Decoupled MOF breathing: pressure‐induced reversal of correlation between orthogonal motions in a diamondoid framework

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, (Me2NH2)[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, non-penetrating 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 behaviour occurs for SHF-62-CHCl3 in CHCl3 (p<0.14 GPa), suggesting minimal ingress of CHCl3. These findings change our understanding of MOF dynamic responses and provide a platform for future responsive materials development.