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

Post‐synthetic modification (PSM) of the interpenetrated diamondoid metal–organic framework (Me2NH2)[In(BDC‐NH2)2] (BDC‐NH2=aminobenzenedicarboxylate) SHF‐61 proceeds quantitatively in a single‐crystal‐to‐single‐crystal manner to yield the acetamide derivative (Me2NH2)[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. Post‐synthetic modification of diamondoid MOF SHF‐61 generates its methylamide analogue [(Me2NH2)[In(BDC‐NH(CO)Me)], SHF‐62, as single crystals. Resulting ligand steric demands and H‐bonding capability lead to a change in dimensionality of the MOF breathing behaviour from 2D breathing (pore width) to 3D breathing (pore width and length), which has been mapped by single‐crystal X‐ray diffraction.