X-Ray Crystallographic Approach to the Design of Phenolic Schiff Base Reagents for the Mutual Separation of Lanthanoids

A novel mutual selectivity of lanthanoids in the N,N′-bis(5-nitrosalicylidene)ethylenediamine (H2Nsalen)-KCl and N,N′-bis(5-nitrosalicylidene)-o-phenylenediamine (H2Nsaloph)-KCl extraction systems was evaluated by the X-ray analysis of similar model complexes for extracted species. Cerium(IV) complexes with N,N′-bis(5-chlorosalicylidene)-ethylenediamine (H2Clsalen), N,N′-bis(salicylidene)-o-phenylenediamine (H2saloph) and N,N′-bis(3,5-dibromosalicylidene)-o-phenylenediamine (H2Br2saloph) were selected as the models. The result of the X-ray analysis suggested that [Ln(III)(Nsalen)2]- and [Ln(III)(Nsaloph)2]- are meridional type (two ligands are oriented perpendicular to each other) and sandwich type (two ligands are oriented parallel to each other), respectively. It was suggested that the selectivity of the meridional structure is superior to that of the sandwich structure in these extraction systems.