Conditions for Crystallization of Various Copper(II) Complexes of Salicylic Acid in Aqueous Solution

Among copper(ll)complexes with salicylic acid, a monomeric, light blue complex, Cu (Hsal)2H20[1] (sal=C6H40000), and a light green one, Cu(sal) H20[3], have already been obtained in an aqueous solution, but conditions for the crystallization of these complexes have not been made clear. The present work was undertaken to clarify what complex species are crystallized out depending upon an initial concentration of copper(II) sulfate and temperature at pH 3.6 and a mole ratio of copper(ll) sulfate to sodium salicylate 1: 2, since the condition for the crystallization was not affected by the mole ratio. Below 50C, the complex [1] was crystallized irrespective of the concentration range of copper(ll), whereas above 50°C the complex [3] was obtained in the concentration of copper(II) above 0.13 mo1-1. In the higher concentrations ranging 0.15∼0.2 mol.l1-l Cu(ll) (