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CF
3
F
3
C
O
O
Cu
O
O
F
3
C
OH
CF
3
Cu(hfac)
2
L
4
OH
N
O
CF
3
F
3
C
O
O
Cu
N
O
O
CF
3
F
3
C
OH
O
L
4
Scheme 13.4
Cu(II)-O
•
-N
5cm
−
1
the
{
<
}
exchange cluster was ferromagnetic (J
=
13
±
)
; that is, the ground state was
H
2
J S
1
S
2
)
the triplet state (here and below the Hamiltonian is recorded as
=−
.Thiseffect,thatis,the
Cu(II)-O
•
-N
possibility of ferromagnetic exchange in the
exchange cluster or mutual repulsion of odd
electrons during direct coordination of the paramagnetic organic fragment to the paramagnetic metal ion,
was explained later.
52-56
The discovery of this phenomenon stimulated the development of the molec-
ular design of heterospin molecular magnets. Molecular magnets will be returned to later; now, another
important result of studies reported in
51
is considered.
From a chemical viewpoint, Cu(hfac)
2
L
4
can be synthesized with the use of water-containing reagents.
This indicates that if a nitroxide contains a strong and readily coordinated donor group, direct coordination
between the metal and the nitroxyl group can appear in the course of crystallization, that is, in the
formation of close packing. Moreover, the product can either be an insoluble polymer phase or simply the
most insoluble solid phase in the given synthetic system.
Possible difficulties in the use of this synthetic approach are evident. Firstly, along with the functional
group on the nitroxide, other donor molecules present in the reaction mixture can take part in coordi-
nation to the metal ion.
57-60
{
<
}
For example, using water-containing solvents or reagents in the reaction of
H
2
O with L
5
led to the formation of Cu(hfac)
2
L
5
(H
2
O), in which the surroundings of the central
atom included a water molecule (Scheme 13.5). This molecule was hydrogen bonded with the oxygen atom
of the nitroxyl group L
5
of the adjacent molecule of the complex, which led to the formation of polymer
chains in the solid. Nevertheless, there is no direct coordination between the metal and the nitroxyl group
in the solid complex. Scheme 13.6 shows the case with donor groups blocking all coordination sites, which
hindered the formation of a polymer structure.
The potential development of the polymer chain restricts the formation of molecules that are converted
into
Cu(hfac)
2
·
a
multinuclear
structure.
Scheme
13.7
shows
different
variants
of
heterospin
complexes
with
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