The influence of elevated temperatures on the formation of 1:1 chloro complexes for Eu3+ and Am3+ are reported. Using a solvent extraction technique, stability constants for the equilibrium M(aq)3++Cl(aq)–MCl(aq)2+ have been measured in the temperature range of 25–75 °C. Modest increases in
1 are observed, and small positive enthalpies for these reactions are reported. These data are discussed in the context of previous reports for the trivalent lanthanide and actinide chloro systems.