Small molecule fixation by a dithiadiazolyl radical: X-ray crystal structures of (CF3C6H3FCNSSN)2 and (CF3C6H3FCNSSN)2·G (G = N2, Ar, CO2 and SO2)

Article abstract of DOI:10.1039/b307509p

The title dithiadiazolyl radical, F₃CC₆H ₃FCNSSN (1) forms inclusion structures with small molecules (such as N₂, CO₂, Ar and SO₂) when sublimed under partial atmospheres of the guest.

Full text of DOI:10.1039/b307509p

Small molecule fixation by a dithiadiazolyl radical: X-ray crystal
structures of (CF3C6H3FCNSSN)2 and (CF3C6H3FCNSSN)2·G (G = N2,
Ar, CO2 and SO2)†
Caroline S. Clarke, Delia A. Haynes, Jeremy M. Rawson* and Andrew D. Bond‡
Department of Chemistry, The University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: jmr31@cus.cam.ac.uk
Received (in Cambridge, UK) 1st July 2003, Accepted 30th September 2003
First published as an Advance Article on the web 20th October 2003
¯
The title dithiadiazolyl radical, F3CC6H3FCNSSN (1) forms
inclusion structures with small molecules (such as N2, CO2,
Ar and SO2) when sublimed under partial atmospheres of
the guest.
space group P1.¶ The molecules are of unexceptional geometry
and associate as cis-oid dimers in the solid state, with four
molecules in the asymmetric unit. The intra-dimer S…S
separations fall in the range 2.096–3.076 Å, typical for
dithiadiazolyl radicals.3 Repulsions between the CF3 groups in
the para-positions leads to a small inclination ( ~ 7°) between
heterocyclic ring planes within each dimer. The dimers are
linked together to form sheets in the ab plane (Fig. 1) through
electrostatic Sd+…Nd2 interactions (3.15–3.32 Å) and
We have been interested for some time in the preparation and
properties of fluorinated1 and perfluorinated2 dithiadiazolyl
radicals. Fluorination has led to some unusual structural
features in comparison to their hydrogenated analogues; For
example, whilst the majority of dithiadiazolyl radicals dimerise
in the solid state,3 the perfluorinated derivatives, p-
BrC6F4CNSSN and p-NC.C6F4CNSSN are both monomeric.2
The latter undergoes a phase transition to a magnetically
ordered state at 36K. As an extension of this work we have
begun to investigate trifluoromethyl derivatives of dithiadiazo-
lyls in which both the electronic and steric effects of the CF3
group are more significant than those of fluorine. Previous work
by Mews4 and Passmore5 have shown that the CF3 group has a
pronounced effect on the properties of thiazyl radicals; Both
CF3CNSSN and F3CCSNSCCF3 have low melting points (mp
37 °C and 12 °C respectively) and belong to a rare group of
paramagnetic liquids.5 Here we report the structure of 1, and its
inclusion complexes with N2, CO2, Ar and SO2.
Sd+
…
d2F3C interactions (3.19–3.42 Å). Packing of these sheets
forms a close-packed structure (Fig. 2a) with further S…N
interactions (3.562 and 3.585 Å) between layers. These are
likely to comprise electrostatic Sd+…Nd2 interactions plus the
possibility of a p*–p* bonding interaction between singly
occupied molecular orbitals.
1
When 1 was sublimed under ca. 3 atm of N2 a new phase was
obtained, 1a, whose structure was also determined by single-
crystal X-ray diffraction.‡ 1a crystallises in the orthorhombic
space group Pbcn with two molecules in the asymmetric unit.
Like 1, the dithiadiazolyl radicals associate as co-facial dimers
of unexceptional geometry, with intra-dimer S…S separations
of 3.03–3.09 Å and with the heterocyclic ring planes inclined at
6.5°. Dimers form a similar layer-like structure to 1 (Fig. 1) in
the bc plane although the structure is now buckled to generate
channels (Fig. 2b) which run parallel to the crystallographic c-
axis. The channels contain diffuse electron density, which could
not be modelled as discrete atoms. Application of a continuous
solvent-area model led to satisfactory refinement,6 suggesting a
contribution of ca. 243 electrons per unit cell from the channel
region. This is consistent with ca. 9 molecules of included N2
per unit cell (ca. 0.5 N2 molecules per dithiadiazolyl radical).
Radical 1 was prepared by standard literature procedures§
with reduction achieved with Zn/Cu couple in liquid SO2.
Sublimation of 1 under a static vacuum led to isolation of red,
block-shaped crystals. Radical 1 crystallises in the triclinic
1
Sublimation of 1 in ca. 3 atm of CO2, Ar or SO2 led to similar
inclusion compounds 1b, 1g and 1d whose unit cell parameters
(see ESI†) were almost identical to 1a. Examination of these
phases by single-crystal X-ray diffraction† again revealed
diffuse electron density in the channels, summing to ca. 270
electrons per unit cell in each case, consistent with ca. 0.38 CO2,
0.94 Ar and 0.26 SO2, respectively, per dithiadiazolyl radical. A
sample of the SO2 inclusion complex 1d stored under N2 in a
gas-phase IR cell for three days exhibited strong gas phase
† Electronic supplementary information (ESI) available: Single-crystal X-
ray diffraction: refinement of inclusion complexes and the solid state
structures for both 1, 1a, 1b, 1g and 1d (excluding included N2) in .pdb
format. See http://www.rsc.org/suppdata/cc/b3/b307509p/
‡ Present address: University of Southern Denmark, Department of
Chemistry, Campusvej 55, 5230 Odense M, Denmark.
Fig. 1 Crystal structure of 1 in the ab plane.
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This journal is © The Royal Society of Chemistry 2003

Table 1 Selected crystal data for 1 and its inclusion compounds with N2, CO2, Ar and SO2
CO-crystal form
Crystal data
Pure 1
N2 (1a)
CO2 (1b)
Ar (1g)
SO2 (1d)
Crystal System
Space Group
a (Å)
b (Å)
c (Å)
a (°)
b (°)
g (°)
V (Å3)
Z
Triclinic
P1
10.6611(6)
11.6471(5)
16.0947(5)
75.318(3)
79.351(3)
89.511(2)
Orthorhombic
Pbcn
17.1674(8)
23.2395(11)
10.6653(4)
90
90
90
4255.0(3)
16
Orthorhombic
Pbcn
17.1277(7)
23.2356(10)
10.6532(2)
90
90
90
4239.7(3)
16
Orthorhombic
Pbcn
17.1483(6)
23.2411(8)
10.6610(2)
90
90
90
4248.9(2)
16
Orthorhombic
Pbcn
17.1333(2)
23.2358(3)
10.6538(4)
90
90
90
4241.3(1)
16
¯
1898.4(2)
8
Data in common: T = 180(2) K
Notes and references
§ Synthesis of 1: LiN(SiMe3)2 (0.888g, 5.307 mmol) and CF3C6H3FCN
(0.949g, 5.158 mmol) were stirred in Et2O (30 ml) for 18 h, to yield a dark
brown solution. The solution was cooled to 0 °C and SCl2 (1.2 ml, 12.7
mmol) added slowly with stirring to yield an immediate orange precipitate.
The solution was stirred for 1 h, filtered washed with Et2O (2 3 20 ml) and
dried in vacuo. Zn/Cu couple (0.054 g, 0.828 mmol) was added to a
suspension of the orange precipitate (0.500 g, 1.653 mmol) in SO2 in a two-
limbed reaction vessel. The solution was stirred for 18 h, filtered, the solvent
removed and the solid sublimed in a static vacuum (1022 Torr, 150–50 °C)
to yield 1. Found: C 35.83, H 1.11, N 10.58; required for C8H3N2S2F4
C
35.96, H 1.12, N 10.49%. +EI-MS: 267.0 (M+) (100%), 221.0 (M+ 2 SN,
36%), 205.2 (C6H3CF3FCN2H2)+ (39%), 189.0 (M+ 2 SNS,19%), 170.0
(C6H3CF3CN+, 22%), 163.0 (C6H3FCF3+, 13%); ESR (290 K, THF) g =
2.010, aN = 4.9 G. Crystals of the inclusion complexes, 1a–1d were grown
1
Fig. 2 Space filling diagrams of (a) the close-packed structure of 1 and (b)
the channel-like structure of 1a.
by sublimation of crude 1 in a sealed tube in the presence of ca. 3 atm of N2,
CO2, Ar or SO2 respectively. Recovered yields typically ca. 65 mg, 5%.
¶ Crystal data for 1: C8H3F4N2S2, M = 267.24, Z = 8, m(Mo-Ka) = 0.591
mm21, 15483 reflections of which all 6425 unique data were used in
calculations (Rint = 0.0494). R1 = 0.0471 (I > 2s(I)), wR2 = 0.1626 (all
data), S = 1.05. Crystal data for 1a: C8H3F4N2S2 · 0.54 N2, M = 282.37,
Z = 16, m(Mo-Ka) = 0.528 mm21, 15146 reflections of which all 3736
unique data were used in calculations (Rint = 0.0684). R1 = 0.0498 (I >
2s(I)), wR2 = 0.1360 (all data), S = 0.95. Crystal data for 1b, 1g and 1d are
available as ESI †
absorptions characteristic7 of released SO2, indicating a dy-
namic diffusion process at room temperature. TGA studies on
1b and 1g indicated a mass loss of ca. 5% and 6% respectively
on heating above 60 °C, consistent with loss of CO2 and Ar.
These values are in reasonable agreement with the values
estimated from the X-ray data (5.9 and 9.4% for CO2 and Ar
respectively) although these values are likely to be approximate
(since partial replacement of guest molecules by N2 is likely to
occur during storage due to the dynamic nature of the inclusion
process).
In contrast, sublimation of 1 in a partial atmosphere of
oxygen resulted in the formation of the dithiatetrazocine, 2, as
a yellow solid. The structure of 2 was elucidated by mass
spectrometry, UV/vis spectrophotometry, and X-ray diffrac-
tion. Previous work by Boeré and co-workers have shown that
dithiadiazolyl radicals react with dioxygen in acetonitrile to
generate dithiatetrazocines.8
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Inclusion of guest molecules into the structures of dithiadia-
zolyl radicals is not without precedent; the prototypal radical
HCNSSN forms an inclusion complex with N2 although this
occurs via rearrangement of the molecules within layers9 rather
than between layers as in 1. It is likely that in both cases
inclusion allows a novel host structure to be adopted which,
although no longer close-packed, optimizes host-packing.
We are currently pursuing the size and chemical selectivity of
1 for other gases including hydrogen and methane, and
examining the dynamics of the inclusion process.
We would like to thank the Cambridge Commonwealth Trust
and the Cecil Renaud Trust (D.A.H), the EPSRC (A.D.B.) and
NERC (C.S.C.) for financial support. We would also like to
thank Prof. C.T. Imrie (University of Aberdeen) for TGA
measurements.
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