Spin-crossover complexes are attractive for their spinswitching functionality. However, only few compounds have been found to remain intact in direct contact to metal surfaces. For the design of new spin-crossover complexes, it is important to understand the mechanisms leading to fragmentation. Here, we investigate, using low-temperature scanning tunneling microscopy along with density functional theory calculations, two Fe(terpyridine) 2 complexes deposited on Au(111) by electrospray ionization with in-line mass selection. Only fragments of the first compound are observed on the surface, while the second compound is strongly flattened. Based on a detailed analysis of the adsorbates on the surface, possible mechanisms for the fragmentation and molecular distortion are proposed.

Magnetic sandwich complexes are of particular interest for molecular spintronics. Using scanning tunneling microscopy, we evidence the successful deposition of 1,3,5-tris(η-borabenzene-η-cyclopentadienylcobalt) benzene, a molecule composed of three connected magnetic sandwich units, on Cu(111). Scanning tunneling spectra reveal two distinct spatial-dependent narrow resonances close to the Fermi level for the trimer molecules as well as for molecular fragments composed of one and two magnetic units. With the help of density functional theory, these resonances are interpreted as two Kondo resonances originating from two distinct nondegenerate d-like orbitals. These Kondo resonances are found to have defined spatial extents dictated by the hybridization of the involved orbitals with that of the ligands. These results opens promising perspectives for investigating complex Kondo systems composed of several "Kondo" orbitals.

Interconnected molecular magnetic centers on metallic surfaces are of interest for molecular spintronics. Complexes composed of two or three cobaltocene units linked by naphthalene or benzene groups are successfully deposited on Au(111) and Cu(111) by sublimation and electrospray deposition. Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate the deposited compounds and their spin state. Although all molecules are composed of the same magnetic cobaltocene unit, only one compound shows a zero-bias feature compatible with a Kondo resonance, whose amplitude varies from molecule to molecule. The amplitude variation and its absence for the other investigated complexes are attributed to different molecule− substrate coupling, which is strongly influenced by the linker. Parameters influencing the molecule−substrate coupling and molecular properties are extracted from the experimental data. These key parameters should be considered for future strategies of interconnected magnetic centers on metallic substrates.

Adding ligands to molecules can have drastic and unforeseen consequences in the final products of a reaction. Recently a surface trans effect due to the weakening of a molecule-surface bond was reported. Here, we show a surface cis effect where an axial ligand at adsorbed transition-metal complexes enables lateral bonding among the molecules. In the absence of this ligand, the intermolecular interaction is repulsive and supramolecular patterns are not observed. Fe-tetramethyl-tetraazaannulene on Au(111) was investigated using low-temperature scanning tunneling microscopy and spectroscopy along with density functional theory calculations. At low coverages, the molecules remain isolated. Exposure to CO leads to axial CO bonding and induces reordering into extended clusters of chiral molecular trimers. The changed self-assembly pattern is due to a CO-induced modification of the molecular structure and the corresponding charge transfer between the molecule and the substrate, which in turn changes the lateral intermolecular forces.

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