ChemInform Abstract: Li2UCl6, Na2UCl6, and Cs2UCl6 Compounds: Enthalpies of Phase Transitions and Electrical Conductivity in the Solid and Liquid States

Abstract

Using several experimental techniques (electrical conductivity measurement, differential thermal analysis and differential enthalpic analysis), the Li2UCl6, Na2UCl6 and Cs2UCl6 Compounds have been investigated. —The joint examination of thermograms and phase diagrams suggests that the fusion of Li2UCl6 and Na2UCl6 compounds is preceeded by small thermal effects which are not always reproducible. —Melting temperatures and enthalpies of transformation and fusion have been measured: These new results were compared with those previously found for similar compounds. The calorimetric and electrical experimental values obtained for Li2UBr6 and Li2UCl6 allowed a parallelity to be established: the very close values of entropy of fusion, 61 and 57 J · mol−1 · K−1, respectively, suggest that the melting mechanism is similar for both compounds. —On the other hand, in spite of similar entropies of fusion, Li2UCl6 and Na2UCl6 exhibit a strongly different behaviour of the electrical conductivity. The electrical properties of Li2UCl6, Na2UCl6 and Cs2UCl6 were also tentatively compared with those of Li2UBr6 and Na2UBr6 but only a qualitative interpretation can be put forward. —However the similar premelting effects and entropies of fusion (13.8 and 15.8 J · mol−1 · K−1 respectively) found for Na2UBr6 and Cs2UCl6 suggest a similar melting mechanism for both compounds. Therefore high temperature structural investigations would be essential and the clue to the electrical and thermodynamic behaviours of Li2UCl6, Na2UCl6 and Cs2UCl6.