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 an 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)_2n). It has the unique honeycomb structure with one-dimensional (1D) channels along the 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 the 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 understanding for thermal expansion mechanism from the perspective of the structural model.