Chemistry Reference
In-Depth Information
by IET is well known as “valence tautomerism” in a metal complex, especially in cobalt-semiquinone
complexes.
55
This phenomenon is speculated to arise from intermolecular hydrogen bond between the
carbonyl moieties in TTF-
6OPO
and the solvent trifluoroethanol, which is absent in dichloromethane
solution. Characterization of the solid state properties and possible switching by applying external stimuli,
such as an electrostatic field or light, is of particular interest in creating novel molecular functionality. In
particular, the realization of a “photo-induced spin center transfer” is also intriguing from the viewpoint
of the solar cell application.
55,56
3.9 Phenalenyl-based zwitterionic radicals
Among the topological isomers of hydroxyphenalenones, synthetic precursors of the
OPO
,9-
hydoroxyphenalenone have a hydroxyl group and a carbonyl group at the adjacent
peri
positions, similar
to acetylacetone. Thus, the corresponding anion derivative can act as a chelate ligand for metal ions. In
the 1970s, 9-hydoroxyphenalenone-based metal complexes,
[PLY(O,O)]
2
M
(
M
transition metal ions
such as Co
2
+
,Zn
2
+
,Mn
2
+
,Ni
2
+
,andFe
2
+
or main group elements such as Na
+
,Mg
2
+
,Be
2
+
,andAl
3
+
),
were prepared.
57a
-
e
Each phenalenyl moiety in these metal complexes is in monoanionic (nonradical)
state. In 1986, Haddon focused on
[PLY(O,O)]
2
Be
and
[PLY(O,O)]
2
B
, and for the first time succeeded
in generating zwitterionic radicals by electrochemical reduction.
57f
Haddon's subsequent studies led to
successful isolation of a series of spiro-conjugated bisphenalenyl boron complexes
[PLY(O,N)]
2
+
B
−
,
58-64
[PLY(N,N)]
2
+
B
−
,
65
and
[PLY(O,O)]
2
+
B
−
.
66
The negative charge on the boron atom is formally
neutralized by the positive charge on one of the phenalenyl ligands, giving the zwitterionic radical
structure. Furthermore, because of the perpendicular nature of the
=
-conjugated planes of the two
phenalenyl moieties, a spiro-conjugated interaction between the molecular orbitals derived from the
NBMO of the pristine
PLY
permits full delocalization of spin and charge. Among these complexes,
the hexyl derivative
[PLY(O,N)]
2
+
B
−
(R
1
π
n
-Hex) was the first phenalenyl-based single-component
molecular conductor, showing a room temperature conductivity of
=
05 S/cm (Figure 3.43), although
there are no intermolecular contacts shorter than van der Waals radius (3.4 A for C
σ
=
0
.
C).
58,67,68
···
This
θ
=−
complex shows a weak antiferromagnetic interaction with Weiss constant of
10 K.
R
3
R
4
M=
Co
2+
,
Zn
2+
,
Mn
2+
,
Ni
2+
,
Fe
2+
,
Na
+
,
Mg
2+
,
Be
2+
,
Al
3+
,
B
3+
O
N
R
2
O
O
N
N
CH
3
O
O
R
1
R
1
=
Et,
n
-Pr,
n
-Bu,
n
-Pen,
n
-Hex,
n
-Oct,
Benzyl,
Cyclohexyl,
Cycloheptyl,
Cyclooctyl
-
B
-
M
B
B
-
R
1
N
O
R
2
O
O
H
3
C
N
N
O
O
+
+
+
R
2
=CH
3
,R
3
=H
R
2
=CH
3
,R
3
=CH
3
R
2
= Hexyl, R
3
=H
R
4
R
4
=H,CH
3
R
3
[PLY(O,N)]
2
+
B
-
[PLY(O,O)]
2
M
[PLY(N,N)]
2
+
B
-
[PLY(O,O)]
2
+
B
-
The ethyl derivative
[PLY(O,N)]
2
+
B
−
(R
1
ethyl) and the butyl derivative
[PLY(O,N)]
2
+
B
−
(R
1
n
-
butyl) show “magneto-optical-electronic bistability”, in which remarkable changes in magnetic, optical, and
=
=
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