For a wide range of 1,10-phenanthroline-2,9-dicarboxylic acid diamides (DAPhen), differing in the structure of the amide substituent and the presence of chlorine atoms in the 4,7-positions of the phenanthroline core, the extraction properties for lanthanides(III) and americium(III) were studied. Protonation and binding constants to Eu(III) were determined by using UV-vis titration. The values of binding constants and protonation constants are higher for nonsubstituted diamides than for 4,7-chlorinated diamides, which is in good agreement with the solvent extraction data. The structures of more than 20 complexes with lanthanide nitrates in the solid state have been determined using X-ray diffraction analysis. Unusual DAPhen ligand complexes with lanthanum and neodymium nitrates were obtained. For the first time, the possibility of entering a water molecule into the internal coordination sphere of neodymium in a complex with the DAPhen ligand was shown, resulting in the coordination number of neodymium increasing to 11. An unusual complex with a bridge structure was obtained for lanthanum nitrate in which the lanthanum ions have different coordination numbers of 10 and 12.