Chemistry Reference
In-Depth Information
solution before use and connected to an external constant current power supply with
no glass frit between cathode and anode. The target coatings, (BEDT-TTF)
2
PF
6
,
have been prepared with BEDT-TTF, TBA
·
PF
6
supporting electrolyte and purified
5
µ
Acm
−
2
) lead to conventional EC and after
48 h tiny black needle crystals scattered on the gold electrode can be observed.
However, for higher current densities of about 10
µ
Acm
−
2
, densely covered black
microcrystalline coatings are produced after 22 h identified as (BEDT-TTF)PF
6
salts. Increasing the current to 20
µ
Acm
−
2
results in (BEDT-TTF)(PF
6
)
2
and
soaking the films in a BEDT-TTF solution overnight leads to the desired (BEDT-
TTF)
2
PF
6
salt.
The second example uses large surface silicon electrodes as anodes (Pilia
et al.
, 2004). Intrinsic-type silicon wafers have a sufficiently high conductivity
(
TCE. Low current densities (
≤
−
1
cm
−
1
) to be used as electrodes. As far as large surface electrodes
are concerned, the use of silicon affords evident benefits versus platinum or gold
in terms of maintenance and cost. We illustrate here the case of the preparation
of
10
−
3
∼
-(BEDT-TSF)
4
[Fe(CN)
5
NO], where [Fe(CN)
5
NO]
−
2
is the photochromic ni-
troprusside anion. The experimental electrodeposition procedure uses an intrin-
sic Si(100) one-face-polished wafer (5 cm diameter, 275 mm thickness) as anode
and a platinum wire as cathode. The silicon wafer is stripped in an NH
4
HF solu-
tion and then washed in distilled water before use. Solutions of BEDT-TSF and
(PPh
4
)
2
[Fe(CN)
5
NO] in TCE and ethanol are introduced into a Schlenk-type cylin-
drical one-compartment electrochemical cell. The galvanostatic oxidation of the
donor is performed at 298 K and at a current density of 0.1 mA cm
−
2
. Within
2 days, microcrystals are observable, which grow homogeneously on the silicon
electrode. A
θ
1
µ
m thin film is obtained after typically 7 days of electrolysis.
When the electrolysis is conducted for 4 weeks typically 60 mg of product can be
collected by scratching the substrate using a glass slide. This is a clear advantage
because it can be regarded as an alternative synthesis method. Figure 3.13 shows a
picture of the experimental set-up.
Following this procedure thin films of TTF[Ni(dmit)
2
]
2
have been prepared us-
ing the following experimental conditions and their metallic character will be dis-
cussed in Section 6.4. A solution of TTF and TBA
∼
·
[Ni(dmit)
2
] in freshly distilled
and degassed CH
3
CN is introduced into the anodic compartment of an H-shaped
electrochemical cell. TBA
[Ni(dmit)
2
] as supporting electrolyte in CH
3
CN is in-
troduced into the cathodic compartment. Galvanostatic electrolysis is conducted at
constant current density of 1.5
µ
Acm
−
2
(de Caro
et al.
, 2004).
·
Dipping
In the case of TTF-TCNQ, sequential immersion at RT of suitable substrates, inside
a glove box, on separate CH
3
CN solutions of TTF and TCNQ leads to surprising
