TRANSITION METAL(II) COMPLEXES OF A BIOLOGICAL BUFFER - STRUCTURAL AND SPECTROSCOPIC STUDY ON CO(II), NI(II), CU(II), ZN(II), AND CD(II) COMPLEXES OF N-[2-HYDROXY-1,1-BIS-(HYDROXYMETHYL)ETHYL]GLYCINE

The structural and spectroscopic properties of complexes of N-[2-hydroxy-1,1-bis-(hydroxymethyl)ethyl]glycine (thmmg) with Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) were investigated. The complex [Zn(thmmg)2] crystallizes in the space group P2(1)/n, with a = 8.796(2), b = 9.050(3), c = 9.926(2) angstrom, beta = 97.35(1)-degrees and Z = 2; the copper(II) homolog is isomorphous. The complex [Ni(thmmg)2].6H2O Crystallizes in the space group P2(1)/n with a = 8.432(8), b = 8.495(2), c = 15.967(1) angstrom , beta = 95.57(2)-degrees and Z = 2; the cobalt(II) homolog is isomorphous. Ni(II) and Zn(II) complexes show an elongated octahedral coordination arising from two symmetry related amino acid molecules acting as a tridentate chelate through the amino nitrogen, one carboxylate oxygen, and one hydroxyl oxygen; the water molecules in the Ni(II) complex are not involved in metal coordination. The same ligand bonding mode may be suggested also for the Cu(II) and Co(II) complexes, while for Cd(II) only the nitrogen atom and the carboxylate oxygens seem to be involved in metal coordination.