Negative Thermal Expansion in the Noncarboxylate Based Metal-Organic Framework Cd(trz)Cl

Negative thermal expansion (NTE), as a counterintuitivephenomenon,has attracted considerable interest owing to its great scientificand technical value. Owing to the inherent structural flexibility,metal-organic frameworks (MOFs) have recently been recognizedas an ideal platform for the study of NTE. However, the reported NTEMOFs are mainly restrained in the carboxylate based ones. Herein,we found that the noncarboxylate MOF Cd(trz)Cl (trz = 1,2,4-trizaole) can also exhibit intrinsic volumetric NTE, anda transition from NTE to PTE at high temperatures can be observed.The combined in situ synchrotron powder X-ray diffraction,Raman spectra measurements, and DFT calculations shed light on thefact that the NTE mainly originates from the synergistic effect ofgeometric flexibility and the enhanced out-of-plane rotation behaviorof the trz ligand. This study not only demonstratesa new NTE material but also can help to extend the scope of NTE tothe more diverse noncarboxylate based MOFs.