%0 Journal Article %T Direct Observation of Hydrogen Adsorption Sites and Nano-Cage Formation in Metal-Organic Frameworks (MOF) %A T. Yildirim %A M. R. Hartman %J Physics %D 2005 %I arXiv %R 10.1103/PhysRevLett.95.215504 %X The hydrogen adsorption sites in MOF5 were determined using neutron powder diffraction along with first-principles calculations. The metal-oxide cluster is primarily responsible for the adsorption while the organic linker plays only a secondary role. Equally important, at low temperatures and high-concentration, H2 molecules form unique interlinked high-symmetry nano-clusters with intermolecular distances as small as 3.0 Ang. and H2-uptake as high as 10-wt%. These results hold the key to optimizing MOF materials for hydrogen storage applications and also suggest that MOFs can be used as templates to create artificial interlinked hydrogen nano-cages with novel properties. %U http://arxiv.org/abs/cond-mat/0507220v1