Ligand Influence on Local Magnetic Moments in Fe-Based Metal–Organic Networks

International audiencePlanar metal−organic networks are highly promising materials due to their modular nature and wide-ranging possible applications from spintronics up to biosensing. Spin state transitions connect local magnetic properties with structural modifications. In this paper, we report on ab initio calculations for two metal− organic planar networks, the Fe-phthalocyanine (Pc) polymer and its precursor material Fe-tetracyanobenzene (TCNB). The spin-polarized generalized gradient approximation to density functional theory with an explicit treatment of the Hubbard-U correction (SGGA+U) indicates a spin state transition between the well confirmed S = 1 state for Fe-Pc and a local, high-spin S = 2 state at the Fe site for Fe-TCNB. The high-spin state at the Fe site is confirmed by X-ray absorption spectroscopy (XAS) measurements of the Fe-TCNB network on the Au(111) substrate in connection with a multiplet analysis. We propose a possible spin state transition between Fe-TCNB and Fe-Pc by the on-surface synthesis of the latter compound. The ab initio results prove also a high chemical stability of the Fe-TCNB network, metallic and ferromagnetic behavior, as well as a partial screening of the Fe spin S = 2 by two antiparallel electrons on the ligand sites to a state with total spin of S = 1. All of this makes the Fe-TCNB network an interesting material for spintronics applications