Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a challenging task in the nuclear fuel cycle due
to their similar charge and chemical behaviour. Some soft donor ligands show selectivity for An(III) over Ln(III) due to the
formation of stronger covalent bonds with the former. The extraction behaviour of Am(III) and Eu(III) is studied in the present
work with a mixture of Cyanex-301 (bis(2,4,4-trimethylpentyl)di-thiophosphinic acid) with several various ‘N’, ‘O’ or ‘S’ donor neutral ligands. Comparison of the
data was done with that of the oxygen donor analogue of Cyanex-301, i.e. Cyanex-272 (bis(2,4,4-trimethylpentyl)phosphinic acid). Effect of the organic diluent on the extraction behaviour of Am(III) using Cyanex-301
in presence of ‘N’ donor synergists was also studied. Ab initio molecular orbital calculations were carried out using GAMESS
software and charges on the donor atoms were calculated which helped in understanding the co-ordination chemistry of the ligands
and explained the separation behaviour.