Complexes of bipyridinecarboxylate and phenanthrolinecarboxylate with trivalent actinides and lanthanides: Binding strength and structure

The binding strengths of ligand 2,2ʹ-bipyridine-6-carboxylate (BiPCA) and 1,10-phenanthroline-2-carboxylate (PhenCA) with trivalent actinides (An) like Am(III) and Cm(III), and lanthanides (Ln) like Nd(III), Sm(III), and Eu(III) were investigated by solvent extraction, potentiometry, and crystallography. Both ligands exhibit good actinides selectivity over lanthanides and radius selectivity for intragroup Ln(III) or An(III). In comparison, PhenCA is more prominent than BiPCA in these capabilities. Single crystal structures of the Nd(III)/Eu(III) with BiPCA and PhenCA illustrate that BiPCA, as well as PhenCA, is tridentate and chelates with Nd(III)/Eu(III) by two aromatic N-donors and a carboxyl O-donor. PhenCA exhibits shorter coordination bonds to the central atom than BiPCA, in agreement with the fact that in solution PhenCA behaves stronger binding strength than BiPCA to the same lanthanide cation. However, for the lanthanide complexes with the same ligand, no regular trend of the coordination bonds has been observed between Nd(III) and Eu(III).