Sulfur and selenium substituted spiro-biphenalenyl-boron neutral radicals

Article abstract of DOI:10.1039/c2jm16001c

We report a synthetic scheme for the preparation of alkylthio, dithio-bridged and diseleno-bridged 9-hydroxyphenalenones and associated spiro-biphenalenyl boron neutral radicals. We show that the strategy of sulfur substitution at the active positions of the phenalenyl units reduces the electrochemical disproportionation potential (ΔE_2-1 = E ₂-E₁, where E₁and E₂ are the first and second reduction potentials of corresponding cations) of the alkylthio-radicals [3,7-SR-PLY(O,O)]₂B, (R = Me, 9), (R = Et, 10) and (R = Pr, 11), but brings about a significant reduction of the ΔE _2-1 value in the case of disulfide and diselenide substitution, [3,4-S,S-PLY(O,O)]₂B (12) and [3,4-Se,Se-PLY(O,O)]₂B (13). The crystal structures of 10 and 11 show that the radicals exist as one dimensional (1-D) π-chains of superimposed phenalenyl units, and the molecular units pack more efficiently than the oxygen-substituted analog [3,7-OMe-PLY(O,O)]₂B (8). Magnetic susceptibility measurements indicate that in the solid state the radicals remain paramagnetic while there is spin-spin interaction between the molecules along the π-chains. Band structure calculations are in accordance with the magnetic measurement data and indicate the presence of interactions between the molecules. The room temperature electrical conductivities of both compounds are found to be σ_RT = 1.5 × 10^-2 S cm^-1. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2jm16001c

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2012, 22, 8245
www.rsc.org/materials
PAPER
Sulfur and selenium substituted spiro-biphenalenyl-boron neutral radicals†
*
Arindam Sarkar,‡ Sushanta K. Pal, Mikhail E. Itkis, Fook S. Tham and Robert C. Haddon
Received 18th November 2011, Accepted 21st February 2012
DOI: 10.1039/c2jm16001c
We report a synthetic scheme for the preparation of alkylthio, dithio-bridged and diseleno-bridged 9-
hydroxyphenalenones and associated spiro-biphenalenyl boron neutral radicals. We show that the
strategy of sulfur substitution at the active positions of the phenalenyl units reduces the electrochemical
½
½
½
½
disproportionation potential (DE2ꢀ1 ¼ E2 ꢀ E1 , where E1 and E2 are the first and second reduction
potentials of corresponding cations) of the alkylthio-radicals [3,7-SR-PLY(O,O)]2B, (R ¼ Me, 9), (R ¼
Et, 10) and (R ¼ Pr, 11), but brings about a significant reduction of the DE2ꢀ1 value in the case of
disulfide and diselenide substitution, [3,4-S,S-PLY(O,O)]2B (12) and [3,4-Se,Se-PLY(O,O)]2B (13). The
crystal structures of 10 and 11 show that the radicals exist as one dimensional (1-D) p-chains of
superimposed phenalenyl units, and the molecular units pack more efficiently than the oxygen-
substituted analog [3,7-OMe-PLY(O,O)]2B (8). Magnetic susceptibility measurements indicate that in
the solid state the radicals remain paramagnetic while there is spin–spin interaction between the
molecules along the p-chains. Band structure calculations are in accordance with the magnetic
measurement data and indicate the presence of interactions between the molecules. The room
temperature electrical conductivities of both compounds are found to be sRT ¼ 1.5 ꢁ 10ꢀ2 S cmꢀ1
.
the on-site Coulomb repulsion (U) which is primarily a molecular
property and measures the energy change for an ionic fluctuation
and clearly relates to the ease with which a conduction electron
can migrate through the lattice.15–18 In the pursuit of phenalenyl
(PLY)-based neutral radical molecular conductors,1 several
mono-,19–27 bis-,28–39 and tris-40,41 phenalenyl-based radicals have
been synthesized and crystallized (Scheme 1).7–9 Progress in the
single phenalenyl based molecular conductors led to the isolation
of the radical in the crystalline state by the introduction of bulky
or delocalizing substituents which prevent intermolecular s- or
p-association.19–27,42 Recently we have introduced substituents
into the bis- and tris-phenalenyl compounds with the goal of
lowering the value of U in order to improve the conductivity.39,41
The substituents have been selected in a way which would not
seriously perturb the desirable electronic properties of the PLY
nucleus or inhibit intermolecular interactions in the solid state.
The introduction of sulfur and selenium into organic molecular
conductors is well known to enhance the intermolecular inter-
actions and electronic stabilization of various oxidation states
which results in improved solid state properties.43–51
Introduction
Neutral organic radicals contain an unpaired electron just as in
classical (mono) atomic metals such as sodium, and they are
promising units for the construction of intrinsic molecular metals
and superconductors.1 Molecular conductors have been widely
explored in the areas of optoelectronics, magnetooptics and
spintronics,2–6 and phenalenyl radicals have been the subject of
a number of recent reviews.7–9 Recently phenalenyl radicals have
been shown to display phase transitions that include reversible
thermochromism that affect the conductivity, transparency and
magnetism.10,11
In organic molecular conductors, improved conductivities
usually result from the design of materials with a higher ratio of
W/U, that is, by increasing the bandwidth (W)12–14 or by reducing
Departments of Chemistry and Chemical & Environmental Engineering,
University of California, Riverside, CA 92521-0403, USA. E-mail:
haddon@ucr.edu
† Electronic supplementary information (ESI) available: Cyclic
voltammetry of 9+ TFPBꢀ, 10+ TFPBꢀ and 11+ TFPBꢀ in acetonitrile
and 12+ TFABꢀ in 1,2-dichlorobenzene reversed after 1st and 2nd
reduction and at scan rates of 5 and 10 mV Sꢀ1; differential pulse
voltammogram of 9+ TFPBꢀ in acetonitrile and 12+ TFABꢀ, 13+
TFPBꢀ in 1,2-dichlorobenzene; details of crystallographic data
collection and refinement of 100 K and 293 K structures of 10 and 11
and 100 K structure of 9+ TFPBꢀ including crystallographic CIF files.
CCDC reference numbers 867315–867319. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c2jm16001c
We have recently succeeded in crystallizing and characterizing
the dithiophenalenyl (DTPLY) radical 1 in the solid state
(Scheme 1);24 the isolation of 1 as its p-dimer shows that sulfur
substitution electronically stabilizes the radical. The electro-
chemistry of 1 and 2 reveals that sulfur substitution significantly
reduces the solution based disproportionation potential
½
½
½
½
(DE2ꢀ1 ¼ E2 ꢀ E1 , where E1 and E2 are the first and second
reduction potentials of corresponding cations) which is closely
related to the on-site Coulomb repulsion (U).
‡ Current address: Department of Chemistry, Ananda Chandra College,
University of North Bengal, Jalpaiguri 735101, West Bengal, India.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8245

View Article Online
Scheme 2
3,4-dimethoxy-9-hydroxy phenalenone by sulfur substitution
proved to be difficult (Scheme 2c). Thus we focused on the
introduction of a better leaving group in these positions in order
to facilitate the replacement by nucleophiles derived from thiols
and hydrogen sulfide [ꢀSR (R ¼ alkyl or H)], and we targeted the
p-toluenesulfonate derivatives. By reacting p-toluenesulfonyl
chloride with the previously reported 3,7,9-trihydroxy phenale-
none (23) and the newly synthesized 3,4,9-trihydroxy phenale-
none (28, Scheme 3) we were able to produce the 3,7- and
3,4-ditosylate derivatives (24 and 29). Compound 24 reacted
smoothly with methanethiol, ethanethiol and 1-propanethiol in
the presence of potassium carbonate to produce ligands L1–L3,
whereas reaction of compound 29 with hydrogen sulfide gave the
disulfide bridged ligand L4 directly, after spontaneous aerial
oxidation of the initial reaction product; ligand L5 was obtained
in a similar manner but using potassium selenoacetate to intro-
duce the desired functionality. This synthetic protocol provides
a route to the full range of chalcogenide derivatives of the
9-hydroxyphenalenone nucleus and the corresponding spi-
robiphenalenyl radicals.
Scheme 1
An important advantage of the spiro biphenalenyl boron
radicals is the quarter-filled band which reduces the onsite
coulomb potential in comparison to that which is characteristic
of the half-filled band which results for radicals containing
a single phenalenyl unit.22 Our most recent results show that
alkoxy-substitution in the spiro-biphenalenyl boron compounds
can lower the DE2ꢀ1 value, as observed in the biphenalenyl
radical (8).39
In the present manuscript we extend this approach by
exploring the further introduction of sulfur and selenium
substituents into the phenalenyl nucleus by modifying the 9-
hydroxyphenalenone building block, which allows the synthesis
of the sulfur and selenium substituted spirobiphenalenyl boron
compounds 9–13 as an alternative strategy to produce radicals
with low values of the disproportionation potential. Electro-
chemistry of the cationic species reveals that sulfur and selenium
substitution is effective in lowering the disproportionation
potentials; radicals 10 and 11 have been crystallized and shown
to have the lowest disproportionation potential among the
radicals characterized in the solid state whereas compounds 12
and 13 have the lowest DE2ꢀ1 value so far reported for any
organic radical. Radicals 10 and 11 show better overlap in the
solid state than the oxygen substituted analogue (8), and the
physical properties are improved.
The syntheses of radicals 9–13 followed the same basic
procedure that has been used to prepare radicals 3–8; we first
prepared the chloride salts (9+ Clꢀ to 13+ Clꢀ) and finally
employed the TFPBꢀ or TFABꢀ anions to obtain the required
solubility properties of the salts (Scheme 4). The salts 9+ TFPBꢀ,
10+ TFPBꢀ, 11+ TFPBꢀ, 12+ TFABꢀ, and 13+ TFPBꢀ were
purified as air-stable red crystals by recrystallization from
dichloromethane and hexane.
Preparation and electrochemistry of 9–13
Results and discussion
The cyclic voltammetry (CV) of 9+–13+, Xꢀ showed two reversible
waves corresponding to the expected triad of oxidation states
(Fig. 1): reversible waves for (0/+1) and (ꢀ1/0) couples, together
with additional reductions in the case of 12 and 13;25,42 the
reduction potentials and the disproportionation potentials are
given in Table 1. Fig. 1 shows the CV of 9–13 recorded in 1,2-
dichlorobenzene (the CVs of compounds 9–11 recorded in
acetonitrile are shown in the ESI†). The cyclic voltammetry of 12
and 13 in acetonitrile was not reversible; the strong cathodic wave
suggests electroreduction of the material coating the electrode.25
Synthesis of phenalenyl precursors and spiro-biphenalenyl salts
Our main goal was the synthesis of the disulfide and diselenide
bridged and dithioalkyl substituted phenalenyls, while main-
taining the 9-hydroxyphenalenone functionality; the disulfide-
bridged phenalenyls 1 and 2 have been already synthesized
according to Scheme 2a,25,42 but this oxidative strategy is not
useful in the present connection. The nucleophilic replacement of
the alkoxy group with thiols is successful in 9-alkoxy-1-phena-
lenone (Scheme 2b),52 but replacement of the methoxy groups of
8246 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Scheme 3
Fig. 2a; nomenclature based on a previous publication);41
whereas compounds 12 and 13 show an extremely low value of
DE2ꢀ1 < ꢀ0.1 V (lowering of DE2ꢀ1 of 12 and 13 with respect to
the oxygen substituted compound has also been verified by
recording the CVs of 6, 8, 9 and 10 in 1,2-dichlorobenzene; Table
1 and Fig. 2b).
We crystallized radicals 10 and 11 by using a chemical
reductant (Scheme 4) in an H-cell and obtained a good yield of
high quality, long red needles of radical crystals; radicals 9, 12
and 13 have not yet been crystallized due to their very low
solubility in common organic solvents. Tetrakis-(dimethyla-
mino)ethylene (TDAE) was used as a reductant as its oxidation
potential (E1/2 ¼ ꢀ0.7 V) falls slightly below the first reduction
potentials of 9+–13+. To ensure high crystal quality for radicals
10 and 11 the H-cell was loaded in a dry box and the solvent
(acetonitrile) was degassed three times on a vacuum line before
mixing the reductant and salt. Crystal growth started on the glass
frit after 6 hours standing, and the crystals reached their
optimum size and quality in about 24 hours. The crystals are
sufficiently stable to allow ambient chemical analyses, X-ray
crystallography and solid-state measurements.
Scheme 4
The first two reductions for 12 and 13 are very close (Fig. 1c and d)
and are nearly merged in the CV experiments, so differential pulse
voltammograms (DPVs) were recorded (ESI†) to confirm the
presence of the two reduction processes. Thus we concluded based
on the CV and DPV data (ESI†) that compounds 12+ and 13+ each
gave rise to three reductions with potentials of ꢀ0.51 V, ꢀ0.64 V,
and ꢀ0.93 V (12+), and ꢀ0.47 V, ꢀ0.55 V, and ꢀ0.63 V (13+) in
acetonitrile, although it may be seen that the second reduction
process of 12+ (Fig. 1c) is not well behaved.
The reductions of the new compounds 9+–13+ occur at less
negative potentials than other spirobiphenalenyl boron
compounds with the exception of 6+ and 7+. However, the
disproportionation potentials (DE2ꢀ1) of 9–11 are lower than
those of the previously reported compounds (1–8) (Table 1 and
X-Ray crystal structures of 10 and 11
The structures of 10 and 11 were determined at two different
temperatures (100 K and room temperature (RT) for 10 and
200 K and RT for 11); the room temperature structures did not
show any significant change in structural parameters from the low
temperature structures ruling out the occurrence of phase tran-
sition in this temperature range. Table 2 provides crystal data, and
Fig. 3 shows ORTEP drawings of both the radicals. The most
important point is the absence of simple s- or p-dimerization of
these radicals in the solid state. There are four molecules of 10 and
11 in the unit cell; the asymmetric units of both of the radicals are
composed of half of the molecule, indicating symmetric solid-state
packing. The main differences between the molecular structures
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8247

View Article Online
Table 1 The half-wave potentials and disproportionation potentials (volts vs. SCE) of phenalenyl-based boron and silicon salts
Salt
Structure
E1
DE2ꢀ1
Solventa
b
½
½
E2
1+ OTfꢀ
DTPLY
TTPLY
ꢀ0.23
ꢀ0.33
ꢀ0.73
ꢀ0.89
ꢀ1.02
ꢀ0.36
ꢀ0.30
ꢀ0.36
ꢀ0.78
ꢀ0.74
ꢀ0.55
ꢀ0.40
ꢀ0.60
ꢀ0.45
ꢀ0.61
ꢀ0.49
ꢀ0.47
ꢀ0.80
ꢀ0.65
ꢀ1.09
ꢀ1.24
ꢀ1.37
ꢀ0.65
ꢀ0.69
ꢀ0.64
ꢀ0.99
ꢀ1.04
ꢀ0.75
ꢀ0.68
ꢀ0.80
ꢀ0.74
ꢀ0.82
ꢀ0.56
ꢀ0.55
ꢀ0.57
ꢀ0.32
ꢀ0.36
ꢀ0.35
ꢀ0.35
ꢀ0.29
ꢀ0.39
ꢀ0.28
ꢀ0.21
ꢀ0.30
ꢀ0.20
ꢀ0.28
ꢀ0.20
ꢀ0.29
ꢀ0.21
CH3CN
C2H4Cl2
CH3CN
CH3CN
CH3CN
CH3CN
C6H4Cl2
CH3CN
CH3CN
C6H4Cl2
CH3CN
C6H4Cl2
CH3CN
C6H4Cl2
CH3CN
C6H4Cl2
C6H4Cl2
2+ BPh4
3+ BPh4
4+ BPh4
5+ BPh4
6+ BPh4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
[PLY(O,N R)]2B; R ¼ Bu
[PLY(O,N Et)]3Si
[PLY(N Me,N R1)]2B; R1 ¼ Me
[PLY(O,O)]2B
[PLY(O,O)]2B
6+ TFABꢀ
7+ TFPBꢀ
8+ TFPBꢀ
8+ TFPBꢀ
9+ TFPBꢀ
9+ TFPBꢀ
10+ TFPBꢀ
10+ TFPBꢀ
11+ TFPBꢀ
12+ TFABꢀ
13+ TFPBꢀ
[5 Me-PLY(O,O)]2B
[3,7-OMe-PLY(O,O)]2B
[3,7-OMe-PLY(O,O)]2B
[3,7-SMe-PLY(O,O)]2B
[3,7-SMe-PLY(O,O)]2B
[3,7-SEt-PLY(O,O)]2B
[3,7-SEt-PLY(O,O)]2B
[3,7-SPr-PLY(O,O)]2B
[3,4-S,S-PLY(O,O)]2B
[3,4-Se,Se-PLY(O,O)]2B
ꢀ0.07b
ꢀ0.08b
a
b
CH3CN ¼ acetonitrile; C2H4Cl2 ¼ 1,2-dichloroethane; C6H4Cl2 ¼ 1,2-dichlorobenzene. DE2ꢀ1 evaluated from differential pulse voltammetry
experiments (ESI†).
of 10 and 11 are (i) 23.5ꢂ bending of the PLY plane at the oxygen
atoms in 11 and (ii) disorder of one of the alkyl carbons in 11
(Fig. 3 and Table 2). However, these differences in molecular
geometry do not influence the packing and solid state properties
of these radicals (see later sections).
for 11. This configuration minimizes the steric interference and
maximizes the overlap between the singly occupied molecular
orbitals (SOMOs) of the adjacent phenalenyl units. By repeating
this superimposed p-overlap, both molecules 10 and 11 form
a highly symmetrical p-chain structure along the z axis and
diagonal to the xz plane.
The sulfur atoms and the carbon atoms connected to sulfur are
almost coplanar with the PLY rings and thus we conclude that
the sulfur atoms are sp2-hybridized and remain in conjugation
with the phenalenyl units in these radicals (Fig. 3). The spiro-
conjugated phenalenyl rings in these molecules deviate from the
usual perpendicular orientation (dihedral angles of 79ꢂ and 81ꢂ
for 10 and 11, respectively). The solid state structures of 10 and
11 reveal that the radicals pack in a continuous array of
p-stacked neighboring phenalenyl units with parallel orientation
and very short intermolecular carbon–carbon contacts so as to
form a polymeric network of neutral radicals (Fig. 4 and 5). It
has been previously established that the orientation of the radical
molecules in the well-spaced, narrow bandwidth lattices plays the
determining role in influencing the conductivity properties.30 In
the present case, it is clear that the carbon atoms with short
intermolecular contacts possess p-orbitals which are oriented for
efficient overlap in radicals 10 and 11. The previously reported
analogous oxygen substituted compound 8 is structurally
different from 10 and 11. Radical 8 did not show a continuous
chain structure at room temperature and carbon–carbon
contacts as well as interplanar separations are higher in the case
of radical 8 (ref. 39) than those in radicals 10 and 11. Exami-
nation of the packing of molecules reveals that phenalenyl units
of nearest neighbor molecules are parallel to each other and are
involved in a superimposed p-overlap by selective registry
between all six pairs of spin-bearing carbon atoms. Thus there is
an almost complete superposition of all six active carbon atoms
of the phenalenyl nucleus with all intermolecular distances
between the spin-bearing carbon centers well below the sum of
the van der Waals atomic separations for carbon (Fig. 4), with
An important aspect in the packing of radical 10 is the pres-
ence of intermolecular S–S interactions (Fig. 4); the sulfur atoms
ꢀ
of the superimposed phenalenyls are at a distance of 3.54 A
which is shorter than the sum of the van der Waals atomic
ꢀ
separations for sulfur (3.6 A). Thus in the crystal lattices of 10
and 11, the molecules form a quasi one-dimensional structure
which is dominated by 1-D p-chains with very short intermo-
lecular contacts, providing an obvious pathway for conduction.
Magnetic susceptibility of 10 and 11
The temperature dependence of the magnetic susceptibility (c) of
10 and 11 was measured over the range of 8–330 K and is shown
in Fig. 6a as the paramagnetic susceptibility cp (after correction
for the sample diamagnetism). In both the radicals, cp increases
with decreasing temperature below 330 K and reaches a broad
maximum at Tmax ¼ 81 K (10) and 57 K (11). We used the
analytical form of the Bonner–Fisher model for the S ¼ 1/2
antiferromagnetic Heisenberg chain of isotropically interacting
spins,53,54 to fit c(T) in the temperature range 40–330 K†, and we
obtained an intrachain exchange constant, J ¼ ꢀ47 cmꢀ1 for 10
and J ¼ ꢀ40 cmꢀ1 for 11, corresponding to antiferromagnetic
interactions which dominate the magnetic susceptibilities at low
temperature. The uniform Heisenberg model53,54 is appropriate
because of the regular chain structures of 10, in which the radical
spins couple through a single type of interaction (fully super-
imposed p-overlap, Fig. 4).
Electrical resistivity of 10 and 11
ꢀ
the closest C–C distance of 3.20 A at low temperature for both
The single crystal conductivities of radicals 10 and 11 were
ꢀ
radicals and mean plane separations of 3.23 A for 10 and 3.26 A
ꢀ
measured using a four probe configuration, and the temperature
8248 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012

View Article Online
½
½
Fig. 2 (a) Comparison of E1 , E2 and DE2ꢀ1 for a variety of phenalenyl
½
½
radicals in acetonitrile; (b) comparison of E1 , E2 and DE2ꢀ1 for
a variety of spiro-biphenalenyl-boron radicals in 1,2-dichlorobenzene.
Table 2 Crystal data for radicals 10 and 11
Compound
10
11
Formula
Fw
C34H30BO4S4
641.63
C38H38BO4S4
697.73
Crystal system
Space group
Z
Monoclinic
C2/c
4
100(2)
19.019(4)
8.549(2)
18.248(3)
90
106.965(4)
90
2.24–32.22
2838.1(9)
5192
R1 ¼ 0.0345
wR2 ¼ 0.0865
R1 ¼ 0.0468
wR2 ¼ 0.0933
3.23
Monoclinic
C2/c
4
200(2)
9.2187(3)
21.9894(7)
16.5888(6)
90
92.6085(6)
90
2.22–29.36
3359.3(2)
6243
R1 ¼ 0.0411
wR2 ¼ 0.1006
R1 ¼ 0.0546
wR2 ¼ 0.1089
3.26
Temp./K
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
a/deg
b/deg
g/deg
q range/deg
ꢀ
Cell volume/A
3
Measured reflections used
Final R indices [I > 2s(I)]
R indices (all data)
Fig. 1 Cyclic voltammetry of (a) 9+ TFPBꢀ, (b) 10+ TFPBꢀ, (c) 12+
TFABꢀ and (d) 13+ TFPBꢀ in 1,2-dichlorobenzene (E1/2 are taken from
differential pulse voltammetry in the ESI†); referenced to SCE via
internal ferrocene (not shown).
Mean plane separation
ꢀ
between phenalenyls/A
Dihedral angles between
phenalenyls/ꢂ
Bending at oxygen atoms/ꢂ
79.0
0
81.0
23.5
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8249

View Article Online
Fig. 3 ORTEP diagrams of radicals (a) 10 and (b) 11.
Fig. 5 Extended representation of solid-state packing of (a) 10 and (b)
11, showing that a single type of repeating superimposed p-overlap leads
to an infinite spiro-conjugated chain in the crystal lattice along the z axis
for 10 and along the diagonal of xz plane for 11 (alkyl groups are omitted
for clarity).
Fig. 4 Superimposed p-overlap in 10 and 11, showing the six pairs of
spin bearing carbon atoms of the adjacent phenalenyl units which interact
ꢀ
with each other with a closest C–C distance of 3.20 A. The interactions
ꢀ
between the sulfur atoms in radical 10 (3.54 A) are also within van der
dependence of the conductivity is shown in Fig. 6c. The
conductivity shows a semiconducting temperature dependence
with activation energy D ¼ 0.28 eV and 0.25 eV for radicals
10 and 11 respectively. The room temperature conductivity
Waals separation (alkyl groups are omitted for clarity, intermolecular
distances of 11 are shown within the brackets).
8250 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Fig. 6 Solid-state properties of crystalline 10 (blue) and 11 (red), showing the strong similarities in the solid state properties of the radicals: (a)
paramagnetic susceptibility as a function of temperature, where the solid line represents the fit of the magnetic susceptibility data of 10 to the Bonner–
Fisher model for the S ¼ 1/2 antiferromagnetic Heisenberg chain of isotropically interacting spins, with J ¼ ꢀ47 cmꢀ1; (b) fraction of Curie spins and
cp*T product (right axis) as a function of temperature; (c) single-crystal conductivity as a function of temperature; (d) single-crystal infrared trans-
mission spectra. (b) Shows the effective fraction of Curie spins per molecule (8cpT/3) as a function of temperature; at high temperatures, these values
approach the Curie free-spin value of one unpaired electron per molecule, a signature of the neutral radicals we have reported previously.28,29,33–35
(sRT ¼ 1.5 ꢁ 10ꢀ2 S cmꢀ1) of radicals 10 and 11 compares
favourably to the other neutral radicals in the same class (1–7).
The higher value of the room temperature conductivity in 10 and
11 in comparison with their oxygen substituted analogue 8
(sRT ¼ 3 ꢁ 10ꢀ3 S cmꢀ1) may result from the packing and lower
value of DE2ꢀ1 in 10.
LUMOs of 10+ and 11+ respectively, for each of the four mole-
cules of radicals 10 and 11 in the unit cell; basically these consist
of the symmetric and antisymmetric combinations of the 1,3,7,9-
tetrasubstituted phenalenyl LUMO.28,59 Alternatively they can
be viewed as arising from the nonbonding molecular orbitals of
each of the eight phenalenyl units in the unit cell.1,60 In this
picture these eight orbitals now accommodate a total of four
electrons, leading to a quarter-filled band complex with two filled
and six vacant bands.
Optical measurement of 10 and 11
To obtain further information on the electronic structure, we
measured the transmission spectra of single crystals of radicals 10
and 11 (Fig. 6d). The most important feature in the transmission
spectra is a strong decrease of absorption between 0.37 eV (Eg)
The maximum band dispersions in 10 are 0.04 eV (along a*),
0.12 eV (b*), 0.05 eV (c*) and 0.14 eV, 0.06 eV, 0.16 eV and
0.17 eV along the diagonal directions (Fig. 7a), whereas the
maximum band dispersions in 11 are 0.19 eV (along a*), 0.02 eV
(b*), 0.04 eV (c*) and 0.18 eV, 0.21 eV, 0.05 eV and 0.19 eV along
the diagonal directions (Fig. 7b).
0
and 0.25 eV (Eg ) in correlation with the activation energy of the
electrical conductivity (D ¼ 0.28 eV, Fig. 6c).
It may be seen that the band dispersions found for 10 and 11
are higher than those for some of the previously reported phe-
nalenyl based radicals such as 1,24 3 (R ¼ propyl, pentyl, hexyl,
octyl),28,30,32,34 4,40 5,35 and their oxygen substituted analogue 8.39
Radical 10 is the first of the spirobiphenalenyl-based neutral
radical conductors to possess a 1-D electronic structure with
intermolecular S–S interactions. The band dispersion is reflected
in the electronic spectrum (Fig. 6d), where the width of the band-
like absorptions is greater than those of a number of other
members of this series such as 3 (R ¼ ethyl, propyl, butyl, pentyl,
hexyl, octyl), 4, 5 and 8.28–30,32,34,35,39,40
Band electronic structures of 10 and 11
€
We carried out extended Huckel theory (EHT) band structure
calculations,55 on the crystal structures of radicals 10 and 11.
Such calculations have been very useful in understanding the
electronic structure of organic molecular superconductors,56,57
and thin-film field effect transistors,58 but cannot be expected to
provide a complete picture of the electronic structure in situa-
tions where the tight-binding approximation is not applicable.
Fig. 7 shows the results obtained for band structure calculations
carried out on the lattices found in the X-ray crystal structures.
The eight bands shown in Fig. 7a and b are derived from the two
The presence of a half molecule in the asymmetric unit of the
solid-state structure at all temperatures confirms the high
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8251

View Article Online
molecular symmetry and the delocalized nature of the 1-D elec-
tronic structure; thus the new radicals may possess the resonating
valence bond (RVB) ground state which is characteristic of
selected members of the spiro-biphenalenyl radical conductors
that were previously reported [3 (R ¼ benzyl, cyclohexyl), 6,
and 7].33,36,37,61,62
Conclusion
A convenient and broadly applicable route for the synthesis of
thioalkyl as well as dithio-bridged substituted-phenalenyl deriv-
atives and their corresponding spiro-biphenalenyl boron
compounds is reported. The first two members (10 and 11) of
a new family of spiro-bis(3,7-dithioalkyl 1,9-di-oxophenalenyl)
boron neutral radical conductors have been synthesized and
characterized in the solid-state. The strategy of thioalkyl as well
as dithio- and diseleno-bridge substitution at the active positions
of the PLY system is shown to be successful in lowering the
½
½
electrochemical disproportionation energy (DE2ꢀ1 ¼ E2 ꢀ E1
)
of radicals 9–13. In the solid state, radicals 10 and 11 pack in
a continuous array of p-stacked phenalenyl units; sulfur substi-
tution at the 3, 7 positions not only lowers the DE2ꢀ1 value but
also leads to a reduced interplanar separation between p stacked
phenalenyls and intermolecular C–C contacts in comparison
with their oxygen analogue 8. The solid state properties are
dictated by the p-chain structure and the sulfur substitution at
the 3, 7 positions. Magnetic susceptibility measurements support
the idea that the radicals do not exist as isolated free radicals
in the crystalline state, and there are spin–spin interactions
between the molecules in the solid state. Band-structure calcu-
lations support the magnetic measurement data and indicate the
presence of significant interactions between the spin bearing
carbons. The low value of DE2ꢀ1 (ꢀ0.20 V) and the more efficient
solid-state packing in 10 and 11 may be responsible for the order
of magnitude increase in the conductivity in comparison to the
oxygen analogue 8. The results indicate that appropriate func-
tionalization of the phenalenyl ring system can increase the
conductivities in this class of compounds.
Experimental section
Materials
Boron trichloride (Aldrich), sodium tetrakis[3,5-bis(tri-
fluoromethyl)phenyl]borate (NaTFPB) (Boulder Scientific
Company),
potassium
tetrakis(pentafluorophenyl)borate
(KTFAB) (Boulder Scientific Company), sodium tetrakis[3,5-
bis(trifluoromethyl)phenyl]borate (NaTFPB) (Boulder Scien-
tific), tetrakis(dimethylamino)ethylene (TDAE) (Aldrich),
p-toluenesulfonyl chloride (Aldrich), ethanethiol (Aldrich),
methanethiol (Aldrich), 1-propane thiol (Aldrich) and acetoni-
trile (dry solvent) (Aldrich) were all commercial products and
were used as received. 3,7,9-Trihydroxyphenalenone (23) and 3-
hydroxy-4,9-dimethoxy phenalenone (27) were prepared
according to literature procedures.39,63 Potassium selenoacetate
was prepared according to literature procedures.64,65 1,2-
Dichloroethane was distilled from CaH2 just prior to use. The
NMR spectra were recorded on a Bruker 300 spectrometer.
Infrared spectra were recorded on a Nicolet Nexus 670 FT-IR
spectrometer at 2 cmꢀ1 resolution. Mass spectra (MALDI) were
Fig. 7 EHT band structures calculated from the experimental structures
of crystalline (a) 10 and (b) 11. Dispersions along reciprocal cell axes,
where X ¼ [½ 0 0], Y ¼ [0 ½ 0], Z ¼ [0 0 ½], A ¼ [½ ½ 0], B ¼ [½ 0 ½], C ¼
[0 ½ ½], and D ¼ [½ ½ ½].
8252 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012

View Article Online
run on a Voyager-DE STR BioSpectrometry Workstation mass
spectrometer. Elemental analyses were performed by the
Microanalysis Laboratory, University of Illinois, Urbana, IL.
layer chromatography [Rf ¼ 0.5, dichloromethane]. After 24 h
the solvent was evaporated and the residue was washed with
water and then with hexane to yield 0.15 g (70%) of a yellow
solid. Mp 180 ꢂC. MS (ESI), m/z ¼ 289.04 (MH+). H NMR
1
(CDCl3): d 16.49 (s, 1H), 8.40 (d, 2H), 7.55 (t, 1H), 6.85 (s, 2H),
2.65 (s, 6H). Anal. calcd (found) for C15H12O2S2: C, 62.47
(62.85); H, 4.19 (4.26)%.
Preparation of 24
3,7,9-Trihydroxy phenalenone (23) (1.4 g, 6.1 mmol) was dis-
solved in acetone (200 mL) and anhydrous potassium carbonate
(2 g, 12.8 mmol) was added. The mixture was stirred for 2 h,
p-toluenesulfonylchloride (2.55 g, 12.8 mmol) was added and the
reaction mixture was stirred at room temperature. The progress
of the reaction was monitored by thin layer chromatography [Rf
¼ 0.6, dichloromethane]. After 2 h the solution was filtered and
the solvent was removed from the filtrate using a rotary evapo-
rator. The compound was purified by column chromatography
(SiO2; dichloromethane). Evaporation of the solvent yielded
1.6 g (49%) of a yellow solid. Mp 195 ꢂC. MS (ESI), m/z ¼ 537.07
(MH+). 1H NMR (CDCl3): d 16.70 (s, 1H), 8.24 (d, 2H), 7.88 (d,
4H), 7.56 (t, 1H), 7.37 (d, 4H), 6.89 (s, 2H), 2.46 (s, 6H). Anal.
calcd (found) for C27H20O8S2: C, 60.44 (60.29); H, 3.76 (3.60)%.
Preparation of L2
Compound 24 (0.4 g, 0.7 mmol) was dissolved in acetone (50 mL)
and anhydrous potassium carbonate (0.5 g, 3.6 mmol) was
added. A large excess of ethanethiol (1.0 mL) was added to the
mixture and the reaction mixture was stirred for 24 h; the
progress of the reaction was monitored by thin layer chroma-
tography [Rf ¼ 0.5, dichloromethane]. After 24 h the solvent was
evaporated and the residue was washed with water and then with
ꢂ
hexane to yield 0.16 g (68%) of a yellow solid. Mp 175 C. MS
1
(ESI), m/z ¼ 317.07 (MH+). H NMR (CDCl3): d 16.49 (s, 1H),
8.42 (d, 2H), 7.54 (t, 1H), 6.90 (s, 2H), 3.16 (q, 4H), 1.51 (t, 6H).
Anal. calcd (found) for C17H16O2S2: C, 64.52 (64.10); H, 5.10
(4.96)%.
Preparation of 28
A mixture of 3-hydroxy-4,9-dimethoxy phenalenone (27) (1.0 g,
Preparation of L3
0.004 mol) and pyridine hydrochloride (3.0 g, 0.026 mol) was
ꢂ
heated to 225 C in an argon atmosphere for 15 min. The reac-
Compound 24 (0.4 g, 0.7 mmol) was dissolved in acetone (50 mL)
and anhydrous potassium carbonate (0.5 g, 3.6 mmol) was
added. Excess of 1-propanethiol (0.5 mL) was added to the
mixture and the reaction mixture was stirred for 24 h; the
progress of the reaction was monitored by thin layer chroma-
tography [Rf ¼ 0.6, dichloromethane]. After 24 h the solvent was
evaporated and the residue was washed with water and then with
tion mixture was allowed to cool to room temperature and then
dissolved in 200 mL 2(N) sodium hydroxide solution. Hydro-
chloric acid, 3(N), was added slowly to adjust the pH of the
solution to 7 at which point the desired compound precipitated.
The brown solid was isolated by filtration, washed several times
with water and dried (0.8 g, 90% yield). Mp > 300 ꢂC. MS (ESI),
m/z ¼ 229.05 (MH+). 1H NMR (CD3OD): d 8.84 (d, 2H), 6.82 (d,
2H), 5.97 (s, 1H). Anal. calcd (found) for C13H8O4: C, 68.42
(68.65); H, 3.53 (3.57)%.
ꢂ
hexane to yield 0.17 g (66%) of a yellow solid. Mp 165 C. MS
1
(ESI), m/z ¼ 345.1 (MH+). H NMR (CDCl3): d 16.50 (s, 1H),
8.44 (d, 2H), 7.54 (t, 1H), 6.90 (s, 2H), 3.11 (t, 4H), 1.88 (m, 4H),
1.51 (t, 6H). Anal. calcd (found) for C19H20O2S2: C, 66.24
(66.87); H, 5.85 (5.96)%.
Preparation of 29
3,4,9-Trihydroxy phenalenone (28) (1.4 g, 6.1 mmol) was dis-
solved in acetone (200 mL) and anhydrous potassium carbonate
(2.0 g, 12.8 mmol) was added. The mixture was stirred for 2 h,
p-toluenesulfonylchloride (2.55 g, 12.8 mmol) was added and the
reaction mixture was stirred at room temperature. The progress
of the reaction was monitored by thin layer chromatography
[Rf ¼ 0.6, dichloromethane]. After 1 h the solution was filtered
and the solvent was removed from the filtrate using a rotary
evaporator. The compound was purified by column chroma-
tography (SiO2; dichloromethane). Evaporation of the solvent
yielded 1.2 g (36%) of a yellow solid. Mp 180 ꢂC. MS (ESI), m/z ¼
Preparation of L4
Compound 29 (0.4 g, 0.7 mmol) was dissolved in acetone (50 mL)
and anhydrous potassium carbonate (0.5 g, 3.6 mmol) was
added. A slow stream of hydrogen sulfide was bubbled for 3 h
and the progress of the reaction was monitored by thin layer
chromatography [Rf ¼ 0.3, dichloromethane]. After 24 h the
solvent was evaporated and the residue was washed with water
and then with hexane to yield 0.10 g (52%) of a brown solid. Mp
170 ꢂC (dec.). MS (ESI), m/z ¼ 258.99 (MH+). 1H NMR (CDCl3):
d 16.05 (s, 1H), 8.18 (d, 1H), 8.11 (d, 1H), 7.62 (d, 1H), 7.37 (d,
1H), 7.08 (s, 1H). Anal. calcd (found) for C13H6O2S2: C, 60.44
(61.37); H, 2.34 (2.56)%.
1
537.07 (MH+). H NMR (CDCl3): d 16.29 (s, 1H), 8.04 (d, 1H),
7.97 (d, 1H), 7.79 (d, 2H), 7.67 (d, 2H), 7.42 (d, 1H), 7.30 (d, 2H),
7.25 (d, 2H), 7.18 (d, 1H), 6.86 (s, 1H), 2.42 (br-s, 6H). Anal.
calcd (found) for C27H20O8S2: C, 60.44 (60.12); H, 3.76 (3.68)%.
Preparation of L5
Compound 29 (1.3 g, 2.6 mmol) was dissolved in acetone
(60 mL). Potassium selenoacetate, KSeAc (1.7 g, 10.4 mmol),
was added slowly to the reaction mixture. The reaction mixture
was stirred overnight (8 h) at room temperature. Acetone was
evaporated completely using a rotary evaporator and the solid
residue was washed with water and diethylether to yield 0.55 g
Preparation of L1
Compound 24 (0.4 g, 0.7 mmol) was dissolved in acetone (50 mL)
and anhydrous potassium carbonate (0.5 g, 3.6 mmol) was
addeꢂd. A slow stream of methanethiol (gas) was bubbled for 2 h
at 0 C and the progress of the reaction was monitored by thin
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8253

View Article Online
(60%) of a brown solid. Mp 105 ꢂC (dec.). MS (ESI), m/z ¼
Preparation of 10+ TFPBꢀ
1
353.86 (MH+). H NMR (CDCl3): d 16.31 (s, 1H), 8.18 (d, 1H),
Starting materials. NaTFPB (0.176 g, 0.19 mmol); 10+ Clꢀ
(0.13 g, 0.19 mmol). The crude product was purified by recrys-
tallization from dichloromethane/hexane to give red crystals of
the desired compound (0.19 g, 66%). Mp 190 ꢂC. MS (MALDI),
m/z ¼ 641 (cation, M+). 1H NMR (CDCl3): d 8.75 (d, 4H), 7.81 (t,
2H), 7.68 (br s, 8H), 7.49 (s, 4H), 7.02 (s, 4H), 3.19 (q, 8H), 1.51
(t, 12H). Anal. calcd (found) for C66H42B2F24O4S4: C, 52.68
(52.80); H, 2.81 (2.51)%.
8.02 (d, 1H), 7.69 (d, 1H), 7.35 (d, 1H), 7.32 (s, 1H). Anal. calcd
(found) for C13H6O2Se2: C, 44.34 (43.89); H, 1.72 (2.11)%.
Preparation of 9+ Clꢀ
0.15 g (0.53 mmol) of L1 in 1,2-dichloroethane (10 mL) was
treated with boron trichloride (0.26 mL of 1 M solution in
dichloromethane, 0.26 mmol) under argon and the mixture was
stirred for 24 h. Hexanes were added to the reaction mixture to
give a yellow precipitate. The compound was isolated as a red
solid (0.110 g) by filtration and used for the next step without
further purification. MS (MALDI), m/z ¼ 585 (cation, M+).
Chloride salts 10+ Clꢀ and 11+ Clꢀ were synthesized by
a procedure similar to that used for the preparation of 9+ Clꢀ.
Preparation of 11+ TFPBꢀ
Starting materials. NaTFPB (0.176 g, 0.19 mmol); 11+ Clꢀ
(0.14 g, 0.19 mmol). The crude product was purified by recrys-
tallization from dichloromethane/hexane to give red crystals of
the desired compound (0.19 g, 66%). Mp 180 ꢂC. MS (MALDI),
m/z ¼ 698 (cation, M+). 1H NMR (CDCl3): d 8.77 (d, 4H), 7.81 (t,
2H), 7.69 (br s, 8H), 7.50 (s, 4H), 7.02 (s, 4H), 3.15 (t, 8H), 1.89
(m, 8H), 1.12 (t, 12H). Anal. calcd (found) for C70H50B2F24O4S4:
C, 53.86 (53.60); H, 3.23 (3.11)%.
Preparation of 10+ Clꢀ
Starting materials. L2 (0.15 g, 0.47 mmol); boron trichloride
(0.24 mL of 1 M solution in dichloromethane, 0.24 mmol). The
compound was isolated as a red solid (0.12 g). MS (MALDI),
m/z ¼ 641 (cation, M+).
Preparation of 12+ TFABꢀ
Preparation of 11+ Clꢀ
Starting materials. KTFAB (0.136 g, 0.19 mmol); 12+ Clꢀ
(0.11 g, 0.19 mmol). The crude product was purified by recrys-
tallization from dichloromethane/hexane to give red crystals of
the desired compound (0.19 g, 80%). The material was further
purified by dissolution in dichloromethane and re-precipitated by
addition of hexane. Mp 160 ꢂC. MS (MALDI), m/z ¼ 525
(cation, M+). 1H NMR (CDCl3): d 8.68 (d, 2H), 8.61 (d, 2H), 8.14
(d, 2H), 7.67 (d, 2H), 7.56 (s, 2H). Anal. calcd (found) for
C50H10B2F20O4S4: C, 49.86 (49.66); H, 0.84 (0.97)%.
Starting materials. L3 (0.15 g, 0.44 mmol); boron trichloride
(0.22 mL of 1 M solution in dichloromethane, 0.22 mmol). The
compound was isolated as a red solid (0.12 g). MS (MALDI),
m/z ¼ 698 (cation, M+).
Preparation of 12+ Clꢀ
Starting materials. L4 (0.15 g, 0.58 mmol); boron trichloride
(0.29 mL of 1 M solution in dichloromethane, 0.29 mmol). The
compound was isolated as a dark red solid (0.1 g). MS (MALDI),
m/z ¼ 525 (cation, M+).
Preparation of 13+ TFPBꢀ
0.25 g (0.28 mmol) of NaTFPB was treated with 0.21 g
(0.28 mmol) of 13+ Clꢀ in 25 mL of dichloromethane for ½ h. The
reaction mixture was filtered and the filtrateꢂwas evaporated to
give a dark red solid (0.20 g, 45%). Mp 125 C, MS (MALDI),
Preparation of 13+ Clꢀ
Starting material L5 (0.1 g, 0.28 mmol) was dissolved in 25 mL of
ꢂ
toluene by heating at 70 C, 0.14 mL (0.14 mmol) of boron tri-
m/z ¼ 713 (cation, M+). H NMR (CDCl3): d 8.63 (d, 2H), 8.43
1
chloride (1 M solution in dichloromethane) was added and the
reaction mixture was stirred at 70 ꢂC for 6 h. The compound was
isolated as a dark brown solid (0.080 g, 76%). MS (MALDI),
m/z ¼ 713 (cation, M+).
(d, 2H), 8.09 (d, 2H), 7.72 (s, 8H), 7.58 (d, 2H), 7.49 (s, 4H), 7.27
(s, 2H). Anal. calcd (found) for C58H22B2O4F24Se4: C, 44.20
(44.21), H, 1.41 (1.57)%.
Preparation of 9+ TFPBꢀ
Crystallization of 10
Solid NaTFPB (0.176 g, 0.19 mmol) was added to the
dichloromethane solution of 9+ Clꢀ (0.12 g, 0.19 mmol) and
stirred for 3 h to give a red solution which was filtered and the
solvent was evaporated under vacuum to give a red solid. The
crude product was purified by recrystallization from dichloro-
methane/hexane to give ꢂred crystals of the desired compound
(0.180 g, 64%). Mp 210 C. MS (MALDI), m/z ¼ 585 (cation,
An invertible H-cell with a glass D frit was loaded in a dry box. A
solution of 80 mg of 10+ TFPBꢀ (0.05 mmol) in 10 mL of dry
acetonitrile was placed in one container, and 30 mg of TDAE
(0.15 mmol) dissolved in 13 mL of dry acetonitrile in the other
container. The H-cell was removed from the dry box and
attached to the vacuum line, and the containers were taken
through three cycles of freeze, pump and thaw to degas the
solutions. The H-cell was inverted slowly and the solutions were
allowed to diffuse through the glass frit. After sitting in the dark
for 48 h, the cell yielded 10 mg (30%) of dark red shining needle
shaped crystals. Anal. calcd (found) for C34H30BO4S4: C, 63.64
(62.46); H, 4.71 (4.45)%.
1
M+). H NMR (CDCl3): d 8.75 (d, 4H), 7.83 (t, 2H), 7.70 (br s,
8H), 7.50 (s, 4H), 6.99 (s, 4H), 2.69 (s, 12H). Anal. calcd (found)
for C62H34B2F24O4S4: C, 51.4 (51.25); H, 2.37 (2.26)%.
Compounds 10+ TFPBꢀ and 11+ TFABꢀ were synthesized by
a procedure similar to that used for the preparation of 9+ TFPBꢀ.
8254 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Crystallization of 11
probe with a Lake Shore 340 temperature controller driven by
LabVIEW software. A Keithley 236 unit was used as a voltage
source and current meter, and two 6517 A Keithley electrometers
were used to measure the voltage drop between the potential
leads in a four-probe configuration.
An invertible H-cell with a glass D frit was loaded in a dry box. A
solution of 90 mg of 11+ TFPBꢀ (0.05 mmol) in 10 mL of dry
acetonitrile was placed in one container, and 30 mg of TDAE
(0.15 mmol) dissolved in 13 mL of dry acetonitrile in the other
container. The H-cell was removed from the dry box and
attached to the vacuum line, and the containers were taken
through three cycles of freeze, pump and thaw to degas the
solutions. The H-cell was inverted slowly and the solutions were
allowed to diffuse through the glass frit. After sitting in the dark
for 48 h, the cell yielded 11 mg (28%) of dark red shining needle
shaped crystals. Anal. calcd (found) for C38H38BO4S4: C, 65.41
(66.67); H, 5.49 (5.76)%.
Band-structure calculations
The band-structure calculations made use of a modified version
€
of the extended Huckel theory (EHT) bandstructure program
supplied by M.-H. Whangbo. The parameter set is chosen to
provide a reasonably consistent picture of bonding in heterocy-
clic organic compounds.58,66
Acknowledgements
X-Ray crystallography
This work was supported by the Office of Basic Energy Sciences,
Department of Energy, under Grant DE-FG02-04ER46138.
X-Ray intensity data were collected at 100 K and 293 K on
a Bruker APEX2 (version 2.0-22) platform-CCD X-ray diffrac-
ꢀ
tometer system (Mo-radiation, l ¼ 0.71073 A, 50 kV/40 mA
References
power). The crystallographic parameters and the unit cell
dimensions for 100 K data are summarized in Table 2. Full
details of data collections are given in the ESI†.
1 R. C. Haddon, Nature, 1975, 256, 394.
2 S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton,
S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova and
D. M. Treger, Science, 2001, 294, 1488.
3 M. M. Matsushita, H. Kawakami, Y. Kawada and T. Sgawara,
Chem. Lett., 2007, 110.
Cyclic voltammetry
Cyclic voltammetric measurement was performed using a CH
Instruments Electrochemical Analyzer, with scan rates of
100 mV sꢀ1 on solutions (<10ꢀ3 M) of 9+ TFPBꢀ, 10+ TFPBꢀ, 11+
TFPBꢀ, 12+ TFABꢀ and 13+ TFPBꢀ in oxygen-free acetonitrile
(distilled from CaH2) or 1,2-dichlorobenzene containing 0.1 M
tetra-n-butylammonium hexafluorophosphate. Potentials were
scanned with respect to the saturated calomel reference electrode
in a single-compartment cell fitted with Pt electrodes and refer-
ence to the Fc/Fc+ couple of ferrocene at 0.38 V vs. SCE for
acetonitrile and ꢀ0.56 V vs. SCE for 1,2-dichlorobenzene.
4 M. M. Matsushita, H. Kwakami, T. Sugawara and M. Ogata, Phys.
Rev. B: Condens. Matter Mater. Phys., 2008, 77, 195208.
5 Y. Takahide, T. Konoike, K. Enomoto, M. Nishimura, T. Terashima,
S. Uji and H. M. Yamamoto, Phys. Rev. Lett., 2007, 98, 116602.
6 V. A. Dediu, L. E. Hueso, I. Bergenti and C. Taliani, Nat. Mater.,
2009, 8, 707.
7 R. G. Hicks, Org. Biomol. Chem., 2007, 5, 1321.
8 R. G. Hicks, Nat. Chem., 2011, 3, 189.
9 Y. Morita, S. Suzuki, K. Sato and T. Takui, Nat. Chem., 2011, 3, 197.
10 Y. Morita, S. Suzuki, K. Fukui, S. Nakazawa, H. Kitagawa,
H. Kishida, H. Okamoto, A. Naito, A. Sekine, Y. Ohashi,
M. Shiro, K. Sasaki, D. Shiomi, K. Sato, T. Takui and
K. Nakasuji, Nat. Mater., 2008, 7, 48.
11 M. E. Itkis, X. Chi, A. W. Cordes and R. C. Haddon, Science, 2002,
296, 1443.
Single-crystal near- and mid-infrared transmission spectroscopy
12 J. Huang and M. Kertesz, J. Am. Chem. Soc., 2006, 128, 1418.
13 J. Huang and M. Kertesz, J. Phys. Chem. A, 2007, 111, 6304.
14 J. Huang and M. Kertesz, J. Am. Chem. Soc., 2007, 129, 1634.
15 A. F. Garito and A. J. Heeger, Acc. Chem. Res., 1974, 7, 232.
16 J. B. Torrance, Acc. Chem. Res., 1979, 12, 79.
The infrared transmission measurements were carried out in
a FTIR Nicolet Nexus 670 ESP spectrometer integrated with
a Continuum Thermo-Nicolet FTIR microscope.
17 R. T. Boere and K. H. Moock, J. Am. Chem. Soc., 1995, 117, 4755.
18 V. Chandrasekhar, T. Chivers, M. Parvez, I. Vargas-Baca and
T. Ziegler, Inorg. Chem., 1997, 36, 4772.
Magnetic susceptibility measurements
19 K. Goto, T. Kubo, K. Yamamoto, K. Nakasuji, K. Sato, D. Shiomi,
T. Takui, M. Kubota, T. Kobayashi, K. Yakusi and J. Ouyang,
J. Am. Chem. Soc., 1999, 121, 1619.
20 Y. Morita, T. Aoki, K. Fukui, S. Nakazawa, K. Tamaki, S. Suzuki,
A. Fuyuhiro, K. Yamamoto, K. Sato, D. Shiomi, A. Naito,
T. Takui and K. Nakasuji, Angew. Chem., Int. Ed., 2002, 41, 1793.
21 K. Fukui, K. Sato, D. Shiomi, T. Takui, K. Itoh, K. Gotoh, T. Kubo,
K. Yamamoto, K. Nakasuji and A. Naito, Synth. Met., 1999, 103,
2257.
The magnetic susceptibilities were measured with a George
Associates Faraday balance operating at 0.5 T. The calculated
diamagnetic susceptibilities were c0 ¼ ꢀ377.1 and ꢀ424.3 emu
molꢀ1 for 10 and 11 respectively.
Electrical conductivity measurements
The single-crystal conductivities (s) of 10 and 11 were measured
in a four-probe configuration using in-line contacts which were
attached with silver paint. The needle-like crystals were freely
positioned on a sapphire substrate, and the electrical connections
between the silver paint contacts on the crystal and the indium
pads on the substrate were made by thin, flexible 25 mm diameter
silver wires to relieve mechanical stress during thermal cycling of
the crystal. The temperature dependence of the conductivity was
measured using a custom made helium variable temperature
22 P. A. Koutentis, Y. Chen, Y. Cao, T. P. Best, M. E. Itkis, L. Beer,
R. T. Oakley, C. P. Brock and R. C. Haddon, J. Am. Chem. Soc.,
2001, 123, 3864.
23 D. Small, V. Zaitsev, Y. Jung, S. V. Rosokha, M. Head-Gordon and
J. K. Kochi, J. Am. Chem. Soc., 2004, 126, 13850.
24 L. Beer, S. K. Mandal, R. W. Reed, R. T. Oakley, F. S. Tham,
B. Donnadieu and R. C. Haddon, Cryst. Growth Des., 2007, 7, 802.
25 L. Beer, R. W. Reed, C. M. Robertson, R. T. Oakley, F. S. Tham and
R. C. Haddon, Org. Lett., 2008, 10, 3121.
26 S. Zheng, J. Lan, S. I. Khan and Y. Rubin, J. Am. Chem. Soc., 2003,
125, 5786.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 8245–8256 | 8255

View Article Online
27 S. Zheng, J. D. Thompson, A. Tontcheva, S. I. Khan and Y. Rubin,
Org. Lett., 2005, 7, 1861.
28 X. Chi, M. E. Itkis, B. O. Patrick, T. M. Barclay, R. W. Reed,
R. T. Oakley, A. W. Cordes and R. C. Haddon, J. Am. Chem. Soc.,
1999, 121, 10395.
29 X. Chi, M. E. Itkis, K. Kirschbaum, A. A. Pinkerton, R. T. Oakley,
A. W. Cordes and R. C. Haddon, J. Am. Chem. Soc., 2001, 123, 4041.
30 X. Chi, M. E. Itkis, R. W. Reed, R. T. Oakley, A. W. Cordes and
R. C. Haddon, J. Phys. Chem. B, 2002, 106, 8278.
31 J. S. Miller, Angew. Chem., Int. Ed., 2003, 42, 27.
32 X. Chi, M. E. Itkis, F. S. Tham, R. T. Oakley, A. W. Cordes and
R. C. Haddon, Int. J. Quantum Chem., 2003, 95, 853.
33 S. K. Pal, M. E. Itkis, R. W. Reed, R. T. Oakley, A. W. Cordes,
F. S. Tham, T. Siegrist and R. C. Haddon, J. Am. Chem. Soc.,
2004, 126, 1478.
48 F. Wudl, Acc. Chem. Res., 1984, 17, 227.
49 M. P. Andrews, A. W. Cordes, D. C. Douglass, R. M. Fleming,
S. H. Glarum, R. C. Haddon, P. Marsh, R. T. Oakley,
T. T. M. Palstra, L. F. Schneemeyer, G. W. Trucks, R. Tycko,
J. V. Waszczak, K. M. Young and N. M. Zimmerman, J. Am.
Chem. Soc., 1991, 113, 3559.
50 C. M. Robertson, A. A. Leitch, K. Cvrkalj, D. J. T. Myles,
R. W. Reed, P. A. Dube and R. T. Oakley, J. Am. Chem. Soc.,
2008, 130, 14791.
51 A. A. Leitch, K. Lekin, S. M. Winter, L. E. Downie, H. Tsuruda,
J. S. Tse, M. Mito, S. Desgreniers, P. A. Dube, S. Zhang, Q. Liu,
C. Jin, Y. Ohishi and R. T. Oakley, J. Am. Chem. Soc., 2011, 133,
6051.
52 K. D. Franz, J. Org. Chem., 1979, 44, 1704.
53 J. C. Bonner and M. E. Fisher, Phys. Rev., 1964, 135, A640.
54 W. E. Estes, D. P. Gavel, W. E. Hatfield and D. J. Hodgson, Inorg.
Chem., 1978, 17, 1415.
34 P. Liao, M. E. Itkis, R. T. Oakley, F. S. Tham and R. C. Haddon,
J. Am. Chem. Soc., 2004, 126, 14297.
35 S. K. Mandal, M. E. Itkis, X. Chi, S. Samanta, D. Lidsky,
R. W. Reed, R. T. Oakley, F. S. Tham and R. C. Haddon, J. Am.
Chem. Soc., 2005, 127, 8185.
55 R. Hoffmann, J. Chem. Phys., 1963, 39, 1397.
56 R. C. Haddon, A. P. Ramirez and S. H. Glarum, Adv. Mater., 1994, 6,
316.
36 S. K. Pal, M. E. Itkis, F. S. Tham, R. W. Reed, R. T. Oakley and
R. C. Haddon, Science, 2005, 309, 281.
37 S. K. Mandal, S. Samanta, M. E. Itkis, D. W. Jensen, R. W. Reed,
R. T. Oakley, F. S. Tham, B. Donnadieu and R. C. Haddon,
J. Am. Chem. Soc., 2006, 128, 1982.
38 S. K. Pal, M. E. Itkis, F. S. Tham, R. W. Reed, R. T. Oakley,
B. Donnadieu and R. C. Haddon, J. Am. Chem. Soc., 2007, 129, 7163.
39 A. Sarkar, S. K. Pal, M. E. Itkis, P. Liao, F. S. Tham, B. Donnadieu
and R. C. Haddon, Chem. Mater., 2009, 21, 2226.
40 S. K. Pal, M. E. Itkis, F. S. Tham, R. W. Reed, R. T. Oakley and
R. Haddon, J. Am. Chem. Soc., 2008, 130, 3942.
41 A. Sarkar, F. S. Tham and R. C. Haddon, J. Mater. Chem., 2011, 21,
1574.
42 R. C. Haddon, F. Wudl, M. L. Kaplan, J. H. Marshall, R. E. Cais and
F. B. Bramwell, J. Am. Chem. Soc., 1978, 100, 7629.
43 R. G. Kepler, P. E. Bierstedt and R. E. Merrifield, Phys. Rev. Lett.,
1960, 5, 503.
44 W. J. Siemons, P. E. Bierstedt and R. G. Kepler, J. Chem. Phys., 1963,
39, 3523.
45 F. Wudl, G. M. Smith and E. J. Hufnagel, Chem. Commun., 1970, 1453.
46 K. Bechgaard, V. D. Parker and C. T. Pedersen, J. Am. Chem. Soc.,
1973, 95, 4373.
57 J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser,
H. H. Wang, A. M. Kini and M.-H. Whangbo, Organic
Superconductors (Including Fullerenes), ed. R. N. Grimes, Prentice
Hall, 1992.
58 R. C. Haddon, T. Siegrist, R. M. Fleming, P. M. Bridenbaugh and
R. A. Laudise, J. Mater. Chem., 1995, 5, 1719.
59 R. C. Haddon, S. V. Chichester and J. H. Marshall, Tetrahedron,
1986, 42, 6293.
60 R. C. Haddon, Aust. J. Chem., 1975, 28, 2343.
61 R. C. Haddon, A. Sarkar, S. K. Pal, X. Chi, M. E. Itkis and
F. S. Tham, J. Am. Chem. Soc., 2008, 130, 13683.
62 S. K. Pal, P. Bag, A. Sarkar, X. L. Chi, M. E. Itkis, F. S. Tham,
B. Donnadieu and R. C. Haddon, J. Am. Chem. Soc., 2010, 132,
17258.
63 R. C. Haddon, A. M. Hirani, N. J. Kroloff and J. H. Marshall, J. Org.
Chem., 1983, 48, 2115.
64 M. Koketsu, F. Nada, S. Hiramatsu and H. Ishihara, J. Chem. Soc.,
Perkin Trans. 1, 2002, 737.
65 C. M. Carcel, J. K. Laha, R. S. Loewe, P. Thamyongkit,
K. H. Schweikart, V. Misra, D. F. Bocian and J. S. Lindsey, J. Org.
Chem., 2004, 69, 6739.
66 A. W. Cordes, R. C. Haddon, R. T. Oakley, L. F. Schneemeyer,
J. V. Waszczak, K. M. Young and N. M. Zimmerman, J. Am.
Chem. Soc., 1991, 113, 582.
47 K. Bechgaard, D. O. Cowan and A. N. Bloch, J. Chem. Soc., Chem.
Commun., 1974, 937.
8256 | J. Mater. Chem., 2012, 22, 8245–8256
This journal is ª The Royal Society of Chemistry 2012