A series of neutral radical CpNi(dithiolene). complexes

Article abstract of DOI:10.1039/b418756n

The heteroleptic neutral radical dithiolene complexes CpNi(dsit) ^., CpNi(dsit)^. and CpNi(dmid)^. (dmit = 1,3-dithiole-2-thione-4,5-dithiolate; dsit = 1,3-dithiole-2-thione-4,5- diselenolate; dmid = 1,3-dithiole-2-one-4,5-dithiolate) are obtained from the reaction of (Cp₂Ni)BF₄ with either (n-Bu ₄N)[Ni(dmit)₂] and (n-Bu₄N)[Ni(dmid) ₂] or PhSb(dmit) and PhSb(dsit), respectively. The three complexes reduce reversibly to the corresponding Ni(II) anions and oxidize reversibly to the cationic state. As deduced from DFT calculations performed on CpNi(dmit)^., the SOMO of these complexes is essentially localized on the dithiolene moiety with little metal contribution. CpNi(dsit)^. is isostructural with CpNi(dmit)^. and crystallizes in the monoclinic system, space group P2₁. In the solid-state structures of both CpNi(dmit)^. and CpNi(dsit)^., molecules interact through a three-dimensional set of intermolecular interactions mediated by short S ... S, Se ... Se and S ... Se contacts, as confirmed from the temperature and field dependence of the magnetic susceptibility by the observation of an antiferromagnetic ground state below T_Neel = 27 K in CpNi(dmit)^., 18 K in CpNi(dsit)^.. Finally, CpNi(dmid)^. crystallizes in the orthorhombic system, space group Pnma. Molecules organize into uniform chains through the stacking of the dmid moieties in a σ-type face-to-face overlap. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b418756n

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F U L L P A P E R
A series of neutral radical CpNi(dithiolene)• complexes†
Marc Fourmigue´* and Narcis Avarvari
Laboratoire “Chimie, Inge´nierie Mole´culaire et Mate´riaux d’Angers” (CIMMA),
UMR 6200 CNRS-Universite´ d’Angers, UFR Sciences, 2 Bd Lavoisier, 49045, Angers,
France. E-mail: marc.fourmigue@univ-angers.fr
Received 13th December 2004, Accepted 7th March 2005
First published as an Advance Article on the web 18th March 2005
The heteroleptic neutral radical dithiolene complexes CpNi(dmit)•, CpNi(dsit)• and CpNi(dmid)• (dmit =
1,3-dithiole-2-thione-4,5-dithiolate; dsit = 1,3-dithiole-2-thione-4,5-diselenolate; dmid = 1,3-dithiole-2-one-4,5-
dithiolate) are obtained from the reaction of (Cp2Ni)BF4 with either (n-Bu4N)[Ni(dmit)2] and (n-Bu4N)[Ni(dmid)2] or
PhSb(dmit) and PhSb(dsit), respectively. The three complexes reduce reversibly to the corresponding Ni(II) anions
and oxidize reversibly to the cationic state. As deduced from DFT calculations performed on CpNi(dmit)•, the
SOMO of these complexes is essentially localized on the dithiolene moiety with little metal contribution. CpNi(dsit)•
is isostructural with CpNi(dmit)• and crystallizes in the monoclinic system, space group P21. In the solid-state
structures of both CpNi(dmit)• and CpNi(dsit)•, molecules interact through a three-dimensional set of intermolecular
interactions mediated by short S · · · S, Se · · · Se and S · · · Se contacts, as confirmed from the temperature and field
dependence of the magnetic susceptibility by the observation of an antiferromagnetic ground state below TNe´el
=
27 K in CpNi(dmit)•, 18 K in CpNi(dsit)•. Finally, CpNi(dmid)• crystallizes in the orthorhombic system, space group
Pnma. Molecules organize into uniform chains through the stacking of the dmid moieties in a r-type face-to-face
overlap.
1 : 1 nickel complexes, formulated as CpNi(dithiolene)•, are
Introduction
very attractive in that respect since these formally d7 Ni(III)
Homoleptic dithiolene complexes and among them, the proto-
neutral species are expected to be paramagnetic, as indeed
typical square-planar nickel bis(dithiolene) complexes, are very
reported for CpNi(tfd)• (tfd = 1,2-bis(trifluoromethyl)ethylene-
well known to exist in several well defined oxidation states,1
1,2-dithiolate) where a magnetic moment of 1.67 lB at room
and corresponding radical paramagnetic species have been
temperature was reported.17 More recently, Faulmann et al.
particularly investigated in the solid state for their conducting or
reported the serendipitous formation of CpNi(dmit)• from the
magnetic properties.2,3 While strong intermolecular interactions
reaction of NaNi(dmit)2 with (Cp2Ni)(BF4) in attempts to
combined with mixed valence allows for the formation of
prepare [Cp2Ni][Ni(dmit)2] but without mention of a possible
partially filled bands and isolation of conducting or even
paramagnetism.18 Considering that the absence of counter-ions
superconducting materials,4 weaker interactions, most often
in these formally d7 neutral radical species could also favour
based on direct exchange between S = 1/2 paramagnetic species
strong intermolecular interactions in the solid state as observed
lead to antiferromagnetic interactions, giving rise to singlet–
•
•
in the d1 Cp2M(dithiolene)+ or CpM(dithiolene)2 complexes,
we decided to investigate more closely these attractive series and
describe here syntheses, electrochemical characterizations, elec-
tronic (DFT) and solid state (single-crystal X-ray diffraction)
structures and magnetic properties of three complexes with a
similar dithiolene backbone, namely CpNi(dmit)•, CpNi(dsit)•
(dsit = 1,3-dithiole-2-thione-4,5-diselenolate) and CpNi(dmid)•
(dmid = 1,3-dithiole-2-one-4,5-dithiolate). In the two last com-
plexes, the all-sulfur dmit ligand is replaced by the selenium-
containing dsit or oxygen-containing dmid ligands in order to
also evaluate the role of these atom substitutions on their solid-
state and magnetic properties.
triplet behaviour in dyadic systems,5 but also low dimensional
magnetic systems such as spin chains with eventually spin-
Peierls transitions6 or spin ladders.7,8 Ferromagnetic interac-
tions were also observed, essentially in decamethylferrocenium
salts9,10 while bulk ferromagnetism was only reported on two
cases, that is [Cp*2Mn][Ni(dmit)2]11 (dmit = 1,3-dithiole-2-
thione-4,5-dithiolate) and [NH4][Ni(mnt)2]·H2O (mnt = 1,2-
dicyanoethylene-1,2-dithiolate).12
Antiferromagnetic interactions13 were also identified in a fam-
ily of heteroleptic dithiolene complexes14 which associate both
the dithiolate and the cyclopentadienyl ligands as 2 : 1 or 1 : 2
Cp2M(dithiolene) or CpM(dithiolene)2 with M = Ti, Zr, Hf, V,
Nb, Ta, Mo, W or in 1 : 1 CpM(dithiolene) with M = Co, Rh, Ni
species. For example, the 2 : 1 cationic15 Cp2M(dithiolene)•+ and
•
1 : 2 neutral16 CpM(dithiolene)2 d1 radical complexes with M =
Results and discussion
CpNi(dmit)• had been obtained18 from the reaction of the
nickelocenium salt (Cp2Ni)(BF4) with the sodium salt of the
square-planar [Ni(dmit)2]− complex as the sole isolated product
in attempts to prepare [Cp2Ni][Ni(dmit)2]. The latter reaction
demonstrated however that nickelocenium was a suitable equiv-
alent of CpNi2+ fragment through Cp− displacement in meta-
thetical reactions with dithiolate ligands. The reaction described
with [Ni(dmit)2]− involved the crude monoanionic complex,
as sodium salt. We investigated the reaction of (Cp2Ni)(BF4)
with isolated n-Bu4N+ salts of [Ni(dmit)2]− and [Ni(dmid)2]−
(Scheme 1) and found that the corresponding CpNi(dmit)• could
be isolated in an improved yield while CpNi(dmid)• was obtained
only in a impure form and low yield.
Mo, W, adopt a variety of solid-state structures, stabilizing spin
chains, spin ladders but also bulk antiferromagnets, an original
feature in the magnetism of dithiolene complexes, which is not
encountered among homoleptic complexes. The occurrence of
an antiferromagnetic ground state is the signature of three-
dimensional interaction networks, favoured in the neutral, but
radical, complexes by the absence on any counter-ion. The
† Electronic supplementary information (ESI) available: Table S1:
Geometry optimized coordinates of CpNi(dmit)• derived by DFT cal-
culations. Table S2: Selected eigenvalues of orbitals of CpNi(dmit)•, cal-
culated using the geometry optimized coordinates. See http://www.rsc.
org/suppdata/dt/b4/b418756n/
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1
1 3 6 5
©

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Table 2 Electrochemical data (n-Bu4NPF6 0.1 M in CH2Cl2, values in
V vs. Fc+/Fc). Values in parentheses refer to the peak-to-peak potential
difference, expressed in mV
E
1/2(−1/0)
E1/2 (0/+1)
CpNi(dmit)•
CpNi(dsit)•
CpNi(dmid)•
−0.71 (100)
−0.72 (100)
−0.80 (110)
+0.28 (100)
+0.28 (100)
+0.26 (95)
Scheme 1
Looking for an alternative method applicable to a variety of
dithiolate ligands which could avoid the systematic preparation
of the oxidized [Ni(dithiolene)2]− complex for each desired
dithiolate, we tried, but without success, the direct reaction of
(Cp2Ni)(BF4) with Na2(dmit). This failure could indicate that
an oxidized complex such as the monoanionic [Ni(dmit)2]− was
necessary to avoid a concurrent oxidation of the dithiolate ligand
by the strongly oxidizing nickelocenium salt. An alternative
to Na2(dmit) can be offered by neutral complexes such as
Cp2Ti(dmit) or Bu2Sn(dmit) which are known to react as
dithiolene transfer reagents19 in a controlled way in the presence
of oxidizing agents such as phosgene20 or thiophosgene.21
Indeed, reaction of Bu2Sn(dmid)22 with (Cp2Ni)(BF4) afforded
the expected CpNi(dmid)• complex but in low yield. Looking for
a possibly more reactive neutral dithiolate derivative, we then
considered the recently described neutral antimony complexes
such as PhSb(dmit) or PhSb(dmid).23,24 PhSb(dsit) was still
unknown and has been prepared from (Me4N)2(dsit) and
PhSbCl2. PhSb(dmit) and PhSb(dsit) were found to react with
(Cp2Ni)BF4, affording CpNi(dmit)• and CpNi(dsit)• in moderate
yields. All three radical complexes are air-stable, dark green
crystalline solids, soluble in halogenated solvents.
Fig. 1 Cyclic voltammogram of CpNi(dmid)• in CH2Cl2.
exact electron count on the two redox processes was ascertained
with the most soluble CpNi(dmid)• complex thanks to a thin
layer cyclic voltammetry (TLCV) experiment,32,33 in the presence
of an equimolar amount of ferrocene as reference. As seen in
Fig. 2, the reversibility of both oxidation and reduction processes
at scan speeds as low as 5 mV s−1 is demonstrated from the
symmetry of each process. Furthermore, comparison of peak
area with that observed for the Fc/Fc+ couple confirms that
both redox processes involve one-electron transfers.
IR spectroscopy can be an efficient tool to evaluate the degree
of charge transfer on the dithiolate ligand since these complexes
can be described either as a Ni(III) [CpNiIII]2+(dithiolene)2−, a
Ni(II) [CpNiII]+(dithiolene)•− species or in an intermediate state.
=
As seen in Table 1, the C C absorption of the dithiolene ligand
is particularly sensitive to the oxidation state of the complexes
since it is observed at lower frequencies in the oxidized salts. The
values observed here for the three CpNi(dithiolene) complexes
are close to those observed in the neutral, square-planar nickel
complexes, implying that the formal description of these com-
plexes would be close to the [CpNiII]+(dithiolene)•− description,
with the radical essentially localized on the dithiolene moiety.
Cyclic voltammetry experiments (Fig. 1 and Table 2) per-
formed in CH2Cl2 show that the three radicals exhibit a
quasi-reversible reduction wave to the anionic Ni(II) species,
CpNi(dithiolene)−, as well a quasi-reversible oxidation wave
to the cationic CpNi(dithiolene)+ species with peak-to-peak
potential differences (≈100 mV) larger than expected for re-
versible one-electron transfer processes. The reversibility and
Table 1 Characteristic IR spectral data
=
C
=
C
C
C–S
S(O)
Ref.
CpNi(dmit)•
1260
1260
1353
1440
1323
1375
1430
1398
1479
1478
1474
879, 901
890
902
1048
1051
1052
1046
1009, 1045
1020, 1040
1024, 1040
1618, 1675
1616, 1672
1618, 1669
1601, 1641
This work
25–27
25–27
25–27
This work
28
0.29−
Ni(dmit)2−
Ni(dmit)2
Fig. 2 Cyclic voltammetry of CpNi(dmid)• under TLCV conditions in
1 mM concentration in CH2Cl2 with n-Bu4NPF6 0.25 M.
2−
Ni(dmit)2
885, 917
CpNi(dsit)•
−
2−
Ni(dsit)2
Ni(dsit)2
28
CpNi(dmid)•
892, 980
896, 978
885, 1023
This work
29
30
Molecular and electronic structures
0.5−
The X-ray crystal structure of CpNi(dmit)• has been already
described by Faulmann et al.18 and was re-determined only for
comparison purposes. CpNi(dsit)• was found to be isostructural
Ni(dmid)2−
Ni(dmid)2
2−
Ni(dmid)2
31
1 3 6 6
D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1

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with CpNi(dmit)•. It crystallizes in the monoclinic system,
space group P21, with one molecule in a general position in
the unit cell (Fig. 3). The NiSe2C2 metallacycle is planar (largest
˚
deviation 0.04(3) A) and is essentially perpendicular to the
Cp ring (85.4(4)◦).
Fig. 3 ORTEP view of CpNi(dsit)•. Thermal ellipsoids are drawn at
50% probability level.
Fig. 4 ORTEP view of CpNi(dmid)•. Thermal ellipsoids are drawn at
50% probability level. The inset shows the disorder model in which the
dotted line is the crystallographic mirror plane.
=
The comparison of the intramolecular Ni–Se, Se–C and C C
bond distances in CpNi(dsit) with other dsit complexes such
as [Ni(dsit)2]2− and [Ni(dsit)2]•− is difficult since no structural
data are available for the dianioinic [Ni(dsit)2]2− species while
the radical anion species is dimerised in the solid state,34 with
one selenium atom entering the coordination sphere of the
nickel atom of the neighbouring complex. Proper comparisons
UB3LYP method37 and 6-31G* basis set, aimed at optimizing
its geometry and, subsequently, at generating the sequence of
molecular orbitals. Characteristic calculated bond distances
compare well with those observed from the X-ray crystal
structure determination (Table 4) with the largest discrepancies
˚
(0.036 A) similar to those found for the calculated geometries of
can be obtained however from the structural characteristics of
38
dithiolene complexes such as [Ni(S2C2Me2)2]0,−,2−
.
As shown
•
2−,
−
the Ni(dsise)2
complexes (dsise = 1,3-dithiole-2-selone-4,5-
in Fig. 5, the SOMO (singly occupied molecular orbital) of
CpNi(dmit)• is essentially localized on the dithiolene moiety,
with a small contribution of the CpNi fragment, thus confirming
the spectroscopic (IR) and structural results. As a consequence,
one can expect that, in the solid state, short intermolecular con-
tacts between molecules which involve the dithiolene moiety, will
lead to strong electronic interactions, as indeed experimentally
observed from the magnetic behaviour of those radical species.
diselenolate) which exhibit a similar Ni–Se coordination scheme.
Both the di- and monoanion35 have been characterized in the
solid state as monomers. As shown in Table 3, the shortening of
the Ni–Se and Se–C bonds in CpNi(dsit)• when compared with
the reduced [Ni(dsise)2]2− or [Ni(dsise)2]•− species also indicate
the large contribution of the dithiolene moiety in the SOMO
(singly occupied molecular orbital) of the complex.
As seen in Table 4, similar trends are observed in the molecular
structure of CpNi(dmid)• which crystallizes in the orthorhombic
system, space group Pnma. The molecule is located on a mirror
plane which includes the Ni(dmid) moiety while the Cp ring is
disordered on two positions related by the same mirror plane
(Fig. 4). The NiS2C2 metallacycle is fully planar by symmetry
and is essentially perpendicular to the Cp ring (88.3(4)◦).
As already noted in CpNi(dsit)•, the evolution of the bond
distances within the metallacycle as well as the characteristic
IR frequencies (Table 1) points for a oxidized dithiolate ligand,
that is close to a Ni(II) [CpNiII]+[dithiolene•−] description.
In order to check this assumption, we have performed
theoretical calculations on CpNi(dmit)• at DFT level with the
Fig. 5 Singly occupied molecular orbital (SOMO) of CpNi(dmit)
(DFT-UB3LYP/6-31G*).
Table 3 Selected intramolecular distances in CpNi(dsit)• and reference
compounds
˚
˚
˚
=
Ni–Se/A
Se–C/A
C
C/A
Ref.
Solid-state structures and magnetic properties
CpNi(dsit)•
2.250(13)
2.250(18)
(2.329)
2.276
1.863(21)
1.871(10)
(1.882)
1.875
1.359(14)
This work
Let us first describe the solid-state and magnetic properties of
isostructural CpNi(dmit)• and CpNi(dsit)• radicals. As shown
in Fig. 6, the radicals organise into layers parallel to the (a,b)
plane without any stacking of the planar dithiolene moieties, an
original feature of these complexes. In spite of these tilt angles,
•
−
•
Ni(dsit)2
(1.342)
1.36
1.364
34
35
35
−
Ni(dsise)2
2−
Ni(dsise)2
2.305
1.883
Table 4 Selected intramolecular distances in CpNi(dmid)•, CpNi(dmit)• and averaged distances in reference compounds. Calculated values for
CpNi(dmit)• (DFT-UB3LYP/6-31G*) are given in italics
˚
˚
˚
=
Compound
Ni–S/A
S–C/A
C
C/A
Ref.
CpNi(dmid)•
CpNi(dmit)•
2.138(1), 2.145(1)
2.138(2), 2.133(2)
2.138(2), 2.143(2)
2.163
1.718(3), 1.712(3)
1.706(8), 1.716(8)
1.716(7), 1.741(7)
1.742
1.352(4)
1.36(1)
1.354(8)
1.366
This work
18
This work
Calc.
25
36
31
0
Ni(dmit)2
2.147
1.700
1.391
•
−
Ni(dmid)2
2.152
2.194
1.718
1.734
1.352
1.340
2−
Ni(dmid)2
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Table 5 Short intermolecular contacts between radicals in CpNi(dmit)• and CpNi(dsit)• and associated calculated b overlap interaction energies
CpNi(dmit)• CpNi(dsit)•
˚
˚
Interaction
Contact/A
b/meV
91.9
Contact/A
b/meV
48.8
A
B
C
S(1) · · · S(2)a
S(3) · · · S(4)a
S(3) · · · S(1)b
S(1) · · · S(3)b
S(2) · · · S(4)c
S(4) · · · S(2)c
3.611(22)
3.737(21)
4.041(6)
4.264(6)
3.948(4)
4.041(4)
Se(1) · · · Se(2)a
S(1) · · · S(2)a
Se(1) · · · S(1)b
S(1) · · · Se(1)b
Se(2) · · · S(2)c
S(2) · · · Se(2)c
3.634(15)
3.854(14)
4.079(5)
4.342(5)
3.911(3)
4.104(3)
25.1
28.9
66.1
27.2
D
E
13.3
10.8
21.4
11.1
Symmetry operations:a 1 + x, y, z. b −x, 0.5 + y, 1 − z. c −1 − x, −0.5 + y, 1 − z.
Fig. 6 A view of one (a,b) layer in CpNi(dsit)• with intra-layer
interaction A running along a and interactions B and C running along
b. Dotted lines show the shortest Se · · · Se, Se · · · S and S · · · S contacts
between one molecule and its neighbours.
Fig. 8 Magnetic susceptibility of CpNi(dsit)• in the low-temperature
regime at different fields.
short Se · · · Se, Se · · · S and S · · · S intermolecular contacts
within the slabs (Table 5) are identified, giving rise to a network
of intermolecular interactions noted A–C in Fig. 6.
The temperature and field dependence of the molar magnetic
susceptibility for CpNi(dmit)• and CpNi(dsit)• are shown in
Figs. 7 and 8, respectively, in the low-temperature regime. At
the higher temperatures, both compounds exhibit a Curie–Weiss
behaviour with hdmit = −66 K and hdsit = −33 K, the signature of
the presence of strong antiferromagnetic interactions in the solid
state. The susceptibility of both compounds exhibits a maximum
at 43 K (dmit) and 23 K (dsit), and below a transition to an
antiferromagnetic ground state with TNe´el(dmit) = 27 K and
T
Ne´el(dsit) = 18 K, as demonstrated from the field dependence
of the magnetic susceptibility below TNe´el in both compounds
(Figs. 7 and 8). This behaviour demonstrates that a three-
dimensional set of intermolecular interactions is present in
both neutral radicals, as confirmed by the calculations of the
extended Hu¨ckel b overlap interaction energies.39 Indeed, as
shown in Fig. 6 for CpNi(dsit)•, each radical interacts with
six neighbouring molecules within the slabs (interactions A–
C), and with four other molecules pertaining to parallel slabs
(interactions D and E). Calculated b values are collected in
Table 5 for both CpNi(dmit)• and CpNi(dsit)•, and confirm
that, (i) the strongest interactions are observed within the slabs,
(ii) the interactions are stronger in CpNi(dmit)•, as exper-
imentally observed from both larger Curie–Weiss and Ne´el
temperatures.
Contrariwise to the two isostructural CpNi(dmit)• and
CpNi(dsit)•, the organisation of CpNi(dmid)• into slabs (Fig. 9)
only holds from a structural point of view since short S · · · S
Fig. 7 Magnetic susceptibility of CpNi(dmit)• in the low-temperature
regime at different fields.
Fig. 9 A view of the slabs of CpNi(dmid)• developing parallel to the
(a,b) plane with interacting molecules within columns along b.
1 3 6 8
D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1

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distances are found only within stacks running along b where one
recovers the more usual face-to-face stacking of the dithiolene
moieties.
dithiolate ligands for investigating possibly conducting mixed-
valence CpNi(dithiolene)•/CpNi(dithiolene)+ salts as well as on
functional dithiolate ligands able to further favour intermolec-
ular interactions through hydrogen or halogen bonding.40
The temperature dependence of the magnetic susceptibility
of CpNi(dmid)• shown in Fig. 10 does not exhibit any field
dependence but still a Curie–Weiss behaviour in the higher
temperatures with hdmid = −55 K, demonstrating again the oc-
currence of strong antiferromagnetic interactions. The presence
of a susceptibility maximum at 32 K with a decrease to almost
zero at the lowest temperatures demonstrates that the radical
species most probably become paired, suggesting a structural
transition and a dimerisation. Calculations of the extended
Hu¨ckel b overlap interaction energies performed on the room-
temperature X-ray crystal structure of CpNi(dmid)• show that
molecules are essentially interacting along the b axis in a uniform
chain (b = 82 meV) while all other intermolecular interactions
are much weaker (< 15 meV). As a consequence, a uniform
chain model was used to fit the magnetic susceptibility data in
the high-temperature regime (Fig. 10), affording a J/k value
of −44 K. Most probably, this uniform chain experiences a
dimerisation around 32 K, leading to a diamagnetic ground
state.
Experimental
General
The syntheses of the complexes were carried out under nitrogen,
using standard Schlenk techniques. Dry CH2Cl2 and CH3CN
were obtained by distillation over P2O5, and THF was distilled
over sodium and benzophenone. Elemental analyses were per-
formed by the “Service d’Analyse du CNRS” at Gif/Yvette,
France. (Cp2Ni)BF4 was prepared according to a described
procedure41 from commercial Cp2Ni (Strem Chemicals) and
(Cp2Fe)BF4.
CpNi(dmit)•.
From (n-Bu4N)[Ni(dmit)2]. To a solution of (Cp2Ni)BF4
(80 mg, 0.29 mmol) in dry CH3N (5 mL) was added a
suspension of (n-Bu4N)[Ni(dmit)2] (200 mg, 0.29 mmol) in
CH3CN (10 mL) and the reaction mixture stirred for 2 h.
Solvent was then removed under vacuum and the remaining
dark green solid Soxhlet extracted with CH2Cl2. Concentration
of the green CH2Cl2 solution, filtration on a short SiO2 column
and concentration of the CH2Cl2 solution afforded CpNi(dmit)
as green crystals, yield 44 mg (47%).
From PhSb(dmit). To a solution of (Cp2Ni)BF4 (100 mg,
0.36 mmol) in CH3CN (5 mL) was added a solution of
PhSb(dmit) (123 mg, 0.31 mmol) in dry THF (15 mL). The so-
lution was stirred overnight, evaporated and the solid extracted
with CH2Cl2, the solution was filtered on a short SiO2 column
and the concentrated solution layered with MeOH. Yield 25 mg
(26%). mmax/cm−1 3500br s, 3090s (C–H), 2057m, 1796m, 1438s
=
=
=
=
(C C, Cp), 1400s (C C, Cp), 1380s (C C, Cp), 1260s (C C),
=
1015s and 1048s (C S), 901s and 879s (C–S). Found: C, 30.15,
H, 1.63. C8H5NiS5 requires C, 30.01; H, 1.57%.
PhSb(dsit). A solution of dsit(COPh)2 (1 g, 2 mmol)42 in
THF (60 mL) was treated with a solution of Me4NOH (2.91 g
25 wt% in MeOH, 8 mmol) in THF (10 mL). A violet precipitate
of (Me4N)2(dsit) was formed within a few minutes and, after
1 h of stirring, the precipitate was filtered off under nitrogen
in order to eliminate the (PhCOO)−(NMe4)+ salt still soluble.
Then, the diselenolate was dispersed in THF (40 mL) and
dichlorophenylstibine43 (0.54 g, 2 mmol) in THF (10 mL) was
rapidly added. The resulting deep red solution was stirred
overnight and then filtered through Celite in order to remove
the precipitated Me4NCl. After evaporation of almost all the
solvent, precipitation upon addition of pentane, filtration on a
glass frit, washing of the resulting powder with methanol, then
with pentane and finally drying under vacuum, PhSb(dsit) was
recovered as a deep red solid. Yield 0.5 g (51%). mmax/cm−1:
Fig. 10 Temperature dependence of the magnetic susceptibility of
CpNi(dmid)•.
In summary, we have first confirmed here that the neutral
CpNi(dithiolene)• complexes are indeed paramagnetic, as an-
ticipated by King forty years ago.17 The synthetic procedure
reported by Faulmann has been improved albeit other routes
still warrant exploration. These attractive radical complexes are
stable in a wide 1 V redox range and their electrochemical
properties can most probably be varied by modifying the
substituents on the dithiolate ligand. We have also shown
by a combination of structural and spectroscopic data, and
theoretical investigations that most of the radical is delocalized
on the dithiolene ligand, an issue of strong interest in the
prospect of building magnetic materials since efficient inter-
molecular interactions can be anticipated. Indeed, the two
isostructural CpNi(dmit)• and CpNi(dsit)• are characterized by
a three-dimensional set of intermolecular interactions which
does not involve the otherwise recurrent face-to-face overlap
between the planar dithiolene moieties. This original solid-
state organisation leads to an ordered antiferromagnetic ground
state at low temperature, thus demonstrating that the absence
of any counter-ions in these neutral radical species allows
indeed for extended intermolecular interactions and for an
ordered magnetic ground state. On the other hand, CpNi(dmid)•
provides an illustrative counter-example where the face-to-
face overlap of the dmid moieties drives the formation of
magnetic chains prone to dimerisation. Further work within
these CpNi(dithiolene)• series will focus on more electron-rich
=
=
=
=
1479m (C C), 1430 (C C), 1056s (C S), 1024s (C S), 947m
(C–S), 733m (C6H5), 693m (C6H5), 509m, 449m (C6H5). Found:
C, 21.87, H, 1.15. C9H5S3Se2Sb requires C, 22.11; H, 1.03%.
CpNi(dsit)•. To
a solution of (Cp2Ni)BF4 (137 mg,
0.5 mmol) in CH3CN (10 mL) was added a solution of PhSb(dsit)
(244 mg, 0.5 mmol) in THF (10 mL). After stirring for 2 h, the
dark precipitated solid was filtered off and recrystallized from
hot toluene to afford CpNi(dsit)• as dark plates. Yield 75 mg
−1
=
(36%). mmax/cm : 3500br s, 3087s (C–H), 1619m, 1402s (C C,
=
=
=
Cp), 1434m (C C, Cp), 1323m (C C), 1009s, 1045s (C S),
892s (C–S). Found: C, 22.77, H, 1.19. C8H5NiS3Se2 requires C,
23.22; H, 1.22%.
CpNi(dmid)•.
From (n-Bu4N)[Ni(dmid)2]. To a solution of (Cp2Ni)BF4
(138 mg, 0.5 mmol) in dry CH3N (10 mL) was added a
suspension of (n-Bu4N)[Ni(dmid)2] (330 mg, 0.5 mmol) in
D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1
1 3 6 9

View Article Online
Table 6 Crystallographic data
Compound
CpNi(dmid)•
CpNi(dmit)•
CpNi(dsit)•
Formula
FW
C8H5NiOS4
304.07
C8H5NiS5
320.13
C8H5NiS3Se2
413.93
Crystal system
Space group
Orthorhombic
Pnma
8.0485(7)
7.2993(7)
17.787(2)
—
1044.97(18)
293(2)
4
Monoclinic
P21
Monoclinic
P21
˚
a/A
5.9185(14)
7.9334(12)
11.732(3)
97.86(3)
545.7(2)
293(2)
6.0750(12)
7.9798(11)
11.8369(19)
97.55(2)
568.85(16)
293(2)
˚
b/A
˚
c/A
b/◦
3
˚
U/A
T/K
Z
2
2
l/mm−1
2.613
2.685
8.607
Total refls.
Unique refls. (Rint
Unique refls. (I > 2r(I))
R1, wR2 (I > 2r(I))a
R1, wR2 (all data)a
5997
1075 (0.0357)
823
0.0263, 0.0585
0.0394, 0.0615
4152
1949 (0.0772)
1101
0.0386, 0.0580
0.0952, 0.0687
4282
2090 (0.0792)
1475
0.0382, 0.0743
0.0669, 0.0805
)
ꢀ
ꢀ
ꢀ
ꢀ
2
4 1/2
a R1 = ꢀFo| − |Fcꢀ/ |Fo|; wR2 = [ w(Fo − Fc2)2/ wFo
] .
CH3CN (20 mL) and the reaction mixture stirred for 3 h.
Solvent was then removed under vacuum and the remaining
dark green solid extracted with CH2Cl2. Concentration of the
green CH2Cl2 solution, filtration on a short SiO2 column,
concentration of the CH2Cl2 solution and layering with pentane
afforded CpNi(dmid)• as green crystals, yield 18 mg (12%).
From PhSb(dmid). To a solution of (Cp2Ni)BF4 (140 mg,
0.5 mmol) in CH3CN (10 mL) was added a solution of
PhSb(dmid) (190 mg, 0.5 mmol) in dry THF (20 mL). The
solution was stirred for 2 h, evaporated and the solid extracted
with CH2Cl2. The solution was filtered on a short SiO2 column
direct methods (SHELXS-97) and refined (SHELXL-97) by full-
matrix least-squares methods. Absorption corrections were ap-
plied. Hydrogen atoms were introduced at calculated positions
(riding model), included in structure factor calculations, and not
refined.
CCDC reference numbers 258291–258293.
See http://www.rsc.org/suppdata/dt/b4/b418756n/ for cry-
stallographic data in CIF or other electronic format.
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=
(6%). mmax/cm : 3500br s, 3107s (C–H), 1675s (C O), 1618s
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D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1

View Article Online
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D a l t o n T r a n s . , 2 0 0 5 , 1 3 6 5 – 1 3 7 1
1 3 7 1