Spectrophotometric Study of Stability Constants of Co(II), Ni(II) and Cu(II) Complexes of 2, 2 – Bipyridine at Different Temperatures

Abstract

Complexation of Co(II), Ni(II) and Cu(II) with 2, 2– bipyridine (bpy) have been studied spectrophotometrically at absorption maxima for Co(bpy), Ni(bpy) and Cu(bpy), of 400, 400 and 680nm respectively. The complexations were carried out at temperatures 30°C, 40°C, 50°C and 60°C at the wavelengths of the respective complexes. The stoichiometry of the complexes were determined using Job’s continuous variation method and the value was found to be 1:2 metal to ligand ratio. Stability constants (K) values were calculated using the continuous variation method and found to be in the order 3.51 x 10³, 3.30 x 10³ and 2.88 x 10³ respectively for Cu-bpy, Ni-bpy and Co-bpy. The complexes were found to be stable over the temperature range used as there was slight change in the color intensity and absorbance values. From the thermodynamic parameters ΔG, ΔS and ΔH values, the reactions were all spontaneous and exothermic.

Keywords: Cobalt(II), Copper(II), Nickel(II), Spectrophotometric, Stability constant, Thermodynamic parameters