Spectrophotometric Studies of Cobalt(II) and Copper(II) Chelates of 2‐Picolylamine

Abstract

Cobalt (II) and copper (II) chelates of 2‐picolylamine have been studied spectrophotometrically in aqueous solution. Formation of 2‐picolylamine chelates was pH dependent, and the optimum pH range of the cobalt (II) chelate was at pH 8.8‐9.6, and copper(II) chelate at 4.7‐6.8, respectively. The mole ratio of 2‐picolylamine to both of metal(II) ions was found to be 2 to 1 stoichiometry. The spectrophotometric sensitivities are 0.23γ of Co/Cm2 and 8.9γ of Cu/Cm3, at 373 mμ, pH 9.0 for Co(II) chelate and 588 mμ, pH 6.0 for Cu (II) chelate. The stability constants (logK) of the chelates CoL22+ and CuL22+ have been evaluated at a constant ionic strength of 0.10 at 20, 25, 30, 35 and 40°C. Enthalpy and entropy changes characterizing the formation of the chelates have been calculated at 25°C The results are collected as follows: