A new family of porous metal-organic frameworks (MOFs) with flexible ligands has been created by UK scientists.

MOFs consist of metal atoms linked by organic ligands. Their porous structure allows them to capture and store gases such as hydrogen and carbon dioxide.

Usually MOFs are made using rigid ligands, but Lee Brammer at the University of Sheffield and colleagues used flexible tetracarboxylate ligands to create their zinc-based MOFs. The flexibility of the ligands allowed their material to rearrange itself when carbon dioxide was removed or replaced.

'The field of MOFs has tremendous potential to deliver applications in a wide range of areas, for example molecular storage, sensing, separation science and catalysis,' said Brammer. 'Our strategy may prove particularly useful for gas storage purposes where flexibility may enable effective "shrink wrapping" of the trapped molecules,' he added.

 'This work really highlights how reactive these materials can be,' said Stuart James, an expert in MOFs from Queen's University, Belfast. 'Whereas conformational flexibility is now quite well-known, bond-breaking and a change of topology during gas sorption is much more dramatic.'

Susan Batten