Metal-organic frameworks (MOFs) are highly tunable, porous crystalline materials formed through the coordination-driven self-assembly of organic linkers and metal nodes.1 Through careful ligand design, a vast number of reactive groups and functionalities can be incorporated into MOF structures to tailor their properties. By incorporating vacant coordination sites into the organic linkers, MOFs can undergo post-synthetic metalation (PSMet) with secondary metal species without disrupting the overall framework.2 These MOFs can act as crystalline sponges, enabling single-crystal X-ray analysis of otherwise unstable or reactive metal species.
Here, we report the isoreticular expansion of flexible indium-based MOFs. These MOFs are synthesised from tetratopic pyrazole-carboxylate linkers of different lengths, one containing an additional phenyl spacer. The resulting series comprises two honeycomb MOFs (InMOF-1 and InMOF-10) with hexagonal pore channels (15 Å and 30 Å, respectively) and two wine-rack MOFs (InMOF-3 and InMOF-30) with diamond-shaped pore channels (12 Å and 18 Å, respectively). All four MOFs contain accessible bispyrazole sites poised for PSMet. Differences in framework flexibility and structural strain result in varying extents of PSMet, providing insight into the structural factors governing this process.