COMPLEX-FORMATION OF 5,6-DIHYDROXY-7-OXA- BICYCLO[2.2.1]HEPTANE-2,3-DICARBOXYLIC ACID WITH 3D-TRANSITION ELEMENTS

Binary carboxylate complexes of bivalent 3 d-transition metal ions wit h oxa-bicyclo[2.2.1]heptane-2-exo,3-cis-dicarboxylic acid (2) have bee n synthesized in aqueous solution and characterized by elementary anal ysis, infrared and electronic spectra and magnetic susceptibility meas urements. The coordination compounds have been found to undergo therma l decomposition with loss of water molecules, followed by the organic ligand to give metal oxides. The stability constants of the complexes have been determined by potentiometric measurements. It could be shown by X-ray analysis, that the dicarboxylate anion of 2 has different co ordination behaviour in complexes [NiL2(H2O)3] . H2O (2c) and [CuL2(H2 O)2] . 2H2O (2d), respectively. In 2c it acts as a tridentate chelatin g ligand forming together with three water molecules an only slightly distorted octahedral coordination sphere and its hydroxyl groups are c oordinatively inactive. In 2 d, however, the oxygen atom of one hydrox yl group is included in coordination and by its interaction with a Cu atom of a neighboring molecule a polymeric chain structure is built up in the crystal. Two corners of the tetragonally extended coordination octahedron are occupied by water molecules. In both complexes the mol ecular packing is stabilized by a network of hydrogen bonds in which a lso the crystal water molecules are included.