Probing nitrosyl ligation of surface-confined metalloporphyrins by inelastic electron tunneling spectroscopy

Shiri R. Burema, Knud Seufert, Willi Auwärter, Johannes V. Barth, Marie Laure Bocquet

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20 Scopus citations

Abstract

Complexes obtained by the ligation of nitric oxide (NO) to metalloporphyrins represent important model systems with biological relevance. Herein we report a molecular-level investigation of surface-confined cobalt tetraphenyl porphyrin (Co-TPP) species and their interaction with NO under ultrahigh vacuum conditions. It is demonstrated that individual NO adducts can be desorbed using the atomically sharp tip of a scanning tunneling microscope, whereby a writing process is implemented for fully saturated regular metalloporphyrin arrays. The low-energy vibrational characteristics of individual Co-TPP-nitrosyl complexes probed by inelastic electron tunneling spectroscopy (IETS) reveal a prominent signature at an energy of ≃31 meV. Using density functional theory-based IETS simulations-the first to be performed on such an extensive interfacial nanosystem-we succeed to reproduce the low-frequency spectrum for the NO-ligated complex and explain the absence of IETS activity for bare Co-TPP. Moreover, we can conclusively assign the IETS peak of NO-Co-TPP to a unique vibration mode involving the NO complexation site, namely, the in-plane Co-N-O rocking mode. In addition, we verify that the propensity rules previously designed on small aromatic systems and molecular fragments hold true for a metal-organic entity. This work notably permits one to envisage IETS spectroscopy as a sensitive tool to chemically characterize hybrid interfaces formed by complex metal-organic units and gaseous adducts.

Original languageEnglish
Pages (from-to)5273-5281
Number of pages9
JournalACS Nano
Volume7
Issue number6
DOIs
StatePublished - 25 Jun 2013

Keywords

  • Ag(111)
  • DFT
  • NO
  • STM
  • inelastic electron tunneling spectroscopy
  • porphyrin

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