Flexible Aliphatic Carboxylates for Colossal Thermal Expansion Engineering: From Local and Extended Structure...

Area of Science:

• Solid-state chemistry
• Materials science
• Crystal engineering

Background:

• Colossal thermal expansion coefficients (CTEs) are crucial for advanced materials.
• Designing materials with colossal CTEs is a key goal in chemistry and solid-state science.
• Molecular rotors offer a promising strategy for colossal thermal expansion materials, but practical applications are limited.

Purpose of the Study:

• To explore the potential of rotationally flexible aliphatic carboxylates as a platform for stimuli-responsive materials.
• To investigate the colossal thermal expansion properties of a 2D-layered praseodymium propionate ([Pr2(H2O)2Prop6]∞, Pr).
• To demonstrate practical applications of the synthesized material in low-temperature devices.

Main Methods:

• Variable-temperature Powder X-ray Diffraction (PXRD) to analyze thermal expansion.
• Single-Crystal X-ray Diffraction (SCXRD), Pair Distribution Function (PDF) analysis, and calorimetry for atomic mechanism studies.
• Density Functional Theory with Dispersion correction (DFT-D) for computational analysis.

Main Results:

• Praseodymium propionate (Pr) exhibits highly anisotropic thermal expansion with peak positive CTE of +1295(22) MK⁻¹ and negative CTE of -837(32) MK⁻¹ near 165 K.
• Flexible ethyl groups and varied intra- and interlayer interactions were identified as drivers of colossal thermal expansion.
• Demonstrated successful application of crystalline Pr samples in an optothermal actuator and a capacitance temperature sensor.

Conclusions:

• Aliphatic carboxylates serve as effective molecular rotors for designing materials with colossal thermal expansion.
• The findings open avenues for tailored design of stimuli-responsive materials using metal carboxylate systems.
• The study highlights a versatile synthetic platform for advanced functional materials.