Morpholine-derived hydrophilic 1,10-phenanthroline-2,9-dicarboxamide for americium-lanthanide separation in phosphine...

A new hydrophilic DAPhen derivative, N²,N⁹-bis(2-morpholinoethyl)-1,10-phenanthroline-2,9-dicarboxamide (L), was synthesized and investigated as a selective aqueous-phase complexing agent for the separation of Am(III) from lanthanides in phosphine oxide-based extraction systems. Potentiometric and spectrophotometric titrations with Eu(III) demonstrated the formation of 1 : 1 and 1 : 2 complexes. X-ray crystallography revealed a unique coordination pattern with progressive substitution of nitrate anions by water molecules across the lanthanide series (La-Er), as well as protonation of morpholine nitrogen atoms under crystallization conditions. Solvent extraction experiments showed that the addition of L to aqueous nitric acid solutions reduces the distribution ratio of Am(III), thereby enhancing separation from Eu(III) and other lanthanides when combined with TOPO in kerosene or F-3. Separation factors SF(Eu/Am) of up to 26 were achieved. Although insufficient selectivity was observed for Am(III)/La(III) separation, the system demonstrates the potential for group separation of An(III) from Ln(III) with subsequent back-extraction of Am(III).