Analysis of multinuclear lanthanide induced shifts. Part 6. Structures of lanthanide(III) tris(oxydiacetate) complexes in aqueous solution

Abstract

The structure of the series of lanthanide(III) tris(oxydiacetate) complexes in aqueous solution has been investigated with the use of ¹H, ¹³C, and ¹⁷O n.m.r. The data show that these complexes are not isostructural. In the first half of the series a nine-co-ordinate structure, with three oxydiacetates bound in a tridenate fashion, predominates. Upon going to the heavier lanthanides a carboxylate of one of the oxydiacetate ligands is expelled from the first co-ordination sphere. As a result of slow exchange between the two enantiomeric forms of the complexes, a separation of the geminal methylene protons is observed at 6 °C and 200 MHz.