Visualizing Intramolecular Distortions as the Origin of Transverse Magnetic Anisotropy

Abstract

The magnetic properties of metal-organic complexes are strongly influenced by conformational changes in the ligand. The flexibility of Fe-tetra-pyridyl-porphyrin molecules leads to different adsorption configurations on a Au(111) surface. By combining low-temperature scanning tunneling spectroscopy and atomic force microscopy, we resolve a correlation of the molecular configuration with different spin states and magnitudes of magnetic anisotropy. When the macrocycle exhibits a laterally-undistorted saddle shape, the molecules lie in a S=1 state with axial anisotropy arising from a square-planar ligand field. If the symmetry in the molecular ligand field is reduced by a lateral distortion of the molecule, we find a finite contribution of transverse anisotropy. Some of the distorted molecules lie in a S=2 state, again exhibiting substantial transverse anisotropy.

Structural Transformation of Surface‐Confined Porphyrin Networks by Addition of Co Atoms

“…Furthermore, the orientation of the molecules with respect to each other can be discerned within the unit cell (black square) overlaid in Figure 2c, where the pyridyl endgroups of neighboring Ni‐DPPyP molecules align parallel to each other. This arrangement is similar to the orientation observed for tetraphenyl and tetrapyridyl porphyrins on metal substrates [29–31] . As shown in the tentative structural model (Figure 2d) the 2D network is stabilized by H‐bonding between the electronegative N‐atom of the pyridyl endgroup and one H‐atom from a neighboring pyrrole moiety [29,31] .…”

Electronic structure of an iron porphyrin derivative on Au(1 1 1)

“…The desorption goes along with a reduction of the oxidation state of Fe from III+ to II+. This assignment of the oxidation state of Fe and the loss of the Cl ligand is corroborated by measurements of inelastic spin excitations, which revealed an integer spin state of S=1 or S=2 depending on the molecular assembly [42]. increases around -0.6 V and around -1.3 V a broad resonance is observed.…”

Robust magnetic anisotropy of a monolayer of hexacoordinate Fe(ii) complexes assembled on Cu(111)

“…It has been shown recently that for planar molecules such as Fe(II)-phtalocyanin or Fe(II)-porphyrin, not only the magnetic anisotropy but also the spin state can be strongly modified on the surface, depending on the adsorption geometry, 3,4 local distortions, and intermolecular interactions. 5 The origin of this large change in the spin electronic structure of this type of molecules is the relatively flexible and unsaturated coordination sphere of Fe(II). They possess, however, a large thermodynamic stability that allows keeping their integrity when sublimated under vacuum and assembled on metallic substrates.…”