Dresden 2020 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Organic Molecules on Inorganic Substrates II: Mainly Porphyrins

O 15.4: Talk

Monday, March 16, 2020, 16:00–16:15, REC C 213

Oxidation-State Tuning and Supramolecular Mixed-Valence Phases: Nickel(II) Porphyrin on Ag(111) — •Jan Herritsch, Qitang Fan, Marie Albus, and J. Michael Gottfried — Fachbereich Chemie, Philipps-Universität Marburg, Germany

Porphyrin complexes are of exceptional importance in the field of surface functionalization. The reactivity and selectivity towards gas molecules depends crucially on the active central atom. Here, we report on the influence of the adsorbate interaction on the electronic structure of a nickel porphyrin (NiOEP) monolayer on coinage metal surfaces studied by XPS and STM. Due to the size mismatch between the small low-spin d8 nickel(II) cation and the larger central cavity of the porphyrin macrocycle, the metal center shows a labile oxidation state which depends on the interaction with the metal surface. On the reactive Cu(111) surface, NiOEP forms a long-range ordered structure in which nickel centers are uniformly reduced, according to XPS. On less reactive Ag(111), NiOEP forms a mixed-valent adsorbate phase in which the Ni centers occur in two different oxidation states. The two separate peaks in the Ni 2p XP spectrum indicate that about 40 % of the Ni centers are reduced. STM shows a superstructure with an ordered arrangement of the metal centers in different oxidations states. Analysis of misaligned metastable domains reveals that the registry with the substrate is critical for obtaining the mixed-valence superstructure. On the most inert Au(111) surface, the oxidation state of the Ni centers remains unaffected by adsorbate interactions.