Benchmark Measurements for Energetic Salts: A Prerequisite toward Improved Estimation Methods for Lattice Enthalpy.

The evaluation of the formation enthalpies of energetic salts is hampered by the inability of current procedures to provide reliable lattice enthalpies, partly due to the lack of reference benchmark values. In this context, we report the synthesis and characterization of twenty-one energetic salts, eight of which had never been described before. In addition to density and thermal stability, special care is devoted to the accurate measurement of formation enthalpy. By subtracting experimental formation enthalpies of the salts from the ab initio formation enthalpies of their constitutive ions, benchmark lattice enthalpies are obtained. On the basis of the resulting dataset, some limitations of the widely used volume-based thermodynamics (VBT) approach are highlighted, and a more physically sound alternative that does not involve any fitting parameter is put forward. The latter should be improvable through a more detailed description of the ions and possibly the introduction of a dose of empiricism that will be made possible by the future extension of the present database to include selected literature data and further measurements.