Spectroscopic Evidence for the Influence of the Benzene Sites on Tightly Bound H2 in Metal−Organic Frameworks with Unsaturated Metal Centers: MOF-74-Cobalt

The role of low binding energy sites on the adsorption of H2 in metal−organic frameworks (MOFs) with unsaturated metal centers has not been identified. For instance, the importance of the benzene sites on H2 adsorption at the metal site in MOF-74 has not been established. We report here experimental evidence that unambiguously shows that the internal mode of H2 adsorbed at the metal site undergoes both a frequency shift and a marked change in its dynamic dipole moment when H2 is adsorbed at the next nearest neighbor “benzene” site in MOF-74-Co. The effect of loading (i.e., occupation of all benzene sites) also induces spectroscopic shifts in H2 at the metal site. These interactions highlight the role of lower binding energy sites in H2 adsorption.