Polarographic Study of Cobalt (II) Complex with
3-Hydroxy-3-o-toly-1-p-sulphonato
(sodium salt) phenyltriazene
Girdhar
Pal Singh, Dr. N.S Chundawat, Dr. R.S. Chauhan* and Dr. A.K. Goswami
Department of Chemistry, M.L. Sukhadia
University, Udaipur – 31 3001 (Raj.), India
*Corresponding Author E-mail: girdharpal@yahoo.com
ABSTRACT:
Polarographic Study of Cobalt (II) Complex
with 3-Hydroxy-3-phenyl-1-p-suphonato(sodium salt) phenyltriazene (HPST) have
been studied in aqueous medium. This is first attempt to study HPST – Co (II)
complexes at d.m.e by Polarography technique in aqueous media in the B-R Buffer
solution between the pH 7.5-8.5. The electrochemical reduction of the complex
is diffusion controlled. Well defined waves are obtained and the E shifts to
more negative side with the addition of HPST. The reduction mechanism indicates
two electron reversible reduction process and the stability constant Log β
value found 6.6.
INTRODUCTION:
Hydroxytriazenes are a class of chelating
agents used extensively for Spectrophotometric studies of transition and non
transition metals1-3. Although the ligands have been studied
in details as spectrophotometric and complexometric reagents, hardly any
attempt has been made on electrochemical behaviour of these ligands and their
metal complexes. Even their electrochemical studies as ligands with transition
metals are of recent origin4. Since the electrochemical
behaviour of electron transfer processes are similar to biological processes.
In view of this the present studies HPST-
Co (II) complexes have been examined Polarographically at d.m.e in aquous
media. The stability constants calculated values are in very good agreement
with the results of Spectrophotometric studies of this system.
MATERIAL AND METHOD:
A- Synthesis-
3-hydroxy-3-o-tolyl-1-p-suphonato (sodium salt) phenyltriazene (0.1M) has been
synthesized by tree step method5 in following manner. In this method
nitrobenzene (12.3 ml) was reduced to Phenyl triazene in the presence of NH4Cl
(5.3 g) at 40-60°C with Zn dust (20g).
Second step involved the preparation of the
diazotized product by adding sodium nitrite (6.9 g) to sulphanilic acid (17.3g)
dissolved in aqueous solution of sodium carbonate (10.6 g in 100 ml).
This solution was added to 40 ml conc. HCl
in 500ml beaker with constant mechanical stirring. Beaker was placed in
freezing mixture to maintain temperature between 0-5°C.
The third step coupling of phenyl hydroxylamine and diazoate products
at 0-5°C in the pH range 4.5-6 with addition of sodium acetate buffer solution.
After complete addition of diazonoum salt, NaCl was added in sufficient
quantity for salting out. The hydroxytriazene was obtained as Brown yellowish3
micro crystals after crystallization from double distilled water. Its purity
was checked by the Physico Chemical Method like M.P and CHN analysis
etc. Results of CHN and M.P. determined %C 47.2, %N 12.7, %H 3.6 and 180oC
respectively. Further the compound was subjected to IR spectral analysis
which yielded the characteristics bands reported for hydroxytriazenes5
and their values for νO-H, νN-H, δN-H and δN-OH are 3550,
3050, 1515 and 1108 respectively. The result establishing purity of
compound.
B- Apparatus and solutions - A Systronics Polarograph 1632 was used for
obtaining current- voltage curves. Metal solution (1M) was prepared
using Cobalt Acetate hexa hydrated and ligand solution was prepared by dissolving
HPST (0.01M) in double distilled water. Briton-Robinson buffer was used to
maintain pH of electrolyte solution. Ionic strength was kept constant by using
KCl as supporting electrolyte. Gelatin (0.002%) was used as maximum suppressor.
The d.m.e. having the following characteristics m = 1.35 mg/sec. t = 1
sec per drop. Solution was deaerated by purging of oxygen free nitrogen through
the polarographic cell. Temperature was maintained at 298 K.
The electrochemical behaviour of Co (II) –
HPST has been studied at d.m.e. in aqueous medium. The shift of half-wave
potentials towards a more negative value4 with
increasing concentration of ligand indicated complex formation and the
diffusion current was found to decrease regularly with increase of HPST
concentration.
RESULTS AND DISCUSSION:
Diffusion controlled nature of each wave
was verified by id Vs C and id Vs 
plots. The plots
were linear in both the cases indicating diffusion controlled nature of the
process.
Investigation of the nature of reduction
process and determination of n (By Heyrovsky-Ilkovic Equation): The slope value of linear plots of
Vs Ede found to be in the range
of 30-33 mV, thereby showing the reversible nature of reduction process
involving two electrons.
The plots of E1/2 Vs log Cx have been found
to be a straight line showing the formation of most stable complex. The value
of coordination number J as determined by slope is 4. This shows that the
complex composition is in 1:2 (M: L) ratio.
The stability constant of the Co (II) –
HPST complex has been determined by classical method of Lingane 7,
as this method is applicable for maximum coordination number and for the
stability constant of highest complex formed. The E ˝ 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.
Here,
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
Thus, the value of log b has been found to be 6.6.
CONCLUSION:
The present work has opened up possibility of studying Co(II) –
hydroxytriazenes complexes by electrochemical method particularly sampled D.C.
polarography. Results obtained with polarography and the log b values obtained are in quite good
agreement with those obtained with spectrophotometric studies of similar
compounds. (Table 1) This proves the validity of polarographic technique for
studies of hydroxytriazene metal complexes6.
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