Interactions between Pr(III) & Sm(III) Cations

Published Date: 24 Jan 2018

pH-metric study of substituted3,5-diaryl isoxazolines complexes in 70% Dioxane solvent media .

S.A.Thorat¹,S.D.Thakur²

ABSTRACT:-

The complex formation between Pr(III)&Sm(III) metal ions and 3-(2-hydroxy-3-nitro-5-methylphenyl)-5-(2-phenylethenyl)isoxazoline[HNMP2EI]L₁,3-(2-hydroxy-3-bromo-4-nitro-5-methyl)-5-(4-methoxyphenyl)isoxazoline[HBNM4MI]L₂,3-(2-hydroxy-3-bromo-4-nitro-5-methyl)-5-(3-nitrophenyl)isoxazoline[HBNM3NI]L₃have been studied at 0.1M Ionic Strength (26±0.1)^oC in 70% Dioxane water mixture by Bjerrum method as adopted by Calvin & Wilson .It is observed that Pr(III)&Sm(III) metal ions form 1:1 & 1:2 complexes with ligand L_1,L₂&L_3.The data obtained were used to estimate & compare the values of proton ligand stability constant (p^K) & metal ligand stability constant (log K).From estimated data (p^K & log K),the effect of substituents were studied.

Key Words:-Substituted 3,5-diarylisoxazoline,Dioxane-water mixture,stability constant.

1.INTRODUCTION:-

The studies in metal ligand complexes in solution of a number of metal ion with carboxylic acids, oximes, phenol etc. Would be interesting which throw light on the mode of storage and transport of metal ions in biological Kingdom.Metal with the view to understand the bioinorganic chemistry of metal ions, Banergee et al^[1] have synthesized a no. of mixed ligand alkaline earth metal complexes. Bjerrums ^[2] dissertation has taken the initiative to develop field. Metal complexation not only brings the reacting molecules together to give activated complex ^[3] but also polarized electrons from the ligand towards the metal. The relation between stability and basicity of ligands is indicated by the formation constant and free energy change value Bulkier group increases the basicity of ligands as well as stability. The stability of complexes is determined by the nature of central metal atom and ligands. Poddar et al ^[4] investigated stability constants of some substituted pyrazolines,isoxaline and diketone Karalmai et al ^[5] have studied formation constants and thermodynamic parameters of bivalent metal ion complexes with3-amino-5-ethyl isoxazole Schiff bases and N,N;N,O and O,O donar ligands in solution.Recently Tihile ^[6] studies on interaction between cu (II), Cr(II), Nd(II) and Pr(II) metal ions and substituted hydroxyl chalcones at 0.1 M ionic strength pH metrically. Thakur et al ^[7,8] have studies the influence of dielectric constants of medium on the complex equilibrium of substituted hydroxyl-1,3- propandiones with Cr(II) metal ions and studies on interaction between Cu(II), Cr(II) and Ni(II) metal ions at 0.1M ionic strength pH metrically. Isoxazolines posses medicinal activities such as anti-inflammatory^[9],antibacterial,anticonvulsant^[10],antibiotic^[11],antituberculer^[12], antifungal^[13]and anxiolytic activity^[14].

In present work an attempt has been made to study the interactions between Pr(III)&Sm(III) Cations At 0.1 M Ionic Strength with Ligand at 0.1 ionic strength,pH metrically in 70% Dioxane-water mixture.

2. MATERIALS AND METHODS

The ligands L_1,L₂,&L₃ was synthesized in the laboratory by known literature method. The purity of these compounds exceeds 99.5% and structures were confirmed by NMR, IR and melting points. The stock solutions of the ligand was prepared by dissolving required amount of ligand in a minimum volume of dioxane subsequently diluted to final volume. Metal ion solution was prepared by dissolving metal nitrate (Sigma - Aldrich) and standardized by EDTA titration method as discussed in literature . Carbonate free sodium hydroxide solution was prepared by dissolving the Analar pellets in deionised water and solution was standardized 22. The stock solution of percholric acid was prepared and used after standardization 23.

2.1. Measurements

All measurements were carried out at (26±0.1) ⁰C. Systronic microprocessor based pH meter with magnetic stirrer and combined glass and calomel electrode assembly used for pH measurements. The sensitivity of pH meter is 0.01 units. The instrument could read pH in the range 0.00 to 14.00 in the steps of 0.005. The pH meter was switched on half an hour before starting the titration for initial warm up of the instrument. It was calibrated before each titration with an aqueous standard buffer solution of pH 7.00 and 9.20 at (26±0.1) ⁰C prepared from a 'Qualigens' buffer tablets. The hydrogen ion concentration was measured with combined glass electrode.

2.2. Procedure

The experimental procedure involved the titrations of

i. Free acid HClO₄ (0.01 mol.dm^-3)

ii. Free acid HClO₄ (0.01 mol.dm^-3) and ligand (20 x 10^-4 mol.dm^-3)

iii. Free acid HClO₄ (0.01 mole dm^-3) and ligand (20 x 10^-4 mol.dm^-3) and metal ion (4 x 10^-4mol.dm^-3) against standard carbonate free sodium hydroxide

(0.15 mol.dm^-3) solution using Calvin-Bjerrum and Calvin-Wilson pH titration techniques. The ionic strength of all the solutions were maintained constant by adding appropriate amount of NaClO₄ solution. All titrations were carried out in 70 percentages of Dioxane-water mixtures and reading were recorded for each 0.1 ml addition. The curves of pH against volume of NaOH solution were plotted (fig 1-3). The Proton-Ligand constants were calculated from pH values obtained from the titration curves using the Irvin-Rossotti method and MATLAB computer program (Table 1) .

3. RESULTS AND DISCUSSION

The extent of deviation may be the dissociation of -OH group. 3-(2-hydroxy-3-nitro-5-methylphenyl)-5-(2-phenylethenyl)isoxazoline[HNMP2EI]L₁,3-(2-hydroxy-3-bromo-4-nitro-5-methyl)-5-(4-methoxyphenyl)isoxazoline[HBNM4MI]L₂,3-(2-hydroxy-3-bromo-4-nitro-5-methyl)-5-(3-nitrophenyl)isoxazoline[HBNM3NI]L₃ may be considered as a monobasic acid having one replaceable H⁺ ion from phenolic -OH group and can be represented as

HL H⁺ + L

The titration data were used to construct the curves [acid curve (A), acid + ligand curve (A+L) and acid + ligand + metal ion curve (A+L+M)] between volume of NaOH against pH.The proton-ligand formation number n_A were calculated by Irving and Rossotti expression (Table1)

Where γ denotes the number of dissociable protons, N is the concentration of sodium hydroxide(0.15 mol.dm-3), (V₂-V₁) is the measure of displacement of the ligand curve relative to acid curve, where V₂ and V₁ are the volume of alkali added to reach the same pH reading to get accurate values of (V₂-V₁): the titration curves were drawn on an enlarged scale: E⁰ and T_L⁰are the resultant concentration of perchloric acid and concentration of Ligand, respectively. V₀ is

the initial volume of reaction mixture (50 cm³). Proton-Ligand stability constant p^k values of Ligand were calculated by algebraic method point wise calculation and also, estimated from formation curves n_A Vs p^H (Half integral method) by noting p^H at which n_A = 0.5[Bjerrum 1957] (Table 2).

Metal-Ligand stability constants (log k) were determined by the half integral method by plotting á¹… Vs pL. The experimental á¹… values determined using expression

Where N, E⁰, V_o and V₂have same significance as in equation (1), V₃ is the volume of NaOH added in the metal ion titration to attain the given p^H reading and T_M⁰ (4 x 10^-4 mol dm-3) is the concentration of metal ion in reaction mixture. The stability constants for various binary complexes have been calculated ( Table 3).

3.1. Metal Ligand Stability Constant (Log K)

It is observed that (Table3 a-c ) sufficiently large difference between log K₁& logK₂Values of Sm(III)for ligand L₁ & L₂&Pr(III) for ligand L₃ indicates the stepwise formation of complex between metal ion and ligand except Pr(III)for ligand –L₁;&L₂ & Sm(III)for ligand L₃. It showed that less difference between log K₁ & log K₂ values indicates complexes are occurring simultaneously. The higher value of ratio(Log K1/ Log K2) forPr(III)- Ligand- L₁ &L₃ & Sm(III)-ligand-L₂ complex indicates the more stable stepwise complex formation as compare to Sm(III) –Ligand-L₁ &L₃ &Pr(III)-Ligand L₂ complexes.

3.2. Proton-Ligand stability constant (pK):-

It is observed from titration curve in (fig.1,2,3)shows that the ligand curves starts deviating from free acid (HClO4) curves at pH > 2.12,2.0,&2.14 respectively. The extent of deviation s may be the dissociation of –OH group completely.

4. CONCLUSION

From the titration curve, it is observed that the departure between (Acid + Ligand) curve & (Acid+Ligand +Metal) Curve for all system of L₁,L₂,&L₃ started from pH=2.12 to 3.38, this indicate the commencement of complex formation. Also change in color from yellow to brown in pH range from 3.35 to 10.07 during the titration showed the complex formation between Metal & Ligand.

Table no.1 :Proton Ligand Formation number (á¹…_A) at (26±0.1)⁰C and at ionic strength µ=0.1 moldm^-3 NaClO₄ in 70%Dioxane-Water mixture.

a) System : HBMP2EI(L₁)

b) System : HBNM4MI(L₂)

c) System : HBNM3NI(L₃)

Table 2: Proton Ligand Stability Constant p^K

Table 3: Metal Ligand Stability Constant(Log K)

a) HNMP2EI (L₁)

b) HBNM4MI(L₂)

c) HBNM3NI(L₃)