Anomalous solution behaviour of isomorphous complexes of zirconium- and hafnium-(IV)

Abstract

The synthesis of [Zr^IV(egta)] and [Hf^IV(egta)] in aqueous solution, where H₄egta = ethylenedioxydiethyl-enedinitrilotetraacetic acid, is reported. The eight-co-ordinate complexes have been characterised by X-ray crystallography, ¹H NMR spectroscopy, mass spectrometry and elemental analysis. The two compounds are isostructural in the solid state. Solution studies by ¹H NMR spectroscopy show that the hafnium analogue has a higher degree of symmetry. In particular, the spectrum of the zirconium complex reveals all of the methylene groups to be inequivalent whereas in the hafnium complex the –N(CH₂CO₂)₂– and the –NCH₂CH₂O– methylene groups show increased magnetic equivalence.