Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with periodic boundary conditions

Abstract

The hydrogen bond (H-bond) energies are evaluated for 18 molecular crystals with 28 moderate and strong O-H···O bonds using the approaches based on the electron density properties, which are derived from the B3LYP/6-311G** calculations with periodic boundary conditions. The approaches considered explore linear relationships between the local electronic kinetic Gb and potential Vb densities at the H···O bond critical point and the H-bond energy E HB. Comparison of the computed EHB values with the experimental data and enthalpies evaluated using the empirical correlation of spectral and thermodynamic parameters (Iogansen, Spectrochim. Acta Part A 1999, 55, 1585) enables to estimate the accuracy and applicability limits of the approaches used. The Vb-EHB approach overestimates the energy of moderate H-bonds (EHB < 60 kJ/mol) by ∼20% and gives unreliably high energies for crystals with strong H-bonds. On the other hand, the Gb-EHB approach affords reliable results for the crystals under consideration. The linear relationship between Gb and EHB is basis set superposition error (BSSE) free and allows to estimate the H-bond energy without computing it by means of the supramolecular approach. Therefore, for the evaluation of H-bond energies in molecular crystals, the Gb value can be recommended to be obtained from both density functional theory (DFT) computations with periodic boundary conditions and precise X-ray diffraction experiments. © 2012 Wiley Periodicals, Inc.