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

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 alpha(v) = -197 x 10(-6) K-1, linear expansion coefficient alpha(c) = -242 x 10(-6) K-1), accompanied by a significant decrease of beta angle (-3.8%).