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Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
3
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
2.5
S
=
3/2
R
R
Cl
Cl
2
Cl
Cl
Cl
Cl
1.5
Cl
Cl
Cl
S
=
1
Cl
Cl
Cl
1
Cl
Cl
Cl
S
=
1/2
0.5
H
-
3
•
R
=
H, H
H
-
3
••
3
•••
R
=
H,
•
0
0
40
80
120
160
R
=•
,
•
Appl. Magn. Field (KOe)
Figure2.6
Fieldstrengthdependenciesofexperimentalmolarmagnetizationsofradicals3
•••
,
H-3
••
and
2H-3
•
.
Solid lines are the calculated molar magnetization curves. Dashed lines are theoretical molar magnetization
curves for S
/
2
paramagnetic molecules. (Reprinted with permission from [18b]. Copyright 1993
AmericanChemicalSociety.)
=
3
/
2
,1and
1
Magnetization measurements of radicals
3
•••
,
H
-3
••
and
H
-3
•
at 4.2 K in the magnetic field range 0 - 5 T
are depicted in Figure 2.6 as a function of the magnetic field
H
. The data can be compared with the
theoretical magnetization curves of ideal paramagnets with
S
/
2
, respectively. Calculated
magnetization curves indicate that the ground states of radicals
3
•••
,
H
-3
••
and
H
-3
•
are the quartet
(
=
3
/
2
,land
1
S
=
3
/
2
)
, triplet (S
=
1) and doublet (S
=
1
/
2
), respectively, in excellent agreement with EPR and
susceptibility results.
Metallocene Units as Intramolecular Ferromagnetic Couplers
One of the basic tools to realize high-spin
molecules is the finding of bridges that may act as robust ferromagnetic couplers when they are connected
to two (or more) open shell subunits. Metallocenes have been used very successfully as building blocks
of molecular solids promoting intermolecular magnetic interactions.
41
Based on their electronic structures
and rich chemistry, metallocenes appear to be promising candidates as ferromagnetic couplers. With this
objective, diradical
6
, consisting of two PTM radical subunits connected by a 1,1
-metalloceneylene bridge,
was constructed. The particular structure and topology of
6
were expected to lead to a non-negligible spin
density on the metallocene moiety, making the magnetic coupling between the two organic radical subunits
feasible. In addition, the location of both radical units far away from each other avoided any possibility of
having intramolecular through-space contacts and, consequently, a significant direct through-space magnetic
interaction.
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