The complexation of selected trivalent lanthanide ions with derivatives of the tetranitrogen donor ligands 6,6'-bis-1R,1H-1,2,3-triazol-4-yl-2,2'-bipyridines (BTzBPs, R = alkyl or aryl) was investigated in solid state and in solution. An anhydrous solid [Ce(Bn-BTzBP)(NO3)(3)] (Bn = benzene) complex was synthesized and characterized by single-crystal X-ray diffraction. Eu(III) complexes with the 2-ethyl(hexyl) derivative EH-BTzBP in methanol were studied by time-resolved fluorescence spectroscopy. Earlier studies have identified the EH-BTzBP as a potentially useful solvent extraction reagent for the separation of americium from lanthanide metal ions, a challenging component of advanced nuclear fuel cycles for actinide transmutation. To help identify species formed in the extraction process, the influence of 2-bromohexanoic acid (identified as an essential component of the separation system) on Eu(III) complexes was investigated. Comparison with an organic phase after extraction of Eu(III) by EH-BTzBP and 2-bromohexanoic acid showed that both 1:1 and 1:2 (Eu/EH-BTzBP) complexes are involved in the extraction. UV-visible spectrophotometry was used to compare Eu(III) stability constants with those of other Ln(III) complexes.