Steric hindrance of phenanthroline diamides enables a hundredfold increase in Am(III) extraction efficiency.

Three novel 1,10-phenanthroline-2,9-dicarboxamides (DAPhen) were prepared and investigated in detail. The presence of alkyl groups in the -positions of the aryl substituent in the ligand amide functions results in completely inhibited rotation around the N-Ar bond and complicated conformational behavior. A very significant effect of ligand steric hindrance on the solvent extraction of lanthanides(III) and Am(III) from nitric acid solution was demonstrated.