Tuning the flexibility of interpenetrated frameworks by a small difference in the fluorene moiety.

[Zn2(FDC)2(bpy)] (LMOF-202) and [Zn2(OFDC)2(bpy)] (LMOF-201) (FDC: fluorene-2,7-dicarboxylate, OFDC: 9-fluorenone-2,7-dicarboxylate, bpy: 4,4'-bipyridine) have interpenetrated isostructures. However, their gas sorption behaviors indicate that LMOF-202 is rigid, whereas LMOF-201 is flexible. We found that the structural flexibility of LMOF-201 was due to the addition of only one oxygen atom into the ligand.