Structure and bonding of mononuclear and homobinuclear chelates of some divalent metal ions with the ligand 1,8-dihydroxyanthraquinone

Abstract

The chelating ability of 1,8-dihydroxyanthraquinone with the divalent metal ions Cu(II), Ni(II), Mn(II), and Zn(II) has been studied. The Cu(II) and Ni(II) metal ions gave both mononuclear and homobinuclear chelates, while Mn(II) and Zn(II) gave only the mononuclear chelates. It is therefore evident that 1,8-dihydroxyanthraquinone can coordinate to the divalent metal ions either through its monoanionic form as a chelating bidentate ligand or through its dianionic form as a chelating tridentate ligand. In the homobinuclear chelates each metal ion is bonded to two terminal oxygen atoms and shares two bridging oxygen atoms with the other metal ion. Most of the chelates were found to contain also molecules of water either as coordinated and/or as crystalline water. The mononuclear and homobinuclear chelates of Cu(II) and Ni(II) gave, on reaction with pyridine, adducts which are also discussed. The structure and bonding of these chelates are discussed in relation to their spectroscopic and magnetic data.