Functional (Supra)Molecular Nanostructures - ruben-group

Habilitation Dr. Mario Ruben
ULP Strasbourg
the ligand altered the spin transition behavior only marginally. Improving the intermolecular
interaction between the tetranuclear centers by introduction of H-bonding between the grid
units (compound 12) increased the HS fraction over the whole temperature range, although
the spin transition remained very gradual and incomplete.
The general result, that the substituent R 1 = Ph produces the most complete spin
transitions properties, while substituent R 2 can be varied without having direct influence on
the spin transition properties of the [Fe II 4L 1 4] system, leads to the design of ligands A and B,
where R 2 is a 4-pyridyl and 3-pyridyl group, respectively (see Figure 4). As shown in chapter
4.1., ligands A and B constitute the structural base for hierarchical self-assembly processes of,
on first level, the gridlike complexes [Fe II 4A4] (1) and [Fe II 4B4] (2), respectively, and, on a
higher level, of the molecular column- and wall-like architectures {[Fe II 4A4]-(La III )4}n 11+ (3)
and {[Fe II 4B4]-(Ag I )4}n 12+ (4) (see Figure 4).
The magnetic solid state investigations revealed that the spintronic modules 1 and 2
represent a collectively generated coordination [2x2] array displaying gradual spin transition
behaviour (Figure 19). In the higher–order architectures 3 and 4, the magnetic behaviour of
the included [Fe II 4L 1 4] spintronic modules exhibits a progressive hindrance of the spin
transition process with increasing dimensionality (Figure 19). Thus, the whole magnetic curve
of the 1D “column”-like architecture 3 is shifted to higher temperature (in comparison to
module 1) by around 200 K. This can be interpreted as a increased preference for Fe II (LS) at
ambient conditions. In contrary, the 2D “wall”-like architecture 4 is blocked at a 2HS / 2LS
situation and does not show any switching behaviour between Fe II (HS) and (LS) states
obviously due to increased steric hindrance in the interconnected, in comparison to the lattice
structure of 2 much stiffer, 2D network.
The variation of the spin transition behaviour at different organisational levels, as
realized in the coordination sequence from A/B to 1/2 to 3/4, show how the architectural
parameters feed back actively on the intrinsic functionalities of complex supramolecular
assemblies.
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