Co-ordination Properties of Sulfanilamide: Equilibrium Studies of Binary Complexes


Shaikh Abdul Rahim1*, Mazahar Farooqui2

1Dept. of Chemistry, Milliya Arts, Sci. and Management College, Beed

2Dept. of Chem. Dr. Rafique Zakariya College for Womens, Aurangabad

*Corresponding Author E-mail:



Study reports interaction between selected metal ions with sulfanilamide in aqueous media at room temperature pH metrically involving Irving Rossoti titrimetric method. Use of cheap and easily reagents NaNO3 and HNO3 are the salient features of the work. Protonation and stability constant values are determined. Order of stability determined which is in agreement with Irving Williams Natural order. Regression analysis is performed so as to get the knowledge of the relationship between the physical properties of metal ions and stability values.


KEYWORDS: pH metry, Irving Rossoti titrimetric method, stability constant values, Irving Williams Natural order.




Sulfur containing ligands are widespread among coordination compounds and are important components of biological transition metal complexes which possess many application like diuretics, antiglacuma or antileptic drugs among others.1The sulfur containing ligands are well known for their anticarcinogenic, tuberculostatic, antifungal, acracidal and antioxidant properties.


Copper complexes of antileptic drug show good efficiency than parent drugs. Recently Fatima A.I. studied metal complexes of sulfamethoxazole, she reported good anticancer behavior against human colon carcinoma cells and hepatocellular carcinoma cells.2 Ananadkumaran et al reported antibacterial, antifungal and antioxidant properties for Schiff’s bases of the sulfanilamide complexes.3 Sulfonamide functional group is responsible for antimicrobial activity which can be altered depending upon the substituent present on the aromatic rings.




Nida et al reported good antimicrobial activities for sulfanilamide metal complexes. It has been reported that biological activity of Sulphur containing ligand increases on complexation.4


Study of metal drug complexes is still in primitive stage. It is a great challenge in synthetic, coordination and bioinorganic chemistry and medicinal chemistry.



All the chemicals used of high purity. Ligand sample was of SD Fine AR grade. All the solutions were prepared in double distilled water. All the solutions were standardized before use by known methods. Metal nitrates were used due to their high solubility in water. 1N(NaNO3) used for maintaining ionic strength. Glass electrode with digital potentiometer (ELICO LI-20) was used for pH measurement. pH meter was calibrated using buffer solution of pH = 4 and pH = 7 before titration. Irving Rossoti5 titrimetric method used for titrations. The experimental procedure involved three titrations (I) HNO3 (A) (II) HNO3 + Ligand (A + L) (III) HNO3 +Ligand + metal (A + L + M) against 0.2 N NaOH. The results obtained for each titration was plotted as a volume of NaOH vs. pH and related volume at succeeding pH determined and calculated. Proton ligand and metal ligand stability constant were determined by using Excel computer programme.


The observed pH values from above three titrations are then plotted against the volume of alkali added. Three titration curves are obtained (Figure 1), corresponding to the titrations mentioned in the experimental part. The titration curves were separated from each other each taking approximately S shape. The end point for the titration increased in the order I > II > III. The maximum value of n did not exceed two for all complexes indicating the formation of 1:1 and 1:2 complexes. Considerable separation of metal complexes curve from reagent curve along volume axis is an evidence for complex formation. The use of very dilute solution ruled out the possibility of formation of polynuclear complexes. Only one pK obtained for sufanilmide.pK1 value 10.3351 obtained is in agreement with the literature values.6-9 This value may be due to-SO2-NH2. Second pK2 value for –NH2 is not detected in our studies. Order of stability for metal complexes observed is Cu (II) > Ni (II) >Pb (II) which in agreement with Irving Williams9 natural order. Higher values of stability reported for Cu (II) complexes than others. The extra stabilization of these complexes may be due to unique electronic configuration of ion. The least stability value reported for lead suggests low affinity of the metal towards ligand than rest members. The order clearly indicates that log K value increases with decreasing atomic radius. Stability values depends upon the ionic size of the metal ions, smaller ions have high stability therefore Cu has highest value. Plot of logK against IP2 gives a straight line. Slight difference between log K1 and logK2 indicates stepwise complex formation.


Regression analysis:

In order to find out the relationship between stability constant and physical properties of the metal ions regression analysis was performed using Origin profession 6.0 programme using equation y= Bx + A, where B is slope and A is intercept to y axis.  Such correlation gives idea about the nature of bonding in complexes and make possible to know the unknown stability constant. It also beneficial in determination of unknown stability values. Values of physical properties taken from F.A.Cotton11. Three physical properties considered for regression and Regression coefficient r values are shown in table 2. It is found that none of the property shows r value above 0.9.Ionisation potential shows good positive correlation r value about 0.83.Electronegativity and ionic radii shows negative correlation r value –0.52.


With respect to increasing electronegativity of the metals, the electro negativity difference between a metal atom and ligand decreases so the metal ligand bond would have more covalent character which results into greater stability of the metal complexes. When stability values are plotted against second ionization potential of metal atoms approximate straight line is obtained as shown in fig.5.


Table.1. Protonation constant and stability constants of metal ion complexes

Metai ion

LOG K1(a)

LOG K2(a)

LOG K1(b)

LOG K2(b)

LOG β(c)







Cu (II)






Ni (II)






Pb (II)






a-Point wise method, b-half integer method, c- average



Figure 1. Titration curve


Figure 2. Protonation curve


Table 2. Regression analysis

Physical property












Ionic radii







Figure 3. Graph of stability values against electronegativity



Figure 2. Graph of stability values against Ionic radii



Figure 5. Graph of stability values vs.IP2



1.     Zahid H. Chohan, Journal of Enzyme Inhibition and Medicinal Chemistry, February 2008; 23(1): 120–130.

2.     Fatima A.I. Khodir, Oriental J.Chem, 31(3), 2015, 1277-1285,

3.     J.Ananadakumaran, M.L. Sundarajan, T.Jeyakumar and M.Nasiruddin, American. Chem.Sci.J. 11(3)2016, 1-14, DIO:10.9734/ACSJ/2016/22807.

4.     NidaIqbal, JavedIqbal, M.Imran, J.ScientificRes.XXXXIX. (1), 2009, 15-19.

5.     Irving H.M. and Rossotti H.S. J. Chem. Soc. (1954) 2904.

6.     Larisa E. Kapinos and Helmut Sigel, Inorgan. Chimica Acta, 337, 2002, 131-142.

7.     M. S. Sun, D. G. Brewer, Can J.Chem.45, 1967, 2729-2739.

8.     Organic structure, mechanism, synthesis, J.David Dawn, Robert J.C., Academic Press, Elsveir, 2018, 80-84.

9.     RedaA.Ammar, Nada M. Arshy, A AlWarthan, Asian J.chem., 6(9), 2014, 2583-2587. 2014.15470

10.   H.Irving, R.J.P.Williams, Nature 162, 1948, 746-747.

11.   F.A. Cotton, G. Wilkinson and P. L. Gaus, Basic-inorganic chem., 3rdedition, 2009, Wiley India pvt.Ltd., 60-71.






Received on 07.04.2018           Modified on 16.05.2018

Accepted on 06.06.2018          © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(9): 4063-4065.

DOI: 10.5958/0974-360X.2018.00747.3