Crystalline sponges are series of organometallic networks developed by Japanese chemist Makoto Fujita. The organic small molecules are  absorbed into the void space of the crystalline sponges. Since the organometallic network of crystalline sponges can interact with the small molecule substrates via non-covalent interactions, the absorption can be selective. That is, the crystalline sponge can enrich certain molecules from a mixture.
As the crystal sponges are highly organized frameworks, the structure of the whole host-guest complex can be characterized by X-ray diffraction. Because the absorbate is encapsulated in a pre-organized environment, no single crystal of the substrate is needed in the X-ray diffraction. Besides, the X-ray crystallography of liquid samples can also be conducted.