Bistriazinyl-phenantroline "BTPhen" ligands L display the remarkable feature to complex trivalent lanthanide and actinide ions, with a marked selectivity for the latter. We report on molecular dynamics studies of tetrasubstituted X(4)BTPhens: L4+ (X = +Et3NCH2-), L4- (X = -SO3Ph-), and L-0 (X = CyMe4) and their complexes with Eu-III in binary octanol/water solutions. Changes in free energies upon interface crossing are also calculated for typical solutes by potential of mean force PMF simulations. The ligands and their complexes partition, as expected, to either the aqueous or the oil phase, depending on the "solubilizing" group X. Furthermore, most of them are found to be surface active. The water-soluble L4+ and L4- ligands and their (L)Eu(NO3)(3) complexes adsorb at the aqueous side of the interface, more with L4- than with L4+. The oil soluble ligand L-0 is not surface active in its endo-endo form but adsorbs on the oil side of the interface in its most polar endo-exo form, as well as in its protonated (LH+)-H-0 and complexed (L-0)Eu(NO3)(3) states. Furthermore, comparing PMFs of the Eu-III complexes with and without nitric acid shows that acidifying the aqueous phase has different effects, depending on the ligand charge. In particular, acid promotes the Eu-III extraction by L-0 via the (L-0)(2)Eu(NO3)(2+) complex, as observed experimentally. Overall, the results point to the importance of interfacial adsorption for the liquid-liquid extraction of trivalent lanthanide and actinide cations by BTPhens and analogues.