Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

We report a strategy to expand the pore aperture of metal-organic frameworks (MOFs) into a previously unattained size regime (>32 angstroms). Specifically, the systematic expansion of a well-known MOF structure, MOF-74, from its original link of one phenylene ring (I) to two, three, four, five, six, seven, nine, and eleven (II to XI, respectively), afforded an isoreticular series of MOF-74 structures (termed IRMOF-74-I to XI) with pore apertures ranging from 14 to 98 angstroms. All members of this series have noninterpenetrating structures and exhibit robust architectures, as evidenced by their permanent porosity and high thermal stability (up to 300°C). The pore apertures of an oligoethylene glycol-functionalized IRMOF-74-VII and IRMOF-74-IX are large enough for natural proteins to enter the pores.

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