Hydrogen Adsorption on Fe-based Metal Organic Frameworks: DFT Study

We study the interaction of H2 molecule with Fe-based MOF cluster which has square paddle-wheel cage structure using the density functional theory-based (DFT-based) calculations. We find that H2 molecule can be adsorbed on the Fe site of MOF-Fe cluster with a side-on configuration and MOF-H2 distance of about 2.071 Å. This adsorption is facilitated by the interaction of 1σ orbital of the molecule and dz2 -like orbital of MOF-Fe cluster. We also find that the subsitution of MOF's metal center from Cu to Fe could significantly strengthen the hydrogen interaction with the MOF. This is because one of important antibonding state between 1σ orbital of H2 with dz2 -like orbital of MOF is only partially occupied in MOF-Fe system, while it is fully occupied on MOF-Cu.