A Case of Macrocyclic N,N'-Diphenyl-Substituted Phenanthrolinediamides: Molecular Dynamics and Eu(3+)/Am(3+) Binding Affinity.

A set of 12 novel macrocyclic 1,10-phenanthroline-2,9-dicarboxamides (DAPhen's) with variable ring size were synthesized. A variety of ligands were prepared with different chain lengths between amide nitrogens; in addition, the corresponding 4,7-dichloro-substituted derivatives were prepared. Using a combination of quantum-chemical modeling, single-crystal X-ray diffraction, and nuclear magnetic resonance spectroscopy methods, the stereodynamics of such compounds was studied in detail. Solvent extraction tests of macrocyclic DAPhen's toward the Eu/Am pair allowed to determine the most effective ligand in the series. It has been shown that 4,7-dichloro-substituted DAPhen's can exhibit much higher extraction efficiency for trivalent -element cations under the same conditions compared to their unsubstituted analogs. These patterns were explained by using quantum-chemical modeling of the complexation of the synthesized macrocycles with lanthanide(III) nitrates.