The Magnetic Behaviour of CoTPP Supported on Coinage Metal Surfaces in the Presence of Small Molecules: A Molecular Cluster Study of the Surface trans-Effect.

Silvia Carlotto,Luca Floreano,Iulia Cojocariu,Vitaliy Feyer,Maurizio Casarin

doi:10.3390/nano12020218

Abstract

Density functional theory, combined with the molecular cluster model, has been used to investigate the surface trans-effect induced by the coordination of small molecules L (L = CO, NH3, NO, NO2 and O2) on the cobalt electronic structure of cobalt tetraphenylporphyrinato (CoTPP) surface-supported on coinage metal surfaces (Cu, Ag, and Au). Regardless of whether L has a closed- or an open-shell electronic structure, its coordination to Co takes out the direct interaction between Co and the substrate eventually present. The CO and NH3 bonding to CoTPP does not influence the Co local electronic structure, while the NO (NO2 and O2) coordination induces a Co reduction (oxidation), generating a 3d8 CoI (3d6 CoIII) magnetically silent closed-shell species. Theoretical outcomes herein reported demonstrate that simple and computationally inexpensive models can be used not only to rationalize but also to predict the effects of the Co–L bonding on the magnetic behaviour of CoTPP chemisorbed on coinage metals. The same model may be straightforwardly extended to other transition metals or coordinated molecules.

Highlights

Transition metal porphyrinato (MP) and phthalocyaninato (MPc) complexes hold a prominent position among countless adsorbates because of their unique characteristics
We present and discuss the outcomes of a series of density functional theory (DFT)-based calculations, carried out by adopting the molecular cluster model to rationalize and hopefully predict the magnetic behaviour of cobalt tetraphenylporphyrinato (CoTPP) surface-supported on different metallic surfaces (Scheme 1), mimicked by a single atom and interacting at the same time with diverse L (L = CO, NH3, NO, NO2 and O2, Scheme 1)
Optimized Cartesian coordinates of the free L molecules, of the free CoTPP complex, and of the MS–CoTPP, CoTPP–L, and MS–CoTPP–L clusters are reported in Tables S1–S29 of the Supplementary Materials (SM), while bonding energies (BEs) and oxidation states for each molecule/adduct/cluster considered are collected in Tables S30–S38 of the SM

Summary

Introduction

Transition metal porphyrinato (MP) and phthalocyaninato (MPc) complexes hold a prominent position among countless adsorbates because of their unique characteristics. Even though a rationale for these evidences has been provided by periodic DFT numerical experiments [18,21,25,26,29,33], it has been shown that less expensive calculations may adequately model experimental results (“switching on”/“switching off” the spin interaction) [15,17,25] In this contribution, we present and discuss the outcomes of a series of DFT-based calculations, carried out by adopting the molecular cluster model to rationalize and hopefully predict the magnetic behaviour of CoTPP surface-supported on different metallic surfaces (Scheme 1), mimicked by a single atom (hereafter, MS; see below) and interacting at the same time with diverse L (L = CO, NH3 , NO, NO2 and O2 , Scheme 1). A schematic sketch of isolated and interacting systems is reported in the inset

Computational Details

Results and Discussion

Conclusions