Sb···S and S···S interactions in the first neutral and oxidized diphenylstibino (Ph2Sb-) derivatives of the redox active tetrathiafulvalene (TTF) core

Article abstract of DOI:10.1039/b205594p

The preparation of the monostibines o-Me₂TTF-SbPh₂ (1) and Me₃TTF-SbPh₂ (2), the ortho distibine o-Me₂TTF-(SbPh₂)₂ (3) and the tetrastibine TTF(SbPh₂)₄ (4) is described together with their electrochemical properties and the X-ray crystal structures of the neutral 1 and 3. In the former, one intermolecular Sb...S contact completes the co-ordination sphere of the antimony atom while in 3 the TTF moieties stack on top of each other with no evidence for Sb...S interactions. Electrocrystallisation of 2 in the presence of [n-Bu₄N]₂[Mo₆O₁₉] affords a 2:1 salt, [2]₂[Mo₆O₁₉] where the 2^+· cation radical species are associated into diamagnetic [2]₂²⁺ dyads through a strong HOMO...HOMO overlap interaction, separated from each other by the [Mo₆O₁₉]^2- counter ions.

Full text of DOI:10.1039/b205594p

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Sb ؒ ؒ ؒ S and S ؒ ؒ ؒ S interactions in the first neutral and oxidized
diphenylstibino (Ph2Sb–) derivatives of the redox active
tetrathiafulvalene (TTF) core
Srinivasan S. Kuduva, Narcis Avarvari and Marc Fourmigué*
“Chimie Inorganique, Matériaux et Interfaces” (CIMI), FRE 2447 CNRS-Université d’Angers,
UFR Sciences, Bât. K, 2 bd Lavoisier, 49045 Angers, France.
E-mail: marc.fourmigue@univ-angers.fr
Received 10th June 2002, Accepted 26th July 2002
First published as an Advance Article on the web 5th September 2002
The preparation of the monostibines o-Me2TTF–SbPh2 (1) and Me3TTF–SbPh2 (2), the ortho distibine o-Me2TTF-
(SbPh2)2 (3) and the tetrastibine TTF(SbPh2)4 (4) is described together with their electrochemical properties and the
X-ray crystal structures of the neutral 1 and 3. In the former, one intermolecular Sb ؒ ؒ ؒ S contact completes the
co-ordination sphere of the antimony atom while in 3 the TTF moieties stack on top of each other with no evidence
for Sb ؒ ؒ ؒ S interactions. Electrocrystallisation of 2 in the presence of [n-Bu4N]2[Mo6O19] affords a 2 : 1 salt,
[2]2[Mo6O19] where the 2ϩ cation radical species are associated into diamagnetic [2]22ϩdyads through a strong
ؒ
HOMO ؒ ؒ ؒ HOMO overlap interaction, separated from each other by the [Mo6O19]2Ϫ counter ions.
Introduction
Results and discussion
The preparation of several tertiary phosphines and o-diphos-
phines bearing a redox active group such as the tetrathia-
fulvalenyl moiety1,2 has recently opened new perspectives
toward the elaboration of hybrid systems associating open-
shell species of organic and inorganic character. For example
the chelating o-Me2TTF(PPh2)2 or TTF(PPh2)4 have been
employed3–5 in various metal complexes where both the TTF
π-redox core and the metal fragment are susceptible to oxid-
ation to open-shell species. On the other hand, attempts to
electro-oxidize the free phosphines in the presence of various
anions invariably led in our hands to the formation of phos-
phine oxides, probably upon reaction of the formed cation
Syntheses
1–4 were prepared as previously described for the phosphorus
analogues from the reaction of the lithium derivative of the
chosen tetrathiafulvalene with ClSbPh2 as illustrated in Scheme
1. The four stibines are air stable and were obtained in crystal-
radical with traces of water. A salt of [Me3TTF–P(O)PPh2]ϩ
ؒ
was even isolated in crystalline form from the electrocrystallis-
ation of the Me3TTF–PPh2 phosphine.6 In order to circumvent
this drawback, we postulated that the analogous tetrathiafulva-
lenyl stibines, where Sb substitutes for P in the above described
phosphines, would be adequate candidates for the elaboration
of stable cation radical salts. Indeed, it is well established in
Group 15 chemistry that SbIII derivatives such as stibines are
harder to oxidize to the SbV stibine oxides than the correspond-
ing phosphines. Furthermore, the larger spatial extension of
the antimony lone pair offers the possibility for electronic
delocalisation through intermolecular Sb ؒ ؒ ؒ Sb and Sb ؒ ؒ ؒ S
interactions.7 We describe here the synthesis of several tetrathia-
fulvalenyl stibines, investigate their electrochemical properties
by comparison with the phosphorus analogues and describe the
X-ray crystal structures of several neutral donor molecules as
well as the first cation radical salt of diphenylstibino-trimethyl-
Scheme 1 Preparation of 1–4.
line form (see below). In the mass spectra, loss of a diphenyl-
stibino (–SbPh2) fragment was identified only in the o-distibines
3 and 4. Cyclic voltammetry experiments show the systematic
presence of two reversible, one-electron waves associated with
the oxidation of the TTF redox core to the mono- and di-cation
respectively (Table 1). Comparison with the analogous phos-
phines as well as with the unsubstituted TTFs demonstrate the
electron rich character of the diphenylstibino substituent whose
influence on the redox properties is comparable or even better
to that of the PPh2 moiety. Indeed, we observed that the tetra-
substituted TTF(SbPh2)4, 4, even oxidises at a lower potential
than 1 or 2. Accordingly, these new donor molecules are
excellent candidates for electrocrystallisation experiments and
2Ϫ
tetrathiafulvalene Me3TTF–SbPh2 with the dianionic Mo6O19
counter ion.
2Ϫ
first attempts performed with 2 in the presence of Mo6O19
afforded a 2 : 1 salt, formulated as [2]2[Mo6O19].
3686
J. Chem. Soc., Dalton Trans., 2002, 3686–3690
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b205594p

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Table 1 Electrochemical data for the newly prepared donor molecules
molecule by translation along the z axis. As a consequence, the
and the analogous phosphines
geometry around the Sb atom, taking into account its lone pair,
can be considered as intermediate between a trigonal bipyramid
and square pyramid depending on the location of the lone
pair.
The neutral ortho distibine 3 crystallises in the monoclinic
system, space group C2/c with one molecule in a general pos-
ition in the unit cell (Fig. 2). Bond lengths and distances within
Donor molecule
E1/2 a/V
E1/2 b/V
Ref.
1
0.35
0.34
0.305
0.28
0.32
0.23
0.27
0.33
0.90
0.87
0.83
0.76
0.70
0.74
0.81
0.73
This work
This work
This work
This work
13
6
5
2
3
4
b
o-Me2TTF–PPh2
Me3TTF–PPh2
o-Me2TTF(PPh2)2
a
a
TTF(PPh2)4
5
a In CH2Cl2 vs. SCE. b In CH3CN vs. SCE.
Analysis of the structural organisation
Neutral 1 crystallises in the monoclinic system, space group
P21/c with one molecule in a general position in the unit cell
(Fig. 1). Bond lengths within the TTF core are in the usual
Fig. 2 ORTEP view of the distibine 3 showing the relative orientation
of the two SbPh2 groups.
the TTF core and around the antimony atom are in the
expected range (Table 2). Of particular interest is the relative
orientation of the two diphenyl stibino groups. As shown in
Fig. 2, the lone pairs of the two Sb atoms point towards rather
than away from each other and are therefore essentially local-
ised within the TTF mean plane. This orientation differs from
what is observed in the only other structurally characterised
o-distibine, i.e. 2,3-bis(diphenylstibino)maleic anhydride,10
where the lone pair of one of the SbPh2 groups are oriented
almost perpendicular to the maleic anhydride mean plane. In
the solid state (Fig. 3), the molecules of the ortho distibine 3 are
organised into stacks along the b axis where the TTF moiety fits
in between the two SbPh2 arms of the molecules with the short-
est Sb ؒ ؒ ؒ S intermolecular contacts observed at 4.04–4.08 Å.
It is hoped that such an organisation could be maintained in
cation radical salts of 3 since it would allow for a effective
electronic delocalisation through the HOMO ؒ ؒ ؒ HOMO over-
lap of the TTF moieties. However, no such salts with 3 could be
isolated up to now; only with the monostibine 2, i.e. Me3TTF–
SbPPh2, as described below.
Fig. 1 The coordination sphere of the antimony atom in 1 (ORTEP18
drawing with thermal ellipsoids at 50% probability).
range for neutral TTF moieties (Table 2). Sb–C distances
[2.143(5), 2.150(4), 2.161(4) Å] and C–Sb–C angles [96.01(16),
94.61(16), 93.95(15)Њ] also compare with those described for the
tertiary Ph3Sb stibine for example [av. Sb–C: 2.155(9), C–Sb–C:
95.1(3)–98.0(3)Њ].8 In the solid state (Fig. 1), the antimony
atom completes its coordination sphere through one Sb ؒ ؒ ؒ S
contact at 4.01(5) Å, slightly above the sum of the van der
Waals radii9 which amounts to 1.80 (S) ϩ 2.12 (Sb) = 3.92 Å,
and involving one sulfur atom pertaining to a neighbouring
The electrocrystallisation of 2 in the presence of the
tetrabutyl ammonium salt of the Linquist anion [Mo6O19]2Ϫ
,
[n-Bu4N]2[Mo6O19], afforded indeed a 2 : 1 salt, formulated as
[2]2[Mo6O19]. It crystallises in the monoclinic system, space
group C2/c with one [Mo6O19]2Ϫ anion located on an inversion
centre while the donor molecule is in a general position in the
unit cell (Fig. 4). Bond distances within the TTF core exhibit the
Table 2 Geometrical characteristics of the TTF core and the Sb environment in the neutral and oxidised donor molecules (The range of values is
given together with the averaged value in italics)
C᎐C bond (a)/Å
᎐
C–S bonds (b)/Å
Sb–C bonds/Å
C–Sb–C/Њ
1
1.337(5)
1.368(11)
1.390(6)
1.749(4)–1.767(4)
1.757
1.749(8)–1.761(8)
1.754
1.707(5)–1.727(5)
1.716
2.143(5)–2.161(4)
2.152
2.116(9)–2.142(9)
2.130
2.148(5)–2.177(5)
2.159
93.9(1)–96.0(1)
94.8
93.3(3)–99.3(3)
96.4
93.8(2)–99.0(2)
95.5
3
2ϩ
a
ؒ
a In [2]2[Mo6O19].
J. Chem. Soc., Dalton Trans., 2002, 3686–3690
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Fig. 5 A view of one of the b,c planes in [2]2[Mo6O19] showing the
facet-to-face arrangement of the organic dyads.
by the large calculated βHOMO ؒ ؒ ؒ HOMO interaction energy within
the dyad, found here at 1.15 eV. As a consequence the two
radicals are associated in the bonding combination of the two
2ϩ
HOMO to afford isolated diamagnetic [2]2 dyads, separated
Fig. 3 The stacking of the neutral distibine 3 along the b axis.
from each other by the [Mo6O19]2Ϫ dianions. Of particular note
is the absence of short Sb ؒ ؒ ؒ Sb or Sb ؒ ؒ ؒ S intermolecular
distances in [2]2[Mo6O19] where the SbPh2 moieties fill the space
inbetween the hybrid slabs identified above; the behaviour is
dominated here by the S ؒ ؒ ؒ S overlap interactions of the open-
shell species. It should be stressed that the isolation of this
cation radical salt fulfils our expectations about the increased
stability of stibines relative to phosphines toward the one-
electron oxidation of the TTF core. In order to decrease the
steric demand of the phenyl substituents, we are now consider-
ing the preparation of monostibines incorporating two or three
TTF moieties.
Experimental
The solvent Et2O was freshly distilled under N2 over sodium
and benzophenone before use. SbClPh2,11 TTF,12 o-DMTTF13
and Me3TTF14 were prepared according to published pro-
cedures. Melting points are uncorrected. 1HNMR spectra were
recorded in CDCl3, containing TMS as internal standard on a
Bruker Avance DRX 500 MHz spectrometer. Mass spectra
were obtained by chemical ionization on a Bruker Biflex III
mass spectrometer. Elemental analyses were performed at the
Institut de Chimie des Substances Naturelles, CNRS, Gif-sur-
Yvette, France.
Synthesis
3-Diphenylstibino-3Ј,4Ј-dimethyltetrathiafulvalene 1. To
a
solution of o-DMTTF (0.465 g, 2 mmol) in dry Et2O (40 mL)
was added successively at Ϫ78 ЊC diisopropylamine (0.31 mL,
2.2 mmol) and n-BuLi (2 M solution in hexane, 1.1 mL,
2.2 mmol). A yellow precipitate formed immediately. After
stirring at Ϫ78 ЊC for 2 h, the yellow suspension was treated
dropwise with chloro(diphenyl)antimony (0.654 g, 2.1 mmol)
in dry Et2O. The resultant solution was slowly warmed to room
temperature and stirred overnight. The suspension was filtered
through Celite® and silica gel (toluene as eluant) and the
solvent was removed. The residue containing 1 and unreacted
o-Me2TTF was purified by subliming o-Me2TTF at 75 ЊC.
Recrystallisation of the residue from Et2O afforded o-Me2TTF–
SbPh2 as orange crystals (0.556 g, 55%), mp 127–128 ЊC [Calc.
(found) for C20H17S4Sb: C, 47.67 (47.35); H, 3.37 (3.38); S, 25.93
(25.28)%]; δH (CDCl3, TMS) 1.90 (s, 6H, Me), 6.24 (s, 1H,
TTF–H), 7.37 (m, 6H, Ph), 7.53 (m, 4H, Ph); MS-CI m/z 174
(100), 506 (Mϩ, 81).
Fig. 4 A view of the unit cell of [2]2[Mo6O19] showing the mixed
organic–inorganic (b,c) slabs. The detail of one of those slabs is shown
in Fig. 5.
usual C᎐C lengthening and C–S shortening by comparison with
᎐
the neutral 1 (Table 2), a signature of the cation radical state of
the donor molecule. In the solid, the donor molecules are
associated into inversion-centred dyads with a very short inter-
planar distance observed at 3.363(1) Å. Those dyads alternate
with the inorganic moieties in the bc planes, as shown in Fig. 5
where one of those hybrid slabs is represented. The short inter-
planar distance and the almost eclipsed interaction within the
dyads are the signature of a strong bonding interaction between
the two [Me3TTF–SbPh2]ϩ radical species, as also confirmed
ؒ
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J. Chem. Soc., Dalton Trans., 2002, 3686–3690

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Table 3 Crystallographic data
Me2TTF–SbPh2, 1
Me2TTF(SbPh2)2, 3
[2]2[Mo6O19]
Formula
Formula mass
Crystal system
Space group
C20H17S4Sb
507.33
Monoclinic
P21/c
C32H26S4Sb2
782.27
Monoclinic
C2/c
C42H38Mo6O19S8Sb2
1922.34
Monoclinic
C2/c
a/Å
b/Å
c/Å
7.7888(16)
38.875(8)
6.8578(14)
92.87(3)
2073.9(7)
293(2)
40.546(4)
6.3151(4)
24.613(2)
99.526(11)
6215.4(9)
293(2)
24.630(5)
13.868(3)
19.166(4)
115.83(3)
5892(2)
293(2)
β/Њ
V/Å3
T /K
Z
4
8
4
µ/mmϪ1
1.734
2.028
2.486
Data collected
Independent data
Rint
18941
4612
0.0558
2981
226
0.0339
0.0867
25617
6151
0.1607
2466
343
0.0497
0.0891
30703
5503
0.0652
3663
349
0.0337
0.0745
Observed data [I > 2σ(I)]
Parameters refined
R(F)obs
wR(F 2)all
3-Diphenylstibino-4,3Ј,4Ј-trimethyltetrathiafulvalene 2. To a
solution of Me3TTF (0.493 g, 2 mmol) in dry Et2O (40 mL) was
added successively at Ϫ78 ЊC, diisopropylamine (0.31 mL, 2.2
mmol) and n-BuLi (2 M solution in hexane, 1.1 mL, 2.2 mmol).
A yellow precipitate formed immediately. After stirring at Ϫ78
ЊC for 2 h, the yellow suspension was treated dropwise with
chloro(diphenyl)antimony (0.654 g, 2.1 mmol) in dry Et2O. The
resultant solution was slowly warmed to room temperature and
stirred overnight. The suspension was filtered through Celite®
and silica gel (toluene as eluant) and the solvent was evapor-
ated. Recrystallisation from Et2O afforded 2 as orange crystals
(0.6 g, 59%), mp 140–143 ЊC [Calc. (found) for C21H19S4Sb: C,
48.54 (48.38); H, 3.73 (3.67); S, 24.41 (24.60)%]; δH (CDCl3,
TMS) 1.90 (bs, 6H, o-Me2), 2.19 (s, 3H, Me), 7.37 (m, 6H, Ph),
7.53 (m, 4H, Ph); MS-CI m/z 520 (Mϩ).
47.72 (49.73); H, 3.48 (3.09); S, 10.11 (9.83)%]; δH (CDCl3,
TMS) 7.32 (m, 3H, Ph), 7.47 (m, 2H, Ph); MS-CI m/z 420 (100),
721, 1028 (Mϩ Ϫ SbPh2), 1304 (Mϩ).
Electrochemistry
Cyclic voltammetry experiments were performed in CH2Cl2
containing 0.1 M n-Bu4NPF6 as electrolyte at a scan rate of
100 mV sϪ1 with an Agϩ/AgCl reference electrode, platinum
working and counter electrodes. Electrocrystallisation experi-
ments were performed in two-compartment cells with Pt elec-
trodes (length = 2 cm, diameter = 1 mm) at 25 ЊC with a current
of 1 µA. The electrolyte, (n-Bu4N)2(Mo6O19), was prepared
according to published procedures15 and recrystallised before
use. Solvents were dried over activated Al2O3 and degassed.
X-Ray crystallography
3,4-Bis(diphenylstibino)-3Ј,4Ј-dimethyltetrathiafulvalene 3. To
a solution of o-Me2TTF (0.697 g, 3 mmol) in dry Et2O (100
mL) was added successively at Ϫ78 ЊC, diisopropylamine
(0.9 mL, 6.2 mmol) and n-BuLi (2 M solution in hexane,
3.1 mL, 6.2 mmol). A yellow precipitate formed immediately.
After stirring at Ϫ78 ЊC for 1 h and at 25 ЊC for 30 min, the
yellow suspension was treated dropwise with chloro(diphenyl)-
antimony (1.931 g, 6.2 mmol) in dry Et2O at Ϫ78 ЊC. The
resultant solution was slowly warmed to room temperature and
stirred overnight. The suspension was filtered and the solid por-
tion was washed twice with ether and the product was obtained
by washing the solid with CH2Cl2. Recrystallisation from Et2O
afforded 3 (1.25 g, 53.3%), mp 217–220 ЊC [Calc. (found) for
C32H26S4Sb2: C, 48.61 (49.13); H, 3.36 (3.35); S, 16.24 (16.39)%];
δH (CD2Cl2, TMS) 1.88 (bs, 6H, Me), 7.36–7.39 (m, 12H,
Ph), 7.54–7.57 (m, 8H, Ph); MS-CI m/z 506 (Mϩ Ϫ SbPh2),
782 (Mϩ).
The X-ray single crystal measurements were carried out using a
Stoe IPDS with graphite-monochromated Mo-Kα radiation
(λ = 0.71069 Å). Details about data collection and structure
refinements are given in Table 3. The structures were solved by
direct methods (SHELXS)16 and refined by full-matrix least-
squares (SHELXL).17 The hydrogen atoms were included at
idealised positions and not refined (riding model).
CCDC reference numbers 187526–187528.
See http://www.rsc.org/suppdata/dt/b2/b205594p/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
S. S. K. thanks the French Ministry for Education and Research
as well as the Ecole Normale Supérieure de Lyon for financial
support.
3,3Ј,4,4Ј-Tetrakis(diphenylstibino)tetrathiafulvalene 4. To a
solution of TTF (0.408 g, 2 mmol) in dry THF (40 mL) was
added successively at Ϫ78 ЊC, diisopropylamine (1.4 mL, 10
mmol) and n-BuLi (2 M solution in hexane, 5 mL, 10 mmol). A
yellow precipitate formed immediately. After stirring at Ϫ78 ЊC
for 3 h, the yellow suspension was treated dropwise with chloro-
(diphenyl)antimony (3.1 g, 10 mmol) in dry THF at Ϫ78 ЊC.
The resultant solution was slowly warmed to room temperature
(colour changes from orange to dark brown and to dark
orange) and stirred overnight. THF was removed under
vacuum and diethyl ether (∼100 mL) was added. The suspen-
sion was filtered over Celite® and the solid portion was washed
twice with toluene. The solvents were removed, and the solid
residue recrystallised from a Et2O–hexane mixture to afford 4
(2 g, 76.7%), mp 98–100 ЊC [Calc. (found) for C54H40S4Sb4: C,
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