Cl···Cl interactions in molecular crystals: insights from the theoretical charge density analysis

Area of Science:

• Solid-state chemistry
• Quantum chemistry
• Crystallography

Background:

• Intermolecular interactions, particularly halogen bonds, are crucial in determining crystal structures and properties.
• Chlorine-chlorine (Cl···Cl) contacts represent a specific type of halogen bond with implications for material science.
• Understanding the nature and strength of Cl···Cl interactions requires advanced computational methods.

Purpose of the Study:

• To computationally investigate the structural, vibrational, and electronic properties of molecular crystals featuring Cl···Cl contacts.
• To quantitatively characterize Cl···Cl interactions using electron density features at bond critical points.
• To evaluate the energy of Cl···Cl interactions and assess methods for their detection in crystalline environments.

Main Methods:

• Solid-state Density Functional Theory (DFT) calculations were employed to model 20 molecular crystals.
• Normal vibration analysis, including IR harmonic frequencies and intensities, was performed.
• Quantum-topological analysis of periodic electron density was utilized to define and quantify Cl···Cl interactions.

Main Results:

• The electron density at the Cl···Cl bond critical point was found to be largely independent of contact type or carbon hybridization.
• The energy of Cl···Cl interactions (E(int)) was evaluated, ranging from 2 to 12 kJ/mol.
• The study highlights the complexity of geometrically detecting multiple Cl···Cl contacts and emphasizes the utility of quantum-topological analysis.

Conclusions:

• Solid-state DFT and quantum-topological analysis provide a robust framework for characterizing Cl···Cl interactions in crystals.
• The electron density at the bond critical point serves as a reliable indicator of Cl···Cl interaction strength.
• Accurate detection and quantification of Cl···Cl interactions are essential for predicting and understanding crystal behavior.