AbstractThe complexation of trivalent lanthanides and minor actinides (Am³⁺, Cm³⁺, and Cf³⁺) by the acyclic aminopolycarboxylate chelators 6,6′-((ethane-1,2-diylbis–((carboxymethyl)azanediyl))bis–(methylene))dipicolinic acid (H₄octapa) and 6,6'-((((4-(1-(2-(2-(2-hydroxyethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)pyridine-2,6-diyl)bis–(methylene))bis–((carboxymethyl)azanediyl))bis–(methylene)) dipicolinic acid (H₄pypa-peg) were studied using potentiometry, spectroscopy, competitive complexation liquid–liquid extraction, and ab initio molecular dynamics simulations. Two studied reagents are strong multidentate chelators, well-suited for applications seeking radiometal coordination for in-vivo delivery and f-element isolation. The previously reported H₄octapa forms a compact coordination packet, while H₄pypa-peg is less sterically constrained due to the presence of central pyridine ring. The solubility of H₄octapa is limited in a non-complexing high ionic strength perchlorate media. However, the introduction of a polyethylene glycol group in H₄pypa-peg increased the solubility without influencing its ability to complex the lanthanides and minor actinides in solution.