Carbon-13 nuclear magnetic resonance study of metal complexes of ethylenedinitrilo-NNN′N′-tetra-acetic acid (H4edta)

Abstract

¹ H-Decoupled ¹³C n.m.r. spectra of Zn^II, Cd^II, Hg^II, Pb^II, Tl^I, Al^III, and Co^III complexes of edta^4– and Hedta^3– are reported. The results confirm and extend earlier studies of the labile complexes of Zn^II, Cd^II, Hg^II, and Pb^II, and reveal averaged hyperfine couplings between the carboxylate carbon atoms and ^IIICd or ¹¹³Cd [²J(C–Cd) 12·1 Hz] or ¹⁹⁹Hg [²J(C–Hg) 35 Hz]. Aluminium(III) gives an unsymmetrical complex at high pH. Spectra of complex ions of the type [Co^III(edta)X]^n– or [Co^III(Hedta)X]^(n–1)–(X = Cl, Br, NO₂, OH, or OH₂) confirm the expected quinquedentate co-ordination of edta^4– and reveal that only one (‘equatorially’ substituted) isomer is present, except when X = Br where two distinct isomers (‘axial’ and ‘equatorial’) exist. A previously reported single isomer of [Co^III(edta) Br]^2– is tentatively assigned an axial structure instead of the expected equatorial configuration.