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tunneling microscopy techniques will be used to investigate the surface-confined
molecular architectures. Complementary to these two concepts, some examples
exhibiting the surface organization of carbon nanotubes (CNTs), which can be
considered as extended 1D molecule with high aspect ratios, will be discussed.
12.2. METAL ION ARRAYS (MIAS)
12.2.1. Synthesis and Properties of Metal Ion Arrays (MIAs)
Grid-like metal ion arrays (MIAs) represent a class of coordination compounds,
in which a set of metal ions is held in a matrix-like arrangement by a second set of
tailor-made organic ligands. The well defined, two-dimensional (2D) arrangement
of an exact number of metal ions strongly resembles the binary coded matrices and
cross bar architectures used in information storage and processing technology.
The metal ions at the crossing points of the finite network architecture can be
supplied with well defined redox, magnetic, and spin-state transitions (all proper-
ties susceptible to use as switching parameters, either globally or locally) in a
controlled manner. Furthermore, due to their very distinguished rectangular
geometry, such metal ion arrays might self-assemble on surfaces into extended
2D ensembles.
The design of such metal ion arrays rests on the direction of the coordination
instructions, which are based on the cross-over coordination algorithms of both
involved metal ions and the ligand's coordination sites (e.g., nature, geometry,
positions of the donor atoms). Therefore, the design of rectangular metal ion
arrays requires perpendicular arrangements of the ligand planes at each metal
center leading (depending on the topocity n and m of the ligands) to array
structures of the n
m type (for n=m to squares). According to this general
procedure, metal ion arrays can be prepared in principle by careful prearrange-
ment of the subunits using any set of metal ions and organic ligands, which opens
access to a high structural and functional flexibility.
The synthesis of the metal ion arrays follows a mixed synthetic/self-assembly
protocol. The organic ligands (rods in Fig. 12.3) are synthesized by conventional
synthetic procedures, mainly heterocyclic chemistry. It is important that these well
established techniques allow for the deliberate choice of combinations of donor
atoms (e.g., N, O, P, etc.) positioned in different overall geometric environments, a
necessary perquisite for the perpendicular metal ion coordination. The organic
ligands are coordinated by the respective metal ions in solution-based self-
assembly processes yielding the metal ion array molecules (MIAs) as bulk after
removal from the solution (see step (i) in Fig. 12.3, left). Using such a general
procedure, a multitude of square-like [n
n] arrays with n up to 5, but also
rectangular [n
m] and more differentiated [p
[n
m]] metal ion architectures
are currently accessible (Fig. 12.4).
Aside from their synthetic accessibility and broad variability, metal ion arrays
(MIAs) show very interesting physical properties in light of their potential to
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