SKM 2023 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 22: Poster Session: Organic Molecules on Inorganic Substrates I

O 22.8: Poster

Montag, 27. März 2023, 18:00–20:00, P2/EG

Ligand Size Controls Surface Chemical Bond: Cobalt Porphyrin versus Cobalt Corrole on the Ag(111) Surface — •Cong Guo, Grigori Pasko, Jan Herritsch, and J. Michael Gottfried — Fachbereich Chemie, Philipps-Universität Marburg

The development of novel functional materials based on biologically relevant molecules such as cobalamins, also referred to as vitamin B12, is an important research topic. In particular, cobalt tetrapyrrole complexes which are related to cobalamins are often-used and well-understood model systems. Due to the structural complexity of the ligands, their interaction and bonding at interfaces is still poorly understood. Using XPS, we compare here a cobalt(II) porphyrin with a related cobalt(III) corrole. The latter exhibits a smaller ring size and acts as a trianionic ligand. In the multilayer, the Co 2p signal of the porphyrin shows the typical appearance of a paramagnetic Co²⁺ center. The corresponding Co 2p signal of the corrole has a similar shape indicating the presence of unpaired electrons in the Co 3d subshell. In the monolayer on Ag(111), both complexes are subject to an interfacial charge transfer from the substrate, as can be seen by the Co 2p signals. Thus, the singly occupied orbitals at the cobalt center are accepting electron density from the substrate. However, the N 1s signal and the valence photoemission spectra indicate that the corrole interacts much stronger with the substrate which is confirmed by periodic DFT calculations. Our study reveals that the two adsorbed complexes differ substantially in their overall interaction with the Ag surface, even though cobalt has a similar electronic state in both cases.