Functional (Supra)Molecular Nanostructures - ruben-group

Habilitation Dr. Mario Ruben
ULP Strasbourg
the occurrence of the Nagaoka mechanism, [48] in which, due to the Pauli principle, a missing
or an excess electron on the ligands (relative to half-filling of the LUMO) can be delocalized
maximally, if the “background” of the remaining electrons is completely spin polarized. Such
a mechanism might open novel ways to molecular high-spin states by the bridging ligand
based reduction of AF-coupled metal ions in multinuclear complexes. [49]
7.2. Current Induced Tunneling Spectroscopy on Co4L 1 4
(in collaboration with Prof. P. Müller, University of Erlangen, Germany)
The structural elucidation of the coordination characteristics of metal centers and coordination
compounds in close contact to metallic surfaces has been described in chapter 4.2.C, but in
order to approach and eventually to use the functionalities of molecular nanostructures in
devices, the influence and eventual feed-back of the environment (here the surface) on the
physical properties of the molecules has to be investigated in detail.
As a test case for the property-environment relationship, we have chosen the grid-like
[Co II 4L 1 4](BF4)8 molecules, those peculiar electronic properties in solution have been
described in detail before (chapter 7.1.). An acetonitrile solution of [Co II 4L 1 4] 8+ molecules was
sputtered onto freshly cleaved graphite substrates at room temperature, where isolated or 1D
arrangements could be used in spectroscopic investigations (Figure 26). In the constant
current STM-mode, the molecules appeared as bright uniform spots without an internal
structure, whereby no direct evidence for the presence of the BF4-anions could be obtained.
Apparently, at room temperature the electrostatically bound BF4-anions show at room
temperature a too fast kinetics to be observed in the STM set-up used.
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