Dynamic properties of a flexible metal-organic framework exhibiting a unique "picture frame" -like crystal morphology

The precise control of the crystal morphology of metal-organic frameworks (MOFs) enables optimization of its adsorptive properties, as well as enables better integration within functional devices. However, the influence of such modifications on the dynamic properties of flexible MOFs is poorly understood. Here, we report the synthesis of a series of Cu₂(bdc)₂(bpy) (bdc^2- = 1,4-benzenedicarboxylate; bpy = 4,4’-bipyridine) crystals having an unusual picture frame-like morphology that results from a restriction in the quantity of bpy pillars added to the reaction mixture during the intercalation of the Cu₂(bdc)₂(MeOH)₂ layers. The width of the frames is found to correlate with the quantity of bpy, and importantly, causes the dynamic properties of the resulting Cu₂(bdc)₂(bpy) material to vary between rigid, elastic, and shape memory modes. In all, the results demonstrate the potential for the properties of MOFs to be optimized via subtle manipulations in the crystal morphology rather than changes in the overall material composition.