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.