Ferrous to Ferric Transition in Fe‐Phthalocyanine Driven by NO₂ Exposure

Abstract

Due to its unique magnetic properties offered by the open‐shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d‐states of FePc and the sp‐band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The FeII ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO2 at room temperature.

Influence of the Fluorination of Iron Phthalocyanine on the Electronic Structure of the Central Metal Atom

“…23,31 For FePc monolayers on Cu(100), three different spin configurations of the Fe ion have been observed upon exposure to NO 2 . 32 In general, magnetic properties of transition-metal compounds depend strongly on the transfer of charge between dorbitals and delocalized ligand states. 22,33 In particular, iron complexes are very flexible in their spin state, 34,35 and the electronic ground state of Fe in FePc has not yet been completely understood.…”

“…Magnetic properties of transition metal phthalocyanines on metal surfaces can be modified by magnetic coupling to the substrate, which can suppress their local magnetic moment. , A graphene buffer layer between a ferromagnetic substrate and the phthalocyanine layer can be inserted to modify the magnetic interaction , or tune the charge transfer at the interface . In this context, graphene may even enable a ferromagnetic or antiferromagnetic coupling. , The coupling between central metal ion and a magnetic layer is often mediated by the organic ligands. ,− Another route to tune electronic properties at interfaces might be a chemical doping. , For FePc monolayers on Cu(100), three different spin configurations of the Fe ion have been observed upon exposure to NO 2 …”

Distortion-driven spin switching in electron-doped metal porphyrins

“…The VB spectrum of the pristine NiTPP layer deposited on Au(111) is consistent with a weak adsorbate–substrate interaction: no peak due to charge transfer phenomena, frequently present at strongly interacting adsorbate–substrate interfaces, 23,25,26 is observed and only features determined by the ionization from the topmost occupied MOs (HOMO/HOMO−1) are detected (see Fig. 1(b) and (c)) and assigned using the photoemission tomography (PT) method (see Methods section for further details).…”

Semiconductor Halogenation in Molecular Highly‐Oriented Layered p–n (n–p) Junctions

“…In the past, the PT approach has been already successfully employed to study the geometry and electronic structure of molecular semiconductors, such as metal porphyrins and phthalocyanines, in self‐assembled single‐layered arrays on metal substrates. [ 27–29 ] From Figure 1c, we note that the resemblance of simulated and measured HOMO state of a 1u symmetry (BE = 1.30 eV) and two degenerate LUMO/LUMO+1 states of e g symmetry (BE = 0.48 eV) is clear; thus, the emission peaks can be assigned to the two molecular states of MPc. The adsorption onto the silver substrate lowers the HOMO‐LUMO energy gap to 0.82 eV, substantially reduced compared to the isolated molecule, where theoretically, a value of 1.58 eV has been reported.…”