Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with...

Area of Science:

• Solid-state chemistry
• Computational chemistry
• Crystallography

Background:

• Accurate evaluation of hydrogen bond (H-bond) energies is crucial for understanding molecular crystal properties.
• Existing methods for calculating H-bond energies have limitations in accuracy and applicability.
• Electron density properties offer a promising avenue for H-bond energy estimation.

Purpose of the Study:

• To evaluate hydrogen bond (H-bond) energies in molecular crystals using electron density-based approaches.
• To compare the accuracy of different methods, including those based on local electronic kinetic (G(b)) and potential (V(b)) densities.
• To identify reliable methods for H-bond energy estimation in crystalline solids.

Main Methods:

• Density functional theory (DFT) calculations using B3LYP/6-311G** with periodic boundary conditions were performed on 18 molecular crystals.
• Linear relationships between electron density properties (G(b), V(b)) at the bond critical point and H-bond energy (E(HB)) were explored.
• Computed energies were compared against experimental data and empirical correlations.

Main Results:

• The V(b)-E(HB) approach showed significant overestimation for moderate H-bonds and unreliable results for strong H-bonds.
• The G(b)-E(HB) approach yielded reliable H-bond energy estimations across the studied molecular crystals.
• The G(b)-E(HB) relationship is free from basis set superposition error (BSSE) and allows energy estimation without supramolecular calculations.

Conclusions:

• The G(b) value derived from electron density is a reliable indicator for estimating H-bond energies in molecular crystals.
• The G(b)-E(HB) approach offers an accurate and BSSE-free method for H-bond energy evaluation.
• Recommended for H-bond energy assessment, G(b) can be obtained from DFT calculations or X-ray diffraction experiments.