Site-specific electronic and geometric interface structure of Co-tetraphenyl-porphyrin layers on Ag(111)

Abstract

We present a combined multimethod experimental and theoretical study of the geometric and electronic properties of Co-tetraphenyl- porphyrin (Co-TPP) molecules adsorbed on a Ag(111) surface. Scanning tunneling microscopy (STM) topographs reveal that Co-TPP forms highly regular arrays with a square unit cell. Hereby, the Co-TPP molecules do not occupy a unique adsorption site on the Ag(111) atomic lattice. The central Co atom of the Co-TPP is found to reside predominantly above fcc and hcp hollow sites of the substrate, as determined from the photoelectron diffraction patterns. A strong adsorption-induced deformation of Co-TPP involving a saddle-shaped macrocycle is evidenced by high-resolution STM images and quantified by near-edge x-ray absorption fine-structure measurements. By scanning tunneling spectroscopy we resolved discrete molecular electronic states and mapped the pertaining spatial charge-density distribution. Specifically, we discuss the interaction of orbitals originating from the Co-metal center with the porphyrin macrocycle and show that the varying adsorption sites induce a modulation in the Co-TPP lowest unoccupied molecular orbital. These findings are corroborated by density-functional-theory calculations

Restoring the Co Magnetic Moments at Interfacial Co-Porphyrin Arrays by Site-Selective Uptake of Iron

“…DFT also predicts the Co-TPP adsorbed on Ag-(111) to have no magnetic moment as found in the experiment. As visible from the orbital resolved density of states (DOS) shown in the Supporting Information ( Figure S1) only the d z 2-orbital exhibits a considerable energy broadening as a result of strong hybridization upon adsorption, 45 in agreement with the multiplet calculations including electron hopping only along the d z 2-orbital. A detailed look to the ground state found in the multiplet calculations reveals that the 2.75 holes in the Co d-orbitals are mainly localized on the d x 2 Ày 2-orbital (0.024 electrons per spin channel) and the d z 2-orbital (0.675 electrons per spin channel).…”

“…Figure 2b). 45 Whereas the electronic structure of the Co-TPP/Ag(111) interface is well characterized, 37,45,47À49 the magnetic properties are addressed in this report for the first time. The Co-edge X-ray absorption spectra (XAS) for circular ( Figure 1cÀe) and linear ( Figure 1f) polarized light were measured for the Co-TPP layer with perpendicular and grazing incidences, respectively (see inset in Figure 1c).…”

“…In agreement with earlier reports, six different orientations of the Co-TPP domains are observed. 45 A bright central protrusion, originating from Co atomic states, dominates the appearance of Co-TPP/Ag(111) at low bias voltages (Figure 1a, À0.4 V). 46 At higher negative bias voltages (V b > À0.5 eV), submolecular resolution evidence a 2-fold symmetry of the Co-TPP macrocycle ( Figure 1b).…”

A surface-anchored molecular four-level conductance switch based on single proton transfer

“…1a) combined with near-edge x-ray absorption spectroscopy data (Fig. S1, Supplementary Information) demonstrate that upon adsorption on the Ag(111) surface, the 2H-TPP adapts to a saddle-shaped macrocycle geometry with pairs of opposite pyrrole rings tilted upwards (α-pyr) or downwards (κ-pyr) 18,28 , respectively (Fig. 1b).…”

Cis-dicarbonyl binding at cobalt and iron porphyrins with saddle-shape conformation

“…Here we report a molecular-level investigation on the interaction of carbon monoxide with simple Fe and Co tetraphenyl-porphyrin model systems adopting a distinct saddle-shape conformation, one of the prominent nonplanar macrocycle geometries, following adsorption on a smooth metal surface. 11,12 Our scanning tunneling microscopy and molecular manipulation experiments reveal a surprising carbonyl binding scheme that contrasts the common wisdom of exclusive axial monocarbonyl ligation at biological or related synthetic porphyrin species. Density functional theory calculations for both adsorbed and isolated Co-tetraphenyl-porphyrin demonstrate that CO in fact can bridge specific pyrrole groups with the metal center, which effect is induced by the saddle-shape conformation and explains the observed mono-and cis-dicarbonyl geometries.…”