Ashleigh Jane Fletcher

Mechanochemistry enables the elimination of highly toxic solvents in the synthesis of porous metal–organic polyhedra.

3D ED is used to study the structures of solvent-exchanged phases in zinc paddlewheel-based MOPs.

Zinc paddlewheels are widely found in metal-organic frameworks, but found more sparingly in porous molecules. Here we report some of the first examples of metal-organic polyhedra containing zinc paddlewheels, where structural adaptations in the cages have been observable thanks to the use of 3D electron diffraction.

Metal-organic polyhedra (MOPs) are the porous molecular counterparts to metal-organic frameworks (MOFs). While mechanochemistry has been successfully applied to a wide range of MOFs, this synthetic approach has found more limited use for MOPs. Herein, two mechanochemical routes have been developed for a series of MOPs presenting a lantern geometry. The cages can be formed through: Route 1, grinding with DMA, and therefore achieving a reduction in solvent usage of 90%; or through Route 2, grinding with MeOH to completely eliminate the use of non-volatile, highly toxic solvents. The development of Route 2 is facilitated by 3D electron diffraction, which proved the formation of discrete cages that would otherwise be inaccessible through direct solvothermal synthesis. The degree of crystallinity in all cases of the mechanochemical products is equal or superior to material obtained through solvothermal methods, and presents comparable porosity. As well as presenting a method for improving the sustainability of the synthesis of these cages, this work extends the range of porous cages to which mechanochemistry can be applied. Given the known dependence of the porosity of MOPs on the crystal packing of their parent solvated forms, Route 2 suggests that future work could probe the formation of new solvated phases that display distinct gas sorption behaviour.

Separation of CO ₂ from gas mixtures is important in applications such as CH ₄ gas purification and blue hydrogen production. Here we report selective CO ₂ uptake by a family of flexible silver coordination polymers (AgCPs) that are ostensibly non-porous but exhibit latent porosity to CO ₂ above a gate pressure, through a mechanism akin to dissolution in fluoroalkanes. The CO ₂ sorption properties are rationally modified by changing the perfluoroalkyl chain length of the constituent perfluorocarboxylate ligands. The AgCPs do not take up CH ₄ owing to failure of the dissolution mechanism, consistent with alkane–perfluoroalkane immiscibility. In situ single-crystal and powder X-ray diffraction enable direct visualization of the CO ₂ molecule binding domains. These techniques also reveal associated structural changes in the AgCPs and confirm the gating mechanism of CO ₂ uptake. The combination of perfluoroalkylcarboxylate ligands with the flexible silver(I) coordination sphere generates highly fluorinated but mobile regions of the crystals that play an integral role in the selective uptake of CO ₂ over CH ₄ .

Porous metal‐organic polyhedra (MOPs) have strong covalent and coordinate bonds that define the intrinsic pore of the cage. The intermolecular interactions between cages tend to be weaker, such that they rearrange during the solvent exchange process preceding gas sorption measurements. The reduction in crystal size that this often causes limits the availability of structural data that could enable understanding of observed gas uptake. Herein, we use 3D electron diffraction (ED) to resolve this problem, and apply this technique to a MOP‐based material that shows cooperative gas capture. 3D ED structure solution reveals both that the MOPs rearrange to form porous 1D polymers, and that these polymers are retained in the activated phase. Molecular simulations using these data suggest gas uptake is facilitated by rotation of functional groups appended to the backbone of the polymers in conjunction with structural expansion as gas is accommodated. Mechanical downsizing of the material leads to the loss of cooperative gas uptake, but a level of porosity is retained, attributed to the conservation of the 1D polymer structure. This work underscores the potential of 3D ED for probing structural transformations in functional supramolecular materials.

Porous metal‐organic polyhedra (MOPs) have strong covalent and coordinate bonds that define the intrinsic pore of the cage. The intermolecular interactions between cages tend to be weaker, such that they rearrange during the solvent exchange process preceding gas sorption measurements. The reduction in crystal size that this often causes limits the availability of structural data that could enable understanding of observed gas uptake. Herein, we use 3D electron diffraction (ED) to resolve this problem, and apply this technique to a MOP‐based material that shows cooperative gas capture. 3D ED structure solution reveals both that the MOPs rearrange to form porous 1D polymers, and that these polymers are retained in the activated phase. Molecular simulations using these data suggest gas uptake is facilitated by rotation of functional groups appended to the backbone of the polymers in conjunction with structural expansion as gas is accommodated. Mechanical downsizing of the material leads to the loss of cooperative gas uptake, but a level of porosity is retained, attributed to the conservation of the 1D polymer structure. This work underscores the potential of 3D ED for probing structural transformations in functional supramolecular materials.

Responsive porous materials can outperform more rigid analogues in applications requiring precise triggering of molecular uptake/release, switching or gradual change in properties. We have uncovered an unprecedented dynamic response in the diamondoid MOF SHF‐62 , (Me ₂ NH ₂ )[In(BDC‐NHC(O)Me) ₂ ] (BDC = 1,4‐benzenedicarboxylate), by using pressure as a stimulus. SHF‐62 exhibits two distinct framework “breathing” motions involving changes in 1) cross‐section and 2) length of its 1D pores. Our study using synchrotron single‐crystal X‐ray diffraction in sapphire‐capillary ( p < 0.15 GPa) and diamond‐anvil (0.15 < p < 5 GPa) cells reveals that different pressure regimes trigger positive and negative correlation between these two motions, requiring an unprecedented mechanical decoupling. Specifically, the DMF‐solvated framework SHF‐62‐DMF , in DMF as pressure‐transmitting medium, undergoes initial hyperexpansion of pore cross‐section ( p ≤ 0.9 GPa), due to DMF ingress, followed by reversal/reduction at p > 0.9 GPa while pore length contracts for all pressure increases, revealing decoupling of the two framework deformations. By contrast, nonpenetrating medium FC‐70 imposes correlated compression ( p < 1.4 GPa) of pore cross‐section and length, resembling framework activation/desolvation motions but of greater magnitude. Similar behavior occurs for SHF‐62‐CHCl ₃ in CHCl ₃ ( p < 0.14 GPa), suggesting minimal ingress of CHCl ₃ . These findings change our understanding of MOF dynamic responses and provide a platform for future responsive materials development.