Stable guest-free porous molecular crystals are uncommon. By contrast, organic molecular crystals with guest-occupied cavities are frequently observed, but these cavities tend to be unstable and collapse on removal of the guests—this feature has been referred to as ‘virtual porosity’. Here, we show how we have trapped the virtual porosity in an unstable low-density organic molecular crystal by introducing a second molecule that matches the size and shape of the unstable voids. We call this strategy ‘retro-engineering’ because it parallels organic retrosynthetic analysis, and it allows the metastable two-dimensional hexagonal pore structure in an organic solvate to be trapped in a binary cocrystal. Unlike the crystal with virtual porosity, the cocrystal material remains single crystalline and porous after removal of guests by heating.
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The authors gratefully acknowledge the Engineering and Physical Sciences Research Council (EP/H000925/1) and European Research Council (ERC) under the European Union's Seventh Framework Programme/ERC Grant Agreement No.  for financial support. K.E.J. is a Royal Society University Research Fellow. We thank R. Clowes for assistance with the sorption measurements and S. Higgins for assistance with the robotic handling apparatus. The authors thank Diamond Light Source for access to beamlines I19 (MT8728) and I11 (EE9282) that contributed to the results presented here and also M. R. Warren and S. A. Barnett for their assistance during the single-crystal gas cell studies.
The authors declare no competing financial interests.
Supplementary information (PDF 14892 kb)
Crystallographic data for 2(CC3-R)([3+2]#5) at 400K. (CIF 2363 kb)
Crystallographic data for 2(CC3-R)([3+2]#5) at 450K. (CIF 2334 kb)
Crystallographic data for (CC3-R)2.[3+2]#5 at 100K. (CIF 2632 kb)
Crystallographic data for (CC3-R)2.[3+2]#5 at 300K. (CIF 2559 kb)
Crystallographic data for (CC3-R)2.[3+2]#5 under dynamic vacuum. (CIF 1427 kb)
Crystallographic data for (CC3-R)2.[3+2]#5.(CHCl3)2.(MeOH)8 at 100K. (CIF 2765 kb)
Crystallographic data for (CC3-R)2.[3+2]#5.(CHCl3)0.5.(MeOH)1.5 at 300K. (CIF 2744 kb)
Crystallographic data for (CC3-R)2.(CH2Cl2)0.5.(MeOH)11.(H2O)10.5. (CIF 5903 kb)
Crystallographic data for (CC3-R)2.(CHCl3)3.(MeOH)7.(H2O)4.75. (CIF 4810 kb)
Crystallographic data for Reduced [3+2]#4.(H2O)15. (CIF 2725 kb)
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Little, M., Briggs, M., Jones, J. et al. Trapping virtual pores by crystal retro-engineering. Nature Chem 7, 153–159 (2015). https://doi.org/10.1038/nchem.2156
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