MOFs with Guest Rooms Metal organic framework (MOF) solids typically boast large pores in their crystal lattices that can accommodate molecular guests and are useful as compact media for gas storage. However, guest binding has generally relied upon nonspecific interactions with the framework components. Li et al. (p. 855 ) have now prepared MOFs that incorporate macrocyclic ethers into the structural ligands comprising the framework walls within which certain cationic guests can bind quantitatively and site-specifically, akin to the molecular docking of drug molecules within protein receptors.