Intertube Interactions in Multivariant Metal-Organic Nanotubes

Incorporating disparate functionalized ligands into phase-pure metal-organic frameworks (MOFs) has been shown to produce multivariate MOFs (MV-MOFs) whose properties often exceed those of the corresponding linker-pure MOFs. The ability to easily prepare MV-MOFs is due to covalent bonds linking MOF ligands and secondary building units in all three dimensions, leaving ample space for the ligands inside the 3D pores. In contrast, metal-organic nanotubes (MONTs), a one-dimensional subclass of MOFs, aggregate into crystalline materials via noncovalent interactions between the tubes. This stark contrast to 3D MOFs leads to increased difficulty in synthesizing MONTs generally, but multivariate MONTs (MV-MONTs) in particular, because interactions between tubes may prevent packing. To investigate the importance of these noncovalent interactions, a series of MV-MONTs were synthesized from binary combinations of three ligands. Each ligand formed a MONT by itself, while also containing different noncovalent interaction modes between the tubes. All MONTs were characterized by complementary diffraction techniques and bulk measurements, including single-crystal X-ray diffraction, ¹H NMR after acid digestion, and powder X-ray diffraction. Intertube interactions in MV-MONTs were found to play a key role in their structures and phase purities in a manner rarely observed in MOFs.