Compression and Thermal Expansion in Organic and Metal-Organic Crystals: The Pressure-Temperature Correspondence Rule

Abstract

Owing to the recent developments in experimental techniques, the number of crystal structures determined under various external stimuli has considerably increased, giving the opportunity for specialized data analysis. In this paper, the nonambient temperature and pressure studies of crystals deposited in the Cambridge Structural Database have been surveyed to better understand the relations between two of the most fundamental properties of crystals, compressibility and thermal expansion. Based on 799 systematic series of experiments, a pressure-temperature correspondence rule was formulated, stating that pressure between 0.2 and 0.5 GPa can be expected to cause the same change of crystal volume as the temperature decrease from 300 to 100 K. The rule has been tested against a set of crystals undergoing monotonic changes and no phase transitions in neither of the investigated pressure or temperature ranges. Additionally, the changes of thermal expansion and compressibility in the function of pressure and temperature have been illustrated by the anisotropy-evolution plots. They demonstrate limited applicability of Hazen and Finger's rule of the inverse relationship of pressure and temperature, particularly for metal-organic crystals.