[en] When nitrate of Am(3) is extracted with dioxides of diphosphines, the following regularity is observed: with alkyl radicals (R) being successively substituted by more electronegative phenyl radicals (Ph), though the electronegativity of the substituents essentially increases and the basicity of the dioxides diminishes, the extraction of Am(3) increases. Anomalous dependence of the strength of complexes on the structure of alkylenediphosphines has also been found to take place in the case of trivalent metals - actinoids and lanthanoids