An X-Ray Diffraction Study on the Structures of Bis- and Tris(ethylenediamine)zinc(II) Complexes in Solution

An X-ray diffraction study has been carried out at 25 °C for aqueous ethylenediamine(en) solutions of zinc(II) nitrate, the mole ratios, en/Zn, in the solutions being 2.252 and 3.204. In the former solution bis(ethylenediamine)zinc(II) complex existed as the main species, while in the latter tris(ethylenediamine)zinc(II) complex was predominant. The X-ray scattering data of the solution containing the bis-complex showed that four nitrogen atoms within the two ethylenediamine molecules were tetrahedrally coordinated to the zinc(II) ion at a distance of 2.131 (9) Å. The nonbonding Zn…C distance was also determined to be 2.89(2) Å. In the tris-complex in which the zinc(II) ion was coordinated with the six nitrogen atoms, the Zn–N and Zn…C distances were 2.276(5) Å and 3.00(1) Å, respectively. Raman spectra of the solutions supported the structures of the complexes.