Nuclear magnetic resonance investigation of intramolecular scrambling processes in meso-(2,3-butylenediamine)tetraacetate. Diamagnetic complexes of transition metal ions

Abstract

The acetate scrambling processes (Δ,Λ conversion and N inversion) occurring in the complexes formed from meso-(2,3-butylenediamine)tetraacetic acid (BDTA) with zinc(II), cadmium(II), mercury(II), scandium(III), yttrium(III) and lanthanum(III) ions have been investigated by line shape analysis of their n.m.r. spectra. Between 308 and 373 K fast conversion between Δ and Λ isomers and slow nitrogen inversion occur except for mercury(II) and yttrium(III) in the latter case. ΔH* = 2.3±0.1 kJ mol−1 and ΔS* = −6.9±0.2 mol−1 J K−1 for the mercury complex; ΔH* = 2.6 ±0.2 kJ mol−1 and ΔS* = −5.5±0.5 mol−1 JK−1 for the yttrium complex. Exchange mechanisms proceeding through different reaction intermediates are discussed on the light of the results obtained in this work as well as previously on other polyaminepolycarboxylate complexes of the same ions.