Radical salts of TTF derivatives with the metal–metal bonded [Re2Cl8]

Radical salts of TTF derivatives with the metal–metal bonded [Re 2Cl 8] 2 anion
Eric W. Reinheimer a,c , José R. Galán-Mascarós b,1 , Carlos J. Gómez-García b , Hanhua Zhao a ,
Marc Fourmigué c,2 , Kim R. Dunbar a, *
a Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842-3012, USA
b Instituto de Ciencia Molecular, Fundación de la Universidad de Valencia, Polígono de la Coma s/n, 46980-Paterna, Spain
c Sciences Chimiques de Rennes, UMR 6226 CNRS-Université Rennes 1, Campus de Beaulieu, 35042 Rennes, France
article info
Article history:
Received 11 December 2007
Received in revised form 14 March 2008
Accepted 19 March 2008
Available online 6 April 2008
Keywords:
TTF
BEDT-TTF
TMTTF
TMTSF
o-Me 2TTF
Octachlorodirhenate
1. Introduction
abstract
The field of organic conductors is one of the most developed
areas in molecular materials because of the many innovative findings
that the field has witnessed in the past few decades. Organicbased
conductors have been found to exhibit properties reminiscent
of traditional inorganic solids, with examples of semiconductors,
metals and even superconductors having been discovered [1].
An intrinsic advantage of molecular materials is the flexibility in
tuning by chemical alterations. Indeed such methods have been
successful in applied research applications since the early development
of conducting polymers [2]. With respect to fundamental
studies, research in molecular conductors has led to several milestones
in materials science such as the preparation of paramagnetic
and antiferromagnetic superconductors, ferromagnetic
metals, field-induced superconductors, chiral conductors and single-component
metals [3–7].
Most of the organic metals and superconductors reported to
date belong to the tetrathiafulvalene (TTF) family of radical salts
or its derivatives. These materials are composed of partially oxi-
* Corresponding author. Tel.: +1 979 845 5235; fax: +1 979 845 7177.
E-mail addresses: ereinheimer@mail.chem.tamu.edu (E.W. Reinheimer), jose.r.
galan@uv.es (J.R. Galán-Mascarós), marc.fourmigue@univ-rennes1.fr (M. Fourmigué),
dunbar@mail.chem.tamu.edu (K.R. Dunbar).
1
Tel.: +34 96354 4420; fax: +34 96354 3273.
2
Tel.: +33 0223236732; fax: +33 0223235243.
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.03.046
Journal of Molecular Structure 890 (2008) 81–89
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Four new salts of the radical cations of TMTSF (tetramethyltetraselenafulvalene), TMTTF (tetramethyltetrathiafulvalene),
BEDT-TTF (bisethylenedithiotetrathia-fulvalene) (ET) and o-Me2TTF (o-4,4 0 -dimethyltetrathiafulvalene)
with the metal–metal bonded dianion [Re2Cl8] 2 were synthesized, and their
structures and physical properties investigated. The structures of these semiconducting salts feature
one-dimensional stacking of the donor molecules interleaved with [Re2Cl8] 2 anions and interstitial solvent
molecules.
Ó 2008 Elsevier B.V. All rights reserved.
dized TTF units that form segregated stacks in the solid state due
to strong S S contacts which lead to the electron delocalization
responsible for the transport properties. While the presence of oxidized
radicals of the TTF family is essential for the observation of
conducting properties in hybrid organic/inorganic materials, the
organic component has allowed for the observation of several phenomena
from solid-state physics including Peierls transitions, anion
ordering, spin density waves (SDWs), magnetic frustration,
charge localization (Mott transitions), charge ordering (CO), Anderson
localizations and field effect transitions [8–15]. Typically the
anions in the salts do not contribute to the transport properties,
but their role is nonetheless crucial. It has been found that the
shape, size, charge and chemical properties help to control the type
of stack that the TTF molecules adopt as well the overall charge of
the cationic units. Thus, given a particular TTF derivative, one can
obtain insulators, semiconductors, metals or even superconductors
by changing the identity of the anion. The bis(ethylene)dithio-TTF
donor, (BEDT-TTF or ET), has produced the largest number of
molecular conductors with diverse transport properties, e.g., (ET)[-
FeBr4] is an insulator, (ET) 8[PNi(H 2O)W 11O 39] 2H 2O is a semiconductor,
(ET)3[CuCl4] H2O is a metal and j-(ET)2Cu[N(CN)2]Cl is a
superconductor, with a T c of 12.8 K at 0.3 kbar, the highest T c for
a superconducting state for a molecular conductor with the exception
of fullerene-based materials [16–20].
Given the many factors involved in determining the packing of a
radical salt, including weak intermolecular interactions, it is difficult
to predict the final structure and properties. In order to probe

82 E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89
the landscape of possibilities, researchers have amassed a library of
salts with different anions over the years. Among the known examples,
only two radical cation salts with metal–metal bonded anions
have been reported to date, namely the compound
Fig. 1. X-ray crystal structure of (TMTTF) 3[Re 2Cl 8] 2CH 3CN (1 2CH 3CN). Interstitial
acetonitrile molecules have been omitted for the sake of clarity.
Fig. 2. X-ray crystal structure of (TMTSF) 5[Re 2Cl 8] 2 6CH 2Cl 2 (2 6CH 2Cl 2). Interstitial
dichloromethane molecules have been omitted for the sake of clarity.
(ET)3[Re2(NCS)10] 2CH2Cl2 which is a semiconductor and a salt of
[Re2Cl8] 2
and dimethyl(diphenyl)TTF (DMDPhTTF) reported in
1991 by Ouahab and coworkers [21,22]. No properties of the latter
material were reported. Several charge transfer salts containing
Fig. 3. X-ray crystal structure of (BEDT-TTF)2[Re2Cl8] (3).
Fig. 4. X-ray crystal structure of (o- Me2TTF)2[Re2Cl8] (4).
Table 1
X-ray crystallographic and refinement data for (1 2CH 3CN) and (2 6CH 2Cl 2)
Compound (TMTTF)3[Re2Cl8] 2CH3CN (TMTSF)5[Re2Cl8]2 6CH2Cl2
(1 2CH3CN)
(2 6CH2Cl2)
Formula C34H42S12N2Re2Cl8 C53H66Se20Re4Cl22 Formula weight 1515.66 3817.98
Space group P1 P1
a (Å) 10.542(2) 13.042(3)
b (Å) 13.786(3) 14.022(3)
c (Å) 19.664(4) 15.283(3)
a (°) 100.64(3) 93.84(3)
b (°) 104.87(3) 103.51(3)
c (°) 107.66(3) 109.76(3)
Volume (Å 3 ) 2522.82 2524.91
Z 4 4
l, (mm 1 ) 10.76 25.53
Temp. 110(2) 110(2)
Reflns. collected 11560 11339
Reflns. I >2r 10068 8429
Parameters 537 467
Restraints 0 0
R a
1
wR
0.0339 0.0992
b
2
Goodness-of-fit
0.0930 0.2746
c
1.042 1.064

Table 2
X-ray crystallographic and refinement data for 3 and 4
Compound (BEDT-TTF)2[Re2Cl8] (3) (o-Me2TTF)2[Re2Cl8] (4)
Formula C20S16Re2Cl8 C16H16S8Re2Cl8 Formula weight 1409.28 1117.56
Space group P1 P1
a (Å) 10.404(2) 8.7469(4)
b (Å) 12.843(3) 10.6444(5)
c (Å) 15.622(3) 16.5506(8)
a (°) 97.16(3) 79.058(2)
b (°) 105.25(3) 81.276(2)
c (°) 100.91(3) 88.963(2)
Volume (Å 3 ) 1943.75 1495.34(12)
Z 3 4
l (mm 1 ) 11.48 9.372
Temp. 110(2) 110(2)
Reflns. collected 4955 6810
Reflns. I >2r 3461 5330
Parameters 410 307
Restraints 0 0
R a
1
wR
0.0735 0.0410
b
2
Goodness-of-fit
0.1038 0.0898
c
1.014 1.081
Table 3
Bond distances for (TMTTF) 3[Re 2Cl 8] 2CH 3CN (1 2CH 3CN) in Å
Re(1)–Re(2) 2.2253(8) S(11)–C(26) 1.718(4)
Re(1)–C1(1) 2.3230(12) S(11)–C(29) 1.751(4)
Re(1)–C1(2) 2.3271(12) S(12)–C(26) 1.726(4)
Re(1)–C1(3) 2.3317(14) S(12)–C(28) 1.742(4)
Re(1)–C1(4) 2.3304(11) C(1)–C(2) 1.505(6)
Re(2)–C1(5) 2.3186(14) C(2)–C(3) 1.338(6)
Re(2)–C1(6) 2.3344(11) C(3)–C(4) 1.507(6)
Re(2)–C1(7) 2.3367(12) C(5)–C(6) 1.357(6)
Re(2)–C1(8) 2.3263(13) C(7)–C(8) 1.499(6)
S(1)–C(2) 1.760(4) C(8)–C(9) 1.341(6)
S(1)–C(5) 1.750(4) C(9)–C(10) 1.492(6)
S(2)–C(3) 1.761(4) C(11)–C(12) 1.500(6)
S(2)–C(5) 1.751(4) C(12)–C(13) 1.362(6)
S(3)–C(6) 1.752(4) C(13)–C(14) 1.491(6)
S(3)–C(8) 1.758(4) C(15)–C(16) 1.399(5)
S(4)–C(6) 1.748(4) C(17)–C(18) 1.506(6)
S(4)–C(9) 1.755(4) C(18)–C(19) 1.350(6)
S(5)–C(12) 1.738(4) C(19)–C(20) 1.499(5)
S(5)–C(15) 1.721(4) C(21)–C(22) 1.499(6)
S(6)–C(13) 1.740(4) C(22)–C(23) 1.360(6)
S(6)–C(15) 1.716(4) C(23)–C(24) 1.496(6)
S(7)–C(16) 1.716(4) C(25)–C(26) 1.392(5)
S(7)–C(19) 1.732(4) C(27)–C(28) 1.489(6)
S(8)–C(16) 1.713(4) C(28)–C(29) 1.352(6)
S(8)–C(18) 1.731(4) C(29)–C(30) 1.491(6)
S(9)–C(22) 1.729(4) C(31)–C(32) 1.438(8)
S(9)–C(25) 1.725(4) C(33)–C(34) 1.442(8)
S(10)–C(23) 1.737(4) C(32)–N(1) 1.136(7)
S(10)–C(25) 1.710(4) C(34)–N(2) 1.137(8)
other rhenium-based anions, more specifically octahedral clusters,
have also been prepared [23]. In this article we report the syntheses
and characterization of four new radical salts of the quadruply
bonded dianion [Re2Cl8] 2
and the donors tetra(methyl)TTF
(TMTTF), the selenium derivative tetramethyltetraselenafulvalene
(TMTSF), o-Me2TTF and ET.
2. Experimental
2.1. Syntheses
The radical salts were synthesized at platinum wire electrodes
of dimensions 1 mm in diameter and 2 cm in length by electrochemical
oxidation of the donor in a U- or H-shaped cell under
E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89 83
the application of a low constant current at room temperature
[24]. TMTSF and ET were used as received without further purification.
TMTTF, o-Me2TTF and [TBA]2[Re2Cl8] were prepared using literature
methods [25–27].
2.1.1. (TMTTF) 3[Re 2Cl 8] 2CH 3CN(1 2CH 3CN)
(TBA)2[Re2Cl8] (0.100 g, 0.088 mmol) was added to each compartment
of the electrochemical cell in 10 mL of CH 3CN. TMTTF
(0.020 g, 0.077 mmol) was added to the anodic compartment and
the cell was subjected to the application of a constant current density
of 0.5 lA. After a period of 2 weeks, black block-shaped crystals
of the product formed on the electrode surface which were removed,
washed with MeCN and dried in air.
Table 4
Bond distances for (TMTSF) 5[Re 2Cl 8] 2 6CH 2Cl 2 (2 6CH 2Cl 2)inÅ
Re(1)–Re(2) 2.257(16) Se(9)–C(22) 1.89(2)
Re(1)–Cl(1) 2.340(5) Se(10)–C(21) 1.87(2)
Re(1)–Cl(2) 2.320(5) Se(10)–C(23) 1.86(2)
Re(1)–Cl(3) 2.329(5) C(1)–C(2) 1.47(3)
Re(1)–Cl(4) 2.329(5) C(2)–C(3) 1.36(3)
Re(2)–Cl(5) 2.327(5) C(3)–C(4) 1.53(5)
Re(2)–Cl(6) 2.327(5) C(5)–C(5) 1.40(4)
Re(2)–Cl(7) 2.331(5) C(6)–C(7) 1.52(3)
Re(2)–Cl(8) 2.330(5) C(7)–C(8) 1.32(3)
Se(1)–C(3) 1.84(2) C(8)–C(9) 1.50(3)
Se(1)–C(5) 1.87(2) C(10)–C(11) 1.38(3)
Se(2)–C(2) 1.90(2) C(12)–C(13) 1.37(3)
Se(2)–C(5) 1.85(2) C(12)–C(15) 1.50(3)
Se(3)–C(7) 1.88(2) C(13)–C(14) 1.48(3)
Se(3)–C(10) 1.87(2) C(16)–C(17) 1.43(3)
Se(4)–C(8) 1.91(2) C(17)–C(18) 1.36(3)
Se(4)–C(10) 1.86(2) C(18)–C(19) 1.50(3)
Se(5)–C(11) 1.87(2) C(20)–C(21) 1.38(3)
Se(5)–C(12) 1.88(2) C(22)–C(23) 1.39(3)
Se(6)–C(11) 1.90(2) C(22)–C(25) 1.47(3)
Se(6)–C(13) 1.89(2) C(26)–C1(9) 1.76(3)
Se(7)–C(17) 1.90(2) C(26)–C1(10) 1.75(3)
Se(7)–C(20) 1.86(2) C(27)–C1(11) 1.72(3)
Se(8)–C(18) 1.868(19) C(27)–C1(12) 1.78(3)
Se(8)–C(20) 1.89(2) C(28)–C1(13) 1.77(3)
Se(9)–C(21) 1.86(2) C(28)–C1(14) 1.64(3)
Table 5
Bond distances for (BEDT-TTF)2[Re2Cl8] (3) inÅ
Re(1)–Re(1) 2.231(19) S(9)–C(11) 1.72(3)
Re(2)–Re(2) 2.222(18) S(9)–C(13) 1.74(2)
Re(1)–Cl(1) 2.337(5) S(10)–C(12) 1.73(3)
Re(1)–Cl(2) 2.340(5) S(10)–C(14) 1.72(2)
Re(1)–Cl(3) 2.335(5) S(11)–C(13) 1.74(2)
Re(1)–Cl(4) 2.318(5) S(11)–C(15) 1.70(2)
Re(2)–Cl(5) 2.334(5) S(12)–C(14) 1.77(2)
Re(2)–Cl(6) 2.335(5) S(12)–C(15) 1.73(2)
Re(2)–Cl(7) 2.308(6) S(13)–C(16) 1.72(2)
Re(2)–Cl(8) 2.334(6) S(13)–C(17) 1.75(2)
S(1)–C(1) 1.81(2) S(14)–C(16) 1.74(2)
S(1)–C(3) 1.72(2) S(14)–C(18) 1.76(2)
S(2)–C(2) 1.80(3) S(15)–C(17) 1.748(18)
S(2)–C(4) 1.78(2) S(15)–C(19) 1.79(3)
S(3)–C(3) 1.77(2) S(16)–C(18) 1.76(2)
S(3)–C(5) 1.70(2) S(16)–C(20) 1.73(3)
S(4)–C(4) 1.74(2) C(1)–C(2) 1.44(3)
S(4)–C(5) 1.731(19) C(3)–C(4) 1.31(3)
S(5)–C(6) 1.706(19) C(5)–C(6) 1.41(3)
S(5)–C(7) 1.76(2) C(7)–C(8) 1.42(3)
S(6)–C(6) 1.73(2) C(9)–C(10) 1.45(3)
S(6)–C(8) 1.71(2) C(11)–C(12) 1.33(4)
S(7)–C(7) 1.71(2) C(13)–C(14) 1.33(3)
S(7)–C(9) 1.83(2) C(15)–C(16) 1.39(3)
S(8)–C(8) 1.71(2) C(17)–C(18) 1.32(3)
S(8)–C(10) 1.79(2) C(19)–C(20) 1.38(4)

84 E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89
Table 6
Bond distances for (o-Me 2TTF) 2[Re 2Cl 8](4) inÅ
Re(1)–Re(2) 2.2249(4)
Re(1)–Cl(8) 2.3071(18)
Re(1)–Cl(5) 2.3267(17)
Re(1)–Cl(6) 2.3385(16)
Re(1)–Cl(7) 2.3411(18)
Re(2)–Cl(3) 2.3158(18)
Re(2)–Cl(2) 2.3254(16)
Re(2)–Cl(4) 2.3279(18)
Re(2)–Cl(1) 2.3378(17)
S(1A)–C(5A) 1.722(7)
S(1A)–C(3A) 1.742(7)
S(2A)–C(5A) 1.702(7)
S(2A)–C(4A) 1.728(7)
S(3A)–C(6A) 1.712(7)
S(3A)–C(7A) 1.727(8)
S(4A)–C(8A) 1.700(8)
S(4A)–C(6A) 1.724(7)
C(1A)–C(3A) 1.502(9)
C(2A)–C(4A) 1.508(9)
C(3A)–C(4A) 1.337(9)
C(5A)–C(6A) 1.401(8)
C(7A)–C(8A) 1.342(11)
S(1B)–C(5B) 1.713(7)
S(1B)–C(3B) 1.746(7)
S(2B)–C(4B) 1.727(7)
S(2B)–C(5B) 1.727(6)
S(3B)–C(7B) 1.717(9)
S(3B)–C(6B) 1.718(7)
S(4B)–C(6B) 1.718(7)
S(4B)–C(8B) 1.719(10)
C(1B)–C(3B) 1.485(10)
C(2B)–C(4B) 1.491(9)
C(3B)–C(4B) 1.356(10)
2.1.2. (TMTSF) 5[Re 2Cl 8] 2 6CH 2Cl 2(2 6CH 2Cl 2)
(TBA)2[Re2Cl8] (0.102 g, 0.090 mmol) was added to each compartment
of the electrochemical cell in 10 mL of CH 2Cl 2 and TMTSF
(0.020 g, 0.044 mmol) was added to the anodic compartment. A
low current density of 0.5 lA was applied to the cell. After a period
Fig. 5. Projection of the crystal structure of (1 2CH 3CN) in the bc plane.
Table 7
Estimated degree of ionicity for the donor molecules for (1 2CH 3CN), (2 6CH 2Cl 2), 3
and 4
Salt Molecule A a (Å) B b (Å) Q c
(TMTTF)3[Re2Cl8] 2CH3CN (1 2CH3CN) A 1.392(8) 1.728(4) +0.95
B 1.399(3) 1.717(5) +1.17
C 1.357(5) 1.750(3) +0.25
(TMTSF) 5[Re 2Cl 8] 2 6CH 2Cl 2 (2 6CH 2Cl 2) A 1.377(9) 1.859(8) +1.10
A 1.377(9) 1.859(8) +1.10
B 1.381(5) 1.877(4) +1.10
B 1.381(5) 1.877(4) +1.10
C 1.401(8) 1.872(7) +1.40
(BEDT-TTF) 2[Re 2Cl 8](3) A 1.408(6) 1.717(5) +1.29
B 1.385(7) 1.725(6) +0.89
(o-Me 2TTF) 2[Re 2Cl 8](4) A 1.401(3) 1.715(3) +1.22
B 1.373(2) 1.717(4) +0.82
a Central C@C bond distance.
b Mean central C–S bond distance.
c Q = charge estimated with the formula Q = 17.92 + 23.43 * (A/B) from Ref. [34].
of 1 week, small black needle-shaped crystals of the salt were
apparent on the electrode surface; the product was carefully removed
with a spatula, washed with CH 2Cl 2 and dried in air.
2.1.3. (BEDT-TTF) 2[Re 2Cl 8](3)
Both compartments of the electrochemical cell were treated with
150 mg (0.131 mmol) of (TBA) 2[Re 2Cl 8] in 10 mL of PhCN. BEDT-
TTF (0.025 g, 0.061 mmol) was added to the anodic compartment
and the entire cell was attached to a potentiostat to insure a constant
oxidative current biased to a low potential of 0.5 lA. After a period of
2 months, small black block-shaped crystals of the title formed on
the electrode surface. The crystals were carefully scraped from the
electrode surface, washed with PhCN and dried in air.
2.1.4. (o-Me2TTF)2[Re2Cl8] (4)
To each compartment of the electrochemical cell was added
(TBA)2[Re2Cl8] (0.100 g, 0.088 mmol) in 10 mL of CH3CN, and o-

Fig. 7. Projection of the crystal structure of (2 6CH 2Cl 2) in the [111] plane.
Me2TTF (0.012 g, 0.052 mmol) was added to the anodic compartment.
The cell was subjected to a low current density of 0.5 lA.
After a period of 2 weeks, small black needle crystals of the salt
formed on the electrode surface which were washed with CH3CN
and dried in air.
2.2. X-ray crystallography
Low temperature X-ray data collections were conducted on a
BRUKER SMART 1000 diffractometer using Mo-Ka radiation
E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89 85
Fig. 6. Projection of the crystal structure of (1 2CH 3CN) in the ac plane.
Fig. 8. Projection of the crystal structure of (2 6CH 2Cl 2) depicting the chains along
the [111] direction.
(k = 0.71073 Å) for (1 2CH3CN). Data collections for (2 6CH2Cl2)
and 3 were performed on a BRUKER D8 GADDS system equipped
with Cu-Ka radiation (k = 1.54 Å). The data for 4 were collected
on a BRUKER APEX II diffractometer using Mo-Ka radiation. Crystals
were secured to crystallographic loops with silicone oil and
transferred directly to the cold stream. All data collections were

86 E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89
conducted at 110 ± 2 K with graphite monochromated radiation
and were corrected for Lorentz and polarization effects. The Siemens
SAINT software package was used to integrate the frames.
The program SADABS was used to correct for absorption effects
[28,29]. The structures were solved by direct methods by the use
of the SHELXS-97 program in the Bruker SHELXTL v5.1 interface
in the XSEED software package [30–32]. The SHELXL-97 program
was used to refine all non-hydrogen atoms with anisotropic thermal
parameters by full matrix least squares calculations on F 2
[33]. Hydrogen atoms were inserted at calculated positions and
constrained with isotropic thermal parameters. The solid-state
structures for (1 2CH 3CN), (2 6CH 2Cl 2), 3 and 4 are shown in Figs.
1–4. Crystallographic information is summarized in Tables 1 and
2. Relevant bond distances are presented in Tables 3–6. The central
Fig. 9. Projection of the crystal structure of 3 in the bc plane.
Fig. 10. Projection of the crystal structure of 3 in the ac plane.
C@C bond and C–S bonds are the most susceptible to the oxidation
state of the donor and have been used by Coppens and coworkers
to develop an empirical relationship that can be used to calculate
the overall oxidation state of the donor molecule [34]. Calculated
average charges for the chalcofulvalenium cations in the compounds,
determined via this method, are listed in Table 7.
2.3. Transport properties
Electrical conductivity was measured with the four probe
technique using a Quantum Design PPMS equipment in the temperature
range 300–220 K on single crystals of (1 2CH 3CN) and 3
(below ca. 220 K the resistance of the samples was higher than
10 MX, the limit of our measurement). The contacts between

the platinum wires (25 lm diameter) and the crystals were secured
using graphite paste. The samples were measured with
cooling and warming rates of 0.5 K min 1 and with a DC intensity
current of 0.1 lA.
3. Results and discussion
3.1. Synthesis and structure
The radical salts were grown by electrochemical oxidation of the
neutral donors ET, TMTTF, TMTSF and o-Me2TTF in the presence of
the anion [Re 2Cl 8] 2 . Although the donors are chemically quite similar,
different solvents were required in order to grow suitable crystals.
(TMTTF) 3[Re 2Cl 8] 2CH 3CN(1 2CH 3CN) and (o-Me 2TTF) 2[Re 2Cl 8]
(4) were grown from acetonitrile, (TMTSF)5[Re2Cl8]2 6CH2Cl2
(2 6CH 2Cl 2) from dichloromethane and (BEDT-TTF) 2[Re 2Cl 8] (3)
from benzonitrile. It has been well established in the literature that,
in the absence of any intermolecular contacts such as p–p or S S
interactions, neutral chalcofulvalene donors are non-planar, often
exhibiting significant bends of up to 30° along intra-molecular
dithiole or diseleno bridges [35]. Upon oxidation of the donor,
structural alterations accompanying the formation of the radical
cation occur including the adoption of a planar conformation and a
lengthening of the central C@C bond with concomitant shortening
of the C–S bonds in the central TTF core [36].
The salt (TMTTF) 3[Re 2Cl 8] 2CH 3CN (1 2CH 3CN) crystallizes in
the triclinic space group P1 and is characterized by segregated
1D stacks of cations with the anions and solvent molecules occupying
the 1D channels present in the structure (Fig. 5). The TMTTF
chains are composed of three crystallographically different molecules:
A, B and C. The latter two exhibit very short intermolecular
contacts (S7–S11 = 3.383(3) Å), less than the sum of the van der
Waals radii (3.6 Å), which is the approximate distance that molecule
A exhibits with its nearest neighbors. Thus, the chain consists
of alternating monomers (A) and dimers (BC) along the a axis. The
anions in the interstices are closer to the BC dimers, but no significant
directional interactions are evident. According to the central
C@C bond and C–S bond distances, molecules B and C bear a charge
close to +1, while A is essentially neutral. These assignments are in
accord with the strong dimerization observed for the [BC] 2+ dimers,
typical of such radical salts, and isolated TMTTF (A) molecules
which are close to being neutral.
The compound (2 6CH 2Cl 2) is also clearly one-dimensional and
crystallizes in the triclinic space group P1. The cations and anions
form segregated stacks parallel to the [111] direction (Fig. 6). The
TMTSF chains consist of three crystallographically independent
TMTSF molecules, arranged in a pattern of the type –BABCC–
(Fig. 6). With respect to the intermolecular distances, short Se–Se
contacts are evident between A and B (Se2–Se6 = 3.586(4) Å), and
between C and C (Se7–Se10 = 3.510(3) Å); in both cases these
interactions are much shorter than the sum of the Van der Waals
radii ( 4.0 Å) for Se–Se contacts. The shortest B–C distances are
over 3.9 Å, thus this chain is actually built from centrosymmetric
dimers (CC) and trimers (BAB). The remainder of the cell contents
consist of [Re 2Cl 8] 2 anions and dichloromethane molecules. The
anions are oriented with their principal axes along the chain and
alternate along the [111] axis their position with the solvent molecules
in a zig-zag arrangement (Fig. 7). According to the stoichiometry,
four positive charges are required to be distributed over
five TMTSF molecules, but the estimated charges found for all molecules
are well over +1, taking into account the bonding distances
of each molecule (+1.4 for A, +1.1 for B and +1.1 for C) [34]. Accurate
determination of each donor’s charge is not always possible
and is dependent on crystal quality. Based on the Coppens’ formula
and the crystallographically derived bond distances, the (CC) di-
E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89 87
mers and (BAB) trimers are estimated to possess an overall +2
charge.
The crystal structure of 3 is quite different from the previous
two cases. In this structure, the anions and cations form mixed layers
in the bc plane with an alternating tetragonal arrangement of
dimerized ET molecules and anions (Fig. 8). There are two crystallographically
independent types of centrosymmetric ET dimers
with similar intermolecular distances and orientations. On the basis
of the stoichiometry of the compound, all ET molecules should
be in the +1 oxidation state. This conclusion was confirmed by the
estimation of the charges from the bonding distances (+0.7 and
+1.2 for each ET in each dimer) [34]. The intra-dimer contacts between
the ET molecules (S S distances range between 3.4 and
3.55 Å) are shorter than the sum of the van der Waals radii
(3.6 Å), an indication of the presence of strong electronic interactions.
There are no short contacts between dimers, as they appear
to be well isolated in the layer by the anions with interlayer distances
longer than 4 Å. There are also two crystallographically
independent [Re2Cl8] 2 anions with different orientations with respect
to the layers, being either perpendicular or parallel to the
mean plane of the layers. Consequently, each ET dimer is surrounded
by four [Re2Cl8] 2 units, two of each kind. Weak hydrogen
bonding is evident between the anions and the ethylene groups,
with shortest C–Cl contacts of 3.46(2) Å (C10–Cl1), to produce
alternating anion–cation chains in the layer.
The solid-state structure of 4 crystallizes in the triclinic space
group P1 and is dominated by short S S contacts at distances

88 E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89
Fig. 12. Projection of the crystal structure of 4 showing the chains along the [111]
direction.
ρ (Ω.cm)
2 105
1 105
5 104
3.2. Physical characterization
The thermal variations of the electrical conductivities for
(1 2CH3CN) and 3 are displayed in Fig. 13. Both compounds exhibit
classical semiconducting behavior with room temperature conductivities
of 2.2 10 4 and 3.0 10 4 Scm 1 and Arrhenius-like
behavior upon decreasing the temperature with activation energies
of 305 and 210 meV for (1 2CH3CN) and 3, respectively (inset
in Fig. 13). The low room temperature conductivity and the semiconducting
behavior can be easily explained in both cases: in 3
each ET molecule bears an integer charge of +1 whereas
(1 2CH3CN) shows an inhomogeneous charge distribution with
ðTMTTFÞ 2þ
2
3
1
Ln ρ
12
11
10
9
8
3.2 3.4 3.6 3.8 4.0 4.2 4.4
1000/T (K-1)
0 100
220 230 240 250 260
T (K)
270 280 290 300
Fig. 13. Thermal variation of the electrical conductivity of (1 2CH 3CN) and 3. Inset
shows the Arrhenius plot of both samples.
dimers and isolated neutral TMTTF molecules. Apart
from the charge distributions of the ET and TMTTF donors in the
salts, it also important to consider the effect of the [Re 2Cl 8] 2 dianion
on the transport properties of (1 2CH3CN) and 3. Unlike monoanoins,
dianions have large external coulombic forces which can
also be responsible for charge localization in molecular materials
[24].
1
3
4. Conclusions
We have presented four new radical salts based upon the
chalcofulvalene donors TMTSF, TMTTF, ET and o-Me 2TTF and the
metal–metal bonded species [Re2Cl8] 2 as the counterion. Compounds
(1 2CH 3CN) and 3 are semiconductors with activation energies
of 305 and 210 meV, respectively. The formation of dimers of
fully oxidized donors in the organic sub-lattice combined with the
strong external coulombic forces inherent to all dianions leads to
charge localization and explains the low conductivities and high
activation energies in the hybrid radical salts.
Acknowledgements
This work was supported by The Welch Foundation (Grant
A-1449) and the US Department of Energy (Grant DE-FG01-
05ER05-01). We also acknowledge the National Science Foundation
(Grant 9807975) for the funds to purchase the X-ray diffractometer.
JRGM thanks the Generalitat Valenciana for a travel grant. MF
acknowledges financial support from the Agence Nationale de la
Recherche (ANR No. NT05-2 42710).
References
[1] (a) D. Jérome, A. Mazaud, M. Ribault, K. Bechgaard, Phys. Rev. Lett. 41 (1980)
95;
(b) J. Tarrés, J. Veciana, C. Rovira, Synth. Met. 70 (1995) 1187;
(c) K. Heuzé, C. Mèziére, M. Fourmigué, P. Batail, C. Coulon, E. Canadell, P.
Auban-Senzier, D. Jérome, Chem. Mater. 12 (2000) 1898;
(d) J.C. Fitzmaurice, A.M.C. Slavin, D.J. Williams, D.J. Woolins, J. Chem. Soc.,
Chem Commun. (1993) 1479.
[2] (a) C.K. Chiang, Y.W. Park, A.J. Heeger, H. Shirakawa, E.J. Louis, A.G.
MacDiarmid, Phys. Rev. Lett. 39 (1977) 1098;
(b) J.H. Burroughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, R.H. Friend, P.L.
Burn, A.B. Holmes, Nature 347 (1990) 539;
(c) Q. Zhou, T.M. Swager, J. Am. Chem. Soc. 117 (1995) 12593;
(d) D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 100 (2000) 2537;
(e) D.T. McQuade, A.H. Hegedus, T.M. Swager, J. Am. Chem. Soc. 122 (2000)
12389.
[3] (a) M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, M.B. Hursthouse, J.M. Caulfield,
J. Singleton, L. Ducasse, P. Guionneau, J. Am. Chem. Soc. 117 (1995) 12209;
(b) L.L. Martin, S.S. Turner, P. Day, F.E. Mabbs, E.J.L. McInnes, J. Chem. Soc.,
Chem. Commun. (1997) 1367;
(c) S. Rashid, S.S. Turner, P. Day, J.A.K. Howard, P. Guionneau, E.J.L. McInnes, F.E.
Mabbs, R.J.H. Clark, S. Firth, T.J. Biggs, J. Mater. Chem. 11 (2001) 2095;
(d) H. Fujiwara, E. Fujiwara, Y. Nakazawa, B.Z. Narymbetov, K. Kato, H.
Kobayashi, A. Kobayashi, M. Tokumoto, P. Cassoux, J. Am. Chem. Soc. 123
(2001) 306.
[4] (a) E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, V. Laukhin, Nature 408
(2000) 447;
(b) A. Alberola, E. Coronado, J.R. Galán-Mascarós, C. Giménez-Saiz, C.J. Gómez-
García, F.M. Romero, Synth. Met. 133-134 (2003) 509;
(c) A. Alberola, E. Coronado, J.R. Galán-Mascarós, C. Giménez-Saiz, C.J. Gómez-
García, E. Martínez-Ferrero, A. Murcia-Martínez, Synth. Met. 135–136 (2003)
687;
(d) A. Alberola, E. Coronado, J.R. Galán-Mascarós, C. Giménez-Saiz, C.J. Gómez-
García, J. Am. Chem. Soc. 125 (2003) 10774.
[5] S. Uji, H. Shinagawa, T. Terashima, T. Yakabe, Y. Terai, M. Tokumoto, A.
Kobayashi, H. Tanaka, H. Kobayashi, Nature 410 (2001) 908.
[6] (a) C. Réthore, N. Avarvari, E. Canadell, P. Auban-Senzier, M. Fourmigué, J. Am.
Chem. Soc. 127 (2005) 5748;
(b) A. Karrer, J.D. Wallis, J.D. Dunitz, B. Hilti, C.W. Mayer, M. Bürkle, J. Pfeiffer,
Helv. Chim. Acta 70 (1987) 942;
(c) M.M. Fruend, J.L. Olsen, J.D. Wallis, A. Karrer, J.D. Dunitz, B. Hilti, Jpn. J. Appl.
Phys. Part 1 26 (1987) 895;
(d) J.S. Zambounis, J. Pfeiffer, G.C. Papavassiliou, D.J. Lagourvados, A. Terzis, C.P.
Raptopoulou, P. Delhaes, L. Ducasse, N.A. Fortune, K. Murata, Solid State
Commun. 95 (1995) 211;
(e) J.S. Zambounis, C.W. Mayer, K. Hauenstein, B. Hilti, W. Hofherr, J. Pfeiffer, M.
Bürkle, G. Rihs, Adv. Mater. 4 (1992) 33;
(f) E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, A. Murcia-Martínez, E.
Canadell, Inorg. Chem. 43 (2004) 8072.
[7] (a) H. Tanaka, Y. Okano, H. Kobayshi, W. Suzuki, A. Kobayashi, Science 291
(2001) 285;
(b) A. Kobayashi, E. Fujiwara, H. Kobayashi, Chem. Rev. 104 (2004) 5243.
[8] (a) D. Jérome, H.L. Schulz, Adv. Phys. 51 (2002) 293;
(b) C.S. Jacobsen, H.J. Pedersen, K. Mortensen, G. Rindorf, N. Thorup, J.B.
Torrance, K. Bechgaard, J. Phys. C. 15 (1982) 2651;
(c) G. Rindorf, H. Soling, N. Thourup, Acta Crystallogr. C40 (1984) 1137.

[9] (a) A. Ota, H. Yamochi, G. Saito, J. Mater. Chem. 12 (2002) 2600;
(b) A. Ota, H. Yamochi, G. Saito, Synth. Met. 133–134 (2003) 463;
(c) A. Ota, H. Yamochi, G. Saito, Synth. Met. 135–136 (2003) 643.
[10] T. Ishiguro, K. Yamaji, G. Saito, Organic Superconductors, second ed., Springer-
Verlag, Heidelberg, 1998.
[11] Y. Shimizu, K. Miyagawa, K. Kanoda, M. Maesato, G. Saito, Phys. Rev. Lett. 91
(2003) 107001.
[12] (a) N.F. Mott, Metal-Insulator Transitions, second ed., Taylor and Francis Ltd.,
London, 1990;
(b) A. Ota, L. Ouahab, S. Golhen, Y. Yoshida, M. Maesato, G. Saito, R. S´ weitlik,
Chem. Mater. 19 (2007) 2455;
(c) K. Heuze, M. Fourmigué, P. Batail, C. Coulon, R. Clérac, E. Canadell, P. Auban-
Senzier, S. Ravy, D. Jerome, Adv. Mater. 15 (2003) 1251.
[13] (a) H. Seo, J. Phys. Soc. Jpn. 69 (2000) 805;
(b) S. Mazmuder, R.T. Clay, D.K. Campbell, Phys. Rev. B 62 (2000) 13400;
(c) D.S. Chow, F. Zamborszky, B. Alavi, D.J. Tantillo, A. Baur, C.A. Merlic, S.E.
Brown, Phys. Rev. Lett. 85 (2000) 1698;
(d) L. Belicas, K. Behnia, W. Kang, E. Canadell, P. Auban-Senzier, D. Jerome, M.
Ribault, J.M. Fabre, J. Phys. I France 4 (1994) 1539.
[14] H. Tsukada, T. Goto, K. Ogasawara, S. Horiuchi, H. Yamochi, G. Saito, J. Phys.
Soc. Jpn. 67 (1998) 1556.
[15] (a) S. Uji, H. Shinagawa, T. Terashima, T. Yakabe, Y. Terai, M. Tokumoto, A.
Kobayashi, H. Tanaka, H. Kobayashi, Nature 410 (2001) 908;
(b) L. Belicas, J.S. Brooks, K. Storr, S. Uji, M. Tokumoto, H. Tanaka, H. Kobayashi,
A. Kobayashi, V. Barzykin, L.P. Gor’kov, Phys. Rev. Lett. 87 (2001) 7002;
(c) V. Jaccarino, M. Peter, Phys. Rev. Lett. 9 (1962) 290;
(d) E. Ojima, H. Fujiwara, K. Kato, H. Kobayashi, H. Tanaka, A. Kobayashi, M.
Tokumoto, P. Cassoux, J. Am. Chem. Soc. 121 (1999) 5581;
(e) H. Fujiwara, E. Fujiwara, Y. Nakazawa, B.Zh. Narymbetov, K. Kato, H.
Kobayashi, A. Kobayashi, M. Tokumoto, P. Cassoux, J. Am. Chem. Soc. 123
(2001) 306;
(f) H. Fujiwara, H. Kobayashi, E. Fujiwara, A. Kobayashi, J. Am. Chem. Soc. 124
(2002) 6816.
[16] T. Mallah, C. Hollis, S. Bott, M. Kurmoo, P. Day, J. Chem. Soc., Dalton Trans.
(1990) 859.
[17] E. Coronado, J.R. Galán-Mascarós, C. Giménez-Saiz, C.J. Gómez-García, S. Triki,
J. Am. Chem. Soc. 120 (1998) 4671.
[18] M. Kurmoo, T. Mallah, L. Marsden, M. Allan, R.H. Friend, F.L. Pratt, W. Hayes, D.
Chasseau, G. Bravic, L. Duchase, P. Day, J. Am. Chem. Soc. 114 (1992) 10722.
[19] J.M. Williams, A.M. Kini, H.H. Wang, K.D. Carlson, U. Geiser, L.K. Montgomery,
G.J. Pyrka, D.M. Watkins, J.M. Kommers, S.J. Boryschuk, A.V. Crouch, W.K.
Kwok, J.E. Shirber, D.L. Overmyer, Inorg. Chem. 29 (1990) 3272.
[20] A.M. Kini, U. Geiser, H.H. Wang, K.D. Carlson, J.M. Williams, W.K. Kwok, K.G.
Vandervoort, J.E. Thompson, D.L. Stupka, D. Jung, M.H. Whangbo, Inorg. Chem.
29 (1990) 2555.
[21] C.J. Kepert, M. Kurmoo, P. Day, Inorg. Chem. 36 (1997) 1128.
[22] M. Fettoui, L. Ouahab, A. Perrin, D. Grandjean, J.M. Fabre, Acta Crystallogr. C47
(1991) 2457.
[23] (a) A. Dolbecq, K. Boubekeur, P. Batail, E. Canadell, P. Auban-Senzier, C. Coulon,
K. Lerstrup, K. Bechgaard, J. Mater. Chem. 5 (1995) 1707;
(b) P. Batail, C. Livage, S.S.P. Parkin, C. Coulon, J.D. Martin, E. Canadell, Angew.
Chem. Int. Ed. Engl. 30 (1991) 1498;
(c) A. Pénicaud, K. Boubekeur, P. Batail, E. Canadell, P. Auban-Senzier, D.
Jerome, J. Am. Chem. Soc. 115 (1993) 4101;
(d) K. Boubekeur, C. Lenoir, P. Batail, R. Carlier, A. Tallec, M.-P. LePaillard, D.
Lorcy, A. Robert, Angew. Chem. Int. Ed. Engl. 33 (1994) 1379;
(e) P. Batail, L. Ouahab, A. Pénicaud, C. Lenoir, A. Perrin, C.R. Hebd, Seances
Acad. Sci. Paris Sér. II 304 (1987) 1111;
(f) A. Pénicaud, C. Lenoir, P. Batail, C. Coulon, A. Perrin, Synth. Met. 32 (1989)
25;
(g) S.A. Baudron, P. Batail, C. Coulon, R. Clérac, E. Canadell, V. Laukhin, R. Melzi,
P. Wzietek, D. Jérome, P. Auban-Senzier, S. Ravy, J. Am. Chem. Soc. 127 (2005)
11785;
E.W. Reinheimer et al. / Journal of Molecular Structure 890 (2008) 81–89 89
(h) A. Deluzet, R. Rousseau, C. Guilbaud, I. Granger, K. Boubekeur, P. Batail, E.
Canadell, P. Auban-Senzier, D. Jérome, Chem. Eur. J. 8 (2002) 3884;
(i) J.-C. Gabriel, K. Boubekeur, P. Batail, Inorg. Chem. 32 (1993) 2894;
(j) J.-C.P. Gabriel, K. Boubekeur, S. Uriel, P. Batail, Chem. Rev. 101 (2001) 2037;
(k) S. Perruchas, K. Boubekeur, P. Batail, Cryst. Growth Des. 5 (2005) 1585;
(l) A. Deluzet, P. Batail, Y. Misaki, P. Auban-Senzier, E. Canadell, Adv. Mater. 12
(2000) 436.
[24] P. Batail, K. Boubekeur, M. Fourmigué, J.-C.P. Gabriel, Chem. Mater. 10 (1998)
3005.
[25] K. Lerstrup, I. Johannsen, M. Jørgensen, Synth. Met. 27 (1988) 9.
[26] F. Gerson, A. Lamprecht, M. Fourmigué, J. Chem. Soc., Perkin Trans 2 (1996)
1409.
[27] F.A. Cotton, N.F. Curtis, B.F.G. Johnson, W.R. Robinson, Inorg. Chem. 4 (1965)
326.
[28] G.M. Sheldrick, SAINT, Program for reflection data integration, University of
Göttingen, Germany, 1996.
[29] G.M. Sheldrick, SADABS, Program for Siemens area detector absorption
correction, University of Göttingen, Germany, 1996.
[30] G.M. Sheldrick, SHELXS-97, Program for crystal structure determination,
University of Göttingen, Germany, 1997.
[31] G.M. Sheldrick, SHELXTL, An integrated system for solving refining and
displaying crystal structures from diffraction data (Revision 5.1), University of
Göttingen, Germany, 1985.
[32] L.J. Barbour, J. Supramol. Chem. 1 (2001) 189.
[33] G.M. Sheldrick, SHELXL-97, Program for crystal structure refinement,
University of Göttingen, Germany, 1997.
[34] T.C. Umland, S. Allie, T. Kuhlman, P. Coppens, J. Phys. Chem. 92 (1988) 6456.
[35] (a) M. Fourmigué, C.E. Uzelmeier, K. Boubekeur, S.L. Bartley, K.R. Dunbar, J.
Organomet. Chem. 529 (1997) 343;
(b) B.W. Smucker, K.R. Dunbar, Dalton Trans. (2000) 1309;
(c) C.E. Uzelmeier, B.W. Smucker, E.W. Reinheimer, M. Shatruk, A. O’Neal, M.
Fourmigué, K.R. Dunbar, Dalton Trans. (2006) 5259;
(d) N. Avarvari, M. Fourmigué, Chem. Commun. (2004) 1300;
(e) N. Avarvari, D. Martin, M. Fourmigué, J. Organomet. Chem. 643–644 (2002)
292;
(f) C. Gouverd, F. Biaso, L. Cataldo, T. Berclaz, M. Geoffrey, E. Levillain, N.
Avarvari, M. Fourmigué, F.X. Sauvage, C. Wartelle, Phys. Chem. Chem. Phys. 7
(2005) 85;
(g) A. Kobayashi, E. Fujiwara, H. Kobayashi, Chem. Rev. 104 (2004) 5243.
[36] (a) A. Alberola, E. Coronado, J.R. Galán-Mascarós, C. Giménez-Saiz, C.J. Gómez-
García, J. Am. Chem. Soc. 125 (2003) 10774;
(b) E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, A. Murcia-Martínez, E.
Canadell, Inorg. Chem. 43 (2004) 8072;
(c) E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, E. Martínez-Ferrero, S.
van Smaalen, Inorg. Chem. 43 (2004) 4808;
(d) M. Clemente-León, E. Coronado, J.R. Galan-Mascarós, C. Giménez-Saiz, C.J.
Gómez-García, E. Ribera, J. Vidal-Gancedo, C. Rovira, E. Canadell, V. Laukhin,
Inorg. Chem. 40 (2001) 3526;
(e) M. Clemente-León, E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, C.
Rovira, V.N. Laukhin, Synth. Met. 103 (1999) 2339;
(f) M. Clemente-León, E. Coronado, J.R. Galán-Mascaros, C. Giménez-Saiz, C.J.
Gómez-García, J.M. Fabre, Synth. Met. 103 (1999) 2279;
(g) H. Kobayashi, H. Tomita, T. Naito, A. Kobayashi, F. Sakai, T. Watanabe, P.
Cassoux, J. Am. Chem. Soc. 118 (1996) 368;
(h) M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, M.B. Hursthouse, J.L. Caulfield,
J. Singleton, F.L. Pratt, W. Hayes, L. Duchase, P. Guionneau, J. Am. Chem. Soc.
117 (1995) 12209;
(i) M. Bousseau, L. Valade, J.P. Legros, P. Cassoux, M. Garbauskas, L.V.
Interrante, J. Am. Chem. Soc. 108 (1986) 1908;
(j) S. Perruchas, K. Boubekeur, P. Auban-Senzier, J. Mater. Chem. 14 (2004) 3509;
(k) O.N. Kazheva, G.G. Alexandrov, O.A. Dyachenko, T.N. Zinenko, A.V.
Kravchenko, V.A. Staroub, A.V. Khotkevich, Synth. Met. 156 (2006) 251;
(l) X. Chi, B. Scott, G. Lawes, A.P. Ramirez, J. Chem. Cryst. 34 (2004) 249.