Molecular rotation induced giant, anisotropic negative thermal expansion in a hydrogen-bonded coordination framework

Abstract

Negative thermal expansion (NTE) is generally caused by the transverse vibration of the bridging groups. Herein, we report a new supramolecular structure of cyanuric acid–melamine–zinc (CA–M–Zn) demonstrating unique molecular rotation induced NTE along the c axis (volumetric expansion coefficient α_v = −197 × 10⁻⁶ K⁻¹, linear expansion coefficient α_c = −242 × 10⁻⁶ K⁻¹), accompanied by a significant decrease of β angle (−3.8%).