CATION CATION COMPLEXES OF NPO2+

The stability constants of two cation-cation complexes, NpO2+ - UO22and NpO2+ - NpO2+, were measured by spectrophotometry and the enthalpi es of formation obtained by the temperature coefficient method. The th ermodynamic parameters for the NpO2+ - UO22+ complex are beta = 2.25 /- 0.03, DELTAH -12.0 +/- 1.7 kJ/mol and DELTAS = -34 +/- 6 J/mol-K. F or the NpO2+ - NpO2+ complex, values of beta = 1.41 +/- 0.14, DELTAH = 0 +/- kJ/mol, and DELTAS = 3 +/- 2J/mol-K were found. The small or ne gative values of the enthalpy and entropy changes would seem to indica te the formation of outer-sphere complexes. If the complexes are inner -sphere, the thermodynamic parameters may mean that the complexes are more hydrated than the individual reactants.