Comparative DFT study of americium and europium complexation with 2,9-bis(1,2-diazin-3-yl)-1,10-phenanthroline ligand in gas phase

[Display omitted] •Comparative study of americium and europium complexation with BTPhen-CH was done.•Both pure cation and its tetraaquatrinitrato complex were used as reactants.•Five different reactions were studied.•In case of pure cation europium forms the more stable complexes.•In case of tetraaquatrinitrato complex americium form the more stable complexes. 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenantroline (BTPhen) based ligands have shown great promise in separation of trivalent lanthanides and actinides. Although many experimental studies have shown that americium is forming stronger complexes with the BTPhen ligands than europium, most theoretical studies have thus far failed to reproduce these results. In the current study, two different metal forms (the naked cation and its tetraaquatrinitrato complex) were used to study five different complexation reactions. It was shown that in case of naked cations europium forms the most stable complex with the 2,9-bis(1,2-diazin-3-yl)-1,10-phenanthroline (BTPhen-CH) ligand in all of the compared reactions. In case of tetraaquatrinitrato complex it was shown that europium gets a higher stabilizing effect and thus americium complexes with BTPhen-CH become the more stable form, as can be seen in the experimental studies.