Physicochemical Studies on Cu(II)‐Ferron Complexes

Experiments were carried out at 25° C and μ of 0.1 M . Spectrophotometric and potentiometric methods gave the ionization constants of ferron, p K 1 =2.50±0.02 and p K 2 =7.12±0.02. Cu(II) and ferron form a sparingly soluble 1:1 complex, [Cu(H 2 O) 2 L] 0 (L: ferronate ion) which in higher acidity media, protonates to give [Cu(H 2 O) 2 HL] + and in lower acidity media, ionizes to give [Cu(H 2 O)(OH)L] − . At p H 2.3, the 1:1 complex gives a minimum solubility and the intrinsic solubility was found to be 1.1×10 ‐4 . The Job's continuous variation method and the molar ratio method gave a formation constant (– p K) for Cu 2+ +L z− ⇌CuL, 10.8±0.1 in the p H range of 0.64 to 1.18 and in the p H range of 5.0 to 5.5 (optimum p H condition for formation of complex), the stoichiometry of the Cu(II)‐ferron chelate is essentially 1:2 (Cu:L) but with slight tendency to form 1:1 chelate if [L]/[Cu] is less than 2. The overall formation constant (– p K) was determined to be 20.0±0.3.