Extended TTF-type donors fused with pyrazine units; Synthesis and characterization

Article abstract of DOI:10.1016/j.tetlet.2013.09.131

Pyrazinedicyanoethylthiotetrathiafulvalene, (pzdc-TTF) (1a), an extended TTF fused with a pyrazine moiety and also a dithiolene ligand precursor, was synthesized through a cross-coupling with triethyl phosphite between pyrazine-1,3-dithiole-2-thione (I) and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2- one (III). This reaction also yields to dipyrazine TTF derivative (1b) and 2,3,6,7-Tetrakis(2-cyanoethylthio)TTF (1c), resulting from the self-coupling reactions of the thione (I) and ketone (III). The crystal structure of 1a is composed by pairs of head to head donor stacks of pzdc-TTF molecules along b in opposite orientations. Single crystals of 1b revealed a new polymorph with a face-to-face π-stacking motif. The electrochemical properties of 1a studied by cyclic voltammetry (CV) in DMF, shows two single electron oxidation processes typical of TTF-based donors; one pair of asymmetric redox waves centered at 627 mV versus Ag/Ag⁺ is ascribed to the couple [pzdc-TTF] ⁺/[pzdc-TTF]²⁺, and one pair of quasi-reversible redox waves centered at 430 mV is ascribed to the couple [pzdc-TTF] ⁰/[pzdc-TTF]⁺.

Full text of DOI:10.1016/j.tetlet.2013.09.131

Tetrahedron Letters 54 (2013) 6635–6639
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Extended TTF-type donors fused with pyrazine units; synthesis
and characterization
a
Sandra Rabaça a, , Sandrina Oliveira , Isabel C. Santos a,b, Manuel Almeida a,
⇑
⇑
a UCQR, IST/ITN, Instituto Superior Técnico/CFMCUL, Estrada Nacional 10, P-2686-953 Sacavém, Portugal
b Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2013
Revised 24 September 2013
Accepted 27 September 2013
Available online 3 October 2013
Pyrazinedicyanoethylthiotetrathiafulvalene, (pzdc-TTF) (1a), an extended TTF fused with a pyrazine moi-
ety and also a dithiolene ligand precursor, was synthesized through a cross-coupling with triethyl phos-
phite between pyrazine-1,3-dithiole-2-thione (I) and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-one (III).
This reaction also yields to dipyrazine TTF derivative (1b) and 2,3,6,7-Tetrakis(2-cyanoethylthio)TTF
(1c), resulting from the self-coupling reactions of the thione (I) and ketone (III). The crystal structure
of 1a is composed by pairs of head to head donor stacks of pzdc-TTF molecules along b in opposite ori-
Keywords:
Extended tetrathiafulvalene donors
Pyrazine
Synthesis
X-ray structure
Cyclic voltammetry
entations. Single crystals of 1b revealed a new polymorph with a face-to-face p-stacking motif. The elec-
trochemical properties of 1a studied by cyclic voltammetry (CV) in DMF, shows two single electron
oxidation processes typical of TTF-based donors; one pair of asymmetric redox waves centered at
627 mV versus Ag/Ag+ is ascribed to the couple [pzdc-TTF]+/[pzdc-TTF]2+, and one pair of quasi-reversible
redox waves centered at 430 mV is ascribed to the couple [pzdc-TTF]0/[pzdc-TTF]+.
Ó 2013 Elsevier Ltd. All rights reserved.
The tetrathiafulvalene molecule (TTF) and its many derivatives,
due to its unique -donor properties, have been at the basis of the
large majority of organic metals and superconductors known so
far.1 This success as a building block for conducting materials is
largely associated with the large possibilities of extending the
coordinate transition metals.4 Aiming at enlarging this type of
complexes we decided to explore new extended dithiolene ligands
that incorporate not only TTF, but also pyrazine units. The extra
p
pyrazine units are expected to enhance the degree of p-delocaliza-
tion over the ligand extremity, while the presence of the nitrogen
atom can favor the side to side intermolecular interaction at the li-
gand periphery, and coordinate to other metals as found in other
simple pyrazine dithiolate type ligands.4b,5
delocalized
other heteroatoms in the molecular periphery. The extension of
the -system in general renders more accessible the different
p-system and incorporation of additional sulfur or
p
oxidation states, and maximizes the intermolecular interactions
between planar molecules that tend to be organized as stacks in
the solid state. The presence of additional sulfur and other hetero-
atoms in the molecular periphery promotes the side intermolecu-
lar interactions along the molecular plane.
In this Letter, we report the synthesis and characterization of a
new extended TTF-type donor fused with pyrazine moieties the
pyrazinedicyanoethylthiotetrathiafulvalene,
(pzdc-TTF)
(1a),
which is also a precursor for the preparation of new extended
pyrazine-TTF fused dithiolene ligands.
Some extended TTF derivatives have been also used in the last
decade as dithiolene ligands, in the preparation of extended transi-
tion metal bisdithiolene complexes2 that deserved special atten-
tion because in their neutral state were often found to lead a
metallic behavior, the so called single component molecular
metals.3
More recently there has been an increasing interest in TTF
derivatives containing N atoms in their periphery which retaining
the electroactive behavior of TTF could in addition be able to
The key compound for the synthesis of the pyrazine substituted
compounds (ligand precursors and donors) is thione I (Pyrazine-
1,3-dithiole-2-thione).6 Although this compound was previously
mentioned,7 and could be obtained from the reaction of 2,3-dichlo-
ropyrazine with potassium trithiocarbonate,8 in this work we report
modifications in the reaction treatment and a full characterization
of this compound. Ketone II (Pyrazine-1,3-dithiole-2-one), which
can be also a key starting compound, was obtained from a regular
S to O exchange reaction of I.9 The preparation of the novel TTF-
based donor, pzdc-TTF (1a),10 was achieved following a synthetic
route first used by Underhill and co-workers2 involving the coupling
with triethyl phosphite between thione I and ketone III (Scheme 1).
This coupling reaction leading to the compound (1a) also gives
rise to other by-products, the dipyrazine TTF derivative (1b) and
⇑
Corresponding authors. Tel.: +351 21 994 6203; fax: +351 21 955 0117
(S. Rabaça); tel.: +351 21 994 6171; fax: +351 21 955 0117 (M. Almeida).
E-mail addresses: sandrar@ctn.ist.utl.pt (S. Rabaça), malmeida@ctn.ist.utl.pt
(M. Almeida).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.09.131

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S. Rabaça et al. / Tetrahedron Letters 54 (2013) 6635–6639
Figure 1. ORTEP diagrams of: (a) compound I (#a = x, ½Ày, z) and (b) compound II,
drawn at 30% probability level with the atomic numbering scheme.
The crystal structure of I is composed by regular chains of essen-
tially coplanar molecules arranged head to tail along the c axis
(Fig. 2). These chains which are made by two hydrogen bonds
involving the pyrazine nitrogen atoms C1-H1Á Á ÁN1 (#a) 2.611 Å
(#a = Àx, 1Ày, 1Àz) are however interlocked, making angles of
71.8°, due to S2 of molecules from one chain lying between two
S1 atoms of another chain at relatively short distances S1Á Á ÁS2
(#b), (#c), (#d) 3.550 Å (#b = ½Àx, 1Ày, À½ + z; #c = ½Àx, À½ + y,
½ + z; d# = ½Àx, 1Ày, ½ + z).
Scheme 1. Reagents and conditions: (a)K2S, CS2, DMF; (b) Hg(OAc)2, AcOH, DCM;
(c) P(OEt)3, Toluene.
2,3,6,7-Tetrakis(2-cyanoethylthio)TTF (1c) resulting from the
self-coupling of thione (I) and ketone (III) respectively as shown
in Scheme 1. However a reasonable yield of 41% was achieved for
1a after column separation, using dichloromethane/ethyl acetate
(20:1) as the eluent. Compound 1a is soluble in usual organic
solvents, such as dichloromethane and acetonitrile. Compounds
1b and 1c are obtained in significantly smaller amounts in yields
of 4% and 18% respectively. The same compounds 1a, 1b, and 1c,
could also have been obtained, possibly in different yields, staring
from ketone II and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-thi-
one. However this last option was not explored in view of the sat-
isfactory reaction yield to obtain the desired compound 1a from II.
Compounds I, II, 1a, and 1b were obtained as single crystals and
a complete analysis of their structure has been carried out based on
X-ray diffraction data (Table 1).11
Thione I crystallizes in the orthorhombic system, space group
Pnma. The asymmetric unit contains half the molecule, the entire
molecule is generated by a mirror plane perpendicular to the
[0,1,0] plane.
The oxo compound II crystallizes in the monoclinic system,
space group P21/c. The asymmetric unit contains one independent
molecule in a general position. Figure 1 shows the ORTEP plots of I
and II, with the corresponding atomic numbering schemes.
Thione I and the oxo compound II are essentially planar (Rms
deviation of the fitted atoms: 0.0168 Å and 0.0243 Å, respectively).
In the structure of compound II (Fig. 3) the molecules area also
arranged head to tail in a coplanar fashion and in chains along
2a+c. However these chains are not regular and molecules con-
nected by pairs of hydrogen bonds between the N pyrazine atoms
C2-H2Á Á ÁN2 (#a) 2.607 Å (#a = 1Àx, 1Ày, 1Àz), alternate with
molecules connected by short contacts N1Á Á ÁS1 (#a) at 3.041 Å
and C1Á Á ÁS1 (#a) at 3.472 Å (Fig. 3a). These chains in this compound
are not interlocked as in I but instead connected along b by hydro-
gen bonds between the oxygen atoms and the hydrogen atoms of
the pyrazine ring, C1-H1Á Á ÁO1 (#b) 2.686 Å and C2-H2Á Á ÁO1 (#b)
2.566 Å (#b = Àx, ½ + y, ½Àz) making layers of almost coplanar
chains. These layers are not interconnected by any short contacts.
Compound 1a crystallizes in the monoclinic system, space
group C2/c. Figure 4 shows the ORTEP plots with the corresponding
atomic numbering scheme. The asymmetric unit contains one
independent pzdc-TTF molecule located in a general position. The
central TTF core and the pyrazine atoms are essentially planar
(Rms deviation of fitted atoms: 0.0287 Å) while the chains contain-
ing a terminal cyanoethyl group are almost perpendicular to the
central plane. Bond lengths and angles in the TTF moiety are in
the range expected for neutral TTF derivatives.12
The crystal structure of 1a is composed by pairs of regular
stacks of pzdc-TTF molecules (1a) along b arranged in pairs in
opposite directions (Fig 5a), In the a,c plane the stacks alternate
their orientation and the angle between the central TTF core of
Table 1
Crystallographic details for compounds I, II, 1a, and 1b
(I)
(II)
(1a)
(1b)
Crystal size (mm)
Crystal color and shape
Empirical formula
Molecular mass
Crystal system
Space group (No.)
a (Å)
0.50 Â 0.20 Â 0.15
Orange prism
C5H2N2S3
186.27
Orthorhombic
Pnma
11.6957(2)
9.7928(2)
5.85710(1)
90
0.40 Â 0.30 Â 0.14
Colorless prism
C5H2N2OS2
170.21
Monoclinic
P21/c
3.9489(2)
16.3596(9)
9.8689(6)
90.00
0.60 Â 0.04 Â 0.02
Orange needle
C14H10N4S6
426.62
Monoclinic
C2/c
36.354(2)
5.1958(6)
24.590(2)
90.00
0.40 Â 0.06 Â 0.05
Yellow needle
C10H4N4S4
308.41
Monoclinic
P21/n
3.8043(3)
8.1512(7)
18.2999(15)
90.00
b (Å)
c (Å)
a
(°)
b (°)
90
90
670.84(2)
4, 1.844
1.010
100.701(3)
90.00
626.47(6)
4, 1.805
131.903(6)
90.00
3457.0(5)
8, 1.639
93.593(3)
90.00
566.36(8)
2, 1.809
c
(°)
V (Å3)
Z, Dcalcd (Mg/m3)
l
(mmÀ1
)
0.763
0.796
0.821
F(000)
376
344
1744
312
Index range (h,k,l)
Tmax./min.
À13/14; À12/12; À6/7
0.6321 / 0.8632
1.107
À4/4, À19/19, À11/9
0.7501/0.9007
1.122
À35/41; À6/6; À29/24
0.6468/0.9843
0.882
À4/4; À8/9; À22/22
0.7349/0.9601
1.040
Goodness-of-fit on F2
Final R1, [I >2
r
(I)], wR2
0.0178, 0.0505
0.0418, 0.1186
0.0661, 0.1446
0.0317, 0.0691

S. Rabaça et al. / Tetrahedron Letters 54 (2013) 6635–6639
6637
molecules in adjacent pairs is circa 82° angle (Fig. 6b). The donor
molecules are interlocked in such a way that the cyanoethyl groups
are segregated from the TTF cores in alternated layers, at variance
with other extended TTFs packing motifs: head to head but with-
out TTF molecules of nearby stacks in opposite directions;13 or
with the more frequent head to tail packing motif.12d In the donors
pair the molecules are connected by a lateral short SÁ Á ÁS contact:
S1Á Á ÁS3 (#a) 3.531 Å (#a = ½Àx, ½Ày, Àz) (Fig 6a). Along the donor
stacks the molecules are connected by short SÁ Á ÁC contacts be-
tween the cyanoethyl groups, S6Á Á ÁC14 (#b) 2.519 Å and between
the TTF core and pyrazine ring S1Á Á ÁC2 (#b) 3.478 Å (#b = x,
À1 + y, z). The cyanoethyl group present other short contacts with
other cyanoethyl group, C14Á Á ÁC14 (#c) 3.316 Å, and with pyrazine
ring, C2 Á Á ÁC11 (#d) 3.299 Å (#c = 1Àx, 1Ày, 1Àz, d = x, 1Ày, ½ + z).
In spite of being a by-product of the coupling reaction and ob-
tained only in 4% yield, single crystal of compound 1b suitable
for X-ray diffraction analysis could be easily isolated and it was
found to crystallize in the monoclinic system, space group P21/n
(see Table 1). The asymmetric unit comprises half molecule with
an inversion center at the central C@C bond and the corresponding
ORTEP diagram is shown in Figure 6.
Figure 2. Crystal structure of compound I viewed along c (a) and along b (b).
The dipyrazine TTF derivative 1b has already been reported
with a crystal structure determined in crystals obtained by subli-
mation, presenting a herringbone-type packing of donors.14 In this
work a different polymorph was obtained, probably as a conse-
quence of the different crystallization conditions used, from solu-
tion. Our crystals obtained by recrystallization present a face-to-
face
p-stacking motif of the donors, as shown in Figure 7, where
Figure 3. Crystal structure of compound II viewed along a (a) and along 2a+c (b).
Figure 4. ORTEP diagrams of compound 1a drawn at the 30% probability level,
showing the atomic numbering scheme in the top and lateral molecular views.
Figure 5. Crystal structure of 1a: (a) viewed along b axis, and (b) perspective detail
of two column pairs.

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S. Rabaça et al. / Tetrahedron Letters 54 (2013) 6635–6639
Table 2
Redox potentials (vs Ag/Ag+) in DMF of 1a as well as of related extended TTF-type
donors
Donor
1E1/2 (V)
2E1/2 (V)
1a, pzdc-TTF
0.43
0.53
0.56
0.64
0.63
0.72
0.73
0.84
dtdt12d
a
-tdt12d
1c, (tCNEt-TTF)a,12d
a
Figure 6. ORTEP diagram of compound 1b drawn at 30% probability level with the
atomic numbering scheme, (#a = Àx, 2Ày, 1Àz).
2,3,6,7-Tetrakis(2-cyanoethylthio)TTF.
the interplanar distance is about 3.452 Å and the shortest intermo-
lecular SÁ Á ÁS distance of 3.709 Å (length-VdW = 0.109) is observed
between staking TTF derivative molecules. The 1,3-dithiole rings
are overlapped with the pyrazine rings, suggesting the presence
of
p–p-intermolecular interaction which might induce the face-
to-face stacking motif. This crystal motif seems also to be stabilized
by the lateral observed short contacts, between the 1,3-dithiole
rings and the lateral pyrazine rings, S1Á Á ÁC1 (#a) 3.456 Å and
S1Á Á ÁN1 (#a) 2.981 Å (#a = 1Àx,1Ày,1Àz).
The redox potentials of the extended TTF-type donor 1a were
measured by cyclic voltammetry (CV) in DMF containing n-Bu4-
NBF4 as a supporting electrolyte at a scan rate of 100 mVsÀ1, using
a platinum working electrode and Ag/Ag+ as the reference elec-
trode. The corresponding half-wave potentials for 1a along with
those of dtdt and
a-tdt, two extended thiophene-TTF fused
donors12d are listed for comparison in Table 2.
In 1a two single electron oxidation processes typical of the TTF-
based donors are observed; one pair of asymmetric redox waves
centered at 627 mV is ascribed to the couple [pzdc-TTF]+/[pzdc-
TTF]2+, while the pair of reversible redox waves centered at
430mV is ascribed to the couple [pzdc-TTF]0/[pzdc-TTF]+ (Fig. 8).
Figure 8. Cyclic voltammogram of 1a.
Acknowledgments
Compared with the donors dtdt and
a-tdt, 1a is the easiest to
This work was partially supported by FCT under contract PTDC/
FIS/113500/2009.
oxidize requiring the lowest potential to remove an electron, both
oxidation potentials of 1a are lowered by approximately 100 mV,
confirming the electron withdrawing effect of the pyrazine group.
In 1a, the asymmetric fusion of the pyrazine ring increases the
donor properties when compared with the tCNEt-TTF (1c).
In conclusion a convenient synthesis of the new pyrazine
extended TTF ligand pyrazinedicyanoethylthiotetrathiafulvalene,
(pzdc-TTF) (1a), which is also a dithiolene ligand precursor, was
achieved. The new donor shows better donor properties when
compared with other extended TTF ligands, confirming the
electron withdrawing effect of the pyrazine group.15 It displays a
crystal structure dominated by SÁ Á ÁS and SÁ Á ÁC contacts with a head
to head donor stacks packing. This TTF donor which is also a ligand
precursor for preparing bisdithiolene complexes with highly
extended ligands, is currently being used in our laboratory explor-
ing the capability of metal coordination by N atoms.
Supplementary data
Supplementary data (crystallographic data for the structural
analysis have been deposited with the Cambridge Crystallographic
Data Centre, CCDC 943880-943883 for compounds I, II, 1a, 1b)
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.tetlet.2013.09.131. These data include
MOL files and InChiKeys of the most important compounds de-
scribed in this article.
References and notes
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phosphite (P(OEt)3) and 10 mL of toluene. The mixture was heated up to 90 °C
under nitrogen atmosphere and stirred for 3 h. During the reaction an orange
precipitate was formed. Upon cooling to ambient temperature the precipitate
was filtered off and washed with 3 Â 10 mL of methanol and dried under
vacuum. The solid was purified by column chromatography, using DCM:ethyl
acetate (v/v = 20:1) as eluent. (0.457 g; 1.07 mmol, yield=41%, Rf = 0.45). Mp
145 °C. 1H NMR (300 MHz, CDCl3, 25 °C, TMS) d = 8.076 (s, 1H), 3.145–3.099 (t,
2H), 2.796–2.750 (t, 2H); 13C (75.3373 MHz), CDCl3: d = 157.506, 139.877,
128.151, 117.612, 112.588, 105.952, 31.519, 19.229; IR kmax (KBr)/cmÀ1: 3066
(w, Ar-H), 2934 (m, –CH2–), 2250 (m, C„N), 1689 and 1496 (w, –C@C-), 1564
(m, C@C), 1525 (m, C@N), 1423 (m, S-CH2-R), 1330 (m, C–N), C14H10N4S6
(426.65): calcd C 39.41, H 2.36, N 13.13, S 45.09; found C 41.40, H 2.68, N
12.85, S 44.17. It was possible to isolate the other 2 products of the coupling
reaction resultant from the self-coupling of the reactants, (compound 1b
0,033 g; 1.072Â10-1 mmol, yield = 4%, Rf = 0.8 and compound 1c 0.263 g;
0482 mmol; yield = 18%, Rf = 0.3). Single crystals of 1a and 1b, suitable for RX
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measurements were obtained from slow evaporation of
dicloromethane:Ethyl Acetate (v/v = 20:1) solution.
a saturated
11. The X-ray diffraction data for compounds I, II, 1a, and 1b were collected on a
6. Pyrazine-1,3-dithiole-2-thione (I): A mixture of potassium sulphide (43%, 3 g,
11.7 mmol), carbon disulphide (2 mL, 33 mmol), and dimethylformamide
(8 mL) was stirred at room temperature for 3 h. To the resulting red
suspension of potassium trithiocarbonate, 2,3-dichloropyrazine (1.48 g,
1,03 mL, 10 mmol) was added, and the mixture was further stirred for 48 h
at 75°C. The mixture was then poured into water (100 mL), filtered, dried in
vacuo, and isolated as a yellow solid after separation by silica gel column
chromatography using CH2Cl2/hexane (v:v = 2:1) as eluent. (1.268 g,
6.8 mmol, yield = 68%, Rf = 0.48). Mp 171°C. 1H NMR (300 MHz, CDCl3, 25°C,
Bruker APEXII CCD diffractometer equipped with an Oxford Cryosystems low-
temperature device at 150 K in the
x and u scan modes. A semi empirical
absorption correction was carried out using SADABS.16 Data collection, cell
refinement, and data reduction were done with the SMART and SAINT
programs.17 The structures were solved by direct methods using SIR9718 and
refined by full-matrix least-squares methods with the SHELXL9719 program
using the WINGX20 software package. Nonhydrogen atoms were refined with
anisotropic thermal parameters whereas H-atoms were placed in idealized
positions and allowed to refine riding on the parent C atom. Molecular graphics
were prepared using ORTEP321 and MERCURY 1.4.2.22
TMS)
d
8.435 (s, 1H), 13C (75.3373 MHz), CDCl3: d = 142.235, 159.637,
3058 (w, Ar-H), 1564 (m, C@C), 1533 (m,
206.716; IR kmax (KBr)/cmÀ1
:
12. (a) Bouguessa, S.; Gouasmia, A. K.; Golhen, S.; Ouahab, L.; Fabre, J. M.
Tetrahedron Lett. 2003, 44, 9275; (b) Liu, S.-X.; Dolder, S.; Rusanov, E. B.;
Stoeckli-Evans, H.; Decurtins, S. C. R. Acad. Sci. Paris, Chimie 2003, 6, 657; (c)
Devic, T.; Avarvari, N.; Batail, P. Chem. Eur. J. 2004, 10, 697; (d) Belo, D.;
Figueira, M. J.; Nunes, J. P. M.; Santos, I. C.; Almeida, M.; Crivillers, N.; Rovira, C.
Inorg. Chim. Acta 2007, 360, 3903.
C@N), 1340 (m, C–N), 1072 (S, C@S); C5H2N2S3 (186.28): calcd C 32.24, H 1.08,
N 15.04, S 51.64; found C 32.91, H 1.08, N 15.16, S 52.47. Single crystals of I
suitable for X-ray measurements were obtained from slow evaporation of
dichloromethane solutions.
7. Chem Abstr. 1962, 57, 13774h.
8. Papavassiliou, G. C.; Yiannopoulos, S. Y.; Zambounis, J. S. Chemica Scripta 1987,
27, 265.
13. Dias, S. I. G.; Rabaca, S.; Santos, I. C.; Pereira, L. C. J.; Henriques, R. T.; Almeida,
M. Inorg. Chem. Commun. 2012, 15, 102.
9. Pyrazine-1,3-dithiole-2-one (II): Under Argon, a solution of mercuric acetate
(2.33 g, 7.33 mmol) in acetic acid (60 mL) was added drop-wise to a solution of
pyrazine-1,3-dithiole-2-thione (0.62 g, 3.33 mmol) in dichloromethane
(200 mL) and stirred for 3 h. The resulting solution was filtered, washed with
a saturated solution of NaHCO3 (3 Â 50 mL), H2O (3 Â 50 mL), and then dried
with MgSO4. The dichloromethane was evaporated and the light yellow residue
was purified on a sílica gel column using dichloromethane as the eluent. After
evaporating the solvent, the resulting pale yellow powder was dried overnight
under vacuum (0.392 g, 2.30 mmol, yield = 69%). Mp 87°C; 1H NMR (300 MHz,
CDCl3, TMS) d = 8.406 (s, 1H); 13C (300 MHz, CDCl3, TMS): d = 142.205, 153.609,
183.527; IR kmax (KBr)/cmÀ1: 3072 (w, Ar-H), 1690 (s, C@O), 1566 (m, C@C),
1525 (m, C@N), 1338 (m, C–N), C5H2N2OS2 (193.24): calcd C 35.28, H 1.18, N
16.46, S 37.68; found C 36.96, H 1.05, N 16.98, S 38.50. Single crystals of II
suitable for X-ray measurements were obtained from slow evaporation of
dichloromethane solutions.
14. Naraso; Nishida, J.; Ando, S.; Yamaguchi, J.; Itaka, K.; Hideomi, K.; Tada, H.;
Tokito, S.; Yamashita, Y. J. Am. Chem. Soc. 2005, 127, 10142.
15. Rabaça, S.; Cerdeira, A. C.; Neves, A. I. S.; Dias, S. I. G.; Mézière, C.; Santos, I. C.;
Pereira, L. C. J.; Fourmigué, M.; Henriques, R. T.; Almeida, M. Polyhedron 2009,
28, 1069.
16. Sheldrick, G. M. SADABS; Bruker AXS: Madison, Wisconsin, USA, 2004.
17. Bruker SMART and SAINT; Bruker AXS: Madison, Wisconsin, USA, 2004.
18. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. App. Crystallogr.
1999, 32, 115.
19. Sheldrick, G.M.; SHELXL97, Programs for Crystal Structure Analysis (Release
97-2), Institut fur Anorganische Chemie der Universitat, Tammanstrasse 4, D-
3400 Goettingen, Germany, 2008.
20. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
21. Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
10. Pyrazinedicyanoethylthiotetrathiafulvalene (1a): Compounds
I
(0.5 g;
22. Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields, G. P.; Taylor, R.;
Towler, M.; van de Streek, J. J. Appl. Crystallogr. 2006, 39, 453.
2.68 mmol) and IV (0.8 g; 2.77 mmol) were suspended in 10 mL of triethyl