Chemistry Reference
In-Depth Information
(a)
(b)
Figure3.43
(a) Stereo view along b-axis and (b) electric conductivity of
[PLY(O,N)]
2
+
B
−
(R
1
=
n-Hex) in the
crystal.(a,bReprintedwithpermissionfrom[58].Copyright1999AmericanChemicalSociety.)
High temperature
paramagnetic state
Low temperature
diamagnetic state
(a)
(b)
Figure3.44
(a)Crystalstructureofand(b)interconversionbetweenthediamagnetic
π
dimer(lowtemperature
dimer(hightemperatureform)of
[PLY(O,N)]
2
+
B
−
(R
1
form)andtheparamagnetic
π
=
ethyl).
electrical properties in the crystalline state depend on temperature.
59
The
n
-butyl derivative possesses a
high electrical conductivity of 0.14 S/cm at around 347 K
59,60
as single-component molecular conductor,
67,68
and forms
dimers than the sum of van der
Waals radius of carbon atom (Figure 3.44a). At temperatures below 320 K, each complex possesses a
spin in the
π
dimers in the crystal without shorter contacts between
π
dimer regions and shows an antiferromagnetic interaction. In a sharp contrast, above 350 K
each complex shows paramagnetic behavior because the spins reside mainly on the phenalenyl moieties
not directly involved in the
π
dimer (Figure 3.44b). This dynamic spin behavior induces a simultaneous
elongation of the intradimer distance from 3.2 to 3.3 A and significant changes in IR transmittance spectra
(Figures 3.45a - c). Figures 3.45d - f show the temperature dependence of IR transmittance, conductivity,
and magnetic susceptibility of
[PLY(O,N)]
2
+
B
−
(R
1
π
n
-butyl). These three physical property changes
occur within the temperature range 320 - 350 K and are hysteretic in nature, indicating the bistability of the
system. An occurrence of the phase transition above room temperature is a rare event, and in general
=
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