α-Magnesium formate [α-Mg3(HCOO)6], a representative lightweight Mg-based metal–organic framework (MOF), has the desirable properties of permanent porosity, unique stability and adsorption capacities for small molecules. Using in situ infrared (IR) and Raman spectroscopy, we investigated the structure and stability of the α-Mg3(HCOO)6 framework at high pressures up to 13 GPa. We found that the framework structure was chemically stable under compression, while an irreversible crystal-to-crystal structural transition was observed above 2 GPa. This new phase is likely isostructural with microporous γ-Mg3(HCOO)6. In contrast, the α-Mg3(HCOO)6 framework loaded with guest molecules such as dimethylformamide and benzene exhibits higher stability to external pressure. Neither a new crystalline phase nor an amorphous material was observed under pressure up to 13 GPa.
