Close contacts and noncovalent interactions in crystals.

Area of Science:

• Solid-state chemistry
• Crystallography
• Computational chemistry

Background:

• Close contacts based on van der Waals radii are frequently used to identify nonbonded interactions in crystal lattices.
• This method, while often effective, has limitations due to uncertainties in van der Waals radii and the assumption of pairwise interactions.

Purpose of the Study:

• To critically evaluate the reliability of using van der Waals radii for identifying crystal lattice interactions.
• To explore the nature of Coulombic interactions within crystal lattices and their relationship to atomic positions and interatomic regions.
• To highlight the significance of σ-hole interactions.

Main Methods:

• Analysis of interatomic separations in crystal lattices.
• Evaluation of the uncertainties associated with van der Waals radii.
• Investigation of Coulombic potential maps to identify regions of electrostatic interaction.
• Examination of specific examples, including σ-hole interactions.

Main Results:

• Van der Waals radii can lead to misidentification of attractive nonbonded interactions in crystal lattices.
• Coulombic interactions are the fundamental driving force, with charge distributions not always centered on atoms but sometimes between them.
• The study provides examples illustrating these findings, particularly concerning σ-hole interactions.

Conclusions:

• The use of close contacts and van der Waals radii as the sole criteria for identifying crystal lattice interactions is potentially misleading.
• A more accurate understanding requires considering the Coulombic nature of interactions and the location of electrostatic potential extrema, which may lie between atoms.
• The importance of specific interactions like σ-hole interactions in crystal packing is emphasized.