Porous materials that can selectively capture or separate gases are attracting increasing attention because of their potential applications in energy and environmental technologies, such as carbon dioxide capture and hydrogen storage. In 2025, research on metal–organic frameworks (MOFs)—porous crystalline materials composed of metal ions and organic molecules—was awarded the Nobel Prize in Chemistry, highlighting the importance of this field. MOFs contain nanoscale pores that allow them to incorporate various molecules and gases.
In this study, we focused on the siloxane linkage (Si–O–Si), whose bond angle can flexibly change, and connected it to a tungsten complex to synthesize a flexible molecular framework that exhibits high adsorption capacity for methane (CH₄) and oxygen (O₂). Single crystal X ray diffraction revealed that the molecules assemble in the crystal to form a narrow one dimensional channel that initially contains solvent molecules. Powder X ray diffraction showed that the crystal structure reversibly changes upon solvent removal and reabsorption, and micro ED analysis of the solvent free crystal indicated that the crystal axes contract by up to ~14%. Gas adsorption measurements demonstrated that the framework takes up five methane and four oxygen molecules per mole and releases them under reduced pressure, exhibiting “gate opening” behavior arising from its structural flexibility. These results show that siloxane based molecular design provides an effective strategy for creating flexible porous materials with potential applications in gas separation, molecular recognition, and related functions.
