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

Abstract

Our first-principles calculation shows that molecular hydrogen (H₂) 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–H₂ interaction, where H₂ coordinates onto the Fe(II) center as a σ-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 H₂ binding energies are 0.08 and 0.35 eV per H₂ at the HS and LS states, respectively. This effect is expected to find applications in spin-control in molecular magnets, hydrogen sensing and storage.