Zero in-Plane Thermal Expansion in Guest-Tunable 2D Coordination Polymers

Area of Science:

• Materials Science
• Chemistry
• Solid State Physics

Background:

• Two-dimensional (2D) materials are crucial for advanced technologies.
• Controlling thermal expansion (TE) in 2D materials is essential for device stability.
• Anisotropic thermal expansion, where materials expand or contract differently in different directions, is a key challenge.

Purpose of the Study:

• To demonstrate zero in-plane thermal expansion in a 2D coordination polymer.
• To investigate the relationship between guest species and TE behavior.
• To engineer a material with a net zero area change over a specific temperature range.

Main Methods:

• Synthesis of single crystals of [Mn(salen)]2[Mn(N)(CN)4(guest)] coordination polymers.
• Variable-temperature single-crystal X-ray diffraction analysis.
• Structural analysis to understand the origin of anisotropic TE.

Main Results:

• The synthesized compounds exhibited anisotropic positive and negative thermal expansion based on guest species (MeOH and MeCN).
• Zero in-plane thermal expansion was achieved in a mixed-guest material: [Mn(salen)]2[Mn(N)(CN)4(MeOH)0.25(MeCN)0.75].
• This zero TE effect was observed between 380 and 440 K.
• The TE behavior is attributed to distortions in the octahedral coordination geometry of [Mn(salen)]+ units within the zigzag layers.

Conclusions:

• Zero in-plane thermal expansion in 2D coordination polymers is achievable.
• The precise control over guest molecules allows for tuning of thermal expansion properties.
• This finding opens avenues for developing dimensionally stable 2D materials for thermal management applications.