Single molecule magnets grafted on gold: magnetic properties from ab initio molecular dynamics

Abstract

The computational characterization of the single molecule magnet (SMM) [Fe 4 (AcS(CH 2 ) 5 C(CH 2 O) 3 ) 2 (dpm) 6 ] (Fe 4 C 5 ) with Ac = CH 3 CO and Hdpm = dipivaloylmethane, grafted on the Au(111) surface (Fe 4 C 5 @Au (111)) is presented. For the first time, ab initio molecular dynamics (AIMD) calculations have been used to study the evolution of the structural properties of a SMM once adsorbed on a metallic substrate. Important structural rearrangements induced by the grafting process can be observed thanks to the AIMD approach. This allows us to elucidate some possible mechanisms that govern the SMM's magnetism on a surface, which wouldn't be revealed by the standard static approach. The sampling of the SMM@Au(111)'s configurational space at finite temperature, together with magneto-structural correlations, makes it possible to study the fluctuation amplitude of magnetic properties, thus revealing that a single minimum of the free energy surface (FES) is populated at 200 K. Starting from the finite temperature scenario, the potential energy surface (PES) was sampled by means of thermal annealing calculations showing that multiple local minima could be populated at 0 K. Both isotropic exchange coupling constants and zero field splitting (ZFS) parameters are calculated for the identified Fe 4 C 5 @Au(111) local minima, thereby allowing an in-depth characterization of the Fe 4 C 5 magnetic properties from the isolated to the grafted scenario. The cutting-edge computational protocol used here shows that the experimentally observed retention of a spin S = 5 ground state upon grafting results from balancing the major modifications on spin Hamiltonian (SH) parameters. The electronic effects of the metal on the magnetic properties of Fe 4 C 5 have been also discussed.

Propeller‐Shaped Fe4 and Fe3M Molecular Nanomagnets: A Journey from Crystals to Addressable Single Molecules

“…Such a finding is not fully unexpected, though not detected in X‐ray absorption experiments. Indeed, ab initio molecular dynamics calculations showed that Fe 4 molecules chemically grafted on a gold surface can access several configurations with similar energy . The differences in the geometrical parameters of such configurations are comparable with those estimated from Mössbauer spectra and significantly affect important SH parameters, such as J values and single‐ion anisotropies.…”

“…Especially relevant to the present Microreview are R groups that allow to promote and control chemisorption on metals, , , , or carbon substrates, from solution. For R = (CH 2 ) n SAc, a fine control of molecular orientation on Au(111) was achieved by tuning the length ( n ) of the spacer unit between the Fe 4 core and the surface‐binding terminations, as detailed below , , . However, some 3 R complexes are also suitable for electrospray deposition (ESD) or even thermal sublimation in UHV.…”

The Role of Anisotropic Exchange in Single Molecule Magnets: A CASSCF/NEVPT2 Study of the Fe_4 SMM Building Block [Fe₂(OCH₃)₂(dbm)₄] Dimer

“…Indeed, although its relatively small intensity, this property happens to be rapidly modulated by the FeOFe degree of freedom, which has been demonstrated to vary of several degrees due to thermal fluctuations [38,39], and thus opening a possible efficient relaxation pathway.…”

The Role of Anisotropic Exchange in Single Molecule Magnets: A CASSCF/NEVPT2 Study of the Fe4 SMM Building Block [Fe2(OCH3)2(dbm)4] Dimer

“…The results presented in the work highlight a possible relevant role of the anisotropic interaction in the SMMs relaxation processes. Indeed, although its relatively small intensity, this property happens to be rapidly modulated by the FeOFe degree of freedom, which has been demonstrated to vary of several degrees due to thermal fluctuations [38,39], and thus opening a possible efficient relaxation pathway. …”