Redox, magnetic, and structural properties of 1,3,2-dithiazolyl radicals. A case study on the ternary heterocycle S3N5C4

Article abstract of DOI:10.1021/ja973338a

The characterization of the heterocyclic radical 1,2,5-thiadiazolo[3,4-b]-1,3,2-dithiazolo [3,4-b]pyrazin-2-yl (TDP-DTA) is described. The compound is prepared by treatment of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-b]pyrazine with S₃N₃Cl₃ and purified by fractional sublimation in vacuo. The results of cyclic voltammetry and ESR analysis of TDP-DTA and related heterocyclic dithiazolyls indicate that the spin distributions and donor/acceptor properties of these radicals are extremely sensitive to the nature of the 4,5-substituents. The crystal structure of TDP-DTA has been determined at two temperatures. At 293 K, the crystals are triclinic, space group P1, with a = 4.4456(8),b = 8.40;7(2), c = 9.671(3) ?, α = 71.34(2), β = 89.28(2), γ = 87.80(2)°, Z = 2 (for C₄N₅S₃); at 150 K the crystals are triclinic, space group P1, with a = 7.489(7), b = 9.593(4), c = 10.759(6) ?, α = 65.77(4), β = 74.10(6), γ = 74.64(6)°, Z = 2 (for C₈N₁₀S₆). At 293 K the structure consists of ribbons of TDP-DTA radicals packed in a slipped π-stack arrangement. In the low temperature phase alternate layers of ribbons are shifted laterally to produce arrays of dimers. Within these dimers three long (3.401(5), 3.460(5):and 3.511(5) ?) interannular S--S contacts link the two molecules. A multiple 'tectonic plate' slippage mechanism is proposed to account for the interconversion of the two phases. The structural results are discussed in the light of variable temperature magnetic susceptibility measurements.

Full text of DOI:10.1021/ja973338a

352
J. Am. Chem. Soc. 1998, 120, 352-360
Redox, Magnetic, and Structural Properties of 1,3,2-Dithiazolyl
Radicals. A Case Study on the Ternary Heterocycle S3N5C4
T. M. Barclay,1a A. W. Cordes,1a N. A. George,1b R. C. Haddon,1c M. E. Itkis,1c
M. S. Mashuta,1d R. T. Oakley,*,1b G. W. Patenaude,1b R. W. Reed,1b
J. F. Richardson,1d and H. Zhang1b
Contribution from the Department of Chemistry and Biochemistry, UniVersity of Arkansas,
FayetteVille, Arkansas 72701, Department of Chemistry and Biochemistry, UniVersity of Guelph,
Guelph, Ontario N1G 2W1, Canada, Department of Chemistry, UniVersity of Kentucky,
Lexington, Kentucky 40506, and Department of Chemistry, UniVersity of LouisVille,
LouisVille, Kentucky 40292
ReceiVed September 23, 1997
Abstract: The characterization of the heterocyclic radical 1,2,5-thiadiazolo[3,4-b]-1,3,2-dithiazolo[3,4-b]pyrazin-
2-yl (TDP-DTA) is described. The compound is prepared by treatment of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-
b]pyrazine with S3N3Cl3 and purified by fractional sublimation in vacuo. The results of cyclic voltammetry
and ESR analysis of TDP-DTA and related heterocyclic dithiazolyls indicate that the spin distributions and
donor/acceptor properties of these radicals are extremely sensitive to the nature of the 4,5-substituents. The
crystal structure of TDP-DTA has been determined at two temperatures. At 293 K, the crystals are triclinic,
space group P1h, with a ) 4.4456(8), b ) 8.407(2), c ) 9.671(3) Å, R ) 71.34(2), â ) 89.28(2), γ ) 87.80(2)°,
Z ) 2 (for C4N5S3); at 150 K the crystals are triclinic, space group P1h, with a ) 7.489(7), b ) 9.593(4), c )
10.759(6) Å, R ) 65.77(4), â ) 74.10(6), γ ) 74.64(6)°, Z ) 2 (for C8N10S6). At 293 K the structure consists
of ribbons of TDP-DTA radicals packed in a slipped π-stack arrangement. In the low temperature phase
alternate layers of ribbons are shifted laterally to produce arrays of dimers. Within these dimers three long
(3.401(5), 3.460(5) and 3.511(5) Å) interannular S---S contacts link the two molecules. A multiple “tectonic
plate” slippage mechanism is proposed to account for the interconversion of the two phases. The structural
results are discussed in the light of variable temperature magnetic susceptibility measurements.
Introduction
The trithiatriazapentalenyl radical 7 (TTTA) represents a sharp
contrast to the previous examples, in that dimerization is not
observed.12 Instead the crystal structure consists of evenly
spaced slipped π-stacks, and thus nominally fulfills the basic
Neutral heterocyclic π-radicals represent versatile building
blocks for applications in the field of molecular materials.2,3
Most work has focused on derivatives of the 1,2,3,5-dithiadia-
zolyl system 1 (DTDA) and their selenium analogues, with the
intent of using them as molecular conductors.4,5 Their potential
as molecular magnets has also been pursued.6
In contrast to the DTDA system, the solid-state structures
and transport properties of derivatives of the 1,3,2-dithiazolyl
ring 2 (DTA) have received relatively little attention, although
the radicals themselves have been known for well over a
decade.7,8 In the solid state the 4,5-dicyano derivative forms
the simple cofacial dimer 3.9 The pyrazine based compound 4
(PDTA) also dimerizes cofacially,10 but the dimers adopt a
stacked dimer structure similar to that observed for many
dithiadiazolyls. Surprisingly, and despite its structural resem-
blance to PDTA, the benzo-derivative 5 (BDTA)11 associates
in a centrosymmetric manner, i.e., 6, but does not form π-stacks.
(5) (a) Cordes, A. W.; Haddon, R. C.; Oakley, R. T.; Schneemeyer, L.
F.; Waszczak, J. V.; Young, K. M.; Zimmerman, N. M. J. Am. Chem. Soc.
1991, 113, 582. (b) Andrews, M. P.; Cordes, A. W.; Douglass, D. C.;
Fleming, R. M.; Glarum, S. H.; Haddon, R. C.; Marsh, P.; Oakley, R. T.;
Palstra, T. T. M.; Schneemeyer, L. F.; Trucks, G. W.; Tycko, R.; Waszczak,
J. V.; Young, K. M.; Zimmerman, N. M. J. Am. Chem. Soc. 1991, 113,
3559. (c) Cordes, A. W.; Haddon, R. C.; Hicks, R. G.; Oakley, R. T.; Palstra,
T. T. M.; Schneemeyer, L. F.; Waszczak, J. V. J. Am. Chem. Soc. 1992,
114, 5000. (d) Cordes, A. W.; Haddon, R. C.; Hicks, R. G.; Kennepohl, D.
K.; Oakley, R. T.; Schneemeyer, L. F.; Waszczak, J. V. Inorg. Chem. 1993,
32, 1554. (e) Bryan, C. D.; Cordes, A. W.; Goddard, J. D.; Haddon, R. C.;
Hicks, R. G.; Mackinnon, C. D.; Mawhinney, R. C.; Oakley, R. T.; Palstra,
T. T. M.; Perel, A. S. J. Am. Chem. Soc. 1996, 118, 330. (f) Bryan, C. D.;
Cordes, A. W.; Haddon, R. C.; Glarum, S. H.; Hicks, S. H.; Kennepohl, D.
K.; MacKinnon, C. D.; Oakley, R. T.; Palstra, T. T. M.; Perel, A. S.;
Schneemeyer, L. F.; Scott, S. R.; Waszczak, J. V. J. Am. Chem. Soc. 1994,
116, 1205. (g) Bryan, C. D.; Cordes, A. W.; Fleming, R. M.; George, N.
A.; Glarum, S. H.; Haddon, R. C.; MacKinnon, C. D.; Oakley, R. T.; Palstra,
T. T. M.; Perel, A. S. J. Am. Chem. Soc. 1995, 117, 6880. (h) Bryan, C.
D.; Cordes, A. W.; George, N. A.; Haddon, R. C.; MacKinnon, C. D.;
Oakley, R. T.; Palstra, T. T. M.; Perel, A. S. Chem. Mater. 1996, 8, 762.
(6) (a) Banister, A. J.; Bricklebank, N.; Lavender, I.; Rawson, J. M.;
Gregory, C. I.; Tanner, B. K.; Clegg, W.; Elsegood, M. R. J.; Palacio, E.
F. Angew. Chem., Int. Ed. Engl. 1996, 35, 2533. (b) Banister, A. J.;
Bricklebank, N.; Clegg, W.; Elsegood, M. R. J.; Gregory, C. I.; Lavender,
I.; Rawson, J. M.; Tanner, B. K. J. Chem. Soc., Chem. Commun. 1995,
679.
(1) (a) University of Arkansas. (b) University of Guelph. (c) University
of Kentucky. (d) University of Louisville.
(2) (a) Banister, A. J.; Rawson, J. M. In The Chemistry of Inorganic
Ring Systems; Steudel, R., Ed.; Elsevier: Amsterdam, 1992; p 323. (b)
Banister, A. J.; Rawson, J. M. AdV. Hetero. Chem. 1995, 62, 137. (c) Oakley,
R. T. Prog. Inorg. Chem. 1988, 36, 299.
(3) (a) Cordes, A. W.; Haddon, R. C.; Oakley, R. T. In The Chemistry
of Inorganic Ring Systems; Steudel, R., Ed.; Elsevier: Amsterdam, 1992;
p 295. (b) Cordes, A. W.; Haddon, R. C.; Oakley, R. T. AdV. Mater. 1994,
6, 798.
(4) (a) Haddon, R. C. Nature (London) 1975, 256, 394. (b) Haddon, R.
C. Aust. J. Chem. 1975, 28, 2343.
(7) (a) Preston, K. F.; Sutcliffe, L. H. Magn. Reson. Chem. 1990, 28,
189. (b) Chung, Y.-L.; Fairhurst, S. A.; Gillies, D. G.; Preston, K. F.;
Sutcliffe, L. H. Magn. Reson. Chem. 1992, 30, 666.
S0002-7863(97)03338-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/01/1998

A Case Study on the Ternary Heterocycle S3N5C4
J. Am. Chem. Soc., Vol. 120, No. 2, 1998 353
structural prescription for a neutral radical conductor.4 Transport
properties, however, have not been reported for this compound.
A strongly slipped π-stack structure has recently been observed
for the benzo-bridged diradical BBDTA 8; variable temperature
magnetic susceptibility and conductivity measurements indicate
that the material is a small (0.2 eV) bandgap semiconductor.13
Scheme 1
Recently, and as part of an exploration of the architectural
issues behind the diverse structural patterns exhibited by DTA
radicals, we reported the solid-state structures and magnetic
properties of the 2,3-naphthalene- and quinoxaline-based deriva-
tives NDTA 9 and QDTA 10.14 As a development of this work
on NDTA and QDTA we have prepared and characterized the
ternary heterocyclic radical 1,2,5-thiadiazolo[3,4-b]-1,3,2-dithia-
zolo[3,4-b]pyrazin-2-yl 11 (TDP-DTA). Measurement and
Scheme 2
transition near 150 K has been interpreted in the light of the
results of single-crystal X-ray structure determinations at 293
and 150 K.
Results and Discussion
Preparation of Dithiazolyl Radicals. A variety of prepara-
tive routes to dithiazolyl radicals has been developed, and, as
Wolmersha¨user has pointed out,10 there is no single method that
serves for all systems. Most methods, indeed, have relatively
restricted applicability. The reduction of dithiazolylium salts
was one of the first approaches developed. The addition of the
+
NS2 cation to alkynes provides an effective route to the
necessary dithiazolylium cations,15 while the condensation of
ortho-bis(sulfenyl chlorides) with trimethyl silyl azide allows
access to aromatic derivatives such as BDTA11 and BBDTA.13
In this work we have employed the latter method to prepare
NDTA. Thus the reaction of naphthalene-2,3-bis(sulfenyl
chloride) 12, itself prepared from the corresponding dithiol,16
with trimethyl silyl azide leads to the dithiazolylium chloride
[NDTA]Cl 13 (Scheme 1). We note that the preparation of the
dithiol requires very stringent control of the oxidizing conditions;
an excess of PhICl2, or the use of more vigorous oxidants, e.g.,
chlorine, leads to chlorination of the aromatic ring. Reduction
of [NDTA]Cl with triphenylantimony affords the neutral radical,
which is extremely sensitive to atmospheric oxygen.
The preparation of QDTA, by the treatment of the corre-
sponding benzenesulfonamide 14 Scheme 2) with ammonia, has
been described by previous workers,9 but in this work we have
isolated and identified the necessary intermediate imide 15
(QDTAH). Oxidation of QDTAH with aqueous ferricyanide
or molecular oxygen then affords the neutral radical QDTA.
Blue solutions of QDTA in methylene chloride can be reduced
to (yellow) QDTAH by treatment with aqueous dithionite. To
our surprise attempts to extend this procedure to the synthesis
of TDP-DTA failed. The necessary sulfonamide 16 cannot be
prepared by the reaction of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-
comparison of the electrochemical and ESR properties of all
three radicals allows an interpretation of their transport properties
in terms of the energetic and electronic criteria required for
charge transport in a neutral radical conductor. Variable
temperature magnetic susceptibility measurements on TDP-DTA
have also been performed, and the nature of the observed phase
(8) (a) Awere, E. G.; Burford, N.; Mailer, C.; Passmore, J.; Schriver,
M. J.; White, P. S.; Banister, A. J.; Oberhammer, A. J.; Sutcliffe, L. H. J.
Chem. Soc., Chem. Commun. 1987, 66. (b) MacLean, G. K.; Passmore, J.;
Rao, M. N. S.; Schriver, M. J.; White, P. S. J. Chem. Soc., Dalton Trans.
1985, 1405. (c) Wolmersha¨user, G.; Kraft, G. Chem. Ber. 1989, 122, 385.
(d) Harrison, S. R.; Pilkington, R. S.; Sutcliffe, L. H. J. Chem. Soc., Faraday
Trans. 1 1984, 80. 669. (f) Fairhurst, S. A.; Pilkington, R. S.; Sutcliffe, L.
H. J. Chem. Soc. Faraday Trans. 1 1983, 79, 439. (g) Fairhurst, S. A.;
Pilkington, R. S.; Sutcliffe, L. H. J. Chem. Soc., Faraday Trans. 1 1983,
79, 925.
(9) Wolmersha¨user, G.; Kraft, G. Chem. Ber. 1990, 123, 881.
(10) Heckmann, G.; Johann, R.; Kraft, G.; Wolmersha¨user, G. Synth.
Met. 1991, 41-43, 3287.
(11) (a) Awere, E. G.; Burford, N.; Haddon, R. C.; Parsons, S.; Passmore,
J.; Waszczak, J. V.; White, P. S. Inorg. Chem. 1990, 29, 4821. (b)
Wolmersha¨user, G.; Schnauber, M.; Wilhelm, T. J. Chem. Soc., Chem.
Commun. 1984, 573.
(12) Wolmersha¨user, G.; Johann, R. Angew. Chem., Int. Ed. Engl. 1989,
28, 920.
(13) Barclay, T. M.; Cordes, A. W.; de Laat, R. H.; Goddard, J. D.;
Haddon, R. C.; Jeter, D. Y.; Mawhinney, R. C.; Oakley, R. T.; Palstra, T.
T. M.; Patenaude, G. W.; Reed, R. W.; Westwood, N. P. C. J. Am. Chem.
Soc. 1997, 119, 2633.
(14) Barclay, T. M.; Cordes, A. W.; George, N. A.; Haddon, R. C.;
Oakley, R. T.; Palstra, T. T. M.; Patenaude,G. W.; Reed,R. W.; Richardson,
J. F.; Zhang, H. J. Chem. Soc., Chem. Commun. 1997, 873.
(15) Parsons, S.; Passmore, J. Acc. Chem. Res 1994, 27, 101.

354 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Barclay et al.
Scheme 3
b]pyrazine 17 with benzene-N,N-dichlorosulfonamide but can
be accessed by the preparation of the titanocene derivative 18
and its condensation with Cl2NSO2Ph (Scheme 3). However,
treatment of the latter with ammonia leads not to the expected
imide but rather to the recovery of benzene-sulfonamide and
starting dithiol. While this route failed, we eventually discov-
ered that TDP-DTA can be prepared, in one step, by treating
the dithiol 17 with trithiazyl trichloride S3N3Cl3. In the course
+
of this reaction the chloride salt of the binary cation S4N3 is
produced as a side product, along with the neutral (unoxidized)
form of TDP-DTA. Under forcing conditions (excess chlorine
gas) TDP-DTA can be oxidized to what we presume is a
chloride salt of the corresponding dithiazolylium cation, but this
material readily reverts to the neutral material (with loss of
chlorine) upon heating it to 60 °C.
Figure 1. Cyclic voltammetry waves on NDTA, QDTA, and TDP-
DTA radicals (in CH3CN, n-Bu4NPF6 supporting electrolyte, ref SCE).
Table 1. Redox and Ecell Potentialsa (volts vs SCE), Computed
(MNDO) Adiabatic IP, and EA and ∆Hdisp Values (eV) for
1,3,2-Dithiazolyls
compd
NDTA
QDTA
TDP-DTA
Cyclic Voltammetry. The most dramatic feature of the
chemistry described above is the variation in redox properties
along the series NDTA, QDTA, TDP-DTA. While NDTA
reacts very rapidly with atmospheric oxygen, QDTA does not.
Indeed QDTA is generated from its imide by treatment of the
latter with oxygen. TDP-DTA is likewise quite resistant to
oxidation, and chloride salts of the cationic state readily
disproportionate on mild heating back to the neutral form (with
loss of chlorine). To quantify these observations we have
performed cyclic voltammetric (CV) measurements over the
triad of oxidation states, i.e., anion, radical, and cation, available
to these systems. The CV waves are illustrated in Figure 1,
and the half-wave potentials for reduction and oxidation are
E1/2(ox)
0.27
-1.08b
1.29c
7.56
1.71
5.85
0.62
-0.73b
1.30c
8.00
2.18
5.84
1.00
-0.06
1.06
8.55
3.02
E
1/2(red)
Ecell
IP
EA
∆Hdisp
5.53
a All potentals are from solutions in CH3CN, reference SCE.
b Irreversible. c This value is taken as the difference in the cathodic
peak potentials, since the reduction wave is irreversible.
systems containing the thiadiazole unit, e.g., 20 (E1/2 (red) )
0.10 V vs SCE).18 This variation in redox potentials is in striking
contrast to the behavior of DTDA radicals, where ligand effects
summarized in Table 1, along with the values of Ecell (Ecell
)
E1/2(red) - E1/2(ox)). For all DTA radicals oxidation is
essentially reversible. Electrochemical reduction of NDTA and
QDTA is, however, strongly irreversible, as is the case for
BDTA and BBDTA.13 Only for TDP-DTA are both the
oxidation and reduction steps reversible. Also presented in
Table 1 are computed (MNDO) values for adiabatic ionization
potentials (IPs) and electron affinities (EAs) as well as the
difference IP - EA, i.e., the enthalpy change ∆Hdisp for the
gas-phase disproportionation reaction shown in eq 1. This
parameter, which is the gas-phase analogue of Ecell, provides
an indication of the Coulombic barrier to electron transfer in a
neutral radical conductor.
(at the 4-position) have relatively little influence on redox
potentials,19 ionization energies, and spin distributions.20 Per-
haps more notable, however, than the shift in potentials is the
change in the value of Ecell, which drops markedly as the electron
accepting ability of the heterocyclic residue attached to the DTA
(16) (a) Figuly, G. D.; Loop, C. K.; Martin, J. C. J. Am. Chem. Soc.
1989, 111, 654. (b) Block, E.; Eswarakrishnan, V.; Gernon, M.; Ofori-
Okai, G.; Saha, C.; Tang, K.; Zubieta, J. J. Am. Chem. Soc. 1989, 111,
658. (c) Smith, K.; Lindsay, C. M.; Pritchard, G. J. J. Am. Chem. Soc.
1989, 111, 665.
2 DTA a DTA+ + DTA- ∆Hdisp ) (IP - EA) (1)
(17) Lichtenberger, D. L.; Johnston, R. L.; Hinkelmann, K.; Suzuki, T.;
Wudl, F. J. Am. Chem. Soc. 1990, 112, 3302.
(18) Yamashita, Y.; Saito, K.; Suzuki, T.; Kabuto, C.; Mukai, T.; Miyashi,
T. Angew. Chem., Int. Ed. Engl. 1988, 27, 434.
(19) Boere´, R. T.; Moock, K. H. J. Am. Chem. Soc. 1995, 117, 4755.
(20) (a) Boere´, R. T.; Oakley, R. T.; Reed, R. W.; Westwood, N. P. C.
J. Am. Chem. Soc. 1989, 111, 1180. (b) Cordes, A. W.; Goddard, J. D.;
Oakley, R. T.; Westwood, N. P. C. J. Am. Chem. Soc. 1995, 111, 6147.
It is immediately apparent that the electrochemical properties
of NDTA, QDTA, and TDP-DTA parallel their chemical redox
behavior. While NDTA is a remarkably powerful donor,
rivalling, for example, TTF 19 (E1/2 (ox) ) 0.30 V vs SCE),17
TDP-DTA is a strong acceptor, akin to closed shell heterocyclic

A Case Study on the Ternary Heterocycle S3N5C4
J. Am. Chem. Soc., Vol. 120, No. 2, 1998 355
Table 2. ESR Hyperfine Coupling Constants g-Values, Hyperfine
Coupling Constants aN (mT) and Calculated (MNDO) Spin
Densities qN for 1,3,2-Dithiazolyls
a
a
compd
g
aN
1.066
1.101
qN
0.459
0.464
DTA, 2 (R ) H)b
BDTA, 5
2.0071
2.0069
2.0061
2.0067
2.0065
2.0071
TTTA, 7c
1.112 (0.084)
1.106
1.089 (0.129)
0.950 (0.207)
0.465 (0.039)
0.458
0.456 (0.037)
0.435 (0.060)
NDTA, 9
QDTA, 10d
TDP-DTA, 11
a Values in parentheses refer to the nitrogen atoms in the pyrazine
ring. b Reference 7. c Reference 12. d Reference 9.
Figure 2. X-band ESR spectrum of TDP-DTA (in CH2Cl2, sweep
width 0.50 mT).
ring is increased. The drop in Ecell is most pronounced for TDP-
DTA. These experimental (solution) results are supported by
the calculated (gas phase) disproportionation energies. The
increase in IP along the series NDTA, QDTA and TDP-DTA
is more than offset by the larger increase in EA in TDP-DTA,
and the value of ∆Hdisp drops by 0.3 eV. The implications of
these results are elaborated below.
Figure 3. (A) Magnetic susceptibility ø of TDP-DTA as a function of
temperature. (B) Plot of 1/ø vs T for TDP-TDA. (C) Fraction of free
Curie spins of TDP-DTA as a function of temperature.
interactions between the plates up and down the π-stack. Upon
cooling the fraction of free spins slowly decreases, so that by
120 K all paramagnetism is quenched.
ESR Spectra. Values of the g-factors and isotropic hyperfine
coupling constants aN for NDTA, QDTA, TDP-DTA, and
several related 1,3,2-dithiazolyl radicals are provided in Table
2,7,21 along with computed (MNDO) estimates of the spin
density qN on nitrogen. For TDP-DTA the ESR spectrum itself
is illustrated in Figure 2. All the radicals show the expected
features for a 1,3,2-dithiazolyl radical, i.e., a large coupling to
the nitrogen within the DTA ring. Taken together, however,
the spectra reveal a progressive and significant decrease in this
internal aN value along the series NDTA, QDTA, and TDP-
DTA. Coupled to this trend is a larger aN value in the pyrazine
ring of TDP-DTA (relative to QDTA). These experimental
results follow closely the trends in computed spin densities. The
singly occupied molecular orbital (SOMO) of TDP-DTA
extends well out onto the pyrazine ring. In essence the
thiadiazolopyrazine ring is an extremely effective sink for spin
density, much more so than simple benzenoid aromatic residues,
such as in BDTA or NDTA, or even simple thiadiazole units
such as in TTTA.
Magnetic Susceptibility. The bulk magnetic properties of
NDTA and QDTA were reported in an earlier communication.14
In the solid state NDTA is essentially paramagnetic at room
temperature, as expected from its herringbone packing pattern,
which affords little opportunity for intermolecular exchange
coupling. Upon cooling it undergoes two phase transitions, with
eventual loss of paramagnetism. The slipped π-stack structure
of QDTA leads to a room temperature magnetic susceptibility
only 30% of that expected for a free spin system. Presumably
this partial quenching reflects some intermolecular exchange
The results of magnetic susceptibility measurements on TDP-
DTA, taken over the temperature range 4-330 K, are shown
in Figure 3A. It is clear that there is a hysteretic phase transition
in the vicinity of 150 K. In fitting the data we have used a
calculated diamagnetic susceptibility correction of -92 ppm
emu/mol. From the fit to the low-temperature data (Figure 3B)
we obtain a Weiss constant for the ordering transition of about
-34 K. This is the same order of magnitude as the hysteresis,
and on this basis we assign the antiferromagnetic interaction as
the origin of the phase transition. These two parameters have
been used in Figure 3C to obtain the fraction of Curie spins as
a function of temperature. It can be seen that Curie spins count
is temperature dependent throughout the whole temperature
range (down to near 50 K).
For the NDTA and QDTA systems the structural origins of
the observed magnetic changes as a function of temperature in
terms of variations in crystal structure were not investigated.
While dimerization of some form provides a facile explanation
for the loss of paramagnetism, the exact nature of how this
process might occur is not known. In contrast to these to
materials, the ground state of TDP-DTA is antiferromagnetic,
and this unusual observation, coupled with the hysteretic phase
transition observed in the region of 150 K, prompted us to
explore the crystal structure of TDP-DTA above and below the
phase transition observed in the magnetic measurements. The
structural results are described below.
Crystal Structures. Although the compounds NDTA,
QDTA, and TDP-DTA are similar at a molecular level, their

356 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Barclay et al.
Table 3. Crystal Data for 16 and TDP-DTA 11
room-temperature solid-state structures are quite different.
NDTA crystallizes as herringbone arrays,14 like many polycyclic
aromatics,22 e.g., naphthalene23 and anthracene,24 while QDTA
adopts a slipped π-stack structure14 similar to that found for
TTTA.12 The different packing patterns exhibited by NDTA
and QDTA provide a striking example of the effect of the
presence, or absence, of CH---ring van der Waals interactions.25
When such structure-making “tilted-T” contacts are possible,
as in NDTA, then the well-known close-packed or herringbone
arrangement is observed. When the opportunity for such
interactions is reduced by CH/N replacement, as in QDTA, then
a slipped π-stack structure prevails. In TDP-DTA there are no
CH units at all, and extension of the previous argument would
suggest a slipped π-stacked structure, as in QDTA and TTTA,
or perhaps a stacked dimer structure, as in PDTA. As it turns
out, both possibilities are correct.
We have investigated three crystal structures in the course
of this work. That of compound 16, the benzenesulfonamide
derivative of TDP-DTA, was determined to establish the effect
of substitution on ring planarity and to create bench mark bond
lengths and angles for comparison with those of the radical (vide
infra). The crystal structure consists of discrete molecules of
16, with two molecules per asymmetric unit, differing primarily
in the degree of torsion about the N-SO2Ph bond. Both
molecules, save for the substituted nitrogen atoms, are planar
to within 0.085 Å, and the three-atom SNS envelope “flaps”
make dihedral angles of 137.89(15)° and 143.17(15)° with the
adjacent SCCS planes. These features are similar to that found
in the toluenesulfonamide of 4,5-dicyano-DTA.9
The crystal structure of TDP-DTA, based on material grown
by fractional sublimation at 110-60 °C/10-2 Torr, has been
determined at both 293 and 150 K. These two temperatures
are respectively above and below the phase transition observed
in the magnetic measurements. While crystal selection and data
collection at 293 K was a relatively simple task, characterization
of the low temperature phase was extremely difficult. In most
cases the crystals fractured, often violently, upon cooling, and
on those occasions when the crystal displayed a sufficient
lifetime at low temperature to allow data collection, the intensity
of the data was low in comparison to the room-temperature
response. The best refinement, the one reported here, is from
a partial data set (θmax ) 21.5°) obtained from a crystal which
fractured after 36 h at 150 K.
Information on the unit cells of the room and low temperature
phases is provided in Table 3, atomic coordinates are listed in
Table 4, and mean intramolecular bond distances are sum-
marized in Table 5. At room temperature crystals of TDP-DTA
belong to the triclinic space group P1h, with two radicals per
unit cell. The space group remains unchanged at 150 K, but
the unit cell is dramatically different, containing two dimeric
units. At 150 K there are three interannular S---S contacts, all
of which are greater than 3.4 Å. As such these contacts are
significantly longer than the interannular S---S “bonds” in other
DTA dimers, e.g., 3 and 6, and fall perilously close to the van
der Waals separation for two sulfurs (3.6 Å).26 Interestingly,
of the three distances the shortest is between the two “tail”
sulfurs (SC---SC in Table 5, i.e., S3 and S31 in Table 4).
Dimerization has virtually no effect on the bonds within
compd
formula
fw
a, Å
b, Å
16
TDP-DTA
TDP-DTA
S6N10C8
428.52
7.489(7)
9.593(4)
10.759(6)
65.77(4)
74.10(6)
74.64(6)
667.5(9)
P1h
S4O2N5C10H5 S3N5C4
355.42
10.2388(8)
11.8299(9)
214.26
4.4456(8)
8.407(2)
c, Å
13.1024(12) 9.671(3)
R, deg
â, deg
γ, deg
V, Å3
space group
Z
115.066(7)
94.083(8)
108.405(6)
1324.7(2)
P1h
71.34(2)
89.28(2)
87.80(2)
342.2(1)
P1h
4
2
2
temp, K
293
0.70
293
0.98
150
1.04
µ, mm-1
data with I > nσ(I) 5484 (n ) 0) 1425 (n ) 2.5) 1364 (n ) 2.5)
parameters refined 380
110
97
R(F), Rw(F)a
0.050, 0.052 0.032, 0.055
0.111, 0.137
a R ) [∑||Fo| - |Fc||]/[∑|Fo|]; Rw ) {[∑w||Fo| - |Fc|| ]/
2
2
[∑(w|Fo| )]}1/2
.
Table 4. Atomic Parameters x, y, z and Biso for TDP-DTA
T ) 293 K
a
x
y
z
Beq
S1
S2
S3
0.82686(11)
1.05427(9)
0.22142(9)
0.4998(3)
0.7509(3)
1.0400(4)
0.2327(3)
0.4537(3)
0.6934(4)
0.4269(3)
0.5523(3)
0.8156(3)
0.53386(5)
0.29869(5)
-0.12463(5)
0.3019(2)
0.0523(2)
0.4939(2)
0.0744(2)
-0.1393(2)
0.3358(2)
0.1383(2)
0.0145(2)
0.2126(2)
0.17330(5)
0.42462(4)
0.17519(4)
0.1116(1)
0.3736(1)
0.3177(2)
0.0846(1)
0.3063(1)
0.2000(2)
0.1552(1)
0.2842(1)
0.3304(1)
2.849(18)
2.335(16)
2.145(15)
2.27(5)
2.11(5)
2.83(6)
2.21(5)
2.32(5)
1.97(5)
1.85(5)
1.80(5)
1.86(5)
N1
N2
N3
N4
N5
C1
C2
C3
C4
T ) 150 K
x
y
z
Biso
S2
S1
S3
S21
S11
S31
N2
N1
N3
0.5750(4)
0.3523(4)
0.5611(4)
0.1045(4)
-0.1122(4)
0.1025(4)
0.623(1)
0.386(1)
0.455(1)
0.645(1)
0.443(1)
-0.074(1)
0.160(1)
-0.025(1)
-0.017(1)
0.186(1)
0.544(2)
0.582(2)
0.463(2)
0.425(2)
-0.034(2)
0.007(2)
0.122(2)
0.079(2)
0.2323(3)
0.2205(3)
0.8819(3)
0.3750(3)
0.3579(3)
1.0177(3)
0.524(1)
0.512(1)
0.132(1)
0.776(1)
0.766(1)
0.646(1)
0.663(1)
0.276(1)
0.902(1)
0.913(1)
0.405(1)
0.643(1)
0.639(1)
0.396(1)
0.533(1)
0.771(1)
0.780(1)
0.543(1)
0.1845(3)
0.4392(3)
0.1939(3)
0.1413(3)
0.3987(3)
0.1592(3)
0.1220(9)
0.3907(9)
0.3315(9)
0.0992(9)
0.3269(9)
0.3565(9)
0.0856(9)
0.2843(10)
0.2917(9)
0.0636(9)
0.2124(11)
0.1684(11)
0.3019(11)
0.3472(11)
0.3083(11)
0.2649(11)
0.1328(11)
0.1737(11)
1.20(7)
1.03(7)
0.99(7)
1.08(7)
1.11(7)
0.97(7)
0.8(2)
0.9(2)
1.2(2)
1.0(2)
1.1(2)
1.2(2)
1.2(2)
1.1(2)
1.2(2)
1.1(2)
0.9(2)
1.1(2)
0.8(2)
0.9(2)
0.9(2)
0.8(2)
0.8(2)
0.8(2)
N5
N4
N11
N21
N31
N41
N51
C4
C3
C2
C1
C11
C21
C31
C41
a Beq is the mean of the principal axes of the thermal ellipsoid.
individual molecules; the bond lengths in the low- and high-
temperature structures are almost identical. Dimerization does
not lead to any significant puckering of either of the molecular
halves, both of which remain planar to within 0.05 Å. The
structural differences observed between TDP-DTA and its
sulfonamide derivative 16 are largely restricted to the dithiazolyl
ring and follow the pattern expected upon reduction of any 1,3,2-
(21) Chung, Y.-L.; Sandall, J. P. B.; Sutcliffe, L. H.; Joly, H.; Preston,
K. F.; Johann, R.; Wolmersha¨user, G. Magn. Reson. Chem. 1991, 31, 625.
(22) Gavezzotti, A.; Desiraju, G. R. Acta Crystallogr. 1988, 44B, 427.
(23) Dunitz, J. D.; Brock, C. P. Acta Crystallogr. 1982, 38B, 2218.
(24) Brock, C. P.; Dunitz, J. D. Acta Crystallogr. 1990, 46B, 795.
(25) Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Am. Chem. Soc. 1994,
116, 3500.
(26) Bondi, A. J. Phys. Chem. 1964, 68, 441.

A Case Study on the Ternary Heterocycle S3N5C4
J. Am. Chem. Soc., Vol. 120, No. 2, 1998 357
Table 5. Mean Structural Parameters (Å) in 16 and TDP-DTA
11a,c
16
TDP-DTA
TDP-DTA
T, K
293
1.73(3)
293
150
1.627(14)
1.73(3)
NA-SA
SA-CA
CA-CA
CA-NB
NB-CC
CC-CC
CC-NC
NC-SC
SA---SA
SC---SC
1.636(3)
1.728(2)
1.448(2)
1.320(2)
1.356(3)
1.447(2)
1.334(4)
1.620(8)
1.755(16)
1.467(6)
1.297(3)
1.368(4)
1.424(4)
1.333(10)
1.620(2)
1.45(2)
1.319(14)
1.357(15)
1.44(3)
1.33(4)
1.614(17)
3.48(5)b
3.401(5)b
a Numbers in parentheses are the greater of the range or ESD.
b Intradimer contacts. c Atoms grouped by ring as shown below. Ring
labeling scheme:
dithiazolyl, notably a lengthening of the S-N and S-C bonds.13
That bond length changes extend into the pyrazine ring provides
additional evidence for the extent of delocalization of the SOMO
in TDP-DTA.
Figure 4 provides several views of the packing of TDP-DTA
at 293 and 150 K. Both structures consist of ribbons of radicals
(or dimers) layered into slipped π-stacks not unlike those found
in QDTA; only the degree of slippage is more marked in the
present case. At 293 K the lateral slippage between adjacent
layers is such that equivalent atoms are separated by 4.454(1)
Å, i.e., the unit cell repeat. In the 150 K structure slippage of
the dimeric units is similar. For example, the tail sulfur (SC)
of one dimer is 4.556(5) Å from the tail sulfur (SC) in the dimer
above it. Outside of the intradimer S---S contacts already noted
there are several short intermolecular (head-to-tail) S---S
interactions (3.350(5) and 3.357(5) Å).
Figure 4. Three views of the TDP-DTA packing at 293 K (left) and
150 K (right). Above: sheets of radicals/dimers. Center: ribbons of
radicals/dimers. Bottom: end-on view of ribbons. Supercells (see Table
6) are shown with heavy lines.
The association of TDP-DTA radicals at low temperature is
not, in itself, a novel finding. Spin pairing by dimerization,
i.e., covalent bond formation, is the fate of most sterically
unencumbered radicals. What is interesting in the present
system is the fact that the association does not lead to a complete
quenching of paramagnetism. Also of interest is the mechanism
of the phase transition; how do the two structures interconvert?
Our suggested mechanism for the structural interchange in
TDP-DTA is built on the premise that lateral displacement or
slippage of molecules within the crystals is reversible,31 as
implied by the magnetic behavior, and that the crystal symmetry
is maintained throughout the phase transition. Accordingly the
interconversion of the two structures can be envisaged as taking
place within the confines of a common P1h supercell. Analysis
of the separate lattices for the two phases of TDP-DTA reveals
two similar supercells comprised of eight layers of the 293 K
structure and four layers of the 150 K structure. The dimensions
of these cells are listed in Table 6 and illustrated in Figure 4.
Individual layers, or plates, within the xy plane of these
supercells experience very little internal reorganization, indeed
the a and b vectors and the associated γ angle are virtually
identical. To a first approximation, conversion of the room-
temperature lattice into the low-temperature structure can be
envisaged as taking place by a series of lateral displacements
of these layers along the x direction, in a tectonic platelike
fashion. The relative motion of the plates can be understood
with reference to the simplified representation shown in Figure
In the many DTDA systems which we have studied, the
π-stacking of plates has been almost invariably superimposable.
Dimerization requires little more than the coupling of the lattice
to a charge density wave parallel to the stacking direction, so
as to produce the characteristic oscillation in interplanar spacing
along the stack.5 In slipped π-stacks such as TDP-DTA
dimerization requires displacive motion of layers of molecules
across the stacking direction rather than along it. The abrupt,
almost explosive fracturing of single crystals of TDP-DTA upon
rapid cooling is reminiscent of the so-called “jumping crystal”
phenomenon described by others.27 Literature precedent for
plate slippage interconversions in molecular crystals are,
however, few. The closest analogy that we have found is the
so-called martensitic28,29 phase transition observed in ttatt-
perhydropyrene.30
(30) Ding, J.; Herbst, R.; Praefcke, K.; Kohne, B.; Saenger, W. Acta
Crystallogr. 1991, 47B, 739.
(31) (a) De´coret, C. Molecules Phys. Chem. Biol. 1988, 1, 159. (b)
Megaw, H. D. Crystal Structures, a Working Approach, W. B. Saunders
Co.: London, 1973.
(27) Dunitz, J. D.; Bernstein, J. Acc. Chem. Res 1995, 28, 193.
(28) Smallman, R. E. Modern Physical Metallurgy, 3rd ed.; Butterworth:
London, 1970.
(29) Etter, M. C.; Siedle, A. R. J. Am. Chem. Soc. 1983, 105, 641.

358 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Barclay et al.
Table 6. Supercell Vectorsa and Dimensionsb for TDP-DTA
is over 1 V. More importantly the attachment of extremely
electron withdrawing substituents, as in TDP-DTA, leads to a
decrease in the cell potential corresponding to the dispropor-
tionation of the radical. This decrease can be related to a lower
barrier to charge transport between radical centers in the solid
state and augurs well for the use of DTA derivatives in the
design of single component neutral radical conductors. The
crystal structure of TDP-DTA at 298 K consists of slipped
π-stacks. However, while this configuration formally fulfills
the structural criteria for a neutral π-radical conductor, i.e.,
evenly spaced plates, charge correlation effects still outweigh
the electronic stabilization afforded by interannular orbital
overlap, and the material remains a Mott insulator, with a
pressed pellet conductivity <10-6 S cm-1. It is not difficult,
however, to imagine more extended heterocyclic frameworks
in which the ∆Hdisp is further diminished by increasing the value
of EA, and we are certainly pursuing the design and synthesis
of such materials. An electronegative molecular metal, akin to
the polymer (SN)x,32 may be possible. The major solid-state
reorganization that accompanies the dimerization of TDP-DTA
represents, to our knowledge, the first full characterization of
such a process for a slipped π-stack structure. While the
magnetic susceptibility changes that accompany the phase
change, i.e., the reduction in free spins, are clearly understand-
able in terms of the observed solid-state rearrangement, it is
noteworthy that some paramagnetism persists after dimerization
and that the structure is a ground state antiferromagnet. This
observation suggests that the intermolecular resonance interac-
tion between the radical halves of the dimer is extremely weak,
comparable to the magnitude of the exchange interaction
between the two unpaired electrons. The implications of this
possibility are currently being pursued.
293 K
150 K
a
b
c
R
â
γ
9.660(2) [110]
11.408(4) [1h11h]
31.923(6) [71h0]
118.78(2)
75.68(2)
77.23(2)
9.593(4) [01h0]
11.300(4) [101h]
29.96(3) [4h00]
113.70(5)
74.64(5)
77.57(3)
a Supercell vectors expressed relative to standard cell. b The values
of a, b, and c are in Å; R, â and γ are in deg.
Figure 5. Qualitative views of the two phases of TDP-DTA, illustrating
the direction and magnitude of “tectonic plate”slippage during the phase
transition. The common supercell is shown with dashed lines.
5. Accordingly layers 2, 3, and 4 all shift in the same direction
but to different extents. The largest shift (over 4 Å) is for layer
4. The motion of layers 5, 6, and 7 mirror these movements
but in the opposite sense (Figure 5), i.e., a large shift for layer
5, with smaller shifts for layers 6 and 7. Insofar as these shifts
are in opposite directions, the strain on the structure from the
associated sheer forces between layers 4 and 5 must be
considerable; the process amounts to a microscopic earthquake!
It is not surprising, therefore, that crystals of TDP-DTA tend
to shatter easily on cooling, as internal strain builds up in the
high temperature structure and then is suddenly released. The
hysteresis in the magnetic measurements can likewise be
attributed to this kinetic effect. That the phase transition failed
to occur (at 150 K) on one occasion underscores the importance
of structural defects in acting as nucleation sites.
While the one-dimensional model for the motion of layers is
conceptually appealing, it is incomplete. The discrepancy in
the magnitude of the supercell c vectors, and the R angles,
signals “tectonic plate” motion in the y direction as well as along
x. The extent of motion along y is, however, much smaller
than along x. A refinement of the supercell model, made by
doubling the supercell from 8 to 16 layers, produces discrep-
ancies in c and R of similar magnitude, but opposite sign.
Clearly, an even larger supercell is required for a perfect match,
but the conclusions of such a treatment would not differ
qualitatively from those resulting from the simple eight-layer
model presented here.
Experimental Section
General Procedures and Starting Materials. Ammonia (Mathe-
son), chloropyrazine (Aldrich), dichloroquinoxaline (Aldrich), naphthalene-
2-thiol (Aldrich), bis(cyclopentadienyl)titanium dichloride (Aldrich),
thiourea, iodobenzene, benzenesulfonamide (Aldrich), potassium fer-
ricyanide (Aldrich), trimethylsilyl azide (Aldrich), triphenylantimony
(Aldrich), silver powder (Aldrich) were all reagent grade chemicals
obtained commercially. The compounds tetrachloropyrazine,33 2,3-
diamino-5,6-dichloropyrazine,34 5,6-dichloro-1,2,5-thiadiazolo[3,4-b]-
pyrazine,34 iodobenzene dichloride,35 5,6-dithiolo-1,2,5-thiadiazolo[3,4-
b]pyrazine 17,36 naphthalene-2,3-dithiol,16 trithiazyl trichloride (S3N3Cl3),37
and N,N-dichlorobenzenesulfonamide38 were all prepared by standard
literature procedures. 1,3,2-Dithiazolo[4,5-b]quinoxaline-2-benzensul-
fonamide was also prepared as described,9 but was recrystallized before
use from chlorobenzene as yellow needles, mp 210-213 °C. Solvents
were of reagent grade and dried by distillation from P2O5 (for CH3CN
and CH2Cl2), Na (for toluene), and Mg (for EtOH). Crystals for X-ray
work were grown by sublimation in an ATS series 3210 three-zone
tube furnace mounted horizontally and linked to a series 1400
temperature control system. Melting points are uncorrected. 1H and
13C NMR spectra were recorded on a Varian Gemini 200 MHz NMR
or a Varian Unity 400 MHz NMR spectrometer; chemical shift values
were internally referenced to TMS or to the residual proton signals of
the solvent (δ, CHCl3). Infrared spectra (Nujol mulls, KBr optics) were
recorded on a Nicolet 20SX/C FTIR spectrometer at 2 cm-1 resolution.
(32) Labes, M. M.; Love, P.; Nichols, L. F. Chem. ReV. 1979, 1, 79.
(33) Allison, C. G.; Chambers, R. D.; MacBride, J. A. H.; Musgrave,
W. K. R. J. Chem. Soc. C 1970, 1023.
(34) Tong, Y. C. J. Heterocycl. Chem. 1975, 12, 451.
(35) Lucas, H. J.; Kennedy, E. R. Organic Syntheses; Wiley: New York,
1955; Collect. Vol. 3, p 482.
(36) Tomura, M.; Yamashita, Y. J. Mater. Chem. 1995, 5, 1753.
(37) Alange, C. G.; Banister, A. J.; Bell, B. J. Chem. Soc., Dalton Trans.
1972, 2399.
Summary and Conclusions
A range of synthetic methods now exists for the attachment
of the 1,3,2-DTA radicals to organic and heterocyclic frame-
works. In contrast to the behavior of 1,2,3,5-DTDA radicals,
the redox chemistry of the DTA residue is markedly dependent
on the donor/acceptor properties of the rest of the molecule.
The shift in reduction potentials between NDTA and TDP-DTA
(38) Akiyoshi, S.; Okuno, K. J. Am. Chem. Soc. 1954, 76, 693.

A Case Study on the Ternary Heterocycle S3N5C4
J. Am. Chem. Soc., Vol. 120, No. 2, 1998 359
Low resolution mass spectra (70 eV, EI) were obtained on a Kratos
MS890 spectrometer using direct probe inlet techniques. X-Band ESR
spectra were recorded on a Varian E-109 spectrometer with DPPH as
a field marker. Elemental analyses were performed by MHW
Laboratories, Phoenix, AZ 85018.
vacuo to yield the crude red-brown disodium salt (1.70 g, 6.9 mmol).
This solid was added to 100 mL of CH3CN, and finely powdered Cp2-
TiCl2 (1.72 g, 6.9 mmol) was slowly added to the stirred mixture. The
red-brown solid was slowly converted into a dark green solid. After
15 h the crude product was filtered off, and Soxhlet extracted
exhaustively (72 h) with CH2Cl2. Addition of toluene to the extracts
and slow rotary evaporation of the dark green solution afforded green
black microcrystals of TDPS2TiCp2 18 (1.06 g, 2.8 mmol, 42%), mp
> 300 °C. IR (1600-400 cm-1), 1379 (m), 1351 (m) 1309 (w), 1248
(w) 1114 (s), 1083 (br, w), 937 (br, w), 882 (m), 829 (br, s), 816 (m),
731 (br, w), 652 (m), 626 (w), 558 (w), 444 (w), 411 (m) cm-1. Anal.
Calcd for C14H10N4S3Ti: C, 44.45; H, 2.66; N, 14.81. Found: C, 44.61;
H, 2.63, N, 14.48. 1H NMR (δ, CDCl3): 5.28 (s, 5H), 6.02 (s, 5H).
Preparation of Compound 16. N,N-Dichlorobenzenesulfonamide
(0.39 g, 1.7 mmol) was added to a slurry of 18 (0.65 g, 1.7 mmol) in
75 mL of CH3CN. The green solution immediately turned red-brown.
After 2 h at room temperature the mixture was filtered, and the filtrate
evaporated to dryness in vacuo to leave a mixture Cp2TiCl2 (red) and
a yellow crystalline material. This mixture was extracted with 50 mL
of warm toluene and the extract evaporated to leave a solid which was
dissolved in 50 mL of warm CH3CN. The solution was then cooled to
0 °C overnight. Subsequent filtration afforded yellow needles of the
benzenesulfonamide 16 (0.30 g, 0.80 mmol, 49%), mp 184-86 °C.
Transparent yellow blocks suitable for X-ray work were grown by
sublimation at 130-80 °C/10-2 Torr. IR (1600-400 cm-1): 1582 (w),
1403 (w), 1324 (w), 1313 (w), 1296 (w), 1250 (w), 1195 (w), 1175
(s), 1112 (s), 1083 (m), 1024, 1002 (w), 943 (w), 908 (w), 1175 (s),
1171 (s), 1129 (m), 818 (m) 813 (m), 781 (s), 757 (s), 726 (s), 689 (s),
Preparation of Naphthalene-2,3-bis(sulfenyl chloride). Freshly
prepared iodobenzene dichloride (4.88 g, 17.8 mmol) was slowly added
portionwise to a stirred solution of naphthalene-2,3-dithiol (1.55 g, 8.1
mmol) in 50 mL of CH2Cl2 at 0 °C, and the resulting mixture allowed
to warm slowly (2 h) to room temperature. The solvent was then
removed in vacuo from the filtrate to leave a yellow crystalline solid
that was recrystallized from 15 mL CH3CN to give naphthalene-2,3-
bis(sulfenyl chloride) (1.62 g, 6.2 mmol, 77%), mp 90-93 °C. IR
(1600-400 cm-1) 1618 (w), 1569 m), 1311 (w), 971 (w), 899 (w),
880 (s), 770 (w), 755 (vs), 722 (w), 470 (s) cm-1 1H NMR (δ, CDCl3)
.
8.1 (s, 2H), 7.85 and 7.55 (AA′BB′, 4H). Anal. Calcd for C10H6NS2-
Cl2: C, 45.99, H, 2.32; Cl, 27.15. Found: C: 46.17; H, 2.40; Cl,
27.40.
Preparation of Naphthalene-2,3-(1,3,2-dithiazolyl) NDTA.
A
solution of trimethylsilyl azide (0.55 g, 4.8 mmol) in 10 mL of CH2-
Cl2 was added dropwise to a stirred solution of naphthalene-2,3-bis-
(sulfenyl chloride) (1.2 g, 4.6 mmol) in 40 mL CH2Cl2. Slow
effervescence of N2 was observed, and the solution changed to a dark
red color. A cherry red precipitate of naphthalene-2,3-(1,3,2-dithia-
zolylium chloride) was also produced. After 2 h the solid was filtered
off, washed with 2 × 20 mL CH2Cl2, and dried in vacuo. IR (1600-
400 cm-1) 1557 (w), 1350 (w), 1323 (w), 1264 (m), 1154 w), 1073
(m), 965 (w), 883 (s), 801 (w), 783 (m), 750 (s), 601 (w), 551 9w),
429 (w), 477 (m), 429 (m) cm-1. This crude salt was slurried in 60
mL of CH3CN and reduced by the addition of a solution of triphenyl-
antimony (0.81 g, 2.3 mmol) in 10 mL CH3CN at 0 °C. After 1 h the
crude product was filtered off and dried in vacuo. Purification was
effected by fractional sublimation at 80-50 °C/10-2 Torr, to afford
purple plates of NDTA 9 (0.28 g, 1.4 mmol, 30% based on bis(sulfenyl
chloride)), mp 149-50 °C. IR (1600-400 cm-1) 1315 (w), 1269 (w),
127 (w), 1195 (w), 874 (vs), 767 (s), 700 (s), 693 (m), 480 (m), 470
637 (m), 599 (s), 569 (s), 549 (s), 494 (w), 472 (m), 424 (w) cm-1
.
MS (EI, m/e): 355 (M+, 16%), 291 ([M - SO2]+, 8%), 214 ([M -
SO2Ph]+, 100%), 141 (SO2Ph+, 64%), 77 (C6H5+, 100%). Anal. Calcd
for C10H5N5O2S4: C, 33.79; H, 1.42; N, 19.70. Found: C, 33.87; H,
1.44; N, 19.81.
Preparation of TDP-DTA. Solid S3N3Cl3 (1.50 g, 6.1 mmol) was
added to a slurry of the dithiol 17 (1.20 g, 5.9 mmol) in 50 mL of
CH3CN, and the mixture was heated at a gentle reflux for 4 h. The
resulting mixture, a red solution and a dark brown solid, was filtered,
and the solid dried in vacuo. IR analysis of this mixture revealed the
presence of neutral TDP-DTA and the salt S4N3Cl (by comparison of
its IR spectrum with that of a known sample39 ). The latter was
removed by reducing the whole with excess Ph3Sb (1.06 g, 3.0 mmol)
in refluxing CH3CN for 30 min (this effected the conversion of S4N3-
Cl to the more soluble S4N4). Hot filtration then afforded black
microcrystals of TDP-DTA 11, which were purified by fractional
sublimation over the range 110-60 °C/ 10-2 Torr as lustrous black
needles (0.56 g, 2.6 mmol, 44%) dec >186 °C. IR (1600-400 cm-1),
1429 (w), 1379 (w), 1316 (br, m), 1246 (w), 1136 (w), 906 (w), 880
(m), 867 (m), 805 (s), 713, 694 (m), 665 (m), 641 (w), 534 (s), 503
(s), 426 (m) cm-1. MS (EI, m/e): 214 (M+, 85%, 1680 ([M - SN]+,
7%), 78 (S2N+, 15%), 46 (SN+, 100%). Anal. Calcd for C4N5S3: C,
22.42; N, 32.69. Found: C, 22.91; N, 33.01.
Cyclic Voltammetry. Cyclic voltammetry on DTA radicals was
performed on a PAR 273A electrochemical system (EG&G Instruments)
with scan rates 50-100 mV s-1 on solutions of the radical (0.1 M
tetra-n-butylammonium hexafluorophosphate) in CH3CN. Potentials
were scanned from -2.5 to 1.5 V with respect to the quasi-reference
electrode in a single compartment cell fitted with Pt electrodes and
referenced to the ferrocenium/ferrocene couple at 0.38 V vs SCE.40
X-ray Measurements. X-ray data were collected on ENRAF-
Nonius CAD-4 diffractometers (at Arkansas and Louisville) with
monochromated Mo KR radiation. Crystals were mounted on glass
fibers with silicone or epoxy. Data were collected using a θ/2θ
technique. The structures were solved using direct methods and refined
by full-matrix least squares which minimized ∑w(∆F)2.
(w) cm-1 MS (m/z): 204 (M+, 100%), 158 ([M-NS]+, 15%), 140
.
(6%), 114 (11%), 102 12%), 69 (4%). Anal. Calcd for C10H6NS2: C,
58.80, H, 2.96; N, 6.86. Found: C, 59.03; H, 3.12; N, 6.83.
Preparation of 1,3,2-Dithiazolo[4,5-b]quinoxaline QDTAH. An-
hydrous ammonia was gently bubbled through a slurry of sulfonamide
14 (2.00 g, 5.76 mmol) in 100 mL of CH2Cl2 held at 0 °C, to produce
an off-white gelatinous precipitate in a green solution. After 15 min
the gas flow was halted, and the precipitate of benzenesulfonamide
filtered off. The solvent was removed in vacuo from the filtrate, and
the residual solid extracted with 100 mL of warm toluene (under
nitrogen). The mixture was again filtered (to remove residual benzene-
sulfonamide), and the solvent was again removed in vacuo. The yellow
green product (0.91 g, 4.4 mmol, 76%) was recrystallized from hot
ethanol as pale yellow needles of QDTAH 15, dec 122-24 °C. IR:
ν(NH) 3168 cm-1 and (1600-400 cm-1) 1559 (w), 1247 (w), 1161
(m), 1130 (w), 1092 (m), 1016 (w), 1008 (w), 932 (m), 770 (m), 757
(s), 669 (w), 643 (m), 595 (m), 466 (w), 412 (m) cm-1 1H NMR (δ,
.
CDCl3): 4.89 (s, NH), 7.62 and 7.86 (AA′BB′, 4H). MS (m/z): 206
(M+, 100%,), 160 ([M - NS]+, 61%), 102 (33%), 77 (21%), 51(18%).
Anal. Calcd for C8H5N3S2: C, 46.36, H, 2.43; N, 20.27. Found: C,
46.53; H, 2.27, N, 20.06.
Preparation of 1,3,2-Dithiazolo[4,5-b]quinoxalin-2-yl QDTA.
Crude QDTAH, prepared as described above from the sulfonamide (2.18
g, 6.3 mmol), was dissolved in 100 mL of CH2Cl2, the solution was
treated with a solution of potassium ferricyanide (2.0 g, 6.1 mmol) in
100 mL of H2O, and the two-phase mixture was vigorously stirred for
8 h. The dark blue organic layer was then separated, dried over sodium
sulfate, and evaporated to dryness to leave QDTA 10 as a blue/black
crystalline solid (1.0 g, 4.8 mmol, 77% from sulfonamide). The product
was purified by fractional sublimation over the range 90-45 °C/10-2
Torr to yield black needles, mp 137-140 °C (lit. 132 °C9).
Magnetic Susceptibility Measurements. Magnetic susceptibilities
were measured over the temperature range 5-330 K on a George
Associates Faraday balance operating at 0.5 T.
Preparation of TDPS2TiCp2 18. Solid 17 (1.50 g, 7.4 mmol) was
added to a solution of sodium ethoxide prepared from sodium (0.34 g,
14.8 mmol) and anhydrous ethanol (30 mL). The resulting slurry was
stirred under N2 for 90 min, and then the solid filtered off and dried in
(39) Jolly, W. L.; Maguire, K. D. Inorg. Syntheses 1967, 9, 102.
(40) Boere´, R. T.; Moock, K. H.; Parvez, M. Z. Anorg. Allg. Chem. 1994,
620, 1589.

360 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Barclay et al.
Electronic Structure Calculations. MNDO calculations were
carried out on a Pentium 166 PC using the MOPAC93 suite of
programs41 compiled to run under DOS. All geometries were optimized
within the constraints of C2V symmetry. The potential for folding of
the anion derivatives13 was not explored. Spin densities qN refer to
the square of the pπ-orbital coefficients in the SOMO.
of us (T.M.B.) acknowledges the Department of Education for
a doctoral fellowship.
Supporting Information Available: Tables of crystal data,
structure solution and refinement, bond lengths and angles, and
anisotropic thermal parameters for the structures reported (14
pages). See any current masthead page for ordering and Internet
access instructions.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada, the NSF/EPSCOR
program, and the State of Arkansas for financial support. One
(41) MOPAC93, Quantum Chemistry Program Exchange.
JA973338A