Mixed-ligand iridium(IV) complexes with amino acids, adenine and hypoxanthine

The complexation in iridium(IV)-purine base (adenine, hypoxanthine)-amino acid (α-alanine, aspartic acid, lysine) systems was studied by pH titration. The stability constants of 1 : 1 : 1 complexes were determined. The stability of 1 : 1 : 1 mixed-ligand complexes with hypoxanthine and adenine increases in the series Ala < Lys < Asp. Reactions between aqueous solutions gave the following coordination compounds: [Ir(C5H 4N4O)(C3H6NO2)Cl]Cl 2, [Ir(C5H4N4O)(C4H 5NO4)]Cl2, [Ir(C5H4N 4O)(C6H13N2O2)]Cl 3, [Ir(C5H5N5)(C3H 6NO2)]Cl3, [Ir(C5H5N 5)(C4H5NO4)]Cl2, and [Ir(C5H5N5)(C6H13N 2O2)]Cl3. The individual character of the complexes was established by chemical and thermogravimetric analyses and powder X-ray diffraction. The complexes were characterized by NMR, IR, and X-ray photoelectron spectroscopy. Alanine and lysine in mixed-ligand iridium(IV) complexes are bidentate (α-NH2 and COO- groups), aspartic acid is tridentate, and purine bases function as polydentate ligands through heterocycle N atoms and functional groups (NH2 in adenine and C=O in hypoxanthine). © Pleiades Publishing, Ltd., 2010.