New anionic acceptors Br2XQNHCH2SO3 - [X=Br, BryCl1-y (y ≈ 0.5), and Cl; Q=1,4-benzoquinone) and their charge-transfer salts

Article abstract of DOI:10.1016/j.physb.2009.10.035

We have prepared new organic anionic acceptors, Br₂XQNHCH ₂SO₃^- (2: X=Br, 3: X = BryCl_1-y (y ≈ 0.5), 4: X=Cl; Q=1,4-benzoquinone), that possess both an electron acceptor part (1,4-benzoquinone) and an

Full text of DOI:10.1016/j.physb.2009.10.035

ARTICLE IN PRESS
Physica B 405 (2010) S2–S5
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Physica B
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New anionic acceptors Br2XQNHCH2SO3ꢀ [X=Br, BryCl1ꢀy (yE0.5), and Cl;
Q=1,4-benzoquinone) and their charge-transfer salts
Ã
H. Akutsu a, , T. Sasai a, J. Yamada a, S. Nakatsuji a, S.S. Turner b
a Graduate School of Material Science, University of Hyogo, Kamigori-cho, Hyogo 678-1297, Japan
b Chemical Science, University of Surrey, Guildford, Surrey GU2 7XH, UK
a r t i c l e i n f o
a b s t r a c t
We have prepared new organic anionic acceptors, Br2XQNHCH2SO3ꢀ (2: X=Br, 3: X=BryCl1ꢀy (yE0.5), 4:
X=Cl; Q=1,4-benzoquinone), that possess both an electron acceptor part (1,4-benzoquinone) and an
anionic part (sulfonate). The reduction potentials of the PPh4 salts of 2, 3 and 4 are ꢀ0.45, ꢀ0.45 and
ꢀ0.46 V (vs. SCE in CH3CN), respectively. The results indicate that they are weaker acceptors than
Keyword:
Organic crystals
chloranil (ꢀ0.13 V) and bromanil (ꢀ0.12 V). Each anionic acceptor (AA) provided two BEDT-TTF salts,
b-
(ET)5(AA)2 ꢁ DCE ꢁ zH2O and
l-(ET)2(AA) ꢁ CH3OH (AA=2, 3, or 4; z=2: 0.97, 3: 0.83 and 4: 0.40). The
structures and transport properties of the salts are reported.
& 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental detail
We have previously prepared several anionic weak acceptors
(AA) that are designed to be both a weak acceptor and a
monoanion [1,2]. If we prepare a charge-transfer (CT) salt with
organic donors (D), with stoichiometry (D)m(AA)n where m, n=1,
2, 3,y, the weak and strong CT interactions can coexist in the salt.
Through the weak CT interaction, the weak acceptor part can
receive a fraction (x51) of an electron from the donor molecule.
The donor is therefore effectively doped by an amount equal to the
partial charge x. To this end, we have prepared several anionic
weak acceptors [1,2] that combine the chloranil moiety with the
sulfonate (–SO3–) group. We have already reported two BEDT-TTF
X-ray diffraction data were recorded using a Rigaku AFC-5R
four-circle diffractometer or a Quantum-1 CCD/AFC-7R diffract-
ometer. Cyclic voltammogram was registered on
a Yanako
polarographic analyzer P-1100. Electrical resistivity was measured
by a standard 4-probe method using a Fuso HECS-994C multi-
channel conductometer.
Bromanil (2.54 g, 6.0 mmol) and aminomethanesulfonic acid
(0.56 g, 5.0 mmol) were stirred for 2 h at room temperature in the
presence of K2CO3 (1.0 g, 7.2 mmol) in 50 mL of dimethylforma-
mide (DMF). Adding 5 mL of concentrated HCl (35%) in 100 mL of
ice water for neutralization, followed by metathesis with PPh4Br
(2.20 g, 5.3 mmol), gave purple crystals (yield 20%). The product
was not assigned as PPh42 but as PPh43 (mixture of 2 and 4) by
FAB-Mass spectrum and X-ray analysis (Table 1). Our conclusion is
that Cl– in HCl reacts with 2 in the neutralization process, yielding
(ET) salts of
1
(Scheme 1),
b
-b
-(ET)2(1) ꢁ 0.5H2O and b00
-
(ET)2(1) ꢁ CH3OH, in both of which no effect of doping appears in
the physical properties. In this work, we prepared a new anionic
acceptor 2 using bromanil instead of chloranil and we also
obtained 3 and 4, where 3 is a mixture of 2 and 4. The molecular
structures of 2–4 are so similar that all the acceptors provide
–
4, where only the Br group opposite to –NHCH2SO3
was substituted with Cl (Scheme 1). Using HBr instead of HCl
gave the pure PPh42 salt (yield 13%), confirmed by FAB-Mass
and X-ray analysis (Table 1) whilst adding 5 mL of HCl in 100 mL
of saturated NaCl solution, then stirring for a day, followed
by metathesis with PPh4Br, yielding the pure PPh44 salt
(yield 15%), which was assigned by FAB-Mass and X-ray analysis
(Table 1).
two ET salts,
b-(ET)5(AA)2 ꢁ DCE ꢁ zH2O and l-(ET)2(AA) ꢁ CH3OH
(AA=2, 3, or 4; z=0.97 for 2, 0.83 for 3 and 0.40 for 4). Although
the molecular structure of 1 is also similar to those of 2–4, the
new salts have different structures from either ET salt of 1.
The structures and transport properties of the new salts are
reported.
Conventional constant-current electrocrystallisation in 1,2-
dichloroethane (DCE) with 15 mg of ET and 70 mg of each PPh4
salts gave black plate-shaped
the solvent from DCE to PhCl/methanol (10%) gave black plates of
-(ET)2(AA) ꢁ CH3OH.
b-(ET)5(AA)2 ꢁ DCE ꢁ zH2O. Changing
Ã
Corresponding author. Tel./fax: +8179158 0164.
E-mail address: akutsu@sci.u-hyogo.ac.jp (H. Akutsu).
l
0921-4526/$ - see front matter & 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2009.10.035

ARTICLE IN PRESS
H. Akutsu et al. / Physica B 405 (2010) S2–S5
S3
O
O
O
O
Bry
Cl1-y
Cl
Cl
Cl
Br
Br
Br
Br
Cl
Br
Br
–
–
–
–
N
H
SO3
N
H
SO3
Br
N
H
SO3
N
H
SO3
O
O
O
O
1
2
4
3
Scheme 1
Table 1
Crystallographic data.
Salt
AA
(PPh4)(AA)
b
-(ET)5(AA) ꢁ DCE ꢁ zH20
l
-(ET)2(AA) ꢁ CH3OH
4
3 (y=0.55)
2
4 (z=0.40)
3 (z=0.83)
(y=0.41)
2 (z=0.97)
4
3 (y=0.64)
2
Formula
C
31H23NO5PS
C31H23NO5
C31H23NO5
PSBr3
C66H50.79N2
C66H51.67N2
C66H51.94N2
C28H23NO6S17 C28H28NO6S17 C28H23NO6
CIBr2
PSCl0.45Br2.55
O10.40S42Cl4Br4 O10.83S42Cl3.19 O10.97S42Cl2Br6 ClBr2
Br4.81
Cl0.36Br2.64
S17Br3
Fw
747.82
772.27
752707
triclinic
792.27
752705
triclinic
2846.27
752709
triclinic
2890.04
752710
triclinic
2945.45
752708
triclinic
1209.77
752712
triclinic
1238.22
752713
triclinic
1254.22
752711
triclinic
CCDC no.
752706
Cell setting triclinic
Space group
P1
P1
P1
P1
P1
P1
P1
P1
P1
Diffracto-
meter
Rigaku AFC5R
quantum CCD Rigaku AFC5R quantum CCD quantum CCD quantum CCD quantum CCD quantum CCD quantum CCD
11.445(3)
13.024(3)
11.178(2)
11.4281(9)
13.0144(11)
11.2048(7)
11.423(3)
13.004(2)
11.2150(18)
11.7756(3)
12.5717(4)
18.9991(13)
11.8229(4)
12.6044(3)
19.145(3)
11.8341(18)
12.582(3)
8.844(3)
14.497(7)
17.419(4)
8.8804(10)
14.4911(5)
17.3823(16)
8.883(2)
˚
a (A)
14.5092(5)
17.396(3)
˚
b (A)
19.0895(7)
˚
c (A)
a
b
g
(1)
(1)
(1)
99.272(17)
111.157(20)
97.98(2)
99.5430(9)
110.606(3)
97.8350(14)
1503.69(20)
99.661(14)
110.316(15)
97.782(18)
1506.0(5)
82.649(3)
82.675(5)
80.165(3)
63.7817(11)
2517.5(4)
82.554(2)
80.334(2)
63.4880(10)
2502.6(7)
79.972(3)
86.273(3)
74.631(3)
2120.0(13)
79.432(3)
86.8191(13)
74.9755(6)
2123.7(3)
79.372(3)
86.9840(12)
75.0320(8)
2128.9(6)
80.2928(15)
63.7346(6)
2481.58(20)
3
1498.1(6)
˚
V (A )
Z
2
2
2
1
1
1
2
2
2
T (K)
m
Data total
unique
used
296
295
296
293
293
295
295
293
295
(cmꢀ1
)
29.680
7384
6890
36.411
12451
5918
41.944
7413
26.729
21704
29.363
21684
33.987
21711
10440
28.611
17168
8641
34.199
18890
9074
37.278
18521
8775
6919
10362
10441
4240 (I41.0
sI)
3213 (I42.0
s
I) 3164 (I41.5
s
I) 6213 (I42.0
s
I) 5260 (I42.5
s
I) 4915 (I43.0
s
I) 2354 (I43.0
s
I) 6182 (I42.0
s
I) 4256
(I43.0sI)
Rint
0.053
0.061
397
0.096
402
0.054
611
0.068
605
0.073
621
0.135
496
0.039
537
0.063
543
Parameters 402
R
0.068
0.064
0.060
1.077
0.78
0.065
0.062
1.091
0.67
0.061
0.058
1.066
0.59
0.062
0.052
1.104
0.71
0.064
0.058
1.129
0.70
0.097
0.092
1.091
0.96
0.068
0.068
1.098
1.17
0.065
0.061
1.118
0.94
Rw
0.056
1.118
0.59
GOF(S)
3
rmax (eꢀ/A )
˚
D
D
3
rmax (eꢀ/A )
ꢀ0.54
ꢀ0.69
ꢀ0.70
ꢀ0.64
ꢀ1.44
ꢀ1.30
ꢀ0.89
ꢀ1.17
ꢀ0.95
˚
3. Results and discussions
disordered water molecule(s). The water contents differ depend-
ing on the AA size since as the anion becomes the smaller the less
water is included (Table 1). The crystals are isostructural so only
the crystal structure of the salt of 2 is shown in Fig. 1. The donor
sheet and the AA/DCE/water sheet alternate along the
3.1. PPh4AA
Crystallographic data are shown in Table 1. PPh42 has the
largest cell volume (V) and PPh44 has the smallest, indicating that
the order of anion size is 24344, as expected from the atomic
radii of Br and Cl. The redox properties of PPh42, PPh43 and PPh44
were measured by cyclic voltammetry. The E1 values
(ꢀ0.45,ꢀ0.45 and ꢀ0.46 V vs. SCE in PhCN [3]) are all slightly
lower than that of PPh41 (ꢀ0.42 V) and much lower than that of
chloranil (ꢀ0.13 V) and bromanil (–0.12 V). This indicates that the
anions 2, 3 and 4 are weaker acceptors.
crystallographic c axis (Fig. 1a). The donor basically forms
b-
type two-dimensional conducting sheets (Fig. 1b) such that each
donor stacks along the a axis as ?A–A–B–C–B–A–A–B–C?.
Within each stack the ET molecular long axes are not exactly
parallel and they present small angles to each other of 0.0, +8.6
and ꢀ13.91 for the A–A, A–B and B–C couples, respectively [4]. In
the anion sheet, each AA forms a face-to-face dimer with a plane–
˚
plane distance of 3.59 A (Fig. 1c). The bond lengths of the AA
quinone skeleton are quite similar to those in the PPh4 salt [5],
suggesting that the acceptor parts are almost neutral and there
seems to be no doping effect. In addition, three short S?Br
3.2.
b-(ET)5(AA)2 ꢁ DCE ꢁ zH2O
˚
contacts within the van der Waals distances (3.80 A) were
Crystallographic data are shown in Table 1. In the asymmetric
unit, there are two and half ET cations, one AA, a half of DCE and
observed between ET and the anion 2 (Fig. 1d). A donor to anion
ratio of 5:2 indicates that each ET molecule has a formula charge

ARTICLE IN PRESS
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H. Akutsu et al. / Physica B 405 (2010) S2–S5
c
o
o
c
a
b
a
b
C
A
3.669(3) Å
B
B
3.776(3) Å
3.708(3) Å
A
A
A
C
A
B
B
B
A
c
C
C
a
A
B
B
A
B
A
C
o
b
A
. .
Fig. 1. Crystal structures of b-(ET)5(2)2 DCE 0.97H2O (ORTEP, 50% probability ellipsoids). (a) A view of the crystal structure showing the alternating layers. (b) b-type
packing motif of the donor layer. (c) A projection of the anion/DCE/H2O layer along the c axis. (d) A view with short contacts between ET and 2. Dashed lines indicate short
˚
contacts (S?S o3.70 and B?S o3.80 A).
˚
Table 2
plane distance of 3.59 A (Fig. 2c). As in the previous structure type,
Transport properties.
the bond lengths of the AA quinone skeleton are not significantly
different from those in the PPh4 salt [5], suggesting that the
acceptor parts are almost neutral and therefore there appears to
be no doping effect. In addition, three S?Br and one S?O short
Salt
b-(ET)5(AA) ꢁ DCE ꢁ zH2O
l
-(ET)2(AA) ꢁ CH3OH
AA
4
3
2
4
3
2
˚
contacts within the van der Waals distances (S?Br=3.80 A and
rRT (S/cm)
Ea (meV)
0.36
84
0.72
76
0.31
64
0.22
74
0.28
134
0.15
227
˚
S?O=3.40 A) were observed between the donor and anion 2
(Fig. 2d). The donor layer forms a two-dimensional conducting
layer with a l-type packing motif (Fig. 2b). Charges on the two
independent ET molecules are +0.45 and +0.72 for cations A and
B (Fig. 2b), respectively, as estimated from a calculation using
bond lengths [6]. The estimated charges for the salt of 3 are +0.75
and +0.47 for A and B, respectively. Therefore, in this salt of 3 it is
not the B molecule but the A molecule that is more positively
charged. Unfortunately, we cannot estimate the values for the salt
of 4 because of the poorer quality diffraction data. The three salts
are semiconductors and have similar room temperature resistivity
(Table 2). However, the activation energy significantly increases
with increasing the AA size which may be caused by the difference
of the charge disproportionation on the donor layers.
of +2/5, although using bond lengths to estimate the charge on
each crystallographically independent ET cations gave +0.89,
+0.35 and +0.43 for A, B and C, respectively (Fig. 1b) [6]. The
values suggest that the holes are mainly located on the A
molecule. The values for the salt of 2 are similar to those of 3
and 4 (3: +0.76, +0.33 and +0.23; 4: +0.76, +0.24 and +0.10 for A,
B and C, respectively), suggesting that their electronic structures
are similar. Indeed their transport properties are similar (Table 2)
as all salts show semiconducting behaviour.
3.3.
l-(ET)2(AA) ꢁ CH3OH
4. Conclusions
Crystallographic data are shown in Table 1. The crystal
structures of 2–4 are isomorphous so that only the crystal
structure of the salt of 2 is shown in Fig. 2. The asymmetric unit
consists of two donors, one AA and one methanol molecule. The
crystal lattice consists of the donor layer and anion/methanol
layer alternating along the c axis (Fig. 2a). In the anion layer, the
quinone skeletons of AA form face-to-face dimers with a plane–
We have prepared three novel anionic acceptors,
Br3QNHCH2SO–3 (2), Br2ClQNHCH2SO–3 (4) and the mixture of 2
and 4 (3) as PPh4 salts, where Q is 1,4–benzoquinone. Each anionic
acceptor (AA) provides two ET salts,
b-(ET)5(AA)2 ꢁ DCE ꢁ zH2O and
l-(ET)2(AA) ꢁ CH3OH (AA=2, 3, or 4; z=0.97 for 2, 0.83 for 3 and

ARTICLE IN PRESS
H. Akutsu et al. / Physica B 405 (2010) S2–S5
S5
o
b
b
c
a
o
c
a
o
3.767(3) Å
b
A
B
B
A
3.661(3) Å
3.464(3) Å
A
B
B
A
A
A
3.228(7) Å
a
B
c
B
A
A
B
B
.
Fig. 2. Crystal structures of
l
-(ET)2(2) CH3OH (ORTEP, 50% probability ellipsoids). (a) A view of the crystal structure showing the alternating layers. (b)
b-type packing
motif of the donor layer. (c) A projection of the anion/CH3OH layer along the c axis. (d) A view with short contacts between ET and 2. Dashed lines indicate short contacts
˚
(S?S o3.70, Br?So3.80 and S?Oo3.40 A).
0.40 for 4). All salts are semiconductors with the transport
properties of the -type salts differing little with the size of AA.
The room temperature resistivity of the -type salts also do not
greatly differ with the AA size although the activation energy
significantly increases with increasing the AA size.
References
b
l
[1] H. Akutsu, J. Yamada, S. Nakatsuji, S.S. Turner, Solid State Commun. 144 (2007)
144.
[2] H. Akutsu, J. Yamada, S. Nakatsuji, S.S. Turner, Cryst. Eng. Commun. 2009, in
press, doi:10.1039/B909519E.
[3] Voltage vs. saturated calomel electrode (SCE) in acetonitrile with 0.1 M Bu4NClO4,
Pt electrode, at room temperature, under nitrogen, scan rate 50 mVsꢀ1
.
[4] The other salts have similar angles, in
and B-C ꢀ13.91; in -(ET)5(4)2 ꢁ DCE ꢁ 0.97H2 A-A 0.01, A-B 8.51 and B-C ꢀ13.91.
[5] Average bond lengths (A) of C=O/C-C/C=C are in PPh42: 1.218/1.481/1.346,
PPh43: 1.220/1.481/1.366, PPh44: 1.219/1.484/1.343, -salt of 2: 1.209/1.490/
1.356, -salt of 3: 1.219/1.497/1.348, -salt of 4: 1.212/1.489/1.351, -salt of 2:
1.212/1.480/1.365, -salt of 3: 1.218/1.485/1.359, -salt of 4: 1.210/1.485/1.370.
b-(ET)5(3)2 ꢁ DCE ꢁ 0.83H2O: A-A 0.01, A-B 8.51
b
Acknowledgments
˚
b
b
b
l
This work has been supported by Grant-in-Aid for Scientific
Research (no. 19550023) from Japan Society for the Promotion of
Science (JSPS).
l
l
[6] P. Guionneau, C.J. Kepert, G. Bravic, D. Chasseau, M.R. Truter, M. Kurmoo, P. Day,
Synth. Met. 86 (1997) 1973.