5,6-Dicyano-2,3-dithiopyrazine (dcdmp) chemistry: Synthesis and crystal structure of Au(III)(dcdmp)2 complexes and 2,3,7,8-tetracyano-1,4,6, 9-tetraazothianthrene

Article abstract of DOI:10.1016/j.poly.2004.02.019

As an effort to explore new complexes of the 2,3-dicyano-5,6- dimercaptopyrazyne (dcdmp) ligand with different transition metals, different salts containing both the Au(dcdmp)₂^- complex and the new species 2,3,7,8-tetracyano-1,4,6,9-tetraazothianthrene (tctata), were obtained and characterized. n-Bu₄N Au(dcdmp)₂ crystallises in monoclinic space group C2/c, Z=8 with unit cell parameters a=35.147(4), b=9.527(1), c=21.792(2) ? and β=109.626(8)°. Its crystal structure consist of almost regular columns of [Au(dcdmp)₂] ^-, stacked along b, surrounded by n-Bu₄N⁺ cations. n-Bu₄N AuBr₂ (tctata) crystallises in triclinic space group P1?, Z=2, with unit cell parameters a=10.986(1), b=13.230(2), c=13.791(1) ?, α=79.150(9)°, β=69.663(6)°, γ=70.254(9)°. The crystal packing is made by zig-zag chains of tctata separated by layers of cations, with AuBr₂ anions located in alternated cavities between the tctata chains and the cation layers. At last, n-Bu₄N[Au(dcdmp)₂] (tctata) crystallises in monoclinic space group P2₁/n, Z=4, with unit cell parameters a=10.693(2), b=40.308(7), c=10.870(1) ?, β=92.16(1)°. Its crystal structure can be seen has a mix of those of the two preceding compounds. It consists of bidimensional layers composed of out of registry parallel zig-zag chains of alternating tctata and [Au(dcdmp)₂]^- units. The adjacent layers are separated by layers of [nBu₄N]⁺. In the last two compounds the tctata appears as a planar molecule.

Full text of DOI:10.1016/j.poly.2004.02.019

Polyhedron 23 (2004) 1351–1359
www.elsevier.com/locate/poly
5,6-Dicyano-2,3-dithiopyrazine (dcdmp) chemistry: synthesis
and crystal structure of Au(III)(dcdmp)2 complexes and
2,3,7,8-tetracyano-1,4,6,9-tetraazothianthrene
*
D. Belo, I.C. Santos, M. Almeida
Departamento de Quꢀımica, Instituto Tecnoloꢀgico e Nuclear, P 2686-953 Sacavꢀem, Portugal
Received 5 November 2003; accepted 11 February 2004
Available online 9 April 2004
Abstract
As an effort to explore new complexes of the 2,3-dicyano-5,6-dimercaptopyrazyne (dcdmp) ligand with different transition metals,
different salts containing both the Au(dcdmp)2ꢀ complex and the new species 2,3,7,8-tetracyano-1,4,6,9-tetraazothianthrene (tctata),
were obtained and characterized. n-Bu4N Au(dcdmp)2 crystallises in monoclinic space group C2=c, Z ¼ 8 with unit cell parameters
ꢁ
a ¼ 35:147ð4Þ, b ¼ 9:527ð1Þ, c ¼ 21:792ð2Þ A and b ¼ 109:626ð8Þ°. Its crystal structure consist of almost regular columns of
[Au(dcdmp)2]ꢀ, stacked along b, surrounded by n-Bu4Nþ cations. n-Bu4N AuBr2 (tctata) crystallises in triclinic space group P1,
ꢂ
ꢁ
Z ¼ 2, with unit cell parameters a ¼ 10:986ð1Þ, b ¼ 13:230ð2Þ, c ¼ 13:791ð1Þ A, a ¼ 79:150ð9Þ°, b ¼ 69:663ð6Þ°, c ¼ 70:254ð9Þ°. The
crystal packing is made by zig-zag chains of tctata separated by layers of cations, with AuBr2 anions located in alternated cavities
between the tctata chains and the cation layers. At last, n-Bu4N[Au(dcdmp)2] (tctata) crystallises in monoclinic space group P21=n,
ꢁ
Z ¼ 4, with unit cell parameters a ¼ 10:693ð2Þ, b ¼ 40:308ð7Þ, c ¼ 10:870ð1Þ A, b ¼ 92:16ð1Þ°. Its crystal structure can be seen has a
mix of those of the two preceding compounds. It consists of bidimensional layers composed of out of registry parallel zig-zag chains
of alternating tctata and [Au(dcdmp)2]ꢀ units. The adjacent layers are separated by layers of [nBu4N]þ. In the last two compounds
the tctata appears as a planar molecule.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: S ligands; Coordination chemistry; Aurates; Thianthrenes
1. Introduction
Square planar coordination geometry with these li-
gands is frequently observed in the anionic form with
metals of Ni and Cu groups and such complexes have
been used as counterions in charge transfer solids with a
variety of donors. This planar geometry often favours
solid state structures presenting more or less regular
staking of the planar units providing chains of extended
interactions in the solid, which can give rise to inter-
esting properties such as ferromagnetism [3], metallic
conductivity [4] or even superconductivity [5,6].
In these type of complexes both the accessibility to
different oxidation states and the magnitude of the solid
state interactions is expected to be favoured by ligands
with more extended p-systems. While sulfur rich ligands
have been extensively explored significantly less effort
has been devoted to the study of other extended di-
thiolene p-ligands containing different heteroatoms like
Transition metal bisdithiolene complexes have, since
their earlier studies during the sixties, attracted a great
interest due to a rich variety of coordination geometry,
and vivid redox behaviour [1]. These characteristics made
them as choice building blocks for molecular materials
displaying unconventional electrical and magnetic
properties [2]. One of the key aspects in the versatility of
these complexes, making them so attractive in the design
of magnetic properties of molecular materials, is that
both by change in the transition metal and in the oxida-
tion state they can display different magnetic moments.
* Corresponding author. Tel.: +351-219946171; fax: +351-
219941455.
E-mail address: malmeida@itn.pt (M. Almeida).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.02.019

1352
D. Belo et al. / Polyhedron 23 (2004) 1351–1359
N and O. These heteroatoms are expected to act also as
an extra coordinating site which may provide an addi-
tional degree of freedom in crystal engineering of these
solids, as recently demonstrated for pyrazinediselenate
[7] and pyrazinedithiolate [8] Cu complexes. With the
2,3-dicyano-5,6-dimercaptopyrazyne (dcdmp) ligand the
only reported complexes previously to our workꢀ are
with nickel in the monoanionic form, Ni(dcdmp)2 [9]
and with it a few charge transfer salts with TTF and
other related donors have been also described.
15.64; S, 15.71%. MS: m=z (%) 580.9 [Mꢀ] (100)
[C12N8S2Au], 242.3 [Mþ] (100) [C16H36N].
4: Tetrabutylammonium salt of gold dibromide with
2,3,7,8-tetracyano-1,4,6,9-tetraazothianthrene, n-Bu4N
AuBr2 (tctata), m.p. 189.2–191.3 °C (followed by de-
e
composition). IR (KBr): V ¼ 428 (S, Au–Br), 742 (m,
CH2–S–CH2), 884 (m), 1170 (S, C–N), 1235 (m), 1325
(S), 1381 (m), 1485 (m, C@NAC), 1507 (m), 2240 (w,
CBN), 28877–2966 (m, C–H alifat) cmꢀ1. UV–Vis
(CH3CN): kmax ¼ 1413, 1721, 1911, 2275, 2496 nm.
Anal. Calc. for CHNS (C28H36N9S2AuBr2): C, 36.57; H,
3.94; N, 13.71; S, 6.97. Found: C, 38.54; H, 3.61; N,
14.04; S, 6.68%. MS: m=z (%) 288.0 (100) [C12N8Sꢀ],
250.0 (39) [C12N7Sꢀ], 356.8 (28) [AuBr2ꢀ], 197.0 (100)
[Auþ], 242.3 (78) [C16H36Nþ].
Preliminaꢀry data on charge transfer salts of
Au(dcdmp)2 with TTF type donors were previously
reported by us [10]. In this paper we report the synthesis
ꢀ
and characterization of the Au(dcdmp)2 complex, and
we describe two salts containing the new species 2,3,7,8-
tetracyano-1,4,6,9-tetraazothianthrene (tctata) obtained
as the product of a side reaction between the ligand with
its precursor.
5: Tetrabutylammonium salt of gold(III)-bis-5,
6-dicyano-2,3-dithiopirazine with 2,3,7,8-tetracyano-
1,4,6,9-tetraazothianthrene, n-Bu4N[Au(dcdmp)2] (tcta-
ta): the isolated amount of this compound was not
enough to any characterization further than its structure
determined by X-ray diffraction.
2. Experimental
2.1. Synthesis
2.2. X-ray structure determination
To a suspension of sodium sulfate monohydrated in
acetone (241 mg, 1 ꢁ 10ꢀ3 mol) was added, under
stirring, an acetone solution of 2,3-dichloro-5,6-dici-
anopyrazine (100 mg, 5.02 ꢁ 10ꢀ4 mol). The formed red
solution was filtered and added to a solution (2 ml) of
potassium tetrachloroaurate (95 mg, 2.51 ꢁ 10ꢀ4 mol)
in acetone, turning to a brown mixture. The inorganic
precipitate was removed and the liquor added to 1 ml
of a solution of tetrabutylammonium bromide (81 mg,
2.51 ꢁ 10ꢀ4 mol) in acetone, giving rise to an orange-
gold solution. The stirring was maintained, in all steps,
until no visible modification was observed. This solu-
tion was then filtered and allowed to a slow evapora-
tion of the solvent in inert atmosphere. The orange
solid obtained was filtered and recrystallised in acetone-
diethyl ether, to afford needle shape crystals with three
different colours. There are red (3) and yellow (4)
crystals dominating the sample, but some green (5)
crystals can be found also. In all cases, the crystals
were suitable for X-ray diffraction measurements, re-
vealing three different compositions. Visual separation
of the crystals afforded the following characterisation
data.
The data collection was performed on two different
Enraf-Nonius CAD4 diffractometer, one equipped with
a
graphite monochromatised Mo Ka radiation
ꢁ
(k ¼ 0:71069 A) and the other equipped with a graphite
ꢁ
monochromatised Cu Ka radiation (k ¼ 1:54150 A), in
the x ꢀ 2h scan mode. The structures were solved by
direct methods using SIR97 [11] and refined by full-
matrix least-squares methods using the program
SHELXL97 [12] and the WINGX software package[13].
All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed in idealised positions and
allowed to refine riding on the parent C atom. Molec-
ular graphics were prepared using ORTEP3 [14] and
SCHAKAL-97 [15]. Crystal data and structure refinement
of are summarized in Table 1.
3. Results and discussion
3.1. Synthesis
The synthesis of the gold complex 3 was performed
following a standard procedure for the preparation of
dithiolates from dichlorides, (Scheme 1) also used to
prepare the Ni analogue [9]. The dithiolate ligand (2) in
solution was obtained from the corresponding chloride
salt (1) by treatment with Na2S, in acetone. This li-
gand, without intermediate isolation was successively
reacted with potassium tetrachloroaurate and n-
Bu4NBr, also in acetone solutions, followed by slow
evaporation of the solvent in inert atmosphere, to give
the gold(III) complex that was obtained as a red needle
3: Tetrabutylammonium salt of gold(III)-bis-5,6-
dicyano-2,3-dithiopyrazine, n-Bu4N Au(dcdmp)2, m.p.
258.3–260.5 °C (followed by decomposition). IR (KBr):
e
V ¼ 434 (w, Au–S), 735 (m, CH2–S–CH2), 1172 (S, C–
N), 1266 (m), 1301 (S), 1455 (m), 1481 (w, C@NAC),
2233 (m, CBN), 2879–2966 (m, C–H alifat) cmꢀ1. UV–
Vis (CH3CN): kmax ¼ 1413, 1721, 1911, 2275, 2496 nm.
Anal. Calc. for CHNS (C28H36N9S4Au): C, 40.82; H,
4.40; N, 15.30; S, 15.56. Found: C, 42.38; H, 3.70; N,

D. Belo et al. / Polyhedron 23 (2004) 1351–1359
1353
Table 1
Crystallographic data for compounds 3, 4 and 5
Compound
3
4
5
Crystal size (mm)
Crystal system
Crystal color/shape
Space group
0.70 ꢁ 0.32 ꢁ 0.14
monoclinic
red/needle
0.7 ꢁ 0.3 ꢁ 0.2
triclinic
yellow/needle
0.50 ꢁ 0.25 ꢁ 0.14
monoclinic
green/needle
P21=n
a ¼ 10:693ð2Þ
b ¼ 40:308ð7Þ
c ¼ 10:870ð1Þ
ꢂ
C2=c
P1
ꢁ
Lattice constants (A, °)
a ¼ 35:147ð4Þ
b ¼ 9:527ð1Þ
c ¼ 21:792ð2Þ
a ¼ 10:986ð1Þ
b ¼ 13:230ð2Þ
c ¼ 13:791ð1Þ
a ¼ 79:150ð9Þ
b ¼ 69:663ð7Þ
c ¼ 70:254ð9Þ
1763.3(3)
C28H36AuBr2N9S2
919.56
b ¼ 109:626ð8Þ
b ¼ 92:16ð1Þ
3
ꢁ
Volume (A )
Formula sum
Formula weight
Z
6873.3(1)
C28H36AuN9S4
823.86
8
4682(1)
C40H36AuN17S6
1144.18
4
2
1.732
qcalc (Mg/m3)
1.592
4.557
3280
1.623
8.824
2280
Absorption coefficient (mmꢀ1
F ð000Þ
)
6.588
896
ꢁ
ꢁ
ꢁ
Wavelength
T (K)
Mo Ka (0.71069 A)
273(2)
Mo Ka (0.71069 A)
293(2)
Cu Ka (1.54150 A)
293(2)
h range (°)
2.22–26.00
)43/40, 0/11, 0/26
x ꢀ 2h
2.07–26.03
)12/13, )16/16, 0/16
x ꢀ 2h
4.28–72.87
)12/0, 0/48, )12/12
x ꢀ 2h
Index range ðh; k; lÞ
Scan type
Number of collected reflections
Number of unique reflections/Rint
Tmax and Tmin
6906
7136
8842
6718/0.0756
0.9975/0.4966
0.901
6840/0.0211
0.9864/0.7158
1.045
8425/0.1277
Goodness-of-fit on F 2
1.017
578
Number of refined parameters
R (observed reflections)
wR2 (observed reflections)
379
0.0666
0.1047
379
0.0669
0.1480
0.0684
0.1582
3 n-Bu4N[Au(dcdmp)2]
N
N
CN
SNa
SNa
CN
CN
Cl
Cl
Na2S.9H2O
Acetone
n-Bu4NBr
KAuCl4
4 n-Bu4N(tctata)AuBr2
CN
N
N
1
5 n-Bu4N(tctata)[Au(dcdmp)2]
2
-
N
N
N
S
S
N
NC
NC
CN
S
S
S
Au
S
NC
NC
CN
CN
N
CN
N
N
N
[Au(dcdmp)2]
6 tctata
Scheme 1.
shaped crystals. The elemental analysis is consistent
with a 1:1 stoichiometry, as confirmed by the X-ray
crystal structure determination. Unexpectedly two
other different kind of complexes were obtained,
n-Bu4N[Au(dcdmp)2] (tcdpdt) (4), as yellow needles
and n-Bu4NAuBr2(tcdpdt) (5) as green needle shaped
crystals, both containing the new species (tctata) (6).
The structures of 3, 4 and 5 were solved by single
crystal X-ray diffraction (Scheme 1).
place between the starting dichloride 1 and the dithiolate
ligand 2. The dithiolate acts as a nucleophilic agent, and
substitutes the chlorine atoms in the pyrazine ring
through an aromatic nucleophilic substitution mecha-
nism which is activated by the cyano groups and further
helped by the presence of the nitrogen atoms in the ar-
omatic ring. Both the cyano groups and the nitrogen
atoms are electroattractors, enhancing an electronic
deficiency on the carbon atoms linked to chlorine
(Scheme 2).
The unprecedented formation of the tetracy-
anotetraazathianthrene 6 incorporated in the structure
of 4 and 5, can be explained by a side reaction, taking
This explanation is supported by the fact that the
above proposed reaction is similar to that previously

1354
D. Belo et al. / Polyhedron 23 (2004) 1351–1359
N
N
S
S
N
N
N
N
CN
CN
Cl
Cl
NC
NC
S
S
NC
NC
CN
CN
S A
N
+
N
N
1
2
6 present in 4 and 5
Scheme 2.
Table 2
Selected bond lengths (A) of [Au(dcdmp)2] complexes in 3 and 5
used to prepare other thiantrenes [16,18], but wewere
not successful in isolating 6 as a pure compound.
Cyclic voltammetry of n-Bu4NAu(dcdmp)2 (3) in
acetonitrile (Fig. 1, full line) shows a pair of symmetric
reversible redox waves at E1=2 ¼ )0.629 V vs Ag/AgCl
ascribed to the couple Au(dcdmp)22ꢀ/Au(dcdmp)2ꢀ. The
cyclic voltammetry of 4 in the same conditions (Fig. 1,
dashed line) shows three irreversible waves at )0.604,
)0.349 and +0.732 V. The last wave is close to the values
reported for the reaction AuBr2ꢀ $ Au+2Brꢀ [17] but
the two first waves are ascribed to tctata.
ꢀ
ꢁ
3
5
Au1–S1
Au1–S2
Au1–S3
Au1–S4
S1–C1
2.303(3)
2.309(3)
2.303(3)
2.313(3)
1.72(1)
1.73(1)
1.73(1)
1.74(1)
1.47(1)
1.43(1)
1.32(1)
1.32(1)
1.30(1)
1.32(1)
1.32(1)
1.33(1)
1.35(1)
1.34(1)
1.42(1)
1.40(1)
1.42(2)
1.44(2)
1.50(2)
1.47(2)
1.16(2)
1.12(2)
1.11(2)
1.17(2)
2.314(3)
2.322(3)
2.325(3)
2.317(3)
1.73(1)
1.73(3)
1.72(1)
1.72(1)
1.44(1)
1.45(1)
1.35(1)
1.34(1)
1.34(1)
1.32(2)
1.34(1)
1.34(1)
1.31(2)
1.34(1)
1.37(1)
1.39(2)
1.41(2)
1.45(2)
1.43(2)
1.45(2)
1.14(2)
1.16(2)
1.14(2)
1.14(2)
S2–C2
S3–C7
S4–C8
C1–C2
C7–C8
C1–N1
C2–N2
C7–N5
C8–N6
N1–C3
N2–C4
N5–C9
N6–C10
C3–C4
C9–C10
C3–C5
C4–C6
C9–C11
C10–C12
C5–N3
C6–N4
C11–N7
C12–N8
3.2. Structural characterisation
The crystal quality made possible to solve the crystal
structure of compounds 3, 4 and 5. The geometry of the
ꢀ
Au(dcdmp)2 complex in 3 and 5 is identical, with av-
ꢁ
erage Au–S bond lengths of 2.307(3) and 2.320(3) A,
respectively (see Table 2). These values are in the upper
side of the range of values reported for other gold(III)
ꢁ
dithiolates that extend from 2.29 to 2.34 A, with an
ꢁ
average value of 2.305 A. In both cases the complex is
almost planar, with significant non planar deviations
observed only in the terminal cyano groups, which are
displaced towards opposite directions giving rise to a
very small chair type distortion (Figs. 2 and 3). In both
complexes the dcdmp ligands are identical within ex-
perimental uncertainty and with a geometry close to that
found in the corresponding Ni analogue [9].
The new tetracyanothianthrene tctata species, present
in complexes 4 and 5, has bond lengths and angles
identical to the corresponding ones in the dcdmp ligand
in the dithiolates and an almost planar geometry in good
agreement with that found in the unsubstituted ana-
logue tetraazothiaantrene [18] (Figs. 3 and 4, Table 3).
The two tctata molecules in 4, are identical with an al-
most planar geometry, with a small twist of the terminal
cyano groups, in opposite directions. The angles of the
central ring range from 126.1° to 127.9°, in the case of
the C@CAS angles, and show the values of 105.6° and
105.9° for the C–S–C angle. In the crystal structure of 5,
the tctata molecule shows a slight deviation from pla-
Fig. 1. Cyclic voltammetry of n-Bu4N[Au(dcdmp)2] (solid line) and n-
Bu4N(tctata)AuBr2 (dashed line), in acetonitrile.

D. Belo et al. / Polyhedron 23 (2004) 1351–1359
1355
To the best of our knowledge tctata, together with
bis(quinoxaline)-2,20,3,30-disulfide [19] and 1,4,6,9-tet-
raazathianthrene [18], are the only azathiaantrenes dis-
playing an essentially planar geometry, while all others
present significant molecular dihedral angles ranging
from 132° to 143°.
The tetrabutylammonium salt 3, crystallises in the
monoclinic system, space group C2=c, Z ¼ 8. The unit
cell contains one independent [Au(dcdmp)2]ꢀcomplex
and one independent tetrabutylammonium cation in
general positions. The crystal structure consists of col-
umns of [Au(dcdmp)2]ꢀpairs, stacked along b (Fig. 5).
The normal to complex plane makes an angle of 51.6°
with this axis. There are two different overlap modes
between complexes characterised by a different dis-
placement along their long axis. The distance between
the average plane of [Au(dcdmp)2]ꢀ complexes are al-
Fig. 2. ORTEP views and atomic numbering scheme of Au(dcdmp)2ꢀ
in 3, with thermal ellipsoids at 40% probability.
,
narity. There is a significant deviation of the sulphur
atom, relatively to the average plane of the molecule and
therefore the dihedral angle between the two half of the
molecule is 174°. The non planarity is also denoted by
the central ring bond angles that in the case of C@CAS
bonds range from 125.5° to 126.6° while those of the C–
S–C bonds are 107.7° and 106.3°. The deviation of the S
atoms from the average molecular plane is certainly due
to short contacts between these atoms and gold and
carbon atoms in neighbouring ditiolate species (see
Table 6).
ꢁ
most identical, being 3.49 and 3.47 A, between and
within the pairs of dithiolates, respectively. The stacks of
the complexes are completely surrounded by [n-Bu4N]þ
cations which prevent any contact between neighbour-
ing stacks (Fig. 6).
The adopted overlap mode between stacked com-
plexes at such a short distance corresponds to the exis-
tence of several short interatomic contacts (see Table 4),
Fig. 3. ORTEP views and atomic numbering scheme of tctata units in 4, with thermal ellipsoids at 40% probability.
(a)
(b)
Fig. 4. ORTEP views and atomic numbering scheme of Au(dcdmp)2ꢀ (a) and tctata (b), in 5, with thermal ellipsoids at 40% probability.

1356
D. Belo et al. / Polyhedron 23 (2004) 1351–1359
Table 3
Selected bond lengths (A) of 6 in 4 and 5
Table 4
Hydrogen bonds and short contacts in the crystal structure of 3
ꢁ
ꢁ
d (A)
ꢁ
5
4 mol1
4 mol2
Angle (°)
d (A)/Rrvdw
S01–C01
S01–C07
S02–C02
S02–C08
C01–N01
C07–N05
C02–N02
C08–N06
C01–C02
C07–C08
C03–N01
C09–N05
C04–N02
C010–N06
C04–C03
C010–C09
C03–C05
C09–C011
C04–C06
C010–C012
C05–N03
C011–N07
C06–N04
C012–N08
1.75(2)
1.74(1)
1.75(1)
1.74(1)
1.31(2)
1.31(1)
1.30(1)
1.31(1)
1.45(1)
1.45(1)
1.32(2)
1.33(1)
1.38(2)
1.32(1)
1.37(2)
1.40(2)
1.50(2)
1.42(2)
1.41(2)
1.44(2)
1.13(2)
1.14(2)
1.16(2)
1.14(2)
1.758(8)
1.732(9)
Auꢂ ꢂ ꢂS4
Auꢂ ꢂ ꢂN2
3.688
3.576
3.824
3.768
2.961
3.026
2.589
4.630
4.202
3.960
3.965
0.89
0.94
0.98
0.97
0.97
0.99
0.96
1.01
1.03
1.04
1.02
1.74(1)
1.72(1)
Auꢂ ꢂ ꢂC2
Auꢂ ꢂ ꢂC8
1.29(1)
1.31(1)
S1ꢂ ꢂ ꢂH23a–C23
S4ꢂ ꢂ ꢂH24a–C24
N3ꢂ ꢂ ꢂH44a–C44
Auꢂ ꢂ ꢂAu
161.56
132.78
173.05
1.30(1)
1.33(1)
Auꢂ ꢂ ꢂS2
Auꢂ ꢂ ꢂN6
1.35(1)
1.35(1)
Auꢂ ꢂ ꢂC4
Rrvdw ¼ van der Waals radii sum
1.33(1)
1.32(1)
some clearly below the sum of van der Waals radii
(dotted lines in Fig. 5), the shortest one being Auꢂ ꢂ ꢂS1
1.47(2)
1.44(1)
ꢁ
(3.71 A). Other interactions are noticed slightly above
the sum of van der Waals radii, as Auꢂ ꢂ ꢂAu exceeding
1.44(1)
1.42(2)
by 1% that sum (dashed line in Fig. 5).
1.17(2)
1.11(1)
The interactions between the dithiolate complexes
and the tetrabuthylamonium cations are established
though several hydrogen bonds (Fig. 7, Table 4), only
one through a pyrazinic nitrogen atom. Clearly the
crystal structure of 3 is determined by the short complex
interactions through both Au–S and Au–Au contacts
and p–p interactions between ligands.
1.12(1)
1.19(2)
Compound 4 crystallises in the triclinic system, space
ꢂ
group P1, Z ¼ 2. The unit cell has two independent units
of tctata located at inversion centres, one independent
tetrabutylamonium cation and one independent AuBr2
anion. The crystal packing is made by zig-zag chains of
tctata, separated by layers of the tetrabutylammonium
cations parallel to the b, a–c plane (Fig. 8). The tctata
units along the chains are connected by short Sꢂ ꢂ ꢂS
Fig. 5. Partial views of the crystal structure of 3 (a) view showing the
short contacts between molecules along the dithiolate columns: the
shortest contacts (dotted line) and contacts exceeding no more than 4%
the sum of the van der Waals radii (dashed line); (b) view along c,
showing the relative positions of dithiolates in two columns.
Fig. 7. Hydrogen bonds between the dithiolate anions and neigh-
bouring cations, in the crystal structure of 3.
Fig. 6. View of the crystal structure of 3 along b.

D. Belo et al. / Polyhedron 23 (2004) 1351–1359
1357
the tctata unit and hydrogen bonds between the Au
atom and the surrounding tetrabuthylamonium cations
(see Table 5). The interactions between the tctata units
and the tetrabuthylamonium cation are made through
several hydrogen bonds (Table 5, Fig. 9), none of them
involving the pyrazinic nitrogen atoms.
The last salt, 5, crystallises in the monoclinic system,
space group P21=n, Z ¼ 4. The unit cell contains one
independent molecule of tctata, one independent tetr-
abutylamonium
cation
and
one
independent
[Au(dcdmp)2]ꢀ complex all located in general in general
positions. Its crystal structure can be seen as a combi-
nation of those of the two preceding compounds. It
consists of bidimensional layers, in the a, c plane,
composed of out of registry parallel zig-zag chains of
alternating tctata and [Au(dcdmp)2]ꢀ units (Fig. 11).
The adjacent layers are separated by cation layers
[nBu4N]þ, along b, (Fig. 10). Several short contacts,
within layer, can be noticed. With exception of the
S3ꢂ ꢂ ꢂS3 interaction between the anions in neighbouring
Fig. 8. (a) View of the crystal structure of 4 along b. (b) Partial view of
the tctata zig-zag chains emphasising the Sꢂ ꢂ ꢂS short contact, along the
chain.
ꢁ
contacts at 3.586 A and the angle between the average
planes of these species is 76.1°. The AuBr2units, with a
linear geometry typical of monoanionic state, are lo-
cated in alternated cavities between the tctata chains and
cationic planes (Fig. 9). There are several short contacts
ꢁ
(ꢃ4 A) between the gold atom and the sulphur atoms of
Fig. 10. View of the crystal structure of 5 along a.
Fig. 9. Partial view of the crystal structure of 4, showing the short
contacts between the different species.
Table 5
Hydrogen bonds and short contacts in the crystal structure of 4
ꢁ
d (A)
Angle (°)
C51–H51aꢂ ꢂ ꢂN04
C31–H31bꢂ ꢂ ꢂS02
C21–H21aꢂ ꢂ ꢂAu
C24–H24bꢂ ꢂ ꢂAu
Auꢂ ꢂ ꢂS02
2.551
2.943
3.291
3.247
4.026
3.924
3.586
152
149
145
163
Fig. 11. View of the tctata and [Au(dcdmp)2]ꢀ layer, in the a, c plane,
in the crystal structure of 5, emphasising the short contact responsible
for the bidimensional network.
Auꢂ ꢂ ꢂS01
S01ꢂ ꢂ ꢂS02

1358
D. Belo et al. / Polyhedron 23 (2004) 1351–1359
Table 6
Hydrogen bonds and short contacts in the crystal structure of 5
dicyanopyrazine ligand no such role is observed. How-
ever the pyrazinic ring contributes to electron delocali-
sation and allows p–p interactions between ligands of
different complexes.
ꢁ
d (A)
Angle (°)
C–H13aꢂ ꢂ ꢂN6
C–H14eꢂ ꢂ ꢂN7
C–H13bꢂ ꢂ ꢂN07
Auꢂ ꢂ ꢂS01
2.641
2.633
2.503
4.004
3.730
4.041
3.648
3.664
3.380
3.431
159.83
174.50
154.04
Auꢂ ꢂ ꢂS02
5. Supplementary material
Auꢂ ꢂ ꢂN01
Auꢂ ꢂ ꢂN06
S3ꢂ ꢂ ꢂS3
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been de-
posited in the Cambridge Crystallographic Data Centre.
The deposition numbers are CCDC 222525, CCDC
222526 and CCDC 222527 for compounds 3, 4 and 5
respectively. Copies of the data can be obtained free of
charge upon application to the director of CCDC, 12
Union Road, GB, Cambridge CB12 1EZ. [Fax:
+441223/336/033, E-mail deposit@ccdc.cam.ac.uk, or
on the web: http://www.ccdc.cam.ac.uk].
S01ꢂ ꢂ ꢂC9
S02ꢂ ꢂ ꢂC9
Acknowledgements
Fig. 12. Hydrogen bonds between the tctata and [Au(dcdmp)2]ꢀ
molecules and neighbouring cations, in the crystal structure of 5.
This work was partially supported by FCT-Portugal
(Contract POCTI/35342/QUI/2000) and also benefited
from COST action D14.
chains, all short contacts are between different species
and involve the sulphur atom of the neutral complex
and the carbon atom of the pyrazine ring in the anion.
The short contacts along the chain are of the Auꢂ ꢂ ꢂS
type and the angle between the units is 62.7° (Fig. 11,
References
[1] (a) J.A. McLeverty, Prog. Inorg. Chem 10 (1968) 29;
(b) D. Coucouvanis, Prog. Inorg. Chem. 11 (1970) 233;
(c) R. Eisenberg, Prog. Inorg. Chem 12 (1970) 295;
ꢀ
Table 6). The neutral tctata and the Au(dcdmp)2 an-
ꢀ
(d) L. Alcacer, H. Novais, in: J.S. Miller (Ed.), Extended Linear
ions in the layer are connected with the tetrabutylam-
monium through C–Hꢂ ꢂ ꢂN hydrogen bonds. The
nitrogen atoms involved in this interaction, are available
both from the anion and the neutral specie (Fig. 12,
Table 6), only one trough the pyrazinic N6 atom. The
crystal structure of this compound is dominated bꢀy
strong interactions between tctata and Au(dcdmp)2
involving S–S and S–Au contacts as in 3 which deter-
mine the formation of layers.
Chain Compounds, vol. 3, Plenum Press, New York, 1983, p. 319
(Chapter 6);
(e) S. Alvarez, V. Ramon, R. Hoffman, J. Am. Chem. Soc. 107
(1985) 6253.
[2] N. Robertson, L. Cronin, Coord. Chem. Rev. 227 (2002) 93.
[3] A.T. Coomber, D. Beljonne, R.H. Friend, J.L. Bredas, A.
Charlton, N. Robertson, A.E. Underhill, M. Kurmoo, P. Day,
Nature 380 (1996) 144.
[4] (a) M. Ahamad, A.E. Underhill, J. Chem. Soc., Chem. Commun.
(1981) 67;
(b) M.M. Ahamad, D.J. Turner, A.E. Underhill, C.S. Jacobsen,
K. Mortensen, K. Carneiro, Phys. Rev. B 29 (1984) 4796.
[5] P. Cassoux, L. Valade, in: D.W. Bruce, D. O’Hare (Eds.),
Inorganic Materials, 2nd ed., Wiley, Chichester, 1996, p. 1.
[6] P. Cassoux, J.S. Miller, in: L.V. Interrante, M.J. Hampden-Smith
(Eds.), Chemistry of Advanced Materials, Wiley–VCH, New
York, 1998, p. 19.
4. Conclusion
In conclusion the Au(dcdmp)2 complex was prepared
and the structure of two salts described in detail. Al-
though tetracyanotetraazothianthrene could no be iso-
lated as a pure compound, two salts containing this new
thianthrene derivative were obtained. In both cases
this thianthrene derivative presents an almost planar
geometry.
At variance with other pyrazinediselenate [7] or pyr-
azinedithiolate [8] salts where the N heteroatom acted as
a new coordination centre in these compounds with the
[7] X. Ribas, J. Dias, J. Morgado, K. Wurst, M. Almeida, J. Veciana,
C. Rovira, Cryst. Eng. Commun. 93 (2002) 4.
[8] X. Ribas, J.C. Dias, J. Morgado, K. Wurst, E. Molins, E. Ruiz,
M. Almeida, J. Veciana, C. Rovira, Chem. – Eur. J. (2004) 1318.
[9] M. Tomura, S. Tanaka, Y. Yamashita, Synth. Met. 24 (1994) 197.
[10] D. Belo, J. Morgado, E.B. Lopes, I.C. Santos, V. Gama, R.T.
Henriques, M. Almeida, Synth. Met. 102 (1999) 1751.
[11] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, G.
Giacovazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Cryst. 32 (1999) 115.

D. Belo et al. / Polyhedron 23 (2004) 1351–1359
1359
[12] G.M. Sheldrick, SHELXL97, A Program for Crystal Structure
€
[16] H.E. Simmons, R.D. Vest, D.C. Blomstrom, J.D.R. Roland, T.L.
Cairns, J. Am. Chem Soc. 84 (1962) 4746.
Refinement, University of Gottingen, Germany, 1997.
[13] L.J. Ferrugia, J. Appl. Cryst. 32 (1999) 837.
[17] C.D. Hodgmam (Ed.), Handbook of Chemistry and Physics, The
Chemical Rubber Publishing Co., Cleveland, OH, 1960, p. 1743.
[18] V.M. Lynch, S.H. Simonsen, B.E. Davis, G.E. Martin, M.J.
Musmar, W.W. Lam, K. Smith, Acta Cryst. C 50 (1994) 1470.
[19] A.G. Pignedoly, G. Peyronel, L. Antolini, J. Cryst. Mol. Struct. 7
(1977) 173.
[14] L.J. Ferrugia, J. Appl. Cryst. 30 (1997) 565.
[15] E. Keller, SCHAKAL-97, A Computer Program for the Represen-
tation of Molecular and Crystallographic Models, Kristallogra-
€
phisches Institut der Universitat Freiburg i. Br., Germany,
1997.