Switchable colossal anisotropic thermal expansion in a spin crossover framework

Abstract

Advanced materials with tunable thermal expansion properties have garnered significant attention due to their potential applications in thermomechanical sensing and resistance to thermal stress. Here, switchable colossal anisotropic thermal expansion (ATE) behaviors are realized in a Hofmann-type framework [Fe(bpy-NH2){Au(CN)2}2iPrOH (Fe·iPrOH, bpy-NH2 = [4,4′-bipyridin]-3-amine) through a three-in-one strategy: a vibrational mechanism, an electronic mechanism and molecular motion. Spin crossover (SCO) centers coordinate with dicyanoaurate linkers to form flexible wine-rack frameworks, which exhibit structural deformations driven by host–guest interactions with iPrOH molecules. By means of the vibrational mechanism, a scissor-like motion driven by the rotation of dicyanoaurate is observed within the rhombic grids, resulting in the emergence of colossal ATE in the high temperature region. When the spin transition comes into play, the electronic mechanism is predominant to form reverse ATE behavior, which is associated with host–guest cooperation involving significant molecular motion of the iPrOH guest and adaptive deformation of the host clathrate. A remarkably high negative thermal expansion coefficient up to −7.49 × 105 M K−1 accompanied by abrupt SCO behavior is observed. As a proof of concept, this study provides a novel perspective for designing dynamic crystal materials with tunable thermomechanical properties by integrating various ATE-related elements into a unified platform.

Graphical abstract: Switchable colossal anisotropic thermal expansion in a spin crossover framework

Supplementary files

Article information

Article type
Edge Article
Submitted
27 Nov 2024
Accepted
03 Apr 2025
First published
08 Apr 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2025, Advance Article

Switchable colossal anisotropic thermal expansion in a spin crossover framework

S. Wu, W. Cui, Z. Ruan, Z. Ni and M. Tong, Chem. Sci., 2025, Advance Article , DOI: 10.1039/D4SC08032G

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