Electrostatic matching versus close-packing molecular arrangement in compressed dimethyl sulfoxide (DMSO) polymorphs

Area of Science:

• Crystallography
• Materials Science
• Physical Chemistry

Background:

• Dimethyl sulfoxide (DMSO) is a widely used polar aprotic solvent.
• Understanding DMSO's behavior under pressure is crucial for various chemical and physical applications.
• Previous studies have explored DMSO's properties, but high-pressure crystal structures require further investigation.

Purpose of the Study:

• To determine the crystal structures of dimethyl sulfoxide (DMSO) at high pressures.
• To investigate the phase transitions and structural changes of DMSO under isochoric conditions.
• To elucidate the molecular aggregation and bonding mechanisms governing DMSO's solid phases.

Main Methods:

• Single crystals of DMSO were grown and frozen in situ within a diamond-anvil cell.
• X-ray diffraction was used to determine crystal structures at pressures of 0.37, 0.56, and 2.4 GPa.
• Analysis focused on molecular packing, intermolecular interactions, and phase transitions.

Main Results:

• At ambient pressure, DMSO freezes into a monoclinic phase (alpha, P2(1)/c) stable down to 2 K.
• Above 540 MPa, DMSO transitions to a more compact triclinic phase (beta, P1).
• Molecular aggregation is governed by electrostatic attractions and CH...O hydrogen bonds, with phase beta achieving tighter packing by altering dipole-dipole and van der Waals interactions.

Conclusions:

• DMSO exhibits distinct crystal phases under high pressure, with a transition to a denser triclinic structure.
• The observed structural changes are driven by the interplay of electrostatic forces and hydrogen bonding, optimizing molecular packing.
• The study provides fundamental insights into the solid-state behavior of DMSO under extreme conditions.