Speciation and structure of dipicolinate complexes and Eu(III) ions in solution

Complexation between Eu(III) ions and dipicolinate tridentate ligands (DPA) have been studied to expand on our current understanding of structural and photophysical properties of lanthanides in solution. The dynamic ligand-exchange of labile lanthanide ions, has made it difficult to properly identify the bis ligated Eu(III) complex, as optical spectroscopy only reveals a weighted average of the present species. In this article, evidence for the bis ligated Eu(III) complex will be presented, which is a necessary component in accurately determining the binding constants and to gain further insight in the structure- property relationship of the systems. Additionally, NMR, luminescence spectroscopy and X-ray scattering were used as structural corroboration to further establish the relationship between the solution structure and the intensities of Laporte parity forbidden f-f transitions, characteristic of the lanthanides.