On prediction of melting points without computer simulation: A focus on energetic molecular crystals

Abstract

Melting point is one of the most important characteristics for molecular engineering of energetic materials. Therefore, methods for prediction of this physical property are essential to the field. In this paper, we have developed two models for prediction of melting point of energetic molecular crystals. The first one uses two parameters (lattice energy and crystal density) and grounds on the correlation of 200 compounds. The second model does not use any calculated quantities (only tabulated data) and is based on 1500 compounds. The first model needs separate calibrations for specific families of compounds; for nitroaromatic compounds, aliphatic nitro- and nitrato compounds and peroxides it provides R2 = 0.82–0.85 and RMSE ≥ 21–54 °C, respectively. Meanwhile, Model 2 is a more universal, but less accurate approach and it was tested for 747 energetic materials of different families providing R2 = 0.62 and RMSE ≥ 64 °C. This makes Model 2 a simple and convenient tool for a fast crude estimation of melting point of a desired energetic molecular crystal using a pocket calculator. Since Model 2 does not need quantum-chemical calculations, it can be effectively applied for any arbitrary composition. In the present work, however, we have considered compounds with a restricted number of constituting elements: C–H–N–O–S–F–Cl–Br–I. Nevertheless, extension of Model 2 is a simple procedure, which assumes estimation of so-called effective densities for other elements via regression analysis of experimentally available data on melting points.