Speaker
Description
Metal-organic frameworks (MOFs) – porous periodic structures, consisting of metal nodes connected via organic linkers – offer a platform for designing materials with tailored electronic properties, owing to their modular chemistry. They host transition metal ions serving as active site for molecular binding, catalysis and magnetic applications. By employing a bottom-up approach on a suitable surface template, MOFs can be synthesized even at the 2D level. Here, I will present a thorough characterization of a porphyrin-based MOF, obtained by nickel deposition on self-assembled manganese tetrapyridylporphyrin (MnTPyP) on Au(100). A multi-technique approach combining low-energy electron diffraction, X-ray photoelectron and absorption spectroscopy, was employed to address the on-surface arrangement of the 2D-MOF, as well as the oxidation states of the metal nodes. Finally, angle-resolved photoemission spectroscopy (ARPES) allowed performing orbital tomography measurements and thus, accessing the geometrical and electronic properties of this 2D-MOF. In particular, we identify a $(5\sqrt{2}\times5\sqrt{2})$R45° 2D-MOF superstructure on Au(100). The symmetry match between MnTPyP and the substrate suppresses the formation of additional rotational domains, which is a significant advantage for ARPES analysis. The change of the resulting momentum maps indicates the formation of hybrid orbitals – a hallmark for MOF formation. For the metal-centers in the 2D-MOF, spectroscopic measurements point towards the +2 oxidation state in case of manganese, while nickel appears to be Ni(I). Overall, our results reveal the successful coordination of the molecules with nickel, yielding a well-ordered 2D-MOF with defined coordination geometry and electronic structure modifications at the metal centers.