Glycoluril-Based Metal-Organic Frameworks

The glycoluril building blocks have only been connected via their NH sides in all the previously reported structures in porous material science, supramolecular chemistry, and many other fields. Here, we present the design and synthesis of a new glycoluril-based metal-organic framework (MOF) through the substitution of dibenzoic moieties in the methine positions of the glycoluril motif. Urea reacts with 4,4'-dioxo-[1,1'-biphenyl]-3,3'-dicarboxylic acid (the 1,2-diketone derivative) to form 4,4'-(2,5-dioxotetrahydroimidazo[4,5-d]imidazole-3a,6a(1H,4H)-diyl)dibenzoic acid (the glycoluril derivative). The reaction proceeds via cyclocondensation, yielding a rigid linker with four free NH groups, two terminal carboxylic acids, and a curved backbone suitable for MOF coordination and molecular recognition. The synthesis of NS-MOF (Zn or Zr) was successfully achieved using a solvothermal method involving the reaction of a glycoluril-based linker with zinc nitrate hexahydrate in dimethylformamide (DMF). The properties of the new MOF structures are discussed for potential applications from gas storage and separation to catalysis and biomedical delivery systems.