Negative linear compressibility exhibited by the hybrid perovskite [(NH₂)₃C]Er(HCO₂)₂(C₂O₄)

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Extended framework materials can display unique mechanical responses to hydrostatic pressure.
• Negative linear compressibility (NLC) is an unusual phenomenon where a material expands in one direction under uniform pressure.
• Winerack structures are a known topology that can exhibit NLC.

Purpose of the Study:

• To investigate the mechanical behavior of two hybrid perovskite frameworks with winerack structures under pressure.
• To identify the first hybrid perovskite exhibiting NLC from ambient pressure.
• To understand the factors influencing the distinct mechanical responses of isostructural materials.

Main Methods:

• Synthesis and characterization of two hybrid perovskite frameworks: [C(NH2)3]Er(HCO2)2(C2O4) and isostructural [(CH3)2NH2]Er(HCO2)2(C2O4).
• High-pressure studies using techniques such as X-ray diffraction to monitor structural changes.
• Analysis of host-guest interactions and hydrogen bond networks to explain observed mechanical properties.

Main Results:

• [C(NH2)3]Er(HCO2)2(C2O4) exhibits negative linear compressibility (NLC) from ambient pressure up to 2.63(10) GPa.
• This material is the first reported hybrid perovskite demonstrating NLC starting from ambient pressure.
• The isostructural [(CH3)2NH2]Er(HCO2)2(C2O4) shows moderate compression along all axes and undergoes a phase transition above 0.37(10) GPa.
• Differences in mechanical behavior are attributed to variations in hydrogen bonding and host-guest interactions.

Conclusions:

• The study successfully identified a novel hybrid perovskite exhibiting ambient pressure NLC.
• The contrasting mechanical responses highlight the sensitivity of framework materials to subtle changes in intermolecular interactions.
• Understanding these structure-property relationships is crucial for designing materials with tailored mechanical responses.