Large negative linear compressibility of Ag3[Co(CN)6].

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Negative linear compressibility (NLC) and negative thermal expansion (NTE) are exotic phenomena in materials.
• Understanding the mechanisms behind these properties is crucial for designing novel functional materials.
• Framework materials with specific structural motifs can exhibit unusual responses to external stimuli.

Purpose of the Study:

• To investigate the high-pressure behavior of Silver(I) hexacyanocobaltate(III) (Ag(3)[Co(CN)(6)]).
• To characterize the structural and compressional properties of Ag(3)[Co(CN)(6)] under hydrostatic pressure.
• To elucidate the microscopic origins of negative linear compressibility and negative thermal expansion in this compound.

Main Methods:

• Single-crystal X-ray diffraction under hydrostatic pressure up to 7.65 GPa.
• Analysis of crystal structures and lattice parameters at various pressures.
• Investigation of thermal expansion properties.

Main Results:

• Silver(I) hexacyanocobaltate(III) displays significant negative linear compressibility (NLC) across all measured pressures.
• A phase transition was observed at 0.19 GPa, forming Ag(3)[Co(CN)(6)]-II, which also exhibits NLC.
• Both phases show anisotropic thermal expansion, including substantial uniaxial negative thermal expansion (NTE).
• The NLC/NTE effect originates from the compression of silver atom layers and flexing of the covalent network.

Conclusions:

• The observed NLC in Ag(3)[Co(CN)(6)] is attributed to the unique interplay between silver atom layers and the covalent network.
• The findings suggest a general principle for designing framework materials with predictable NLC/NTE behavior.
• This study provides insights into the structure-property relationships governing unusual compressibility in coordination compounds.