Scientists in Northern Ireland have found a simple and efficient way to make microporous metal-organic frameworks. 

Stuart James and colleagues at Queen's University Belfast formed a microporous metal-organic framework (MOF) by grinding together metal salts and bridging organic ligands, in the absence of solvent. The reaction happens within minutes and without any heating, they report. 

MOFs are polymers made up of alternating metal ions linked by organic molecules. When connected in two or three dimensions, said James, the frameworks are stable enough to support permanent open cavities. This means they have potential for applications like gas storage or molecular sieves. Usually MOFs are formed at high temperature using solvents, but the route developed by James's team offers a greener alternative. 

The team used a ball mill to grind together copper acetate and isonicotinic acid. Then they removed water and by-products to give the porous framework. 

James said he was motivated to pursue this simple method after hearing a talk by Gerd Kaupp at the University of Oldenburg on solvent-free organic synthesis. After purchasing their first ball-mill 'some of my research group were sceptical and wanted to trade it in for a plasma TV,' said James. But colleagues Anne Pichon and Ana Lazuen-Garay 'persevered,' he said, 'and got some remarkable results.' 

So far the team has identified MOFs whose structures are already known by comparing the x-ray diffraction patterns. They say that characterising new MOF structures from the x-ray powder pattern is harder to do, but that this is their goal. The team now collaborates with Sam Motherwell at the Cambridge Crystallographic Data Centre, who is working in this area.

Katherine Davies