title: Probing nitrosyl ligation of surface-confined metalloporphyrins by inelastic electron tunneling spectroscopy.
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.
authors.affiliation: Laboratoire de Chimie, CNRS UMR 5182, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 CEDEX07 Lyon, France.
authors.forename: Shiri R
authors.initials: SR
authors.lastname: Burema
authors.forename: Knud
authors.initials: K
authors.lastname: Seufert
authors.forename: Willi
authors.initials: W
authors.lastname: Auwärter
authors.forename: Johannes V
authors.initials: JV
authors.lastname: Barth
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Bocquet