The studies reported here focus on the extraction of La(III), Eu(III), and Yb(III) by chelating hexadentate 3-alkoxy-2-hydroxyphenyl substituted diimine ligands using the extraction system Ln(NO₃)₃–Zn(NO₃)₂–NaNO₃–buffer–H₂O/diimine-n-caprylic acid–CHCl₃. Significant synergistic enhancement has been observed for the Ln(III) extraction from nitrate media in the presence of Zn(II) and n-caprylic acid. These effects can be interpreted by self-assembly of heterodinuclear Zn(II)/Ln(III) complexes with both deprotonated extractants in the organic phase taking into account solution and solid-state structural studies. The structures identified and the extraction behavior as well as the different factors influencing the process will be discussed in detail. The goals of these experiments are to find preferred structure-extractability relationships for the synergistic systems investigated.