We find a design principle for tailoring thermal expansion properties in nearly-spherical molecular networks. Using 2D fullerene networks as a representative system, we realize positive thermal expansion along intermolecular [2\,+\,2] cycloaddition bonds and negative thermal expansion along intermolecular C−C single bonds by varying the structural frameworks of molecules. The microscopic mechanism originates from a combination of the framework's geometric flexibility and its transverse vibrational characteristics. Based on this insight, we find molecular networks beyond C60 with tunable thermal expansion. These findings shed light on the fundamental mechanisms governing thermal expansion in molecular networks towards rational materials design.
@article{arxiv.2504.02037,
title = {Negative and positive anisotropic thermal expansion in 2D fullerene networks},
author = {Armaan Shaikh and Jiaqi Wu and Bo Peng},
journal= {arXiv preprint arXiv:2504.02037},
year = {2025}
}