Zero thermal expansion in metal-organic framework with imidazole dicarboxylate ligands

Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion. Metal-Organic Framework (MOF) with unique structure flexibility is ideal material to study the thermal expansion. This work adopts the high-resolution variable-temperature powder X-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF ([Sr(DMPhH2IDC)2]n). It has the unique honeycomb structure with 1D channels along c-axis direction, the a-b plane displays layer structure. The thermal expansion behavior has strong relationship with the structure, ZTE appears in the a-b plane and large PTE along c-axis direction. The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands, while along the c-axis direction is not. This work not only reports one interesting zero thermal expansion material, but also provides new understand for thermal expansion mechanism from the perspective of structural model.