Metal-organic frameworks (MOFs) are composed of metal nodes and organic linkers. These materials have tunable properties that make them useful for applications such as catalysis or gas separation. Creating MOFs using non-toxic metals such as bismuth would be preferable, however, only three Bi-MOFs which retain their porous structure had been reported so far.

Norbert Stock, University of Kiel, Germany, and colleagues have discovered new Bi-MOFs by investigating a combination of bismuth(III) nitrate pentahydrate and a triazine-2,4,6-triyl-trisbenzoic acid linker (H₃TATB, pictured) in mixtures of either water or methanol and dimethylformamide (DMF). Using a water/DMF mixture and long reaction times of about five days, the team synthesized a MOF of the composition [Bi₂(O)(OH)(TATB)], named CAU-35. In a methanol/DMF mixture, a MOF of the type [Bi(TATB)], named CAU-7-BTB, was created in 20 minutes.

The researchers also used an amino-derivative of TATB to create a functionalized MOF with the composition [Bi(TATB-NH₂)]∙5 H₂O∙0.5 DMF (CAU-7-TATB-NH₂). According to the team, this is the first example of a functionalized Bi-MOF. This framework can be further modified by treating it with different anhydrides.

• Synthesis, functionalisation and post-synthetic modification of bismuth metal-organic frameworks,
  Milan Köppen, Ole Beyer, Stefan Wuttke, Ulrich Luening, Norbert Stock,
  Dalton Trans. 2017.
  DOI: 10.1039/c7dt01744h