Coordination of Metal Ions by Indolic Acids. Complexes of Indole-2-Carboxylic, -3-Acetic, -3-Propanoic and -3-Butanoic Acids With Some Divalent Metal Ions

Metal complexes of indole-2-carboxylic (ICH), -3-acetic (IAH), -3-propanoic (IPH) and -3-butanoic (IBH) acids, were prepared and characterized by means of thermal analysis, magnetic measurements. ESR. IR and electronic spectroscopy. While Cu(IA)2 · H2O, Cu(IP)2 · H2O, Cu(IP)2 and Cu(IB)2 are tetracarboxylatebridged dimers of the copper(II) acetate monohydrate-type, Cu(IC)2 · 2H2O appears to be monomeric with the copper atom in square planar coordination involving two carboxylate groups and two water molecules. Six-coordination at the metal ions, most likely involving bjdentate carboxylate groups and water molecules, is suggested for the complexes M(IC)2 · 2 H2O (M=Co, Ni, Mn and Zn). All the ligands appear to behave as simple carboxylic acids, being able to coordinate metal ions through the carboxylic groups alone.