Pressure-induced structural phase transformation in cobalt(II) dicyanamide

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Magnetic molecular framework materials offer tunable properties.
• Understanding pressure-induced structural changes is crucial for designing new materials.
• Cobalt dicyanamide [Co(dca)2] is a known magnetic material with a rutile-like structure.

Purpose of the Study:

• To investigate the pressure-dependent structural behavior of Co(dca)2.
• To determine the crystal structure of the high-pressure phase.
• To characterize the compressibility and structural distortions under pressure.

Main Methods:

• In situ synchrotron powder diffraction was employed.
• High pressure was applied using a diamond anvil cell.
• Crystallographic data was analyzed to determine structural parameters.

Main Results:

• An orthorhombic (Pmnn) to monoclinic (P2₁/n) phase transition occurred at 1.1 GPa, forming γ-Co(dca)2.
• The rutile-like topology was preserved in the high-pressure phase.
• Bulk moduli for α-Co(dca)2 and γ-Co(dca)2 were determined as 13.15(18) GPa and 9.0(6) GPa, respectively.
• Negative linear compressibility (K ≈ -4 TPa⁻¹) was observed across the pressure range.

Conclusions:

• Co(dca)2 exhibits a pressure-induced phase transition with retained topology.
• The material displays significant compressibility and negative linear compressibility.
• These findings provide insights into the structural response of magnetic molecular frameworks to pressure.