Molecular crystals sublimation: structural clusterization of the database as an approach for prediction of the thermodynamic functions

Abstract

The database of sublimation thermodynamic functions including 3200 entries/records for various molecular crystals has been developed. Comparative analysis of crystal distribution functions for the sublimation Gibbs energies and enthalpies, as well as the melting points and molecular weights have been carried out. Relative contributions to the sublimation Gibbs energy from the enthalpy and entropy terms have been calculated. The entropy contribution to the sublimation Gibbs energy was shown to increase with the reduction of the weight-average molecular weight of the substance. A similar trend was observed for the weight-average value of the melting point. The values of the fusion enthalpies relative to the sublimation enthalpies were evaluated. Correlation models for predicting the sublimation Gibbs energy using the clusterization of the database for the structurally related compounds with the Tanimoto similarity coefficients were developed. For the first model the sublimation Gibbs energy within each cluster was described by an equation using the melting temperature as a descriptor. For the second model a multivariate equation including the melting point and HYBOT descriptors describing the specific and non-specific interactions between the molecules was used. It was shown that the second model describes the sublimation Gibbs energies better as compared to the first one, according to the standard deviations (3.12 and 2.85).