Crystal Structures and Intermolecular Interactions in α $\alpha$ - and β $\beta$ -phosgene.

Area of Science:

• Solid-state chemistry and crystallography.
• Materials science and condensed matter physics.

Background:

• Phosgene exists in multiple crystalline forms with distinct structural and electronic properties.
• Understanding these structures is crucial for predicting reactivity and intermolecular forces.

Purpose of the Study:

• To elucidate the crystal structures of alpha- and beta-phosgene using neutron diffraction.
• To investigate the intermolecular interactions and vibrational dynamics of both phosgene phases.
• To computationally model the interplay of interactions and vibrational mode mixing.

Main Methods:

• Variable temperature neutron powder diffraction.
• Quantum chemical calculations (solid-state and gas-phase dimer models).
• Inelastic neutron scattering spectroscopy.

Main Results:

• The stable alpha-phosgene structure (I4_1/a) and a new metastable beta-phosgene structure (Cmc2_1) were determined.
• Both phases exhibit dipole-dipole interactions; alpha-phosgene shows significant sigma-hole interactions.
• Computational studies revealed complex intermolecular interactions and unusual mixing of vibrational modes (C-Cl stretch and out-of-plane bend) in alpha-phosgene.

Conclusions:

• The study provides a detailed structural and dynamic characterization of alpha- and beta-phosgene.
• Intermolecular interactions, including sigma-hole interactions, play a significant role in phosgene crystal structures.
• Unusual vibrational mode mixing in alpha-phosgene has implications for understanding solid-state dynamics.