POLAROGRAPHIC BEHAVIOUR OF SOME DIVALENT METAL COMPLEXES OF 4-METHOXYBENZALDEHYDE THIOSEMICARBAZONE

Analysis of the complexes formed by 4-methoxybenzaldehyde thiosemicarbazone with Manganese (II), Iron (II),Cobalt (II) ,Nickel (II) and Zinc(II) metal ions was made through the polarographic technique. 4-methoxybenzaldehyde thiosemicarbazone was obtained by the reaction of hydrazinecarbothioamide with para-methoxybenzaldehyde in ethyl alcohol. Polarographic technique is best suited for the study of coordination complexes and their substitution reactions and more significantly the technique is especially useful in calculating stability constant of complexes that are formed by direct combination of metal ion and the ligands. A sharp change is observed in the E 1/2 values of the transition metal ions in presence of the ligand indicating complexation .Irreversible polarographic behaviour has been

Analysis of the complexes formed by 4-methoxybenzaldehyde thiosemicarbazone with Manganese (II), Iron (II),Cobalt (II) ,Nickel (II) and Zinc(II) metal ions was made through the polarographic technique. 4-methoxybenzaldehyde thiosemicarbazone was obtained by the reaction of hydrazinecarbothioamide with para-methoxybenzaldehyde in ethyl alcohol. Polarographic technique is best suited for the study of coordination complexes and their substitution reactions and more significantly the technique is especially useful in calculating stability constant of complexes that are formed by direct combination of metal ion and the ligands. A sharp change is observed in the E 1/2 values of the transition metal ions in presence of the ligand indicating complexation .Irreversible polarographic behaviour has been shown in all the compounds studied and kinetic parameter α n and k o f ,h have been calculated .All the complexes prepared were found to have 1:2 stoichiometry.

…………………………………………………………………………………………………….... Introduction:-
The ligands Thiosemicarbazone are found to be of significant interest due to their structural diverseness , biological applications ,bonding modes and ability of ion sensing (1) . Thiosemicarbazones are basically obtained by combining a thiosemicarbazide either with an aldehyde or with a ketone and represent an important class of useful ligand type for obtaining coordination spheres with mixed N and S donors. Thiosemicarbazones are widely studied in coordination chemistry , analytical applications (2) and pharmacology (3). Derivatives of thiosemicarbazones having general formulae R 1 R 2 C=N-NH-C(=S)-NR 3 R 4 have presented a broad spectrum of properties against a number of diseases due to their antifungal (4) , antibacterial , antidiabetic (5), anticancer (6) and antiinflammatory (5) activities . Introduction of metal ions like Cu(II), Co(II) and Ni(II) into the thiosemicarbazone ligands dramatically increases or decreases their biological activities like antibacterial, anti HIV, antifungal and antiinflammatory (7)(8)(9)(10). A wide range of survey on the importance and utility in various fields of the transition metal complexes of substituted thiosemicarbazone have revealed the pharmacological importance of both ligand as well as complex (11). In the Present work attempt has been made to establish the stoichiometry by polarographic studies of substituted thiosemicarbazone complexes with the number of transition metal ions such as Mn(II), Fe (II) ,Cobalt(II) ,Nickel(II), and Zinc(II) metal complexes.
Polarography is the technique based on current voltage curve obtained on electrolysis of solution of electrooxidisable or reducible substance at d.m.e (i.e dropping mercury electrode) . The technique of polarography was ISSN: 2320-5407 Int. J. Adv. Res. 9(02), 751-765 752 developed for the first time in 1922 by Heyrovsky (12). Polarography is a voltammetric technique (Voltammetry comprises a group of electrochemical methods in which information about the analyte is derived from the measurement of current as per a function of applied potential). Usually this method is successfully employed with reversible waves to study the complex formation and also to calculate the stability constant etc. Half wave potential or (E 1/2 ) may be defined as the potential on a polarographic curve at which the current reaches half of its limiting value. E 1/2 value is dependent on the nature of electrolyzed substance and therefore on the constitution of the solution .It is a quantity that may be used to reflect chemical effects, such as complexation of the electro active substance (13) The reduction wave of polarograph of a simple aqua metal ion is shifted in the direction of more negative potential on addition of a complex forming agent .Direct computation of the shifting in half wave potential can serve for the determination of stability constants of complexes in solutions , provided that the reaction occurring at the dropping mercury electrode is reversible. With suitable modifications , however the irreversible cases can be studied within many instances (14).
Only in a few cases direct application of simple theory serves for the determination of stability constants. In a number of cases the reduction waves have been found to be both kinetically controlled as well as diffusion controlled and the rates of dissociation of complex species control to a greater or lesser extent , the shapes of waves .Systems that consists of several complexes are encountered in which both reducible and non reducible species occur , in which equilibria between some species are less mobile than others .The overall kinetics of many of such systems have been elucidated and the nature , structure and behaviour of each species identified in addition to the calculation of their stability constant . From such applications it has been established that polarographic technique may be employed as a useful tool for the determination of the structure of the complexes . The value of E 1/2 and αn are obtained from plot of log − -0.546log t vs E d.e.
Literature survey:-Complex forming agents are widely used as reagents in various titrimetric , spectrophotometric , polarographic and electrophoretic methods. Substituted thiosemicarbazones represent an imperative class of Nitrogen and sulphur donor ligands over past few decades of time on account of their varying donor properties, structural divergence and biological utility (15) . For their biological and medicinal importance chemistry of thiosemicarbazones have been widely studied in the field of coordination chemistry (16) . Thiosemicarbazones may act as flexible polydentate chelating ligands that may coordinate with various transition metal ions by coordinating through the sulphur (S) as well as hydrazinic nitrogen (N) atoms (17,18) .A number of workers have investigated thiosemicarbazones polarographically at d.m.e (19,20). Polarographic behaviour of Thiosemicarbazones of Fe (II)and Zn (II) was studied by Sugam Shivhare (21).Polarographic studies of cobalt (II) in different supporting electrolytes reveals the existence of reversible and irreversible cathodic waves .Positive shift in E 1/2 value has been reported by many workers (22).Well defined cathodic waves are observed in the reduction of nickel (II) at d.m.e in presence of supporting electrolytes. The important feature of electrochemical reduction of Nickel (II) at d.m.e is + shift in the half wave potential on complexation. For simultaneous determination of copper and cobalt differential pulse polarography has been employed and Well-defined diffusion-controlled waves were obtained for both systems. Both Reversible as well as irreversible waves have been observed for copper (Cu) and cobalt (Co) systems, respectively (23) 753

Experimental :
Ligand (structure.1) was synthesized by the reaction of hydrazinecarbothioamide with paramethoxybenzaldehyde in ethanol . Purity of ligand was checked before use.

Structure.1
All the chemicals used such as Potassium nitrate ,Potassium chloride, Manganese Sulphate , Ferrous ammonium sulphate ,Nickel sulphate, Cobalt sulphate and Zinc sulphate etc. were of AnalaR B.D.H grade .standard solutions of metal ions were prepared in doubly distilled air free conductivity water . Freshly prepared 0.1% solution of gelatin was used as maximum suppressor to avoid ageing and hydrolysis.

Apparatus:
A Toshniwal manual Polarograph associated with pye galvanometer was used .The polarograph contained saturated calomel electrode connected to a cell through a salt bridge .Triply distilled mercury was used as d.m.e. Alkali accumulators were used to give a voltage of 4 volts.

Procedure:
Various known volumes of standard solutions of metal ions and ligands were mixed in pyrex tubes fitted with stoppers. The deaeration of these solutions was done by passing purified nitrogen for ten minutes.

Conclusion:-
In the current work we have discussed the polarographic behaviour of thiosemicarbazones of Manganese(II), Iron(II),Cobalt (II) , Nickel (II) and Zinc(II) metal ions . Polarographic measurements have proved the complex formation of thiosemicarbazones with these metal ions. Keeping in view the biological as well as therapeutical