Post‐Synthetic Modification Unlocks a 2D‐to‐3D Switch in MOF Breathing Response: A Single‐Crystal‐Diffraction Mapping Study

Abstract Post‐synthetic modification (PSM) of the interpenetrated diamondoid metal–organic framework (Me 2 NH 2 )[In(BDC‐NH 2 ) 2 ] (BDC‐NH 2 =aminobenzenedicarboxylate) SHF‐61 proceeds quantitatively in a single‐crystal‐to‐single‐crystal manner to yield the acetamide derivative (Me 2 NH 2 )[In(BDC‐NHC(O)Me) 2 ] SHF‐62 . Continuous breathing behaviour during activation/desolvation is retained upon PSM, but pore closing now leads to ring‐flipping to avert steric clash of amide methyl groups of the modified ligands. This triggers a reduction in the amplitude of the breathing deformation in the two dimensions associated with pore diameter, but a large increase in the third dimension associated with pore length. The MOF is thereby converted from predominantly 2D breathing (in SHF‐61 ) to a distinctly 3D breathing motion (in SHF‐62 ) indicating a decoupling of the pore‐width and pore‐length breathing motions. These breathing motions have been mapped by a series of single‐crystal diffraction studies.