Structures of selected transition metal complexes with 9-(2-hydroxyethyl)adenine: Potentiometric complexation and DFT studies

Abstract

The dissociation constants of ligand 9-(2-hydroxyethyl)adenine (9-HOEtAde) and the molecular property stability constant (Kf1) of ML complex has been potentiometrically determined with different media and temperatures. Fe(III) and Cu(II) form very stable ML complexes with Kf1 11.02 and 9.17 respectively in 75% Ethanol-water medium at 25 °C, while Kf1 with Mn(II), Co(II), Ni(II) and Zn(II) range from 6.25 to 6.47. The formation of ML complexes is spontaneous and exothermic. Complexes of Co(II), Zn(II) and Cd(II) with 9-HOEtAde were synthesized and characterized by FTIR, NMR, thermal analysis and elemental analysis. The molecular structural property of Co(II) and Zn(II) complexes were studied by X-ray diffraction. Co(II) atoms in Co(acac)2(9-HOEtAde-N7)2.2H2O (1) displayed octahedral CoO4N2 coordination with four oxygen atoms of acetylacetonate ligands occupying the equatorial plane and two N7 atoms of 9-HOEtAde ligand in the axial plane. While Zn(9-HOEtAde-N7)2Cl2 (2) has a tetrahedral structure with π-π stacking. H-bonding in complexes (1) and (2) results in formation of chains and 3D-supramolecular array. CAM-B3LYP/6-31G(D)/LanL2DZ level of theory predicted the properties of tetrahedral Zn(9-HOEtAde-N7)2Cl2 (2) and the optimized structure was computed by DFT.