Metal-organic framework (MOF) structure, molecular model. MOFs are highly crystalline porous materials made up of 3D networks of metal ions connected by organic molecules. This is MOF-5, which has benzodicarboxylic acid connecting zinc-oxygen clusters (red and gold). Up to 91 per cent of their volume can be made up by nanoscale pores. Uses of MOFs include gas storage, gas purification, gas separation, or as catalysts. Hydrogen atoms are not shown in this view.