Equilibrium and solution structural study of the interaction of tri- and tetra-dentate polyimidazole ligands with transition metal ions

Copper(II) and zinc(II) complexes of two polyimidazole derivatives, 4-(imid azol-4-ylmethyl)-2-(imidazol-2-ylmethyl)imidazole (TRIM) and bis[4-(imidazo l-4-ylmethyl)-imidazol-2-yl]methane (TIM), containing three and four methyl ene-linked imidazole rings as donor groups, have been studied by potentiome try, UV-VIS, EPR and NMR spectroscopic methods. The data revealed that both ligands form extremely stable and varied complexes with zinc(II) and coppe r(II). In equimolar solutions of the metal ions and TRIM, two and three imi dazole co-ordinated MAH and MA species were formed. The complex Zn(TRIM) pr obably has tetrahedral geometry. The formation of bis-complexes has also be en detected with the ligand in excess. The data revealed 6N and 5N co-ordin ated central ions in ZnA(2) and CuA(2), respectively. In MA complexes of TI M, the ligand is co-ordinated to the metal ions via all the four imidazole units. Formation of bis-complexes has only been found in the zinc(II) conta ining system. Ternary systems of zinc(II)-TRIM and -TIM have also been stud ied with L-cysteine as a second ligand. The potentiometric and NMR results established the formation of ternary complexes with different protonation s tates in relatively high amount, in spite of the high stability of the pare nt complexes.