Fluorine segregation in crystalline materials: Structural control and solid-state [2+2] cycloaddition in CF3-substituted tetrathiafulvalene derivatives

Article abstract of DOI:10.1002/chem.200501078

The well-known influence of long perfluorinated chains on the structures and stability of amphiphilic molecules in liquid crystalline mesophases or mesoscopic micellar arrangements is evaluated here in the realm of crystalline materials based on rigid aro

Full text of DOI:10.1002/chem.200501078

DOI: 10.1002/chem.200501078
Fluorine Segregation in Crystalline Materials: Structural Control andSolid-
State [2+2] Cycloaddition in CF3-SubstitutedTetrathiafulvalene Derivatives
[a]
Olivier Jeannin andMarc FourmiguØ*
Abstract: The well-known influence of
long perfluorinated chains on the struc-
tures and stability of amphiphilic mole-
cules in liquid crystalline mesophases
or mesoscopic micellar arrangements is
evaluated here in the realm of crystal-
line materials based on rigid aromatic
4,4,4-trifluorotetrolate with ethylenetri-
thiocarbonate. The structures of neu-
tral (Z)-1, (E)-1, 2, and 3 as indicated
by single-crystal X-ray diffraction
measurements reveal the recurrent for-
mation of layered structures with a
strong segregation of the fluorinated
moieties and formation of fluorous bi-
layers, attributed to the amphiphilic
character of those TTF derivatives
upon CF3 functionalization, and with-
out need for longer CnF2n+1 (n>1) per-
fluorinated chains. The short intermo-
lecular distance between outer C=C
double bonds observed in the layered
structure of (E)-1 allows a solid-state
[2+2] photocyclization with formation
of chiral dyads incorporating the char-
acteristic cyclobutane ring. These dyads
containing two dihydrotetrathiafulva-
lene moieties facing each other exhibit
reversible oxidation to the mixed-va-
lence radical cation state and organize
in the solid-state into the same layered
structures with fluorous bilayers.
molecules bearing only
a
limited
number of CF3 moieties. Tetrathiaful-
valene (TTF) derivatives bearing one
or two CF3 groups, that is, (Z)- and
(E)-(CF3)2TTF ((Z)-1, (E)-1), EDT-
TTF-CF3 (2), and EDT-TTF(CF3)2 (3)
(EDT=ethylenedithio) are prepared
from the 1,3-dipolar reaction of methyl
Keywords: crystal engineering
·
cycloaddition · fluorine · layered
compounds · tetrathiafulvalene
Introduction
soft-matter chemistry, where amphiphilic molecules with a
strong incompatibility between the different parts adopt a
variety of mesophase morphologies based on the segrega-
tion of hydrophilic versus hydrophobic but also rigid versus
flexible fragments.[4] When available, crystals of such amphi-
philic molecules often exhibit layered structures based on
these segregation effects.[5] Replacement of alkyl chains with
fluorinated or semifluorinated chains has become very pop-
ular since mesophases are stabilized due to the increased in-
compatibility of such chains with the aromatic cores.[6,7] Fur-
thermore, a variety of novel mesophase topologies are intro-
duced, as observed in ABC triblock copolymers,[8] linear
polyphilic block molecules,[9,10] or calamitic molecules with
both terminal and lateral chains.[11] The combined hydro-
The control of solid-state architectures of molecular organic
solids through directional, strong intermolecular interactions
such as hydrogen[1] or halogen[2] bonds forms the basis of su-
pramolecular solid-state chemistry,[3] a very successful ap-
proach that has allowed a very fine control of supramolecu-
lar solid-state architectures. In that respect, little attention
has been given to the exclusive use of nondirectional van
der Waals interactions for the targeted construction of or-
dered architectures of specific dimensionality, that is, the se-
lective crystallization into chains, columns, layers, or three-
dimensional ordered structures of organic molecules devoid
of any functional group for hydrogen (alcohols, acids,
amides, amines, and so forth), or halogen (Cl, Br, I) bond-
ing, p–p aryl/perfluoroaryl interactions, or metal coordina-
tion. On the other hand, this approach is routinely used in
and lipophobia of fluorinated compounds can be used to
[12]
generate complexnano- to mesomeric phases
such as seg-
regated micelles,[13] liposomes,[14] and bidimensional films.[15]
Also, the successful incorporation of trifluoro-[16] or hexa-
fluoroleucine[17] as the sole hydrophobic core residue in a
designed coiled coil provided the very first examples of
highly specific protein–protein interaction based on fluorina-
tion of the hydrophobic core.
[a] O. Jeannin, Dr. M. FourmiguØ
Laboratoire Chimie, IngØnierie MolØculaire et MatØriaux(CIMMA)
UMR 6200 CNRS-UniversitØ d’Angers
Bât K, UFR Sciences
2 Bd Lavoisier, 49045 Angers, (France)
Fax: ( +33)241-735-405
We wanted to take advantage of such segregation effects
of fluoroaliphatic groups in crystalline molecular materials
E-mail: marc.fourmigue@univ-angers.fr
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FULL PAPER
to obtain controlled solid-state organizations. For example,
long perfluorinated chains directly linked to oligo-[18] and
polythiophenes[19] have a strong influence on molecular
packing and the absorption and emission spectra,[20] enable
solubility[21] in supercritical CO2, and afford n-dopable semi-
conductors.[22] Among conducting materials, semifluorinated
tetrathiafulvalene (TTF) derivatives have been prepared for
Langmuir–Blodgett film formation,[23] while incorporation of
À
highly fluorinated anions such as (CF3)3CF(CH2)2-SO3 in
TTF salts also stabilized the formation of layered materi-
als.[24,25] The very strong contrast offered by fluoroaliphatics
in polymer science, biochemistry, and soft-matter chemistry
let us infer that even single CF3 groups rather than long
CnF2n+1 perfluoroalkyl chains, adequately positioned on the
rigid core, could be sufficient to provide a segregation and
formation of layered crystalline structures, as very recently
observed in hexafluoroacetylacetonate (hfac) complexes.[26]
Indeed, the two-dimensional structures often encountered in
cation radical salts are also highly desirable in the structures
of the neutral TTF-like donor molecules if one is interested
in the design of crystalline thin films for transistor devices.[27]
A more systematic investigation should produce a selection
of the best molecules for producing high-quality thin films
with high intralayer mobilities.[22] We therefore decided to
prepare various aromatic cores substituted with a limited
number of the shortest perfluorinated chain, that is, the tri-
fluoromethyl group, and selected the tetrathiafulvalene
(TTF) backbone as a useful candidate for CF3 functionaliza-
tion. Indeed, among the few TTF-based donor molecules
with aliphatic fluorine moieties, the only crystallographically
characterized examples already indicate an efficient segrega-
tion of the fluorinated moieties, as observed in: 1) tetrakis-
(trifluoromethyl)-tetrathiafulvalene (CF3)4TTF,[28] 2) TTF
molecules substituted with 2,2’-difluoropropylene-1,3-dithio
groups such as (F2PDT)2TTF,[29] and very recently, 3) nickel
dithiolene complexes of bis(trifluoromethyl)tetrathiafulvale-
nedithiolate moieties.[30]
Figure 1. The structural organization of (CF3)4TTF, viewed along the b
stacking axis (fluorine atoms are shown in green).
segregation of the fluorinated and aromatic moieties. To
evaluate the robustness of this segregation principle, we de-
cided to investigate the functionalization of the rigid TTF
core with only one or two CF3 moieties, to evaluate the in-
fluence on the solid-state structure of the neutral donor mol-
ecules of the successive introduction of CF3 moieties on dif-
ferent positions of the TTF core.
We describe the synthesis of TTF derivatives 1–3 that
have been substituted by mono- and bis(trifluoromethyl)
moieties, the determination and analysis of their X-ray crys-
tal structures, and their electrochemical properties. We also
show that this specific fluorine segregation can favor a close
proximity between TTF derivatives in the crystal, that are
thus prone to a solid-state [2+2] cycloaddition reaction
under irradiation, leading to a rare example of a dimeric
donor molecule with a rigid cyclobutane bridge and strongly
interacting, redox-active, dihydrotetrathiafulvanyl moieties.
Results andDiscussion
For example, the crystal structure of (CF3)4TTF as derived
from X-ray crystallography (Figure 1), exhibits a pseudo-col-
umnar arrangement with the outer surface of each stack
being essentially covered with fluorine atoms. The columns
organize in the solid in a close-packed hexagonal structure,
very similar to those observed in liquid-crystalline discotic
CoIh phases. These examples demonstrate that the introduc-
tion of CF3 or CF2 moieties on the rigid TTF core can
induce a molecular contrast strong enough to force a micro-
Synthesis: TTF(CF3)4 is the only tetrathiafulvalene deriva-
tive described so far that includes a trifluoromethyl substitu-
ent linked directly to the TTF core. The preparations descri-
bed are based on the reaction of the volatile hexafluorobu-
tyne either with CS2,[31] metal complexes thereof as
[(triphos)Ni(h2-CS2)] (triphos = 1,1,1-tris(diphenylphosphi-
nomethyl)ethane),[32] or with boiling sulfur to give the corre-
sponding bis(trifluoromethyl)dithiete[33] for further reaction.
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O. Jeannin and M. FourmiguØ
The preparations are therefore limited to this specific deriv-
ative, together with the added inconvenience of the availa-
bility and handling of this gaseous alkyne. On the other
hand, the 1,3-dipolar-addition reaction of activated acety-
lenes with ethylenetrithiocarbonate has proven to be one of
the main routes in tetrathiafulvalene chemistry[34] since it af-
fords, often in very good yield, 1,3-dithiole-2-thiones for fur-
ther phosphate-or phosphine-coupling reactions to the TTF
derivatives. For the introduction of only one CF3 group on
the dithiole ring, we therefore chose to start from the tri-
fluoromethyl-substituted alkyne 6, where the presence of
two electron-withdrawing groups, an ester and a trifluoro-
methyl group, should confer a good reactivity towards ethyl-
enetrithiocarbonate, as was observed (see below).
bis(trifluoromethyl)tetrathiafulvalenes (E)-1 and (Z)-1.
Indeed, the phosphite-coupling reaction of the 1,3-dithiole-
2-thione 7 afforded the bis-trifluoromethyl-bis-carbometh-
oxytetrathiafulvalene 8 as a Z-E isomeric mixture. The two
isomers were separated by successive recrystallizations from
methanol, affording first the less-soluble (E)-8 isomer, while
the more-soluble (Z)-8 isomer was obtained from the
mother liquors. Both compounds appear to be pure as
shown by TLC. Treatment of isolated isomers with LiBr in
warm DMF led to decarboxylation and both E-1 and (Z)-1
were obtained in 63 (E) and 88 (Z)% yield, respectively.
We observed that (Z)-1 was obtained but also that partial
isomerization to (E)-1 occurred during the decarboxylation
of (Z)-8, since the final product contains 15–20% of E
isomer, as deduced from NMR spectrum as well as the X-
ray crystal structure of (Z)-1 (see below). The high solubility
and close polarity of both isomers did not allow for a com-
plete purification of the Z isomer.
The methyl ester of the alkyne 6 was prepared according
to a procedure described for its ethyl analog,[35] from triphe-
nylphosphine oxide (Ph3PO) elimination of the correspond-
ing phosphoranylidene 5, as shown in Scheme 1, and isolat-
Similarly, as shown in Scheme 3, following the transforma-
tion of the 1,3-dithiole-2-thione 7 into the corresponding di-
thiole-2-one 9 with Hg(OAc)2, the cross-coupling reaction of
Scheme 1.
ed after distillation as a clear liquid. Reaction with ethylene-
trithiocarbonate under refluxin toluene afforded the corre-
sponding dithiole-2-thione 7 in good yield (Scheme 2). The
latter was the starting material for the preparation of tri-
fluoromethyl-substituted TTF derivatives since the carbome-
thoxy group(s) can be easily removed by reaction with LiBr
in DMF,[36] as shown in Scheme 2 for the synthesis of the
Scheme 3.
9
with 5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiine-2-thione
10 afforded the asymmetrically substituted EDT–TTF deriv-
ative 11 bearing both the carbomethoxy and trifluoromethyl
substituents, separated from the symmetrical-coupling prod-
ucts BEDT-TTF and (Z,E)-8 by chromatography. Treatment
of 11 with LiBr in warm DMF[36] afforded the trifluorometh-
yl EDT–TTF derivative 2 in good yield, isolated in a crystal-
line form after recrystallization.
The synthesis of the bis(trifluoromethyl) EDT-TTF deriv-
ative EDT-TTF(CF3)2 (3) relies on a similar phosphite cou-
pling of 5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiine-2-one[37]
10 with 4,5-bis(trifluoromethyl)1,3-dithiole-2-thione 12 as
described in Scheme 4. The latter has been prepared follow-
ing a described procedure involving the nucleophilic dis-
placement of chlorine atoms in 2,3-dichloro-1,1,1,4,4,4-hexa-
fluoro-2-butene with K2CS3.[38] (Z)-1, (E)-1, 2, and 3 are
highly soluble in all common solvents excluding water. They
were satisfactorily recrystallized from EtOH/H2O mixtures.
Solid-state structures: towardfluorine segregation : Let us
first consider the trifluoromethyl EDT-TTF derivative 2
Scheme 2.
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Fluorine Segregation in Crystalline Materials
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Figure 3. Detail of the bond-over-ring overlap between A and B mole-
cules in the stacks of compound 3.
Scheme 4.
bearing only one CF3 group. It crystallizes in the monoclinic
system, space group P21/c, with one molecule in a general
position in the unit cell. Of particular note is the strong fold-
ing of the two dithiole rings, 23.28(15)8 on the dithioethy-
lene side, 20.99(14)8 on the CF3 side. In the solid state
(Figure 2), molecules associate into inversion-centered
Figure 4. Solid-state organization of EDT-TTF(CF3)2 (3) showing the flu-
orine segregation (fluorine atoms are shown in green).
formation of fluorous bilayers. Such layered structures are
most often found in the mixed-valence conducting BEDT-
TTF salts with alternating organic and inorganic layers but
are almost never found in structures of neutral donor mole-
cules unless cohesive interactions stabilize the interface be-
tween layers, as observed for example in the structure of
neutral dithienotetrathiafulvalene[42] with S···S van der
Waals interactions or in the neutral EDT-TTF(CONH2)2 di-
amide with a set of hydrogen-bond interactions.[43] Here in
derivative 3, the planarity of the central TTF core, the stack-
ing of the molecules, and the association of stacks within a
layered structure occur only on the basis of the incompati-
bility between different parts of the molecules, without any
stabilizing intermolecular interactions such as hydrogen
bonds.
In other words, the functionalization of the highly polariz-
able (soft) sulfur-containing EDT-TTF core in derivative 3
with two weakly polarizable (hard) CF3 substituents pro-
vides the molecule with a strong amphiphilic character. As a
consequence, the energy of its solid-state associations is ex-
pected to be lowest if both opposite fragments segregate, in
order to suppress direct contacts between fragments of op-
posite polarity as far as possible. It is also noteworthy that
this specific bilayer formation is observed here with a very
limited number of CF3 moieties while the few described ex-
amples involved longer perfluoroaliphatic CnF2n+1 (n=5)
chains.[44]
Figure 2. Solid-state arrangement of compound 2, showing the dyadic as-
sociation (fluorine atoms are shown in green).
dyads, a recurrent feature among neutral, nonsubstituted
EDT-TTF derivatives such as EDT-TTF itself,[39] BEDT-
TTF,[40] and others,[41] demonstrating that the S···S van der
Waals interactions that stabilize these dyads essentially over-
come possible fluorine segregation effects here, as also con-
firmed by the absence of any F···F short distances below
3 Š. On the other hand, a segregation of the fluorinated
moieties is readily observed in the TTF derivatives bearing
two CF3 groups, as indeed observed in EDT-TTF(CF3)2 (3),
(Z)- and (E)-(CF3)2TTF, ((Z)-1 and (E)-1). EDT-TTF(CF3)2
(3) crystallizes in the monoclinic system, space group P21/n,
with two crystallographically independent molecules A and
B in the asymmetric unit that differ from each other by a
disorder of the ethylenic moiety and a strong folding of the
dithiole ring bearing the two CF3 moieties (308) in one of
the two molecules. In the solid state, molecules A and B as-
sociate into AB head-to-tail dyads (Figure 3). Alternating
ABABAB stacks form along axis b, and organize laterally
along the a axis through S···S van de Waals contacts to form
slabs with a striking segregation of the fluorinated moieties
at the interface between slabs (Figure 4), giving rise to the
The (Z)- and (E)-(CF3)2TTF (Z)-1 and (E)-1 derivatives
also display an amphiphilic character but with a completely
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O. Jeannin and M. FourmiguØ
different topology when compared with derivative 3 since
the two CF3 moieties are now on opposite sides of the rigid
TTF core. The noncentrosymmetric (Z)-1 isomer crystallizes
in the monoclinic system, space group I2/a. Note that the
CF3 groups are found disordered on the four outer C atoms
of the TTF core, which could correspond to a 90:10 distribu-
tion of the two possible orientations, or better to an 80:20
mixture of the Z and E isomers, as already identified from
the NMR data. In the solid state, molecules related by inver-
sion centers (Figure 5) alternate into stacks running along
Figure 8. Solid-state organization of (E)-(CF3)2TTF ((E)-1) showing the
fluorine segregation (fluorine atoms are shown in green).
Figure 5. Detail of the bond-over-ring overlap between derivative (Z)-1
molecules in the stacks.
The analogy between the structures of derivatives 3, (Z)-
1, and (E)-1 despite different locations of the CF3 moieties
on the rigid core, is due to the recurrent tendency of the
TTF core to form bond-over-ring dyads through S···S van
der Waals interactions (Figures 3, 5, and 7). As a conse-
quence, a similar bimolecular motif incorporating two rigid
cores and four CF3 groups (Scheme 5), located on both ends
of the dyad, is found at the origin of the comparable solid-
state organizations in the three structures shown in Fig-
ures 4, 6, and 8.
axis b. Combination of the stacks along axis c affords a lay-
ered structure organization, again with fluorinated bilayers
(Figure 6), similar to those observed in the structure of de-
Figure 6. Solid-state organization of (Z)-(CF3)2TTF ((Z)-1) showing the
fluorine segregation (fluorine atoms are shown in green).
rivative 3. In (E)-(CF3)2TTF, two crystallographically inde-
pendent molecules A and B, each located on an inversion
¯
center crystallize in the triclinic system, space group P1.
Scheme 5. Solid-state organization of derivatives (E)-1, (Z)-1, and 3 into
a recurrent inversion-centered dyadic motif bearing four CF3 moieties.
They form alternating ABABAB stacks along the b axis
(Figure 7), further interacting through S···S van der Waals
forces into slabs, separated from each other by the fluorine
double layer (Figure 8).
The lamellar topologies observed in the structures of de-
rivatives (Z)-1, (E)-1, and 3 infer that they could eventually
exhibit mesophases upon heating. While derivatives (Z)-
and (E)-1 do not exhibit any special feature, the differential
scanning calorimetry (DSC) thermogram of derivative 3
shows, before the fusion peak at 1688C (55.5 JgÀ1), a pre-
peak at 1208C, but with a low enthalpy (3.8 JgÀ1) attributa-
ble to
a crystal–crystal transition. Direct observation
through a polarizing microscope showed no evidence of any
birefringent fluid phase upon slowly heating solid compound
3 or slowly cooling 3 from its melt.[45]
Figure 7. Detail of the overlap between A and B molecules in (E)-
(CF3)2TTF ((E)-1).
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Fluorine Segregation in Crystalline Materials
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Solid-state [2+2] cycloaddition: We also observed that crys-
tals of derivative (E)-1 kept in sunlight slowly changed color
from orange to yellow within a few days and simultaneously
slowly lost their crystallinity, while those kept in the dark re-
mained unchanged for months. MALDI-TOF experiments
on this yellow powder showed the presence, besides the
starting TTF derivative (E)-1, of a compound of double
mass (679.74 uma) and some degradation products. Since
the crystallinity of (E)-1 was lost upon irradiation, the re-
covered solid was recrystallized in EtOH to afford a com-
pound denoted (EE)-13 in the form of elongated thin plates,
together with minor quantities of other compounds. A
second experiment with Hg-lamp irradiation, followed by
successive column chromatography with CH2Cl2 and CS2,
and recrystallization of the mixture from CH3CN, afforded
two other compounds denoted (EZ)-13 and (ZZ)-13. A
Figure 10. Detail of the solid-state organization of derivative (E)-1.
1
combination of H and 19F NMR, and X-ray crystal-structure
While the C6S4-TTF core in molecule B is essentially planar
(largest deviation from the C6S4 mean plane: 0.03 Š), mole-
cule A is more distorted with the dithiole rings folded along
the S···S hinge by 8.36(8)8. As a consequence, the intermo-
lecular distances between the carbon atoms of the outer C=
C double bonds cluster into two groups, 3.731(4) and
3.766(4) Š on one side, 4.033(4) and 4.073(4) on the other
side. The [2+2] photocyclization takes place between near-
est C=C double bonds, affording either one or the other
isomer, as shown in Scheme 6. These two possibilities of-
determinations on the three products allowed the unambigu-
ous determination of their molecular structures, demonstrat-
ing that a [2+2] photocyclization of derivative (E)-1 had
taken place to afford compound (EE)-13. The product ex-
1
hibits H NMR signals at 5.80 ppm (in [D6]acetone) attribut-
able to a cyclobutane ring while signals due to two different
CF3 groups were observed in 19F NMR spectra, also compat-
ible with a [2+2] photocyclization involving the outer C=C
double bond of the TTF core. Compound (EE)-13 crystalli-
zes in the orthorhombic system, space group P2221 with one
molecule located on a twofold axis (Figure 9). The chiral
Figure 9. A view of derivative (EE)-13. Cyclobutane moiety characteris-
i
i
À
À
tics: C2 C3: 1.571(7), C2 C3 : 1.584(7) Š; C2-C3-C2 : 90.0(4), C3-C2-
C3i: 89.5(4)8 (i: Àx, y, 0.5Àz). The two orientations of the disordered CF3
groups have been marked with normal and dashed bonds.
nature of the P2221 space group let us infer that one single
isomer is present but refinement of the Flack parameter
converged to 0.47(19) during refinement cycles. The some-
what large esd on the Flack parameter might originate from
the weakness of the anomalous dispersion effect since the
sulfur atoms (the only substantial anomalous scatterers)
form pseudocentrosymmetric motifs in the structure. On the
other hand, this Flack parameter value can also indicate the
presence of racemic twinning.[46] Indeed, a rationale for the
formation of two enantiomers during the [2+2] photocycli-
zation can be found in the peculiar organization of deriva-
tive (E)-1 in the solid state (Figure 10). Two crystallographi-
cally independent molecules, denoted A and B, each of
them located on an inversion center, stack along the b axis.
Scheme 6. [2+2] Photodimerization of derivative (E)-1 upon single-crys-
tal irradiation.
fered for a given molecule for the [2+2] photodimerization
most probably explain the loss of crystallinity of the com-
pound during irradiation, since many defaults can be antici-
pated. Note also that this process could eventually lead to
oligomeric species linked by cyclobutane motifs. Indeed,
once a pair of molecules reacts, each end of the dimer still
has a double bond that could undergo a second [2+2] cycli-
zation to give a longer oligomer. Such species were not ob-
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O. Jeannin and M. FourmiguØ
served by MS analysis on irradiated crystals of derivative
(E)-1.
pound was found to crystallize in the monoclinic system,
space group P2/n, with one molecule in a general position in
the unit cell (Figure 11). It indeed displays the cyclobutane
This [2+2] photocyclization is similar to that observed
upon irradiation of carbamoyl tetrathiafulvalenes[47,48] as
well as an amidopyridyl tetrathiafulvalene formulated as
EDT-TTF-CONH(3-Py)[49] where a single-crystal-to-single-
crystal transformation was revealed due to a favorable ori-
entation of the molecules through p–p interactions. Follow-
ing the pioneering work of Schmidt on the [2+2] photodi-
merization of cinnamic acids,[50] several geometrical rules
have been established as guidelines for evaluating the possi-
ble occurrence of such dimerizations.[51] Considering the D
distance, q1, q2, and q3 angles defined in Table 1, it is nor-
Figure 11. A view of derivative (ZE)-13. Cyclobutane moiety bond
À
À
À
lengths [Š] and angles [8]: C2 C3 1.559(4), C10 C11 1.568(4), C2 C10
À
1.568(4), C3 C11 1.579(4); C2-C3-C11 89.4(2), C10-C11-C3 89.5(2), C3-
C2-C10 90.2(2), C2-C10-C11 89.2(2). The two orientations of the disor-
dered CF3 groups have been marked with normal and dashed bonds.
Table 1. Geometrical characteristics of the TTF dyads before [2+2] cycli-
zation.
ring characteristic of the [2+2] cycloaddition but in one of
the two dihydrotetrathiafulvalene moieties, the two CF3
groups are now found in a cis configuration to each other,
implying that an isomerization has taken place. Such isomer-
izations of the central C=C double bond of the TTF core
are often observed,[52] catalyzed by traces of acid or on SiO2
columns. Indeed, protonation of the central double bond
allows for a free rotation of the dithiole rings, affording
compound (ZE)-13 from (EE)-13 (Scheme 7). This process
Compound
D[Š]
q1 [8]
q2 [8]
q3 [8]
Ref.
(E)-1
3.75
4.05
3.79
3.81
3.54
9.2
9.3
3.5
3.3
0
94.3
98.6
91.0
90.3
71.6
72.8
74.3
71.0
75.8
77.8
this work
(Z)-1
3
this work
this work
[48]
EDT-TTF-CONH(3-Py)
mally expected that photocyclizations might occur if D<
4.2 Š, q1 is close to 08, q2 and q3 are close to 908, the most
stringent condition being that the two C=C double bonds
are essentially parallel, that is q1 is close to 08. Values of D,
q1, q2, and q3 are presented in Table 1 for derivative (E)-1,
together with those for derivatives (E)-1, 3, and the only
other described example, EDT-TTF-CONH(3-Py). They
confirm the favorable geometry for dimerization in deriva-
tive (E)-1 or EDT-TTF-CONH(3-Py) and we can infer that
similar cyclizations could also be observed in derivatives
(Z)-1 or 3.
Indeed, irradiation of derivative (Z)-1 also led to a partial
discoloration of the crystals. However, chromatographic sep-
aration allowed the isolation of (EE)-13 in only 1.6% yield,
while the starting (Z)-1 compound was recovered essentially
unaltered. Similarly, irradiation of derivative 3 was also at-
tempted given the close proximity (3.82 Š) between the
outer C=C double bonds of the dithiole ring bearing the S-
CH2CH2-S moiety and the dithiole ring bearing the two CF3
groups. No color change was observed and the crystals re-
mained unchanged, demonstrating the lack of reactivity of
the ethylene-rich (RS)2C=C(SR)2 system.
Two other compounds were obtained after attempted
chromatographic separations and recrystallizations of com-
pound (EE)-13. They both exhibit the cyclobutane proton
signals, at d=5.786 and 5.795 ppm for compound (EZ)-13
(two signals) and d=5.82 ppm (in [D6]acetone) for com-
pound (ZZ)-13, while signals due to two CF3 groups are ob-
served with 19F NMR spectroscopy in compound (ZZ)-13
and four CF3 groups in compound (EZ)-13. The latter com-
Scheme 7. Isomerization of derivatives (EE)-13 to (ZE)-13 and (ZZ)-13
through rotation around the central C=C bonds.
was already observed here (vide infra) during the prepara-
tion of derivative (Z)-1 to afford a fraction of derivative
(E)-1. By the way, the crystallization of compound (ZE)-13
in a centrosymmetric space group confirms the presence of
both enantiomers in the starting (EE)-13 compound, as an-
ticipated from the presence of racemic twinning in com-
pound (EE)-13. The third compound (ZZ)-13 corresponds
to the structure where both CF3 groups of each dihydrote-
trathiafulvalene moiety are now found in a cis configuration
to each other, implying that a second isomerization from
compound (ZE)-13 to (ZZ)-13 has also taken place.
3000
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Chem. Eur. J. 2006, 12, 2994 – 3005

Fluorine Segregation in Crystalline Materials
FULL PAPER
Besides providing a rare example of [2+2] photocycliza-
tion in TTF chemistry, the solid-state structures of com-
pounds (EE)-13 and (ZE)-13 also offer another opportunity
to evaluate the robustness of the segregation principle de-
veloped above. As a matter of fact, the bimolecular motifs
bearing four CF3 moieties identified in the structures of de-
rivatives 3, (E)-1, and (Z)-1 (Scheme 5) occur in compounds
(EE)-13 and (ZE)-13. Indeed, despite different unit cell pa-
rameters and symmetry characteristics, their solid-state ar-
rangement (Figures 12 and 13) still exhibit the recurrent lay-
ered structures with strong fluorine segregation, further ex-
emplifying the ability of this dyadic motif to stabilize the
formation of layered crystals with these characteristic fluo-
rine bilayers.
multi-stage redoxbehavior was expected from the face-to-
face interaction between the two redox-active moieties.
Electrochemical properties of the trifluoromethyl-substitut-
edTTF derivatives andtheir [2
+2] cycloaddition adduct:
Since the tetrakis(trifluoromethyl)tetrathiafulvalene,
(CF3)4TTF, oxidizes at high potential due to the presence of
the four electron-withdrawing CF3 groups, we were interest-
ed to evaluate the influence of only one or two such CF3
groups on the redoxproperties of the TTF core, also to de-
termine the air-stability of the corresponding cation radical
salts. The TTF derivatives 1–3 described here exhibit the
two characteristic reversible oxidation waves (Table 2), to
Table 2. Redoxpotentials for compounds 1–3 and reference compounds,
in V versus Fc+/Fc. Values for reference compounds reported against
SCE have been corrected by À0.40 V for comparison purposes.
Compound
Solvent
E1 [V]
E2 [V]
Ref.
EDT-TTF
EDT-TTF-CF3 (2)
EDT-TTF(CF3)2 (3)
TTF
(E)-1
(Z)-1
CH3CN
CH2Cl2
CH2Cl2
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
0.04
0.21
0.37
-0.07
0.40
0.40
0.65
0.35
0.64
0.76
0.31
0.78
0.78
0.88
[39]
this work
this work
[55]
this work
this work
[31]
TTF(CF3)4
the mono and dicationic species. Note that the introduction
of one electron-withdrawing CF3 group on each dithiole
ring, as in derivatives (E)-1 and (Z)-1, leads to a strong
anodic shift (+ 0.47 V) of the first oxidation potential of the
TTF core[55] while the introduction of two CF3 groups on the
same dithiole ring as in derivative 3 induces a smaller
(+0.33 V) shift. To evaluate the extent of intramolecular
interactions between the two dihydrotetrathiafulvalene
moieties in the cyclobutane-linked dimers 13, the major
(EE)-13 product was also investigated by cyclic voltammetry
(Figure 14). Two reversible oxidation waves (Table 3) are
observed at 0.69 and 0.88 V versus Fc+/Fc, followed by an
Figure 12. Solid-state organization of derivative (EE)-13 showing the flu-
orine segregation (fluorine atoms are shown in green).
Figure 13. Solid-state organization of derivative (ZE)-13 showing the flu-
orine segregation (fluorine atoms are shown in green).
In conclusion, the specific organization of derivative (E)-1
within the columns and the softness of the lattice provided
by the weakly interacting fluorous layers allowed a remarka-
ble solid-state transformation, but also provided a novel mo-
lecular motif where two dihydrotetrathiafulvalene moieties
are now constrained to face each other, a case model for all
TTF dimers[53] and cyclophanes[54] described to date where
Figure 14. Cyclic voltammetry results of derivative (EE)-13 (1.4mm in
CH2Cl2 with nBu4NPF6 0.2m).
Chem. Eur. J. 2006, 12, 2994 – 3005
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3001

O. Jeannin and M. FourmiguØ
Table 3. Redoxpotentials for compound ( EE)-13 and reference compounds.
sufficient to induce a strong
amphiphilic character in aro-
matic molecules, while other
examples of such segregation
effects with similar fluorous bi-
layer formation rely on mole-
cules bearing long CnF2n+1 (n=
5) perfluoroalkyl chains. This
concept appears to be extreme-
ly robust since molecules with
diverse CF3 locations as in de-
Compound
Solvent
Reference
E1 [V]
E2 [V]
E2ÀE1 [mV]
E3 [V]
Ref.
TTF
TTFH2
(E)-1
(EE)-13
14
15
16
17
CH3CN
CH3CN
CH2Cl2
CH2Cl2
PhCN
PhCN
PhCN
PhCN
SCE
SCE
0.33
0.405
0.40
0.69
0.28
0.57
0.57
0.41
–
–
–
0.88
0.41
0.67
0.70
0.56
–
–
–
190
130
100
130
150
0.71
0.89
0.78
1.26
0.90
1.15
0.98
0.83
[55]
[54]
this work
this work
[56]
[57]
[58]
[59]
Fc+/Fc
Fc+/Fc
INIST
Ag/Ag+
Ag/AgCl
Ag/AgCl
irreversible process at 1.26 V, indicating that each dihydrote-
trathiafulvalene moiety in compound (EE)-13 oxidizes suc-
cessively to the cation radical. The first oxidation potential
of the dihydro derivative (EE)-13 appears at a more anodic
potential (+290 mV) than that of the corresponding fully
conjugated TTF derivative (E)-1. This anodic shift due to
the loss of conjugation upon cyclobutane formation is much
larger than that observed between TTF and dihydrotetra-
thiafulvalene (TTFH2) themselves (+75 mV). Furthermore,
the separation (DE) of 190 mV between the two first oxida-
tion processes in compound (EE)-13 indicates a strong intra-
molecular interaction between the two dihydrotetrathiaful-
valenyl redoxcenters.
rivatives (Z)-1, (E)-1, and 3 systematically produce such lay-
ered structures, built from a recurrent bimolecular motif,
almost identical to that also formed upon [2+2] photocycli-
zation. It is therefore expected that many aromatics func-
tionalized with a limited number of CF3 moieties might ex-
hibit similar layered structures, an important feature in the
search for n-dopable molecular semiconductors, an issue of
current strong interest.[18,22]
Furthermore, the photodimerization of derivative (E)-1
represents a very first example of a solid-state transforma-
tion involving molecules whose relative positioning is con-
trolled only by the segregation of fluoroaliphatic moieties.
Indeed, in most examples described so far of crystalline
solid-state reactions such as the polymerization of diacety-
lenes or the [2+2] cycloaddition of alkenes, the favorable
orientation of molecules is achieved either by serendipity or
purposely through the involvement of directional intermo-
lecular interactions such as hydrogen bonding,[60] halogen
bonding,[61] or p–p interactions.[48,62] Here, the relative orien-
tation of the two TTF moieties is obtained within a layered
structure occurring due to the amphiphilic character of the
molecules.
This DE value largely exceeds those reported for compa-
rable TTF dimers and cyclophanes such as compounds 14–
17 (Scheme 8 and Table 3) where the two TTF redoxcenters
The resulting photocyclization product includes two
redox-active dihydrotetrathiafulvalene moieties, constrained
in a face-to-face structure through the short and rigid cyclo-
butane fragment, an original feature that allows an unprece-
dented, strong intramolecular interaction evidenced by their
large potential difference between the two first oxidation
potentials.
Scheme 8. Examples of TTF dimers and cyclophanes exhibiting face-to-
face interactions and sequential one-electron redoxprocesses (see
Table 3).
Experimental Section
All reagents were commercially available unless otherwise stated. Nucle-
ar magnetic resonance spectra were recorded at 500.04 MHz for 1H and
125.75 MHz for 13C NMR spectroscopy (s: singlet; q: quadruplet). Mass
spectrometry was performed in the MALDI-TOF mode except for com-
pounds 7 and 9 that were analyzed in the High Resolution (HR) mode.
(Carbomethoxymethyl)triphenylphosphonium bromide 4 was prepared as
described in reference [63], bis(trifluoromethyl)-1,3-dithiole-2-thione 12
was prepared as described in reference [38], and 5,6-dihydro-
[1,3]dithiolo[4,5-b][1,4]dithiine-2-one 10 as described in reference [37].
are constrained in a face-to-face conformation.[56–59] The
main difference between compounds 14–17 and compound
(EE)-13 is in the very close proximity of the redox moieties
in compound (EE)-13 due to the cyclobutane ring and also
in its increased rigidity while molecules 14–17 still exhibit
degrees of freedom.
Methyl 4,4,4-trifluoro-2-(triphenylphosphoranylidene)acetoacetate (5):
NEt3 (130 mL, 0.93 mol) was slowly added to a suspension of compound
4 (184 g, 0.44 mol) in dry THF at 08C under nitrogen atmosphere. The
mixture was stirred for 1 h at 08C. Trifluoroacetic anhydride (100 g,
0.47 mol) was added dropwise at 08C over about 1.5 h. Stirring was main-
tained for 2 h before the suspension was filtered. The white precipitate
Conclusion
We have demonstrated here, by using the rigid TTF core,
that a very limited number of trifluoromethyl groups was
3002
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Chem. Eur. J. 2006, 12, 2994 – 3005

Fluorine Segregation in Crystalline Materials
FULL PAPER
was washed with cold THF (500 mL) and the mother liquors were con-
centrated. The oily residue was triturated in water (1 L), filtered, and was
washed with water (1 L) to give a pale-yellow solid. After recrystalliza-
tion in a methanol/water mixture, the product was obtained as very pale
yellow crystals (183.93 g, 96%).
1H NMR (CDCl3): d=3.3 (s, 3H), 7.48 (m, 6H), 7.58 (m, 3H), 7.66 ppm
(m, 6H); 31P NMR (CDCl3): d=19.9 ppm (s); elemental analysis calcd
(%) for C23H18F3O3: C 63.95, H 4.21; found: C 64.19, H 4.22.
calcd: 339.89; found: 339.17. (E)-1: 1H NMR (CDCl3): d=6.89 ppm (s);
13C NMR (CDCl3): d=111.18 (s, C=C), 119.82 (q, 1JC,F =269.9 Hz; CF3,),
124.36 (q, 2JC,F =37.5 Hz; CCF3), 124.59 ppm (q, 3JC,F =5.1 Hz; CH);
19F NMR (CDCl3): d=À60.92 ppm (s); elemental analysis calcd (%) for
C8H2F6S4: C 28.23, H 0.59; found: C 28.30, H 0.62; MS: calcd: 339.89;
found: 339.17.
4-Carbomethoxy-5-trifluoromethyl-1,3-dithiol-2-one (9): Compound
7
(5.22 g, 0.02 mol) was dissolved in a chloroform/acetic acid mixture (3:1,
800 mL). Mercuric acetate (12.89 g, 0.04 mol) was added and the mixture
was stirred under nitrogen atmosphere for 2.5 h. The white precipitate
was filtered through Celite and was washed with dichloromethane. The
filtrate was washed with a saturated NaHCO3 solution and then with
water. The yellow precipitate that appeared during the washing was not
added to the organic phase. After drying over magnesium sulfate, sol-
vents were evaporated to give compound 9 as a salmon-colored oil
(4.53 g, 91%). 1H NMR (CDCl3): d=3.92 ppm (s, 3H); 13C NMR
(CDCl3): d=53.86 (s, CH3), 118.91 (q, 1JC,F =273.5 Hz; CF3), 128.83 (q,
3JC,F =3 Hz; C-(CO2Me)), 130.03 (q, 2JC,F =38.4 Hz; C-CF3), 157.31 (s,
C(=O)OMe), 184.41 ppm (s, C=O); 19F NMR (CDCl3): d=À54.88 ppm
(s); elemental analysis calcd (%) for C6H3F3O3S2: C 29.51, H 1.24; found:
C 29.74, H 1.33.
Methyl 4,4,4-trifluorotetrolate (6): Compound 5 (193 g, 0.45 mol) was py-
rolyzed by slowly warming under reduced-pressure (1 mbar) up to 160–
1658C when it started to melt. The distillate was condensed in a Dewar
condenser cooled with liquid N2 gas. The pale yellow liquid was dried
over magnesium sulfate and was distilled at 398C under 208 mbar pres-
sure to give the acetylenic derivative as a colorless liquid (106.19 g;
80.5%). Owing to the instability of the compound, it was not stored but
was directly used in the cycloaddition reaction with ethylenetrithiocar-
bonate to afford compound 6.
1H NMR (CDCl3): d=3.87 (s, 3H); 13C NMR (CDCl3): d=54.3 (s, CH3),
71.04 (q, 2JC,F =54.7 Hz; C-CF3), 75.97 (q, 3JC,F =6.41 Hz; CCO2Me),
1
114.12 (q, JC,F =260.3 Hz; CF3), 151.83 ppm (s, C=O); 19F NMR (CDCl3):
d=À52.80 ppm (s, CF3).
4,5-Ethylenedithio-4’-carbomethoxy-5’-trifluoromethyltetrathiafulvalene
(11): Compounds 9 (0.5 g, 1.14 mmol) and 10 (0.46 g, 2.05 mmol) were
slowly heated up to 1108C in trimethylphosphite (24 mL) under a nitro-
gen atmosphere. After 160 min at 1108C, the mixture was concentrated
to half the original volume and was cooled to 48C before filtration of the
precipitated BEDT-TTF. The filtrate was evaporated and purified by
chromatography on SiO2 and was eluted with petroleum ether/ethyl ace-
tate (3:1) to give first the mixture of Z-E diesters 8 (0.16 g, 17%) fol-
lowed by the desired compound 11, obtained as a dark-purple powder
(0.45 g, 52%). The product was recrystallized in ethanol to give com-
pound 11 as purple platelets (0.33 g, 38%); m.p. 1088C (EtOH);
1H NMR (CDCl3): d=3.31 (s, 4H), 3.85 ppm (s, 3H); 13C NMR (CDCl3):
4-Carbomethoxy-5-trifluoromethyl-1,3-dithiol-2-thione (7): Freshly pre-
pared methyl 4,4,4-trifluorotetrolate 6 (66.16 g, 0.43 mol) and ethylenetri-
thiocarbonate (59.27 g, 0.43 mol) were warmed under refluxfor 24 h
under N2 atmosphere in dry toluene (310 mL). The solvent was then
evaporated and the residue was purified by chromatography on SiO2, and
eluted with pentane/dichloromethane (4:1) to afford the yellow dithiole-
thione 7, after recrystallization from methanol (145.4 g, 74.4%); m.p.
338C (MeOH); 1H NMR (CDCl3): d=3.92 ppm (s, 3H); 13C NMR
(CDCl3): d=53.96 (s, Me), 118.07 (q, 1JC,F =275.52 H; CF3), 137 (s, C
À
(CO2Me)), 136.98 (q, 2JC,F =39.23 Hz; C CF3), 156.17 (s, C=O),
À
204.79 ppm (s, C=S); 19F NMR (CDCl3): d=À55.66 ppm (s, CF3); ele-
mental analysis calcd (%) for C6H3F3O2S3: C 27.43, H 1.07; found: C
27.68, H 1.16; HRMS: m/z: calcd: 259.9247; found: 259.9241.
d=30.197 (s, CH2CH2), 53.46 (s, Me), 112.19 (s), 113.94 (s), 114.17 (s),
2
119.36 (q, 1JC,F =274.51 Hz; CF3), 130.52 (s, C-CO2Me), 132.58 (q, JC,F
=
(Z-E)-Bis-trifluoromethyl-bis-carbomethoxytetrathiafulvalene ((E)-8 and
(Z)-8): Compound 7 (0.81 g, 3.15 mmol) was dissolved in dry toluene
(15 mL) and treated with 2.25 equivalents of trimethylphosphite
(0.84 mL, 7.1 mmol). The mixture was refluxed under N2 gas for 2 h. The
solvent was then evaporated and the solid residue triturated in hot meth-
anol (25 mL). After cooling and filtration, a red-purple powder (0.24 g)
was obtained. This sample showed two spots with TLC (petroleum ether/
dichloromethane 2:1) attributed to the two isomers. The filtrate was puri-
fied by chromatography on SiO2 and was eluted with petroleum ether/di-
chloromethane (2:1) to give 0.23 g of the two isomers. The global yield of
the Z-E mixture was 0.57 g (65%). Elemental analysis calcd (%) for
C12H6F6O4S4: C 31.58, H 1.32; found: C 31.76, H 1.31; MS: m/z: calcd:
455.905; found: 455.97. The two isomers were separated after several re-
crystallizations in methanol to give the pure (TLC) Z and E isomers.
(Z)-8: m.p. 102–1048C; 1H NMR (CDCl3): d=3.89 ppm (s, 6H);
13C NMR (CDCl3): d=53.53 (s), 108.49 (s), 119.19 (q, 1JC,F =273 Hz),
130.89 (s), 132.51 (q, 2J=38 Hz), 157.61 ppm (s); 19F NMR (CDCl3): d=
À56.11 ppm (s). (E)-8: m.p. 188–1958C; 1H NMR (CDCl3): d=3.89 ppm
(s, 6H); 13C NMR (CDCl3): d=53.59 (s), 108.54 (s), 119.203 ppm (q,
1JC,F =275 Hz), 130.7 (s), 132.63 (q, 2J=38.60 Hz), 157.59 ppm (s);
19F NMR (CDCl3): d=À56.11 ppm (s).
76.46 Hz; C-CF3), 157.89 ppm (s, COOMe); 19F NMR (CDCl3): d=
À56.3 ppm (s); elemental analysis calcd for C11H7F3O2S6: C 31.41, H
1.68; found: C 31.57, H 1.65; MS: m/z: calcd: 419.87; found: 419.93.
4,5-Ethylenedithio-4’-trifluoromethyltetrathiafulvalene (2): Compound 11
(0.48 g, 1.14 mmol) and LiBr (1.2 g) were heated at 808C for 7 h in DMF
(25 mL) under nitrogen. The mixture was then poured into distilled
water (100 mL) and the orange precipitate was filtered off. After drying,
the product was recrystallized in isopropanol to give compound 2 (0.31 g,
75.6%) as orange flakes; m.p. 109.68C (iPrOH); 1H NMR (CDCl3): d=
3.3 (s, 4H), 6.86 ppm (q, 4JH,F =1.41 Hz, 1H); 13C NMR (CDCl3): d=
30.12 (s, CH2CH2), 109.848 (s), 113.43 (s), 113.89 (s), 114.08 (s), 119.9 (q,
1JC,F =271.37 Hz; CF3), 123.99 (q, 2JC,F =37.47 Hz; C-CF3), 124.621 ppm
(t, 1JC,H =5.28 Hz; =C-H); 19F NMR (CDCl3): d=À60.3 ppm (s); elemen-
tal analysis calcd (%) for C6H5F3S6: C 29.82, H 1.39; found: C 29.66, H
1.29; HRMS: m/z: calcd: 361.86; found: 361.1.
Bis(trifluoromethyl)ethylendithiotetrathiafulvalene (3): 4,5-Bis(trifluoro-
methyl)-1,3-dithiole-2-thione 12 (0.43 g, 1.67 mmol) and compound 10
(0.41 g, 1.83 mmol) were heated in trimethylphosphite (15 mL) under a
nitrogen atmosphere. After 2 h at 1108C, the mixture was evaporated
and toluene (15 mL) was added. The suspension was triturated and fil-
tered to give BEDT-TTF (0.1 g, 14.5%). The filtrate was evaporated and
purified by chromatography on silica gel and was eluted with petroleum
ether/dichloromethane (3:1) to give first the orange tetrakis(trifluorome-
thyl)tetrathiafulvalene (0.17 g, 22%) followed by the desired product 3
(Z- and E)-Bis(trifluoromethyl)tetrathiafulvalene ((E)-1 and( Z)-1): Typ-
ical procedure: pure (TLC) (Z)-8 or (E)-8 isomers (0.3 g, 0.66 mmol) and
LiBr (1 g) were dissolved in DMF (10 mL). The mixture was heated at
808C for 6 h. After cooling, water (100 mL) was added to precipitate the
product. After filtration and drying, the crude product was recrystallized
in an ethyl alcohol/water mixture to give orange needles. The filtrate was
purified by chromatography on SiO2 and eluted with pentane/dichloro-
methane (8:1). The global yield was 0.14 g (63%) for the (E)-1 isomer
1
(0.11 g, 16%); m.p. 168.78C (hexane); H NMR (CDCl3): d=3.31 ppm (s,
4H); 13C NMR (CDCl3): d=30.20 (s, CH2-CH2), 105.62 (s), 114.71 (s),
114.63 (s), 118.9 (q, 1JC,F =275.64 Hz; CF3), 128.443 ppm (q, 2JC,F =42 Hz;
C-CF3); 19F NMR (CDCl3): d=À56.82 ppm (s); elemental analysis calcd
(%) for C10H4F6S6: C 27.90, H 0.94; found: C 27.83, H 0.76; HRMS: m/z:
calcd: 429.85; found: 429.84.
and 0.19 g (88%) for isomer (Z)-1. (Z)-1: 1H NMR (CDCl3): d=
1
6.89 ppm (s); 13C NMR (CDCl3): d=111.27 (s, C=C), 119.82 (q, JC,F
=
3
269.9 Hz; CF3,), 124.23 (q, 2JC,F =38.4 Hz; CCF3), 124.78 ppm (q, JC,F
=
Cyclization product (13): Orange crystals of compound (E)-1 that were
allowed to stand in the sunlight for two weeks at room temperature
slowly lost their crystallinity and turned yellow. The starting TTF deriva-
5.8 Hz; CH); 19F NMR (CDCl3): d=À60.92 ppm (s); elemental analysis
calcd (%) for C8H2F6S4: C 28.23, H 0.59; found: C 28.72, H 0.64; MS:
Chem. Eur. J. 2006, 12, 2994 – 3005
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3003

O. Jeannin and M. FourmiguØ
tive (E)-1 was eliminated by washing with pentane. Recrystallization in
EtOH afforded derivative (EE)-13 as elongated thin plates together with
in Table 4. Structures were solved by direct methods (SHELXS-97) and
refined (SHELXL-97) by full-matrixleast-squares methods. Absorption
corrections were applied for all structures. Hydrogen atoms were intro-
duced at calculated positions (riding model), were included in structure
factor calculations, and not refined. CCDC 282792–282797 contain the
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
1
a microcrystalline yellow powder. 19F and H NMR measurements on this
mixture revealed the presence of about 20% of product (ZZ)-13.
In a second experiment, single crystals of derivative (E)-1 were irradiated
for two days in a sealed tube with a 400-W Hg-lamp with regular manual
shaking of the sample. The product was purified by silica-gel chromatog-
raphy (first column with CH2Cl2 elution, second column with CS2 elution)
but afforded a mixture of compounds (EE)-13 and (ZZ)-13 in a 30:70
ratio according to 19F NMR. Recrystallization of this mixture in CH3CN
yielded yellow plates of compound (ZE)-13 according to the X-ray dif-
fraction experiment. Concentration of the mother liquors afforded a few
crystals, identified by X-ray diffraction as compound (ZZ)-13. Mother
liquors still contained 52% of compound (ZE)-13, 40% of compound
(EE)-13, and 8% of compound (ZZ)-13c.
Electrochemistry: Cyclic voltammetry was performed in dry CH2Cl2 with
0.1m (nBu4N)(PF6) at a scan rate of 100 mVsÀ1, with an Ag/AgNO3 refer-
ence electrode. The ferricinium/ferrocene system was used as internal ref-
erence.
[1] G. A. Jeffrey, W. Saenger, W. Hydrogen Bonding in Biological
Structures, Springer, Berlin, 1991.
NMR data in CDCl3: Derivative (EE)-13: 1H NMR (CDCl3): d=5.14 (s,
19
[2] a) J. P. M. Lommerse, A. J. Stone, R. Taylor, F. H. Allen, J. Am.
Chem. Soc. 1996, 118, 3108; b) P. Metrangolo, G. Resnati, Chem.
Eur. J. 2001, 7, 2511; c) R. S. Walsh, C. W. Padgett, P. Metrangolo, G.
Resnati, T. W. Hanks, W. T. Pennington, Cryst. Growth Des. 2001, 1,
165.
[3] a) G. R. Desiraju, Angew. Chem. 1995, 107, 2505; Angew. Chem. Int.
Ed. Engl. 1995, 34, 2311; b) G. R. Desiraju, Crystal Engineering: The
Design of Organic Solids, Elsevier, Amsterdam, 1989; c) J. L.
Atwood, J. M. Lehn, J. E. D. Davies, D. D. MacNicol, F. Vogtle,
Comprehensive Supramolecular Chemistry, Pergamon Press, 1996.
[4] For a recent review, see: C. Tschierske, J. Mater. Chem. 2001, 11,
2647.
À À
À
À
C C H), 6.7 ppm (s, C=C H); F NMR (CDCl3): d=À60.64 (s, C=C
CF3), À73.26 ppm (s, C C CF3). Derivative (ZE)-13: 19F NMR (CDCl3):
À À
À
À
À À
d=À59.88 (s, C=C CF3), À61.40 (s, C=C CF3), À73.48 (s, C C CF3),
À73.55 ppm (s, C C CF3). Derivative (ZZ)-13: 1H NMR (CDCl3): d=
À À
5.14 (s, C C H), 6.81 ppm (s, C=C H); 19F NMR (CDCl3): d=À61.25 (s,
À À
À
À
À À
C=C CF3); À73.22 ppm (s, C C CF3).
NMR data in [D6]acetone: Derivative (EE)-13: 1H NMR ([D6]acetone):
d=5.8 (s, C C H); 7.48 ppm (q, 4JF,H =1.36 Hz; C=C H); 19F NMR
À À
À
À
À À
([D6]acetone): d=À61.27 (s, C=C CF3), À74.02 ppm (s, C C CF3). De-
1
À À
rivative (ZE)-13: H NMR ([D6]acetone): d=5.786 (s, 1H; C C H),
À À
À
À
5.795 (s, 1H; C C H), 7.39 (q, 1H; C=C H), 7.47 ppm (q, 1H; C=C
19
À
H); F NMR ([D6]acetone): d=À60.56 (s, 3F; C=C CF3), À62.03 (s, 3F;
[5] W. Haase, N. A. Athanassopoulou, Struct. Bonding (Berlin) 1999,
94, 139.
À
À À
À À
C=C CF3), À74.05 (s, 3F; C C CF3), À74.08 ppm (s, 3F; C C CF3).
Derivative (ZZ)-13: 1H NMR ([D6]acetone): d=5.82 (s, C C H),
À À
[6] a) P. Kromm, H. Allouchi, J. P. Bideau, M. Cotrait, Mol. Cryst. Liq.
Cryst. 1994, 257, 9; b) P. Kromm, H. Allouchi, J. P. Bideau, M. Co-
trait, H. T. Nguyen, Acta Crystallogr. Sect. C 1995, 51, 1229.
[7] X. H. Cheng, S. Diele, C. Tschierske, Angew. Chem. 2000, 112, 605;
Angew. Chem. Int. Ed. 2000, 39, 592.
19
À
À
7.47 ppm (q, C=C H); F NMR ([D6]acetone): d=À61.7 (s; C=C CF3),
À À
À73.86 ppm (s, C C CF3); MS: m/z: calcd: 679.79; found: 679.74.
Crystal structure determinations: Crystals were mounted on top of a thin
glass fiber. Data were collected on
a Stoe Image-Plate Diffraction
System (IPDS) or an Enraf Nonius Kappa CCD with graphite-monochro-
mated MoKa radiation (l=0.71073 Š). The crystal data are summarized
[8] I. W. Hamley, The Physics of Block Copolymers, Oxford University
Press, Oxford, 1998.
Table 4. Crystallographic data.
Compound
2
3
(E)-1
(Z)-1
(EE)-13
(ZE)-13
formula
fw
C9H5F3S6
362.49
C10H4F6S6
430.53
C8H2F6S4
340.34
C8H2F6S4
340.34
C16H4F12S8
680.67
C16H4F12S8
680.67
cryst syst
space group
a [Š]
b [Š]
c [Š]
monoclinic
P21/c
9.8622(11)
8.4530(7)
16.0641(19)
90
102.82(1)
90
1305.8(2)
4
monoclinic
P21/n
12.7780(10)
8.1930(19)
27.946(5)
90
93.330(10)
90
2920.7(9)
8
triclinic
P1
monoclinic
I2/a
12.730(3)
7.7000(15)
23.588(5)
90
101.60(3)
90
2264.9(8)
8
orthorhombic
P2221
6.7094(5)
11.6717(9)
14.7671(10)
90
monoclinic
P2/n
18.4374(10)
6.6670(2)
18.8335(16)
90
101.221(7)
90
2270.8(2)
4
¯
6.3953(10)
7.7454(13)
11.956(2)
97.81(2)
97.399(19)
100.456(19)
569.82(16)
2
a [8]
b [8]
90
90
g [8]
V [Š
À3
]
1156.41(15)
2
1.955
Z
1calcd [MgmÀ3
]
1.844
1.958
1.984
1.996
1.991
diffractometer
Stoe-IPDS
150(2)
1.058
Kappa CCD
150(2)
0.991
Stoe-IPDS
150(2)
0.888
Stoe-IPDS
150(2)
0.894
Kappa CCD
293(2)
0.875
Kappa CCD
293(2)
0.891
T[K]
m [mmÀ1
]
q-range [8]
2.12–25.86
9837
2520
2.59–27.50
46038
6590
1.74–25.86
5383
2003
1.76–25.65
10213
2047
2.22–27.50
8945
2529
2.20–27.0
74490
4954
measd reflns
independent reflns
Rint
0.0406
0.0614
0.0425
0.0359
0.0772
0.0624
I>2s(I) refls
abs corr
Tmax,Tmin
2177
4815
1713
1716
1976
3569
multi-scan
0.839, 0.661
167
0.030
0.0761
multi-scan
1.0, 0.727
416
0.0452
0.1104
multi-scan
1.14, 0.773
171
0.0335
0.0918
multi-scan
0.746, 0.643
225
0.0339
0.1049
multi-scan
1.174, 0.778
190
0.0476
0.1639
multi-scan
1.0, 0.8994
379
0.0392
0.1248
refined parameters
R(F), I>2s(I)
wR(F2), all
À3
D1 [eŠ
]
+0.48, À0.27
+0.74, À0.43
+0.33, À0.35
+0.37, À0.37
+0.72, À0.89
+0.51, À0.4
3004
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 2994 – 3005

Fluorine Segregation in Crystalline Materials
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Received: September 1, 2005
Revised: November 16, 2005
Published online: January 27, 2006
Chem. Eur. J. 2006, 12, 2994 – 3005
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3005