On-Surface Atom-by-Atom-Assembled Aluminum Binuclear Tetrabenzophenazine Organometallic Magnetic Complex

Abstract

The Kondo effect results from the interactions of the conduction electrons in a metal bulk with localized magnetic impurities. While adsorbed atop a metallic surface, the on-surface nanoscale version of this effect is observed when a single magnetic atom or a single magnetic molecule (SMM) is interacting with the conduction electrons. SMMs are commonly organometallic complexes incorporating transition-metal atoms in different oxidation states. We demonstrate how a single nonmagnetic neutral tetrabenz­o­[a,c,j,h]­phenazine molecule can be on-surface-coordinated with exactly two aluminum metal atoms (between Al­(I) and Al­(II) oxidation state on the Au(111) surface) by low-temperature scanning tunneling microscope (LT-STM) single-atom manipulation. It results in a Kondo measurable localized molecular magnetic moment. This opens a new way to design SMM complexes without the need for heavy transition-metal atoms and complex ligands to stabilize the molecular coordination sphere.

Doublet-Singlet-Doublet Transition in a Single Organic Molecule Magnet On-Surface Constructed with up to 3 Aluminum Atoms

“…Zooming now around the Au(111) Fermi energy, i.e., around zero bias voltage, d I /d V Kondo resonances were observed when positioning the STM tip apex at the center of the Al 1 and Al 3 complexes but not observed at the center of the bare HATA molecule nor at the center of its Al 2 complex (Figure a). As already demonstrated on Au(111), even with no transition metal atom involved, the on-surface coordination of an aza-like aromatic molecule with Al adatoms is able to create noninteger spin states delocalized on the conjugated molecular core of this complex . Here, we went a step further, observing an on-surface doublet-singlet-doublet transition with no d electron transition metal atom involved.…”

“…On-surface coordination chemistry uses various metals (Au, Ag, Cu, Fe, etc.) and ligands (cyano, isociano, pyridyl, carboxylic chemical groups), resulting in the formation of different coordination complexes as compared to solution chemistry. − For example, a 3-fold coordination is typically encountered using a single Au adatom on a Au(111) metal surface, but not in solution. − For a light nontransition-metal atom-like aluminum, we have recently demonstrated that its oxidation state on a Au(111) surface is between Al­(I) and Al­(II), leading to the on-surface formation of a magnetic molecule after coordinating two Al adatoms to a tetrabenzophenazine nonmagnetic molecule . Such light-atom magnetic molecule is not accessible in solution yet.…”

“…Looking at the electronic structure of the Al x –HATA complexes, we find that the Al 1 and Al 3 complexes are spin-polarized, as it can be observed on the DFT calculated projected densities of states (PDOS) (Figure c). This spin polarization can be understood by considering that each Al atom donates around two electrons, one to the molecule and one to the surface, such that each Al atom is in an oxidation state between Al­(I) and Al­(II) on the Au(111) surface . When the number of Al atoms is odd, the molecule gets an odd number of electrons, which gives rise to an unpaired electron and, therefore, to spin polarization.…”

A Single-Molecule Digital Full Adder

“…9 For the metal inputs, we have selected single Al ad-atom since the oxidation state of a single Al on Au (111) is between Al(I) and Al(II). 10 The LT-UHV-STM molecular manipulations are used to stabilize a single Al ad-atom in the middle of two nitrogen atoms on different branches of an aza-starphene molecule and leads to a change of its tunneling spectrum.…”

“…To benefit from the complete calculating power of our aza-starphene molecule, we have also exploited the magnetic properties of aza conjugated molecules when coordinated with Al ad-atoms on the Au(111) surface. 10 As described below, it brings the sum logical output of our aza-starphene molecule-adder exactly at a V = 0 bias voltage according to The experimental results presented here were obtained with a low temperature ultra-high vacuum 4-STM instrument (LT-UHV 4-STM) having four independent LT-UHV-STM able on the same surface to operate in parallel with the same dI/dV spectral and atomic manipulation precisions than a single tip LT-UHV-STM. 11 The atomically clean Au (111) single crystal surface was prepared by a repeated Ar+ sputtering and heating up to 780 K in UHV.…”