Polarographic Studies on Ni (II) Chelates of
3-Hydroxy-3-Phenyl-1-p-Sulfonato (Sodium Salt) Phenyltriazene and
3-Hydroxy-3-p-Tolyl-1-p- Sulfonato (Sodium Salt) Phenyltriazene
Neelam Pareek, Pooja joshi, Dipen Upadhyay, Girdharpal
Singh, R.S. Chauhan and A.K. Goswami*
Coordination Chemistry Lab., Dept. of Chemistry, M.L.
Sukhadia University, Udaipur – 31 3001 (Raj.), India
*Corresponding Author E-mail: akumargoswami@rediffmail.com
ABSTRACT:
Polarographic studies of Ni (II) -
3-hydroxy-3-phenyl-1-p-sulfonato (sodium salt) phenyltriazene (HPST) and Ni
(II) - 3-hydroxy-3-p-tolyl-1-p-sulfonato (sodium salt) phenyltriazene (HTST)
have been done in aqueous medium. The study deals with influence of methyl
group at para position of the present compounds, upon the stabilities of the
metal chelates formed by them. Both systems are reversible and diffusion
controlled in nature.
KEYWORDS: Ni (II) - 3-hydroxy-3-phenyl-1-p-sulfonato (sodium
salt) phenyltriazene, 3-Hydroxy-3-p-tolyl-1-p-sulfonato (sodium salt)
phenyltriazene, Polarographic reduction, Chelate.
INTRODUCTION:
In the present work complex formation of Ni (II) with
3-hydroxy-3-phenyl-1-p-sulfonato (sodium salt) phenyltriazene and
3-hydroxy-3-p-tolyl-1-p-sulfonato (sodium salt) phenyltriazene have been
examined polarographically and stability constants for both cases have been
determined. The electro-chemical reduction of these complex ions is two electrons
reversible process.
MATERIALS AND METHOD:
Synthesis:
The compounds 3-hydroxy-3-phenyl-1-p-sulfonato (sodium
salt) phenyltriazene
(HPST) and 3-hydroxy-3-p-tolyl-1-p-sulfonato (sodium
salt) phenyltriazene (HTST) have been synthesized as per as reported method1.
Their purity was checked by m.p. determination and CHN analysis. M.P. was
found 157°C and 170°C respectively. The theoretical and experimental values
of %C, %N and %H were found (for HPST) to be (Th.) 43.2, 12.6, 3.6 and (Exp.)
42.2, 12.6, 3. and for HTST (Th.) 40.90, 11.01, 2.91 and (Exp.) 40.31, 11.22,
2.90 respectively.
Further the compounds was subjected to IR spectral
analysis which yielded the characteristics bands reported for hydroxytriazenes2
and their values for νO-H, νN-H, δN-H
and δN-OH are 3450, 3190, 1590 and 940 respectively. The
IR spectra confirmed their presence establishing purity of compounds.
Apparatus and solutions:
A Systronics Polarograph 1632 was used for obtaining
current- voltage curves. Metal solution (1mM) was prepared using nickel
sulphate heptahydrate and ligand solutions were prepared by dissolving HPST and
HTST (.01M) in double distilled water separately. Citric acid and Na2HPO4
solutions were used as buffer to maintain pH of test solution. Ionic strength
was kept constant by using KCl as supporting electrolyte. Gelatin (.002%) was
used as maximum suppressor. The D.M.E. had the following characteristics: m =
1.35 mg/sec.; t = 1 sec / drop.
Solution was deaerated by purging of oxygen free
nitrogen through the polarographic cell for about 20 minutes. Temperature was
maintained at 298 K.
Study of Ni (II) – HTST System:
Solutions of Ni (II) 1 mM mixed with various
concentrations of ligands were prepared from the stock solution and
polarographed. The shift of half-wave potentials towards a more negative value
with increasing concentration of ligand indicated complex formation and the
diffusion current was found to decrease regularly with increase of ligand
concentration.
RESULTS AND DISCUSSION:
A single well defined wave was obtained for Ni (II)
–HPST and Ni (II) – HTST systems between pH 7.5 to 8.5 and 6.5 to 7
respectively. Diffusion controlled nature of each wave was verified from id Vs
C and id Vs plot.
Where id =diffusion current in µA
C= Conc. of ligand in mole lit1-
h = height of mercury column.
Slope of the linear plots of Vs Ede was
found to be in the range of 30-32 mV, thereby showing the reversible nature of
reduction process involving two electrons.
Determination of coordination number:
The plot of half wave potential E1/2 Vs log
Cx (where Cx = concentration of ligand in mole lit1-)
have been found to be a straight line showing the formation of most
stable complex. The coordination number (J) of the metal in the complex is
obtained from the slope of this plot, as may be expressed by:
Where n = no. of electrons involved (here n = 2). The
value of j as determined by slope is 4. This shows that the complex composition
is in 1:2 (M: L) ratio.
Determination of stability constant:
The stability constant log b of the complexes has been determined by classical
method of Lingane3, as this method is applicable for the stability
constant of highest complex formed. The DE1/2 has a linear correlation with ligand
concentrations; which shows that there is only one complex formed in the
solution. The following equation has been used to calculate the stability
constant of the complex studied.
DE
= Difference of half wave potentials
of simple metal ion and complexed ion.
N = Number of transferred electrons
Log b =
Stability constant of complex formed.
J = Coordination number
Cx = Concentration of ligand
The value of log b has been found to be 10.88 for Ni (II) – HPST and
11.01 for Ni (II) – HTST. Polarographic data are given in Table I.
CONCLUSION:
A comparison of the values of overall stability constants
of Ni (II) chelates of para substituted hydroxytriazene with parent
hydroxytriazene reveals that the stabilities of chelate given by methyl substituted
compound are higher than those of the parent hydroxytriazene. This is due to +
I effect (electron pushing) of the methyl group.
REFERENCES:
1.
Mehta C, Ph.D Thesis, “3-Hydroxy-3-alkyl
or aryl-1-phenyltriazenes in copper determinations.” M. L. Sukhadia
University, Udaipur 1992.
2.
Purohit DN, Spectro
Chimica Acta, 1985; 41(A); 873.
3.
Lingane J, J. Chem.
Rev., 1941; 21; 1.