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40
20
1
2
11 10 9
8
7
65
43
0
Electrons
−
20
−
40
−
60
−
80
−
3.0
−
2.5
−
2.0
Potential Ev(Qj) Fc
−
1.5
−
1.0
−
0.5
0.0
(a)
(b)
=
2] CO
4
II
[2
×
[2
×
2] CO
4
II
CO
2
II
=
Figure
12.5.
(a) Solution cyclovoltammogramm showing the well-resolved single
electron reductions of a [22] Co
I
4
metal ion array in potential window between
0 and 3V. Below, the X-ray structure and its translation into the cellular
automata symbol are shown [15a]. (b) STM image showing the aligning of the
[22] Co
I
4
metal ion arrays along the step edges of a graphite substrate after
drop casting [16]. (c) Constitution and symbol of the mixed valence [22]
Co
I
2
Co
II
2
metal ion array [17].
However, questions concerning the degree of intramolecular delocalization and
the strength of the intermolecular Coloumb interaction remain to be investigated
before the utility of the metal ion arrays within the frame of the cellular automata
concept can be proven. In addition, on the apparatus' side, single molecule
techniques discriminating between the two charge states of a cell rest to be
developed as feasible read-out tools.
Among the physical molecule properties that may be considered for magnetic,
molecular data storage systems, the spin transition (ST) phenomenon featuring
the transition between the low spin (LS) and the high spin (HS) states of Fe
II
ions
is an attractive process [18]. Molecular ST systems possess a unique concomitance
of possible ''write'' (temperature, pressure, light) and ''read'' (magnetic, optical)
parameters [19]. Investigations along these lines revealed spin transition behavior
in several [2
2] Fe
4
II
metal ion arrays. The internal spin states of the incorpo-
rated Fe
II
ions can be switched successively between their diamagnetic Fe
II
(LS)
and the paramagnetic Fe
II
(HS) spin states by applying external field triggers
(temperature, pressure, light) on macroscopic samples (Fig. 12.6) [10, 20].
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