-224 °C.

The structure of the ligand and complex compounds were confirmed by IR and NMR spectroscopy.

Potentiometric titrations: Potentiometric titrations were carried out in 75% dioxan-water mixtures. 0.1 N HCl, 1 M KCl, 0.1 N NaOH, 0.001 M Th(NO3)4 5H2O, 0.001 M Ce(NO3)3

5H2O, 0.001 M UO2(NO3)2 6H2O solutions were prepared. Below titrations were done: Titration V1: 10 mL 1 M KCl + 5 mL 0.1 N HCl

Titration V2: 10 mL 1 M KCl + 5 mL 0.1 N HCl + 10 mL 0.002 M ligand solution

Titration V3: 10 mL 1 M KCl + 5 mL 0.1 N HCl + 10 mL 0.002 M ligand + 4 mL 0.001 M metal solution

Titration V4: 10 mL 1 M KCl + 5 mL 0.1 N HCl + 4 mL 0.001 M metal solution

The last volume of each was adjusted to 100 mL by 75 % dioxan-water mixture and each of them was titrated with 0.1 N NaOH.

Calculational Method

According to Calvin-Bjerrum’s method, the average number of protons associated with the anionic ligand, nA is given by below equation:

n A y + ( \ j - V2)(N° + E o)

y (V o + V1)(Bot) (1)

where

y : total proton number associated with the original ligand,

V1 : total volume of 0.1 N NaOH solution used for the titration of acid solution

corresponding to a given pH value,

V2 : total volume of 0.1 N NaOH solution used for the titration of acid + ligand solution

corresponding to the same pH given above, V0 : initial volume of the acid + ligand solution, N0 : normality of NaOH solution,

Using this equation, nA values versus pH were obtained and plotted.

Proton-ligand stability constants were calculated according to below equation given by Corsini [3].

, , + ( n A - n +1) logKn = -lo g H + log ——---—

(n - n A) (2)

logK values can be found using nA values not equal to zero or integer values in this equation. Least -square treatment method:

This method is given by Corsini and Billo [3]. According to this method:

n a = (2 - Ha)[h + ] K

--- = --- KiK 0 — Ki

(nA - 1)[H + ] (nA - 1 ) 1 2 1 (3)

must gives a straight line. K1 and K2 can be found from intercept and slope. However the method is very sensitive to experimental errors close to integer values of nA, therefore the points close to integer of nA were rejected in this treatment.

Metal-ligand Stability Constants:

Irving-Bjerrum method gives the following equation for the complex formation function, ni, i.e., average number of ligands bound to metal cation.

n [(V4 -V1)-(V3 - V2)](N° + E o)

(V o + V1)n AM oT (4)

where

V3 : volume of 0.1 N NaOH solution used for the titration of acid + ligand + metal solution. V4 : volume of 0.1 N NaOH solution used for the titration of acid + metal solution

MoT : initial concentration of metal cation.

nA, No, Eo, Vo, V1, V2: the same definition as given in Eq. (1).

ni values were obtained for different pH values from this equation.

pL, inverse of logarithm of free ligand concentrations can be found from equation (5),

pL = log

2

>

r

where

Lt : total ligand concentration,

n : ligand number associable with metal cation, Mt : total metal ion concentrations,

Vo : initial volume,

V3 : NaOH volume that is spent for acid + ligand + metal + mixtures. Pn : total proton-ligand stability constants up to n.

Metal-ligand formation constants were found by least square treatment method. Least- square treatment method

According to this method, n . = (2 - n i)[L] 1

( n - 1)[L] (ni - 1 ) - K i (6)

must gives a straight line and intercept gives -K 1 [4]. However, between 0.95< ni<1.05 values are very sensitive to experimental errors. The points in this small region are therefore best rejected in this treatment [4]. K1 and K2 values found by linear regression by using equation 6. Obtained results are shown in table 2.

RESULTS AND DISCUSSION

Proton-ligand stability constant values were computed according to equation 2 and least square treatment method. An EXCEL computer program were used. Obtained results for 8-hydroxyquinoline derivatives is shown in table-1. The decreasing order of electron donor of halogens are Cl>Br>I, for this reason proton-ligand stability constant for 5-chloro-

8-hydroxyquinoline is smaller than 5-iodo derivative. In the case of nitro substitution stability constant values decrease because of electron withdrawing effect of this group. These substituents increase the acidity. For this reason they cause steric protonation hindrance on the aromatic ring, then protonation constant decreases. However this effect hasn’t been seen for 5-chloro-7-nitro-8-hydroxyquinoline. It is concluded that nitro and chloride groups are affected oppositely with each other.

In metal ligand stability constants the results were found by least square treatment method. The stability constant values change for metal complexes which formed with relevant ligands. The ionic radii and ionic charge of metals affect the stability constant of complexes. The other factor that affects the stability is substituted groups on the aromatic ring.

order of stability constants has changed as compared to the other ligands. The stability constants of thorium complex is less than the cerium complex. Decreasing chelate formation of thorium can be explained as the increasing tendency of the formation of complex with increasing electron density and the other effect is nitro group.

On the other hand hydrolysis behavior of Th(IV) and Ce(III) ions is very complex. Hydrolysis of thorium is important at low pH, this may need some corrections. For this reason titration V4 were done for each Th (NO3)4 and Ce (NO3)3 solutions to determine hydrolysis effect.

When the ligands are slightly soluble in water, dioxan-water mixtures can be used to potantiometric titrations as reported by other researchers [3, 10-11, 15]. In the previous work, titrations were recorded in various solvents ranging from pure water to 75 per cent (v/v) dioxan [5]. Since our ligands are slightly soluble in water, 75 per cent (v/v) dioxan has been used in this study.

REFERENCES

1. P. Unak, T. Ozkayalar, D. Ozdemir, F. Yurt, J. Radioanal. Nucl. Chem. Lett., 196, 2, (1995)323.

2. H. Gershon, J. Med. Chem., 34, (1968), 3268.

3. A. Corsini, E. J. Billo, J. Inorg. Nucl. Chem., 32, (1970), 1241. 4. A. Corsini, E. J. Billo, J. Inorg. Nucl. Chem., 32, (1970), 1249. 5. H. M. N. H. Irving, U.S. Mahnot, Inorg. Nucl. Chem., 30 (1968) 1215.

6. C.F. Richard, R. L. Gustafson, A. E. Martell, J. Am. Chem. Soc., (1959) 81, 1033. 7. J. Fresco, H. Freiser, Inorganic Chemistry, (1963) 82, 2, 1.

8. P. Unak, D. Ozdemir, T. Unak, J. Radioanal. Nucl. Chem., 176 (1993) 55. 9. P. Unak, D. Ozdemir, T. Unak, J. Radioanal. Nucl. Chem., 186 (1994) 325.

10. A K. Bandopadhyay, A. K. Chaudhury, Indian J. Chem., 26A, (1987) 853. 11. H. Freiser, R. G. Charles, W. D. Johnston, J. Am . Chem. Soc., 74 (1952) 1383. 12. T. Moellar, V. Ramaniah, J. Am. Chem. Soc., 76 (1954) 2022.

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Table-1: Proton-Ligand Stability Constants.

logKi logK2 log^2

Ligand Corsini Least-square

treatment Mean Corsini

Least-square

treatment Mean Mean

5-C l-8O H Q 2.90±0.41 3.21±0.19 3.05±0.15 10.87±0.50 11.29±0.33 11.08±0.21 14.13±0.26 5-I-8O H Q 3.35± 0.07 3.28 3.31±0.03 12.03±0.84 11.06 11.54±0.48 14.85±0.51 5-C l-7-N O 2-8O H Q 2.81±0.53 2.81±0.53 11.17±0.01 11.17±0.01 13.98±0.54 5-I-7-N O 2-8O H Q 2.41± 0.28 3.04±0.08 2.72±0.31 10.66±0.22 11.08±0.8 10.87±0.21 13.59±0.52

Table-2: Metal-Ligand Stability Constants.

UO2+2 Ce+3 Th+4

L igand logK: logK2 lo gP2 lo g K: L ogK2 lo gP2 lo g K: logK2 lo gP2

8-OHQ 8.55 5.10 13.65 — _{9.30 6.20 15.50} Unak et al.,1993, 1994

2-metil-8OHQ 10.28 10.28 — — — _{C orsini et al., 1971}

7-t-butil-8OHQ 13.40 11.6 25.00 — — — _{C orsini et al., 1971}

5-Cl-7-NH2-8OHQ 9.43 7.61 17.04 — _{11.11 9.38 20.49 U n ak e t al., 1995}

5-SO3H-8OHQ 8.25 4.15 12.40 — _{8.75 6.15 14.90} Unak et al.,1993, 1994

5-C1-8OHQ 11.45 < 0 11.45 12.34 < 0 12.34 12.65 < 0 12.65 T his study 5-I-8OHQ 9.10 0.18 9.28 11.13 < 0 11.13 12.79 0.61 13.40 T his study 5-Cl-7-NO2-8OHQ 11.30 < 0 11.30 11.95 < 0 11.95 12.24 < 0 12.24 T his study 5-I-7-NO2-8OHQ 9.76 < 0 9.76 12.59 0.37 12.96 12.40 < 0 12.40 T his study