Molecular crystals cannot be designed like macroscopic objects because they do not assemble according to simple, intuitive rules. Their structure results from the balance of many weak interactions, unlike the strong and predictable bonding patterns found in metal–organic frameworks and covalent organic frameworks. Hence, design strategies that assume a topology or other structural blueprint will often fail. Here, we combine computational crystal structure prediction and property prediction to build energy–structure–function maps describing the possible structures and properties available to a candidate molecule. Using these maps, we identify a highly porous solid with the lowest density reported for a molecular crystal. Both crystal structure and physical properties, such as the methane storage capacity and guest selectivity, are predicted using the molecular diagram as the only input. More generally, energy–structure–function maps could be used to guide the experimental discovery of materials with any target function that can be calculated from predicted crystal structures, such as electronic structure or mechanical properties.

The stable, guest-free crystal form of the simple molecular cavitand, Me,H,SiMe2, is shown to be intrinsically porous, possessing discrete, zero-dimensional (0D) pores/microcavities of about 28 Å(3). The incollapsible 0D pores of Me,H,SiMe2 have been exploited for the enclathration and room temperature (and higher) confinement of a wide range of small gases. Over 20 isostructural x(gas/guest)@Me,H,SiMe2 (x ≤ 1) clathrates (guest = H2O, N2, Ar, CH4, Kr, Xe, C2H4, C2H6, CH3F, CO2, H2S, CH3Cl, CH3OCH3, CH3Br, CH3SH, CH3CH2Cl, CH2Cl2, CH3I, CH3OH, BrCH2Cl, CH3CH2OH, CH3CN, CH3NO2, I2), and a propyne clathrate (CH3CCH@Me,H,SiMe2·2CHCl3), have been prepared and characterized, and their single crystal structures determined. Gas enclathration is found to be highly selective for gases that can be accommodated by the predefined, though slightly flexible 0D pore. The structure determinations provide valuable insight, at subangstrom resolution, into the factors that govern inclusion selectivity, gas accommodation, and the kinetic stability of the clathrates, which has been probed by thermal gravimetric analysis. The activation (emptying) of several clathrates (guest = H2O, N2, CO2, Kr, CH3F) is shown to occur in a single-crystal-to-single-crystal (SC → SC) fashion, often requiring elevated temperatures. Akin to open pore materials, water vapor and CO2 gas are shown to be taken up by single crystals of empty Me,H,SiMe2 at room temperature, but sorption rates are slow, occurring over weeks to months. Thus, Me,H,SiMe2 exhibits very low, but measurable, gas permeability, despite there being no obvious dynamic mechanism to facilitate gas uptake. The unusually slow exchange kinetics has allowed the rates of gas (water vapor and CO2) sorption to be quantified by single crystal X-ray diffraction. The data are well fit to a simple three-dimensional diffusion model.

So far, most organic semiconductor photocatalysts for solar fuels production have been linear polymers or polymeric networks with a broad distribution of molecular weights. Here, we study a series of...

The guest-free crystal forms of eight related small molecule cavitands (Scheme 1; simplified nomenclature: R,R',Y) are investigated as candidate discrete molecule microcavity materials (DMMMs). Due to their rigid bowl-like molecular structures, many cavitands are incapable of efficient crystal packing in pure form, yielding zero-dimensionally porous apohost phases. By molecular modifications that eschew self-inclusion, emphasis is placed on engineering structures that exhibit uniform microcavities that are large enough to accommodate small molecules of interest (e.g., gases or volatile organic compounds). The most thermodynamically stable guest-free crystal forms of several cavitands-namely, H,H,CH 2 , H,Me,CH 2 , α-Me,H,CH 2 , Me,Me,CH 2 , Br,Me,CH 2 , Me,Et,CH 2 , Me,Et,SiMe 2 , and Me,i-Bu,CH 2 -appear to be as-close-packed-as-possible, yet exhibit relatively large microcavities (or, zero-dimensional pores) in the range of 27-115 Å 3 . Where self-inclusion is ineffective, the microcavities predictably assimilate the intrinsic cavitand molecular cavity, yet the ultimate size and shape of cavities are also strongly influenced by crystal packing. It is demonstrated that some cavitand solvates, CH 2 Cl 2 @H,Me,CH 2 , xH 2 O@Me,Et,SiMe 2 , and CH 2 Cl 2 @Me,iBu,CH 2 (84:16 rccc:rcct) maintain host crystal packings that are equivalent to their empty, intrinsically porous phases and it is argued that the intrinsic pores of DMMMs are particularly suited to selective gas enclathration and/or storage. As a proof-ofconcept demonstrations, the porous phase of Me,Et,SiMe 2 is shown to capture and temporarily hold Freon-41 (fluoromethane, bp = -78 °C) at room temperature. A single crystal of empty Me,Et,SiMe 2 is shown to uptake CO 2 gas at room temperature, allowing structure determination of xCO 2 @Me,Et,SiMe 2 , and single-crystal-to-single-crystal dehydration of xH 2 O@Me,Et,SiMe 2 demonstrates its permeability to water.

A hydrogen-bonded organic framework is an effective photocatalyst for producing hydrogen from water. Its crystal structure is key to its activity; a chemically identical, amorphous version is almost inactive, as rationalized by crystal structure prediction.