Abstract: Two long-chain multidentate ligands, 2,9-di(n-2′,5′,8′-triazanonyl)-1,10-phenanthroline (L1) and 2,9-di(n-4′,7′,10′-triazaundecyl)-1,10-phenanthroline (L2), were synthesized and characterized using 1H NMR and elemental analysis. The thermodynamic properties of the ligands and their complexes with transition metal ions and rare earth metal ions were investigated using potentiometric titrations. The coordination capabilities of the ligands with the transition metal ions followed the Irving-William sequence: Co(II)Zn(II). The stability constants of the ligands with the rare earth metal ions increase from La(III) to Gd(III). The coordination ratio of the ligands and the metal ions is 1?1. The similarities and the differences between the two series of complexes were studied. In addition, the factors influencing the results were researched. The results of this study indicate that all rare earth complexes in this study have the species 11-1, which can catalyze the hydrolysis of biological macromolecules. This property means that they are potentially useful as a good model of hydrolysis enzyme that has the capacity to cleave DNA and diester phosphate.

Key words: 1,10-phenanthroline, Transition metal ion, Rare earth metal ion, Stability