Functional (Supra)Molecular Nanostructures - ruben-group

2. Summary
Habilitation Dr. Mario Ruben
ULP Strasbourg
The self-assembly of functional molecular nanostructures was investigated in solution, in
the solid state, and at surfaces. Hydrogen bonding and metal ion coordination concepts were
used to organize the supramolecular structures. Hierarchical self-assembly was studied
rendering solid state molecular nanostructures with increasing complexity: Organic ligands
were used in a first organization level to self-assemble tetranuclear [M II 4L4] array structures,
which preorganize the coordination site sets for second-level assembly steps resulting in a 1D
columnar and in wall-like 2D layer superstructures. Furthermore, in situ metal ion
coordination directly on metallic surfaces rendered infinite grid-like 2D network
nanostructures with a ([M II 2L4/2])n steochiometry. Unusual coordination geometries for the
coordinated metal ion dimers were observed at the crossing points of the networks, where the
metal ions are coordinated to organic ligands in close contact to the metallic surfaces.
In solution and in solid state, the optical, magnetic and electrochemical properties of
different series of grid-type complexes of the general composition [M II 4L4]X8 (with M =
transition metal) were investigated thoroughly. Optically, Co II 4-complexes displayed pH-
dependent absorption behaviour in the visible spectrum (pale-yellow to deep-violet) in
solution. Magnetically, the intramolecular exchange coupling behaviour of Co II 4-complexes
was investigated and the results allowed them to be described as molecular metamagnets. The
analogous Fe II 4-complexes exhibit evidence of the spin transition phenomena for the Fe II -ions,
whereby the emergence of the spin transition is directly coupled to the nature of the ligand.
All ligand systems which favor strong ligand fields remain completely in the diamagnetic low
spin state, while ligands which attenuate the ligand field by steric (and to a lesser extent
electronic) effects exhibit spin transition behavior triggered by temperature, pressure and
light. The hierarchical self-assembly of complex supramolecular architectures allows for the
emergence of different spin transition properties at different levels of complexity. Thus, each
of the two levels of structural complexity generated by the two sequential self-assembly steps
corresponds the emergence of novel functional features due to the modulation of the intrinsic
spin transition process.
For the first time, quantum tunneling of the strongly anisotropic magnetic moment of
complexes of the type [Ln(Pc)2] - was observed and a new class of so-called Single-Ion
Molecular Magnets (SIMMs) is described. The effective barrier height determined for the
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