Speciation of cobalt, nickel and zinc-ethylenediaminediacetate complexes with N-heterocycle ligand – Synthesis, spectroscopic and structural studies

Cobalt, nickel and zinc N-heterocycle chelated ethylenediaminediacetates [Co(edda)(phen)]·(NH4Cl)·1/3H2O (1), [Ni(edda)(phen)]·3H2O (2), [Co(edda)(bpy)]·(NH4Cl)·2H2O (3), [Ni(edda)(bpy)]·4H2O (4), [Zn(edda)(bpy)]·4H2O (5) (H2edda = ethylenediaminediacetic acid, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) were isolated in pure forms and characterized spectroscopically. The X-ray structural analyses reveal that neutral mononuclear complexes contain both edda and phen/bpy ligands. Divalent metal ions are octahedrally bound by a bidentate phen or bpy ligand, and a tetradentately edda through carboxyl and amine groups. The co-existences of phen/bpy and edda in the complexes show no decomposition between phen/bpy and edda ligands. This is supported by the trace of 13C NMR spectra with less-bound zinc complex. Further comparisons of the bond distances between Co2+/Ni2+/Zn2+ ions with edda indicate that cobalt and nickel interact much stronger than those of zinc complexes.