Sublimation Enthalpies of Organic Compounds: A Very Large Database with a Match to Crystal Structure Determinations and a Comparison with Lattice Energies

A database of 1655 critically evaluated sublimation enthalpies of organic compounds is presented. Experimental techniques are briefly reviewed. The consistency of experimental measurements is critically analyzed also as a function of temperature. Isomer effects and chain-length trends in linear substituted alkanes are described. For 737 entries, a match is found with the X-ray structure determination of the corresponding crystalline material as reported in the Cambridge Structural Database. Out of these, lattice energies are calculated for 679 crystals by atom–atom potentials and for 500 crystals by the Pixel method. The procedure for the comparison between sublimation enthalpy and lattice energy is analyzed with its importance for many issues in crystal and theoretical chemistry. With Pixel, 87% of the sublimation enthalpy–lattice energy comparisons show a discrepancy below 15% with a root mean square deviation of 8.7 kJ mol–1; with atom–atom potentials, the corresponding figures are 74% and 8.3 kJ mol–1, but by Pixel no deviation is larger than 30%; atom–atom energies for some compounds show very large, unexplained deviations. The intrinsic accuracies of calculated lattice energies and experimental sublimation enthalpies are similar and are found to be in the 5–10 kJ mol–1 range. Success and failures of theoretical methods are related to the fundamentals of intermolecular interactions.