  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.
