On‐Surface Metalation and 2D Self‐Assembly of Pyrphyrin Molecules Into Metal‐Coordinated Networks on Cu(111)

Abstract

The metalation of the tetradentate molecule pyrphyrin by copper substrate atoms on a Cu(111) surface is studied. Pyrphyrin, in contrast to porphyrin, consists of four fused pyridine groups instead of pyrrol groups. Using thermal desorption spectroscopy (TDS) and N 1s X‐ray photoelectron spectroscopy (XPS), we show that metalation of the monolayer of pyrphyrin with Cu atoms from the Cu(111) surface occurs at 377 K. The formation of an extended two‐dimensional (2D) network is observed with scanning tunneling microscopy (STM). A honeycomb‐like lattice of metalated pyrphyrin molecules is formed by intermolecular connection via the two cyano groups at the periphery of pyrphyrin as well as Cu adatoms. Dehydrogenation at the periphery of the molecule is observed during annealing at 520 K. The surface‐adsorbed metal‐pyrphyrin has the potential to serve as a molecular catalyst.

Identification of On-Surface Reaction Mechanism by Targeted Metalation

“…Second, the experimental data is consistent with two components which are Fe bound nitrogen (399.25 eV) in the macrocycle and cyano-N (398.8 eV). The same has been observed in N1s XP spectra acquired from in-situ synthesized CoPyr22 and CuPyr23 . Third, the C / N reveals that the cyano groups are not removed.…”

“…[22][23][24] Pyrphyrin has three non-equivalent nitrogen species, but due to the similar chemical shifts of the cyano nitrogen (-CN, 398.8 eV) and the iminic nitrogen (=N-, 399.1 eV), only two peaks are observed. 22,23 The pyridinic nitrogen (-NH-) is found at 400.8 eV. 22,23 Very similar spectra are observed for 3 ML 2HPyr on Ag(111) ( Figure S2).…”

“…[26][27][28][29] The N1s binding energy of the nitrogens in the macrocycle (398.4 eV) is consistent with N-Ag in Ag-phthalocyanine obtained by metalation on Ag(110) 26 and significantly lower than for N-Cu in Cu-pyrphyrin/Cu(111). 23 Due to the small size of the pyrphyrin macrocycle, it is unlikely that a Ag adatom penetrates the macrocycle and is coordinated exactly in the molecular plane. Presumably, is weakly coordinated somewhat below the molecular plane.…”

Ranking the Stability of Transition-Metal Complexes by On-Surface Atom Exchange

“…Under low bias voltage tunneling conditions with generally high tunnel current set-points and with a suitable STM tip, a shallow protrusion in the center may be seen in CuPyr. 26 As shown later, under these conditions, NiPyr can be distinguished by its brighter central contrast from CuPyr. Normal tunneling conditions are used to distinguish FePyr from CuPyr or NiPyr.…”

“…All atom exchange and metalation experiments in this study start from 1 monolayer (ML) of 2HPyr on Cu(111), obtained by thermal sublimation of the molecule onto the sample kept at 295 K. One ML CuPyr is obtained by metalation of 2HPyr by annealing to 423 K. 26 Under normal tunneling conditions the center of CuPyr appears dark (i.e., low) because the Cu 3d orbitals in this square-planar complex lack out-of-plane states around the Fermi energy. 26−30 Because out-of-plane 3d states are also absent in low-spin Ni(II) complexes, they are also imaged dark.…”