Perylene salts of unsymmetrical nickel and gold dithiolene complexes with 3 : 2 stoichiometry: Conformational polymorphism and strong antiferromagnetic interactions

Article abstract of DOI:10.1039/b608420f

The square-planar Au^III complex of the unsymmetrical tfadt dithiolate ligand (tfadt: 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate) is found to exhibit conformational polymorphism in its n-Bu₄N ⁺ salt, as both cis and tr

Full text of DOI:10.1039/b608420f

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Perylene salts of unsymmetrical nickel and gold dithiolene complexes
with 3 : 2 stoichiometry: conformational polymorphism and strong
antiferromagnetic interactions
´
Olivier Jeannin and Marc Fourmigue*w
Received (in Montpellier, France) 14th June 2006, Accepted 29th August 2006
First published as an Advance Article on the web 12th September 2006
DOI: 10.1039/b608420f
The square-planar AuIII complex of the unsymmetrical tfadt dithiolate ligand (tfadt:
2-(trifluoromethyl)acrylonitrile-1,2-dithiolate) is found to exhibit conformational polymorphism in
its n-Bu4N1 salt, as both cis and trans isomers were found to crystallize separately in the same
crystallization batch. Electrocrystallization of perylene in the presence of the diamagnetic
[n-Bu4N][Au(tfadt)2] or the paramagnetic (S ¼ 1/2) [n-Bu4N][Ni(tfadt)2] nickel analog affords
isostructural salts with an unusual 3 : 2 stoichiometry, that is [Per]3[M(tfadt)2]2 (M ¼ Au, Ni),
21
2ꢀ
with an alternation of dicationic [Per]3 perylene triads and dianionic [M(tfadt)2]2 dithiolene
complex dyads within one-dimensional chains. These salts are characterized by strong
2ꢀ
antiferromagnetic interactions within perylene triads and [Ni(tfadt)2]2 dyads and an essentially
diamagnetic behaviour.
with the tfd dithiolate ligand, the redox potentials of both
Introduction
partners disfavour the electron transfer. This drawback was
circumvented using an anionic CuIII dithiolene complex as
[Cu(qdt)2]ꢀ (qdt: quinoxaline-2,3-dithiolate) which is stable at
the oxidation potential of perylene.11 In this 2 : 1 [Per]2
[Cu(qdt)2] salt, perylene stacks were still observed but strongly
affected by tetramerization. Another 1 : 1 salt was also
described with [Ni(Cl4bdt)2]ꢀ (Cl4bdt: tetrachlorobenzene-
1,2-dithiolate).12 Despite the fact that [Ni(Cl4bdt)2]ꢀ oxidizes
at þ0.73 V vs. SCE, that is at a lower potential than the
perylene oxidation (þ0.90 V vs. SCE), the relatively high
conductivity of this semi-conducting salt was taken as an
indication of a partial charge transfer, a question still open
in the absence of X-ray crystal structure determination.
We have recently described13 a novel nickel dithiolene
complex based on a asymmetrically substituted dithiolate
ligand, hereafter noted tfadt (tfadt: 2-(trifluoromethyl)acrylo-
nitrile-1,2-dithiolate), which incorporates both the nitrile
group of the mnt ligand and the CF3 group of the tfd ligand.
Considering the rich structural and physical properties of the
perylene salts with [M(mnt)2]1ꢀ anions, we decided to investi-
gate the electrocrystallization of perylene in the presence of
this paramagnetic [Ni(tfadt)2]ꢀ complex and also extended this
investigation to the still unknown, diamagnetic gold complex
[Au(tfadt)2]ꢀ. We describe here the preparation, X-ray struc-
ture determination and electrochemical properties of the gold
The perylene molecule has been used in the last 30 years in the
preparation of molecular conductors with anions as different
as halogens, simple inorganic counter ions or metal dithiolene
ꢀ
complexes.1 Among them, the perylene salts2 of M(mnt)2
ꢁ
dithiolene complexes3 (M ¼ Ni, Pt, Pd, Au; mnt = 1,2-
dicyano-1,2-ethylenedithiolato) (Chart 1) have been exten-
sively investigated and particularly the origin of the metal-
to-insulator transition and its variations essentially depending
on the nature of the metal in the dithiolene complex. It was
shown for example that the Peierls transition affecting the
perylene stack in [Per]2[Pt(mnt)2] was coupled with a spin-
Peierls transition on the paramagnetic [Pt(mnt)2]ꢀ while the
ꢁ
analogous salt with the diamagnetic gold complex [Au(mnt)2]ꢀ
gave a pure Peierls transition.4 In that regard, properties of
solid solutions involving both [Pt(mnt)2]ꢀ and [Au(mnt)2]ꢀ
ꢁ
were also investigated in the [Per]2[Au1ꢀxPtx(mnt)2] salts.5
Other perylene salts withꢀdimeric [Fe(mnt)2]2 and6 [Co(mnt)2]2
or7 trimeric [Co(mnt)2]3 moieties8 also exhibit segregated
perylene stacks. Considering the rich physics of these perylene
salts with [M(mnt)2]ꢀ dithiolene complexes, it is surprising
that only a few other dithiolene complexes have been investi-
gated in their association with perylene.
Older reports include insulating 1 : 1 complexes with
[Ni(tfd)2] and [Pt(tfd)2] (tfd = 1,2-bis(trifluoromethyl)-1,2-
ethylenedithiolato) which exhibit alternated stacks of neutral
perylene and dithiolene complexes,9,10 demonstrating that,
1
complex [Au(tfadt)2]ꢀ in its PPh4 and n-Bu4N1 salts. The
electro-crystallization of the perylene donor molecule with
both nickel and gold anions afforded two isostructural salts,
Laboratoire Chimie, Inge´nierie Mole´culaire et Mate´riaux (CIMMA),
´
UMR 6200 CNRS- Universite d’Angers, UFR Sciences, 2 Bd
Lavoisier, 49045 Angers, France. E-mail: marc.fourmigue@
univ-rennes1.fr
w Permanent address: Sciences Chimiques de Rennes, UMR 6226
CNRS-Universite Rennes 1, Equipe MaCSE, Bat 10C, Campus de
´
Beaulieu, 35042 Rennes cedex, France.
Chart 1
ꢂc
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Scheme 1
which only differ by the spin state of the anion, S ¼ 1/2 in the
complex [Ni(tfadt)2]ꢀ and S ¼ 0 in [Au(tfadt)2]ꢀ. The struc-
ꢁ
tures of both salts and their magnetic properties will be
described and compared.
Results and discussion
Fig.
1
Cyclic voltammetry of the gold complex [(n-Bu)4N]
Synthesis
[Au(tfadt)2].
The gold complexes (Ph4P)[Au(tfadt)2] and (n-Bu4N)[Au
(tfadt)2] were prepared (Scheme 1) as previously described13
for the dianionic [Ni(tfadt)2]2ꢀ nickel complex from the corre-
sponding 4-cyano-5-trifluoromethyl-1,3-dithiol-2-one14 by
treatment with MeONa in MeOH, addition of KAuCl4 and
precipitation as Ph4P1 or (n-Bu)4N1 salt by addition in a
solution of Ph4PBr or (n-Bu)4NBr, respectively.
that the tfadt ligand exhibits a behaviour close to that of the
mnt and tfd ligands.
Structural determinations
1
[Ph4P][Au(tfadt)2] crystallizes in the monoclinic system, space
group C2/c, with the Ph4P1 cation located on a two-fold axis
and the [Au(tfadt)2]ꢀ on an inversion center, thus with a trans
configuration relative to the CN and CF3 groups. The CF3
group is further disordered on two positions related to each
other by a 601 rotation. This salt is actually isostructural with
the analogous nickel complex [Ph4P][Ni(tfadt)2].13 On the
other hand, both kinds of crystals isolated from the recrystal-
lization of [n-Bu4N][Au(tfadt)2] were found to crystallize in the
Recrystallization of the PPh4 salt afforded green crystals
while the recrystallization of the (n-Bu)4N1 salt by slow eva-
poration of a MeOH solution afforded a mixture of green
prisms and brown plates, identified from the X-ray diffraction
studies as the cis and trans isomers, respectively (see Scheme 2).
Variable temperature (VT) NMR studies were performed on
this salt in order to evaluate the activation energy for a
possible cis–trans isomerism in solution, by analogy with
similar studies performed on the diamagnetic [Ni(tfadt)2]2ꢀ
nickel complex.13 In the latter indeed, the two isomers were
identified on 19F NMR spectra below 260 K (coalescence
temperature) with an associated activation energy DG# of
52.6 kJ molꢀ1. Similar 19F NMR experiments performed on
[n-Bu4N][Au(tfadt)2] show the presence of one single reso-
nance from room temperature down to 200 K in CH2Cl2,
demonstrating that in the same conditions, the gold complex
equilibrates between both isomers at a faster rate than the
nickel complex, the probable consequence of a lower asso-
ciated activation energy.
ꢀ
triclinic system, space group P1, with both cation and anion in
general position in the unit cell. The brown crystals were
identified as the trans isomer (Fig. 2) while the green crystals
are the cis isomer (Fig. 3). Bond lengths and angles within the
metallacycles are collected in Table 2 for comparison. Note the
differences between the C–S bond lengths (b and b0), depend-
ing on the nature of the substituent (–CN or –CF3) on the
carbon, a consequence of the unsymmetrical nature of the
dithiolate ligand. This shortening of the (F3C–)C–S bond (b0)
relative to the (NC–)C–S bond (b) was observed in the nickel
complexes and, as shown in the scheme of Table 2, is attrib-
uted to an unsymmetrical mesomeric form due to the more
strongly withdrawing effect of the –CN moiety when com-
pared with the –CF3 one.
Cyclic voltammetry experiments conducted in CH2Cl2 (Fig.
1) shows the presence of two reversible redox waves, one in
reduction at E1/2 ¼ ꢀ1.35 V vs. Fc1/Fc, attributable to the
[Au(tfadt)2]2ꢀ/[Au(tfadt)2]1ꢀ process while the wave observed
in oxidation at E1/2 ¼ þ0.745 V vs. Fc1/Fc corresponds to the
[Au(tfadt)2]1ꢀ/[Au(tfadt)2]0 redox process. Values of the cor-
responding symmetrical [Au(mnt)2] and [Au(tfd)2] complexes
have been also collected in Table 1 for comparison, showing
It is also important to note here that the isolation of a
square-planar dithiolene complex in its cis form is highly
unexpected. Indeed, considering the few described examples
Table 1 Cyclic voltammetry data, vs. Fc1/Fc. Values in parentheses
are original data reported vs. SCE. For comparison purposes, a
correction of ꢀ0.40 V has been applied to generate potentials vs.
Fc1/Fc
Compound
E1/2(ꢀ2/ꢀ1)
E(ꢀ1/0)
Solvent Ref.
[Au(mnt)2]ꢀ2,ꢀ1,0 ꢀ1.33 (ꢀ0.93) þ0.70 (1.10) CH2Cl2 15
[Au(tfadt)2]ꢀ2,ꢀ1,0 ꢀ1.35
þ0.745
CH2Cl2 This work
[Au(tfd)2]ꢀ2,ꢀ1,0
ꢀ1.37 (ꢀ0.97) þ0.92 (1.32) CH2Cl2 16
Scheme 2
ꢂc
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Fig.
2
ORTEP view (at 50% probability level) of the trans-
Fig.
3
ORTEP view (at 50% probability level) of the cis-
[Au(tfadt)2]ꢀ species as its (n-Bu)4 salt.
1
[Au(tfadt)2]ꢀ species as its (n-Bu)4 salt.
1
of square planar dithiolene complexes involving asymmetri-
cally substituted 1,2-dithiolate ligands and crystallographi-
from the VT NMR studies. This salt represents to our knowl-
edge the very first example of reported simultaneous crystal-
lization of both cis and trans isomers.
cally characterized (Chart 2), as [Ni(adt)2]2ꢀ,1ꢀ 17,18
,
[Ni(dmt)2]ꢀ,19 the fused thiophene derivatives [Au(dtpdt)2]ꢀ
or20 [M(a-tpdt)2]ꢀ with M ¼ Ni,21 Co,22 Pt,22 the phenyl
dithiolate [Ni(sdt)2],23 or their pyridine analogs [Au
(3-pedt)2]ꢀ, [Au(4-pedt)2]ꢀ,24 they all are found to crystallize
in the trans form, except two, [Au(sdt)2]ꢀ and [Au(2-pedt)2]ꢀ,
which were very recently described to crystallize in the cis
In the crystal, the anions adopt very different solid state
organizations. Indeed, in the cis isomer (Fig. 4), the complex
anions form chains running along c, separated from each other
by the bulky n-Bu4N1 cations and characterized by lateral
intermolecular Sꢃ ꢃ ꢃS van der Waals interactions.
On the other hand, as shown in Fig. 5, the trans complex
adopts a dimeric structure with an intermolecular Auꢃ ꢃ ꢃAu
distance at 4.13 A, the shortest Sꢃ ꢃ ꢃS distances in 4.11–4.13 A
range and Auꢃ ꢃ ꢃS distances at 3.86 A. These short Auꢃ ꢃ ꢃS
interactions are probably at the origin of this dimer formation
and drive its crystallization, since it is not isostructural with
the isosteric nickel [n-Bu4N][trans-Ni(tfadt)2] complex.
1
form, in their PPh4 salts.24
Earlier DFT calculations13 performed on the cis- and trans-
isomers of the nickel [Ni(tfadt)2]2ꢀ,1ꢀ had shown that the
energy difference between both isomers was negligible. It is
probably also the case here for the gold complex. However, the
fact that we can isolate both isomers in the same crystallization
batch demonstrates not only that the molecular cis and trans
structures are very close in energy and that they interconvert
easily (cf. VT NMR data) but also that the solid state
structures have essentially the same energy under the crystal-
lization conditions used here. This form of polymorphism has
been described as conformational polymorphism,25 where a
molecule adopts significantly different conformations in dif-
ferent crystal polymorphs. McCrone’s criterion26 is that poly-
morphs are different in crystal structure but identical in the
liquid or vapor states. This implies that crystals containing
molecules with different atomic arrangements are to be classed
as polymorphs if the molecules concerned interconvert rapidly
in the melt or in solution to give the same equilibrium mixture.
This is indeed the case here in [Au(tfadt)2]ꢀ, as demonstrated
Perylene salts
Electrocrystallization experiments were performed with pery-
lene in the presence of either the paramagnetic [(n-Bu)4N]
[Ni(tfadt)2] or the analogous diamagnetic [(n-Bu)4N][Au
(tfadt)2] complex. Crystals were harvested on the anode and
structurally and magnetically characterized. X-Ray crystal
structure determinations showed that both salts are isostruc-
tural and can be formulated as [Per]3[M(tfadt)2]2 (M ¼ Ni,
Au), that is a highly unusual 3 : 2 stoichiometry. They
ꢀ
crystallize in the triclinic system, space group P1 with one
perylene on an inversion center, one other perylene and a
dithiolene complex in general position in the unit cell. In both
Table 2 Bond lengths within the metallacycle in the gold dithiolene complexes
a
a0
b
b0
c
trans-[Au(tfadt)2]ꢀa
trans-[Au(tfadt)2]ꢀb
2.2948(16)
2.306(2)
2.307(2)
2.304(1)
2.305(1)
2.2933(16)
2.3120(14)
c
2.2848(15)
2.305(2)
2.314(2)
2.302(1)
2.305(1)
1.742(6)
1.747(8)
1.755(8)
1.753(5)
1.754(5)
1.764(6)
1.760(5)
1.720(6)
1.743(7)
1.745(7)
1.734(4)
1.738(4)
1.730(7)
1.730(7)
1.336(7)
1.350(10)
1.332(10)
1.341(6)
1.340(6)
1.326(9)
1.340(9)
trans-[Au(tfadt)2]ꢀc
cis-[Au(tfadt)2]ꢀb
2.3045(19)
2.3132(15)
a
b
As its Ph4P1 salt. As its (n-Bu)4N1 salt. As its perylene salt.
ꢂc
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Chart 2
Fig. 5 A projection view (perpendicular to the molecular planes) of
2ꢀ
the dimeric entities [Au(tfadt)2]2 in [n-Bu4N][trans-Au(tfadt)2].
salts, the dithiolene complex adopts a trans conformation,
with one of the two CF3 groups affected by disorder. In the
solid state (Fig. 6), the perylene molecules associate into
inversion-centred triads, alternating with inversion-centred
metal dithiolene dyads into stacks ꢃ ꢃ ꢃ[Per]3[M(tfadt)2]2
[Per]3[M(tfadt)2]2ꢃ ꢃ ꢃ running along the [1 0 ꢀ1] direction.
Such a stoichiometry with trimeric perylene units is rather
unusual and the only comparable system described so far is
based on an modified perylene, the perylo[1,12-bcꢁd]thiophene
(pet, Chart 3) which exhibits with [Ni(mnt)2]ꢀ the same
stoichiometry, that is [pet]3[Ni(mnt)2]2.27 In this salt however,
the solid state organization strongly differs as segregated
stacks of anions and cations are observed, with trimerized
pet chains alternating with strongly dimerized [Ni(mnt)2]
chains.
monoanionic state is indeed the actual oxidation state in
[Per]3[Ni(tfadt)2]2, affording the very same formulation as with
the gold complex, that is [Per]321[Ni(tfadt)2]2ꢀ. The question
then arises of the magnetic state of both dicationic and
dianionic moieties in these salts.
The temperature dependence of the magnetic susceptibility
was determined on both salts from SQUID measurements on
polycrystalline samples. As shown in Fig. 7, the gold salt is
essentially diamagnetic with a negligible Curie tail at the
lowest temperatures corresponding to 0.6% S ¼ 1/2 magnetic
defects. The nickel complex also exhibits a Curie type beha-
viour but with a Curie constant corresponding to about 9% of
a S ¼ 1/2 species. Tacking into account the S ¼ 0 state of the
[Au(tfadt)2]ꢀ gold dithiolene complex, the diamagnetic char-
acter of its perylene salt unambiguously demonstrates that the
One important point to be addressed here is the actual
electronic state of the perylene and the [M(tfadt)2] moieties in
both salts. Indeed, the 1 : 1 tfd salts, that is [Per][Ni(tfd)2], are
known to be neutral insulators while most salts with
[M(mnt)2]ꢀ are mixed-valence conducting salts, with the ꢁex-
ception of a 1 : 1 [Per][Pt(mnt)2] salt.28 The [Ni(tfadt)2]ꢀ is
known to oxidize reversibly to the neutral complex at 0.51 V
vs. Fc1/Fc while [Au(tfadt)2]ꢀ oxidizes at a notably higher
potential, 0.745 V vs. Fc1/Fc. We should therefore compare
those values with the oxidation potential of perylene itself in
order to determine if the dithiolene complexes might even-
tually oxidize below perylene. The latter oxidizes at 0.90 V vs.
SCE, that is around 0.50 V vs. Fc1/Fc and thus close but
below the oxidation potentials of both Ni and Au tfadt
complexes. It is therefore expected that during the electro-
crystallization experiments, the perylene is oxidized rather
than the dithiolene complexes. Furthermore, analysis of the
bond lengths within the [Ni(tfadt)2] complex, as a monoanion
21
dicationic [Per]3 trimer is also in a singlet ground state at
room temperature and below. As a consequence, the weak
magnetic contribution in the nickel salt can only arise from the
[Ni(tfadt)2]ꢀ complex.
ꢁ
1
in its (n-Bu)4N1 or PPh4 salt (Table 3) shows that the
Fig. 6 A projection view of one (a,c) layer showing the perylene
triads and metal dithiolene dyads. The two disordered positions of one
CF3 groups are shown.
1
Fig. 4 A view of the unit cell of [n-Bu4N][cis-Au(tfadt)2]. The n-Bu4
cations have been omitted for clarity.
ꢂc
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Chart 3
Despite the isostructural character of both salts, slight
structural differences are observed within the inorganic dyads
and organic triads. The most spectacular one is shown in Fig.
8: the diamagnetic [Au(tfadt)2]ꢀ complex exhibits an overlap
with lateral offset together with intermolecular Auꢃ ꢃ ꢃAu dis-
tance at 3.98 A, a structure close to that described above in its
n-Bu4N1 salt (Fig. 5). On the other hand, with the radical
[Ni(tfadt)2]ꢀ nickel complex, the metal dithiolene dyads
ꢁ
adopt an almost perfectly eclipsed configuration. Indeed, the
shortest Sꢃ ꢃ ꢃS intermolecular contacts are found at 3.662 and
3.740 A within the [Ni(tfadt)2]2 dyads while they exceed 3.979
and 4.031 A in the gold [Au(tfadt)2]2 dyads. Similarly, the
plane-to-plane distances amount to 3.632(5) A in [Ni(tfadt)2]2
dyads and 3.822(3) A in [Au(tfadt)2]2 dyads.
Fig. 7 Temperature dependence of the magnetic susceptibility of
[Per]3[M(tfadt)2]2, M ¼ Au, Ni.
b2
written as J ¼ U , where U is the on-site Coulomb repulsion,
These features are clearly the consequence of the radical
nature of the nickel [Ni(tfadt)2]ꢀ complex. The interaction
which amounts to B1 eV in most molecular materials. Ac-
cordingly, the calculated 0.409 eV value for bNi–Ni corresponds
to a very large JNi–Ni/kB value of 1856 K. As a consequence,
the triplet state of the nickel complex dyad will be essentially
unoccupied at room temperature or below and should not
contribute to the magnetic susceptibility.
ꢁ
between the singly occupied molecular orbitals of both
[Ni(tfadt)2]ꢀ moieties leads to a bonding and antibonding
ꢁ
combinations which can be characterized by the calculation of
the interaction energy, bij ¼ hji|Heff|jji, where ji and jj are
the relevant frontier orbitals of each pair of neighbour com-
plexes.29 The calculated interaction energy bNi–Ni within the
nickel dyad amounts to 0.409 eV, a value associated with very
strong coupling. The magnetic susceptibility of such a single-
t–triplet system is described by the Bleaney–Bower equation
(eqn (1)) where J is the energy gap between the singlet and
The interaction between perylene molecules develops within
triads, with one perylene on an inversion center, flanked by
two perylene molecules corresponding to each other by the
same inversion center. The overlap between the centrosym-
metric central molecule and one other perylene molecule is
shown in Fig. 9 for both compounds. We observe a lateral
offset in both salts, together with a noticeable longitudinal
shift only in the salt of the gold complex. The centrosymmetric
and an neighbour perylene molecules are almost parallel, with
an angle between the molecular mean planes of 0.40(4)1 in the
nickel complex salt and 0.69(4)1 in the gold complex salt and
an averaged plane-to-plane distance of 3.36–3.37 A. The
corresponding calculated overlap interaction energy bPer–Per
amounts to 0.362 eV in the nickel complex salt, which would
correspond to a JPer–Per/kB evaluated at 1520 K. Accordingly,
triplet state, NA is Avogadro’s number, g the Lande factor, mB
´
the Bohr magneton, kB the Boltzmann constant and T the
absolute temperature.30
2NAg2m2B
kBT 3 þ expðꢀJ=kBTÞ
1
wST
¼
ð1Þ
In a Hubbard model, the relationship between the interaction
parameter J and the calculated interaction energy bij can be
Table 3 Bond lengths within the metallacycle in the nickel tfadt complexes
a
a0
b
b0
c
Ref
[Ni(tfadt)2]2ꢀa
[Ni(tfadt)2]ꢀa
[Ni(tfadt)2]ꢀb
2.167
2.139
2.137(2)
2.140(2)
2.170
2.140
2.138(2)
2.143(2)
1
1.745
1.726
1.740(5)
1.733(5)
1.729
1.704
1.706(5)
1.711(5)
1.356
1.358
1.339(7)
1.327(7)
13
13
This work
Averaged values from the (n-Bu)4N1 and PPh4 salts. In its perylene salt.
a
b
ꢂc
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Fig. 8 A view of the overlap between [M(tfadt)2]ꢀ within the dyads
ꢁ
in [Per]3[M(tfadt)2]2, M ¼ Au (top) or Ni (bottom). The two orienta-
Fig. 9 A view of the overlap between perylene molecules within the
triads in [Per]3[M(tfadt)2]2, M ¼ Au (top) and Ni (bottom).
tions of the disordered CF3 group have been shown.
the dicationic perylene triad is also expected to be diamag-
netic, as indeed experimentally observed in the gold complex
salt. The weak Curie–Weiss paramagnetism observed in the
nickel salt most probably arises from non-interacting para-
magnetic [Ni(tfadt)2]ꢀ defects.
described. MeOH was dried by refluxing on Mg and distilla-
tion prior to use.
[n-Bu4N][Au(tfadt)2]
4-Cyano-5-trifluoromethyl-1,3-dithiol-2-one (0.6 g, 2.64
mmol) was added to a solution of Na (0.15 g, 6.52 mmol) in
dist. MeOH (10 mL). After stirring for 45 min, KAuCl4 (0.5 g,
1.32 mmol) was added and the mixture was stirred overnight.
n-Bu4NBr (0.72 g, 2.23 mmol) was then added to the solution,
followed by distilled water (50 mL). The precipitate was
filtered, washed with water and Et2O (5 mL) to yield the title
compound (0.41 g, 55%) as a green powder. Crystallization by
slow evaporation of a MeOH solution yielded a mixture of
green prisms and brown plates. MALDI-TOF-MS: Calc.
562.85; Found. 562.83. Anal. Calcd for C24H36F6N3AuS4: C,
35.77; H, 4.50; N, 5.21. Found: C, 35.57; H, 4.37 N, 5.24%. IR
(KBr) n (cmꢀ1): 2211.5 (CRN).
Conclusion
Square-planar complexes of unsymmetrical dithiolate ligands
such as (tfadt: 2–(trifluoromethyl)acrylonitrile-1,2-dithiolate)
are found to exhibit conformational polymorphism in the n-
Bu4N1 salt, as both cis and trans isomers were found to
crystallize separately in the same crystallization batch. Elec-
trocrystallization of perylene in the presence of the diamag-
netic [n-Bu4N][Au(tfadt)2] or the paramagnetic (S ¼ 1/2)
[n-Bu4N][Ni(tfadt)2] nickel analogue affords isostructural salts
with an unusual 3 : 2 stoichiometry, that is [Per]3[M(tfadt)2]2
21
(M ¼ Au, Ni), with an alternation of dicationic [Per]3
2ꢀ
[Ph4P][Au(tfadt)2]
perylene triads and dianionic [M(tfadt)2]2 dithiolene com-
plex dyads within one-dimensional chains. These salts are
characterized by strong antiferromagnetic interactions within
4-Cyano-5-trifluoromethyl-1,3-dithiol-2-one (0.9 g, 4.26
mmol) was added to a solution of Na (0.3 g, 13 mmol) in dist.
MeOH (10 mL). After stirring for 45 min, KAuCl4 (1.02 g,
2.24 mmol) was added, the mixture stirred for 1 h and Ph4PBr
(0.95 g, 2.26 mmol) was added. After stirring overnight, the
precipitate was filtered, dissolved hot in CH3CN and filtered
again. After cooling, the green brown precipitate was filtered
and washed with Et2O. Diffusion of pentane into an acetone
solution yielded the salt (1.2 g, 62%) as of green elongated
plates. Anal. Calcd for C32H20F6N2AuS4P: C, 42.58; H, 2.23;
N, 3.10. Found: C, 42.54; H, 2.23 N, 3.02%.
2ꢀ
perylene triads and [Ni(tfadt)2]2 dyads and an essentially
diamagnetic behaviour.
Experimental
Syntheses
The nickel complex (n-Bu4N)[Ni(tfadt)2] and 4-cyano-5-tri-
fluoromethyl-1,3-dithiol-2-one were prepared as previously
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Table 4 Crystallographic data
Compound
(PPh4)[Au(tfadt)2]
trans (n-Bu4N) [Au(tfadt)2]
cis (n-Bu4N) [Au(tfadt)2]
[Per]3 [Ni(tfadt)2]2
[Per]3 [Au(tfadt)2]2
Formula
Fw
Cryst. system
Space group
a/A
b/A
c/A
a/deg
C32H20AuF6N2 PS4
902.68
Monoclinic
C2/c
25.7658(12)
8.0568(5)
17.6766(9)
—
117.347(4)
—
3259.4(3)
4
1.840
Kappa-CCD
293(2)
4.880
2.38–27.52
11788
3728
0.0295
2700
C24H36AuF6N3S4
805.76
Triclinic
C24H36AuF6N3S4
805.76
Triclinic
C38H18F6N2NiS4
803.49
Triclinic
C38H18F6N2AuS4
941.79
Triclinic
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
11.1550(13)
11.7052(13)
13.5301(15)
73.117(13)
78.734(14)
67.536(13)
1555.1(3)
2
11.5030(12)
12.2691(14)
12.5077(14)
104.268(13)
113.245(12)
92.870(12)
1550.2(3)
2
10.8853(14)
12.6566(14)
13.1882(16)
113.253(13)
103.614(14)
94.149(14)
1594.4(3)
2
10.8670(13)
12.7568(16)
13.2210(15)
111.176(13)
103.135(14)
96.571(15)
1624.9(3)
2
b/deg
g/deg
V/A3
Z
Dcalc/Mg mꢀ3
Diffractometer
T/K
1.721
1.726
1.674
1.925
Stoe-IPDS
293(2)
5.054
1.94–25.87
15016
5563
0.0641
4285
Gaussian
0.8603, 0.2489
343
Stoe-IPDS
293(2)
5.069
1.85–25.97
14990
5543
0.0323
4711
Gaussian
0.5580, 0.2872
343
Stoe-IPDS
293(2)
0.94
1.78–25.99
15531
5735
0.0516
2597
Gaussian
0.9650, 0.6801
515
Stoe-IPDS
293(2)
4.853
1.97–25.94
15849
5865
0.0394
4750
Gaussian
0.8153, 0.1486
487
m/mmꢀ1
y-range/deg
Meas. reflns
Indep. reflns
Rint
I 4 2s(I) reflns
Abs. corr.
Tmax, Tmin
Refined par.
R(F),I 4 2s(I)
wR(F2), all
Empirical
1.0, 0.6334
238
0.0397
0.1187
0.0385
0.0946
þ1.15,ꢀ1.74
0.0334
0.0879
þ1.60, ꢀ1.24
0.046
0.1385
þ0.57, ꢀ0.52
0.0258
0.0499
þ0.56, ꢀ0.50
Dr (e Aꢀ3
)
þ1.75, ꢀ1.29
[Per]3[Ni(tfadt)2]2
squares methods. Numerical absorption corrections were ap-
plied for all structures. Hydrogen atoms were introduced at
calculated positions (riding model), included in structure
factor calculations, and not refined. Disorder models on the
CF3 groups had to be applied in both perylene salts, affecting
strongly one of the CF3 groups in both Ni and Au complexes
with two sets of 50 : 50 occupation parameters, rotated from
each other by 601 in the Au complex, by B451 in the Ni
complex. The second CF3 group of the Ni complex was also
separated into two equal contributions, differing by a rotation
of a few degrees only.
A solution of (n-Bu4N)[Ni(tfadt)2] (33 mg) in CH2Cl2 (15 mL)
was shared in a two-compartment cell divided by a glass frit
while perylene (20 mg) was added to the anodic compartment.
A 1 mA current was applied for two weeks giving black plates
on the anode. IR (KBr) n (cmꢀ1): 2207.64 (CRN).
[Per]3[Au(tfadt)2]2
A solution of (n-Bu4N)[Au(tfadt)2] (20 mg) in a mixture of
dist. CH2Cl2 (9 mL) and CH3CN (3 mL) was shared in a two-
compartment cell divided by a glass frit while perylene (10 mg)
was added to the anodic compartment. A 0.5mA current was
applied for two weeks giving black hexagonal plates on the
anode. IR (KBr) n (cmꢀ1): 2211.5 (CRN).
Magnetic measurements
Magnetic susceptibility measurements were performed on a
Quantum Design MPMS-2 SQUID magnetometer operating
on the range 2–300 K at 5000 G with polycrystalline samples.
Gelatin capsules were used with a magnetization contribution
of ꢀ2.37 10ꢀ6 þ (2.2 10ꢀ6/(T þ 2)) emu G gꢀ1 which was used
for correction of the experimental magnetization. Molar sus-
ceptibilities were then corrected for Pascal diamagnetism.
Electrochemistry
Cyclic voltammetry was performed in CH2Cl2 containing
n-Bu4NPF6 0.05 M as electrolyte. A platinum disk and
platinum wire were used as working and counter electrode
respectively together with an Ag1/Ag reference. Ferrocene
was added at the end of the experiment.
Acknowledgements
Crystallographyz
We thank Ph. Molinie (Institut Jean Rouxel, Nantes, France)
´
Crystals were mounted at the end of a glass fiber with
Aralditet glue. Data were collected on a Stoe Imaging Plate
Diffraction System (IPDS) with graphite monochromated Mo-
Ka radiation (l ¼ 0.710 73 A). The crystal data are summar-
ized in Table 4. Structures were solved by direct methods
(SHELXS-97) and refined (SHELXL-97) by full matrix least-
for giving us access to the SQUID magnetometer. This work
was supported by the CNRS, and by the Ministry of Educa-
tion and Research (France) through a PhD grant (to O. J.).
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ꢂc
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1780 | New J. Chem., 2006, 30, 1774–1781

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