Altering the spin state of transition metal centers in metal-organic frameworks by molecular hydrogen adsorption: a first-principles study

Our first-principles calculation shows that molecular hydrogen (H-2) adsorption at an exposed Fe(II) site in metal-organic frameworks could induce a spin flip in the Fe(II) center resulting in a spin-state transition from a triplet high-spin (HS) to a singlet low-spin (LS) state. The Kubas-type Fe-H-2 interaction, where H-2 coordinates onto the Fe(II) center as a sigma-ligand, is found commensurate in strength with the exchange interaction of Fe 3d electrons, which is responsible for the occurrence of the spin-state transition in this system. The H-2 binding energies are 0.08 and 0.35 eV per H-2 at the HS and LS states, respectively. This effect is expected to find applications in spin-control in molecular magnets, hydrogen sensing and storage.