METAL-ION COMPLEXATION IN AQUEOUS-SOLUTION BY 5-THIA-2,8-DIAZANONANE-N,N'-DIACETIC ACID.

The stability constants of the open-chain 5-thia-2,8-diazanonane-N,N′-diacetic acid with Mg(II), Ca(II), Mn(II), Co(II), Ni(II), Zn(II), Cd(II) and Pb(II) have been determined in aqueous solution (25°C, ionic strength 0.1 mol dm−3 KNO3) by pH potentiometry. The complexation enthalpy change with Cu(II) has been determined by adiabatic calorimetry. The electronic absorption spectra of the Cu(II) and the Ni(II) complexes were recorded. The complexation properties of the ligand are compared with those of the macrocyclic homologue 1-thia-4,7-diazacyclononane-N,N′-diacetic acid. The influence of N-acetic acid substitution on the parent linear diamine 5-thia-2,8-diazanonane is discussed.