An X-Ray Diffraction Study on the Structures of Mono(glycinato)zinc(II) and Tris(glycinato)zincate(II) Complexes in Aqueous Solution

Article abstract of DOI:10.1246/bcsj.58.1651

The structure of zinc(II) complexes with glycinate ion in solution was investigated by the X-ray diffraction method.The measurements were performed at 20 deg C for the solutions with the C_gly/C_Zn mole ratios of 1.49 (solution A) and 5.09 (solution B), where C_i denotes the total concentration of species i.From the analysis of the radial distribution curve of solution A, in which comparable amounts of the hexaaqua- and mono(glycinato)zinc(II) complexes existed, it was found that the mono(glycinato)zinc(II) complex combined with four water molecules at the distance of (2.12+/-0.01) Angstroem.The Zn-OH2 bond length within the complex was longer than that within the hexaaquazinc(II) ion (2.08 Angstroem).The Zn-O and Zn-N distances, where O and N denote oxygen and nitrogen atoms within the glycinate ion in the ⁺ complex, were both (2.12+/-0.02) Angstroem.Thus the mono(glycinato)zinc(II) complex had a regular octahedral structure.The nonbonding Zn...C distance was found to be (2.84+/-0.02) Angstroem.The X-ray diffraction data of solution B, which contained the ^- ion as a predominant species, showed that the tris(glycinato)zinc(II) complex had a regular octahedral structure with the both Zn-O and Zn-N bond distances of (2.12+/-0.01) Angstroem.The nonbonding Zn...C(COO), Zn...C(CH2), and Zn...O(O=C) lengths were (2.87+/-0.03) Angstroem, (2.93+/-0.03) Angstroem, and (4.10+/-0.04) Angstroem, respectively.The solubility of the bis(glycinato)zinc(II) complex was so low that the structural determination of the complex by the present X-ray diffraction method was not possible.