A study of the complexation and extraction of Cu(II) sulfate and Ni(II) sulfate by N3O2-donor macrocycles

Comparative solvent extraction (water/chloroform) studies of Ni(II) and Cu(II) employing a dinonyl-substituted N3O2-donor macrocycle (L2) as extractant have been undertaken from sulfate, chloride, nitrate and acetate-containing aqueous media. Contrary to expectations, efficient extraction of both metal sulfates was observed, the degree of extraction being comparable (or slightly enhanced) relative to that observed for each of the other anionic systems. X-Ray diffraction studies of [NiL1(H2O)3]SO4 x 4H2O and [CuL1(H2O)]SO4 x 6.67 H2O (where L1 is the unsubstituted derivative of L2) show that each complex occurs as a hydrogen-bonded 'cluster', with the sulfate anions involved in hydrogen bonded networks that incorporate ligand amine protons and water molecules; in the copper complex, which adopts a dimeric arrangement, simultaneous sulfate binding to a copper site is also present. In each complex the macrocyclic ligand fails to coordinate via its ether oxygen donors but instead is arranged so that the metal ion and sulfate anions are somewhat shielded hydrophobically from the exterior of the complex cluster assembly.