[CpNi(dithiolene)] (and diselenolene) neutral radical complexes

Article abstract of DOI:10.1021/ic0608546

Various preparations of the neutral radical [CpNi(dddt)] complex (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were investigated with CpNi sources, [Cp₂Ni], [CP₂Ni](BF₄), [CpNi(CO)]₂, and [CpNi(COd)](BF₄), and dithiolene transfer sources, O=C(dddt), the naked dithiolate (dddt^2-), the monoanion of square-planar Ni dithiolene complex (NBu₄)-[Ni(dddt)₂], and the neutral complex [Ni(dddt)₂]. The reaction of [CpNi(cod)](BF₄) with (NBu₄)[Ni(dddt)2] gave the highest yield for the preparation of [CpNi(dddt)] (86%). [CpNi(ddds)] (ddds = 5,6-dihydro-1,4-dithiin-2,3- diselenolate), [CpNi(dsdt)] (dsdt = 5,6-dihydro-1,4-diselenin-2,3-dithiolate), [CpNi(bdt)] (bdt = 1,2-benzenedithiolate), and [CpNi-(bds)] (bds = 1,2-benzenediselenolate) were synthesized by the reactions of [Cp₂Ni] with the corresponding neutral Ni dithiolene complexes [Ni(ddds) ₂]₂, [Ni(dsdt)₂], [Ni(bdt)₂], and [Ni(bds)₂], respectively. The five, formally Ni^III, radical complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region, from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with ε values between 2500 and 5000 M^-1 cm^-1. The molecular and solid state structures of the five complexes were determined by X-ray structure analyses. [CpNi(dddt)] and [CpNi(ddds)] are isostructural, while [CpNi(dsdt)] exhibits a closely related structure. Similarly, [CpNi(bdt)] and [CpNi(bds)] are also isostructural. Correlations between structural data and magnetic measurements show the presence of alternated spin chains in [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)], while a remarkably strong antiferromagnetic interaction in [CpNi(bdt)] and [CpNi(bds)] is attributed to a Cp...Cp face-to-face σ overlap, an original feature in organometallic radical complexes.

Full text of DOI:10.1021/ic0608546

Inorg. Chem. 2006, 45, 8194−8204
[CpNi(dithiolene)] (and Diselenolene) Neutral Radical Complexes
Mitsushiro Nomura,†,‡ Thomas Cauchy,†,§ Michel Geoffroy,| Prashant Adkine,| and Marc Fourmigue´*,†,‡
Laboratoire “Chimie, Inge´nierie Mole´culaire et Mate´riaux d’Angers” (CIMMA), UMR 6200
CNRS, UniVersite´ d'Angers, UFR Sciences, Baˆt. K, 2 Bd. LaVoisier, 49045 Angers, France,
Sciences Chimiques de Rennes, UMR 6226 CNRS, UniVersite´ Rennes I, Campus de Beaulieu,
35042 Rennes Cedex, France, Department de Quimica Inorganica, UniVersitat de Barcelona,
Diagonal 647, 08028 Barcelona, Spain, and Department of Physical Chemistry, UniVersity of
GeneVa, 30 Quai Ernest Ansermet, 1211, GeneVa, Switzerland
Received May 17, 2006
Various preparations of the neutral radical [CpNi(dddt)] complex (dddt
investigated with CpNi sources, [Cp2Ni], [Cp2Ni](BF4), [CpNi(CO)]2, and [CpNi(cod)](BF4), and dithiolene transfer
sources, O
C(dddt), the naked dithiolate (dddt2-), the monoanion of square-planar Ni dithiolene complex (NBu4)-
[Ni(dddt)2], and the neutral complex [Ni(dddt)2]. The reaction of [CpNi(cod)](BF4) with (NBu4)[Ni(dddt)2] gave the
highest yield for the preparation of [CpNi(dddt)] (86%). [CpNi(ddds)] (ddds 5,6-dihydro-1,4-dithiin-2,3-diselenolate),
[CpNi(dsdt)] (dsdt 5,6-dihydro-1,4-diselenin-2,3-dithiolate), [CpNi(bdt)] (bdt 1,2-benzenedithiolate), and [CpNi-
(bds)] (bds 1,2-benzenediselenolate) were synthesized by the reactions of [Cp2Ni] with the corresponding neutral
) 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were
d
)
)
)
)
Ni dithiolene complexes [Ni(ddds)2]2, [Ni(dsdt)2], [Ni(bdt)2], and [Ni(bds)2], respectively. The five, formally NiIII, radical
complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region,
from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with
ꢀ values between 2500 and 5000
M- cm-1. The molecular and solid state structures of the five complexes were determined by X-ray structure
analyses. [CpNi(dddt)] and [CpNi(ddds)] are isostructural, while [CpNi(dsdt)] exhibits a closely related structure.
Similarly, [CpNi(bdt)] and [CpNi(bds)] are also isostructural. Correlations between structural data and magnetic
measurements show the presence of alternated spin chains in [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)], while
a remarkably strong antiferromagnetic interaction in [CpNi(bdt)] and [CpNi(bds)] is attributed to a Cp‚‚‚Cp face-
1
to-face
σ overlap, an original feature in organometallic radical complexes.
Introduction
several well-defined oxidation states.6 Heteroleptic complexes
associating dithiolate and cyclopentadienyl ligands have been
much less investigated. Such Cp-metal-dithiolene com-
plexes can be classified into four main categories:7 the 2:2
Cp/dithiolene complexes formulated as [CpM(dithiolene)]2
(M ) group 5, 6, and 8 metals), the 2:1 Cp/dithiolene
complexes [Cp2M(dithiolene)] (M ) group 4-6 metals), the
Dithiolene complexes with a central Ni atom are the most
investigated of the metal dithiolene complexes. Since the first
square-planar Ni bis(dithiolene) complex reported in 1960,1
Ni dithiolene complexes have been thoroughly investigated
from the viewpoint of optical,2 magnetic,3 and conductive
studies.4 Most of these Ni dithiolene complexes are of the
square-planar type,5 and they are well-known to exist in
(3) (a) Fourmigue´, M. Acc. Chem. Res. 2004, 37, 179. (b) Coomber, A.
T.; Beljonne, D.; Friend, R. H.; Bredas, J. L.; Charlton, A.; Robertson,
N.; Underhill, A. E.; Kurmoo, M.; Day, P. Nature 1996, 380, 144. (c)
Faulmann, C.; Cassoux, P. Prog. Inorg. Chem. 2003, 52, 399.
(4) (a) Cassoux, P.; Valade, L.; Kobayashi, H.; Kobayashi, A.; Clark, R.
A.; Underhill, A. E. Coord. Chem. ReV. 1991, 110, 115. (b) Olk, R.-
M.; Olk, B.; Dietzsch, W.; Kirmse, R.; Hoyer, E. Coord. Chem. ReV.
1992, 117, 99. (c) Kato, R. Chem. ReV. 2004, 104, 5319. (d)
Matsubayashi, G.; Nakano, M.; Tamura, H. Cood. Chem. ReV. 2002,
226, 143.
* To whom correspondence should be addressed. E-mail:
marc.fourmigue@univ-rennes1.fr.
† Universite´ d'Angers.
‡ Universite´ Rennes I.
§ Universitat de Barcelona.
| University of Geneva.
(1) (a) Schrauzer, G. N.; Meyweg, V. P. J. Am. Chem. Soc. 1962, 84,
3221. (b) Davison, A.; Edelstein, N.; Holm, R. H.; Maki, A. H. J.
Am. Chem. Soc. 1963, 85, 2029. (c) Schrauzer, G. N.; Meyweg, V. P.
J. Am. Chem. Soc. 1965, 87, 1483.
(5) Beswick, C. L.; Schulman, J. M.; Stiefel, E. I. Prog. Inorg. Chem.
2003, 52, 55.
(6) Wang, K. Prog. Inorg. Chem. 2003, 52, 267.
(2) (a) Cummings, S. D.; Eisenberg, R. Prog. Inorg. Chem. 2003, 52,
315. (b) Kisch, H. Coord. Chem. ReV. 1993, 125, 155.
(7) Fourmigue´, M. Coord. Chem. ReV. 1998, 178, 823 and references
therein.
8194 Inorganic Chemistry, Vol. 45, No. 20, 2006
10.1021/ic0608546 CCC: $33.50
© 2006 American Chemical Society
Published on Web 09/06/2006

[CpNi(dithiolene)] Neutral Radical Complexes
Chart 1
Chart 2
1:2 Cp/dithiolene complexes [CpM(dithiolene)2] (M ) group
4-7 metals), and the 1:1 Cp/dithiolene complexes [CpM-
(dithiolene)] (M ) group 9 and 10 metals). The CpNi
dithiolene complexes are included into the fourth category
but are quite rare. King first reported the synthesis of [CpNi-
(tfd)] (tfd ) 1,2-bis(trifluoromethyl)dithiolate, Cp ) η5-
cyclopentadienyl),8 and Wharton reported the η4-cyclobuta-
diene Ni dithiolene complex which is formulated as [(η4-
C4R4)Ni(mnt)] (mnt ) maleonitriledithiolate).9 More recently,
Faulmann et al. synthesized [CpNi(dmit)] (dmit ) 1,3-
dithiol-2-thione-4,5-dithiolate) serendipitously from the reac-
tion of [Cp2Ni](BF4) with Na[Ni(dmit)2]. The expected salt
[Cp2Ni][Ni(dmit)2] was not obtained but rather the neutral
paramagnetic complex [CpNi(dmit)].10 We have recently
started a thorough investigation of the chemistry of the CpNi
dithiolene complexes,11,12 for the following attractive rea-
sons: (1) their synthetic methods are unique (Schemes 1-3)
and provide new organometallic reactions; (2) these com-
plexes are paramagnetic in the neutral state (formally NiIII),
hence strong magnetic interactions in the crystalline solid
state can be anticipated from the absence of any counterion;11
(3) these complex are quite soluble in organic solvents thanks
to the Cp ligand, and single crystals are easily obtained by
recrystallization11,12 without need for electrocrystallization
experiments;13 and (4) some of these complexes exhibit an
electronic absorption in the near-IR region,12 an original
feature also observed in the square-planar Ni dithiolene
complexes.14 Therefore, the CpNi(dithiolene) complexes are
very attractive from the organometallic, magnetic, and optical
points of view. We report here a comparative investigation
of different synthetic methods for the preparation of such
complexes based on the novel complex [CpNi(dddt)] (dddt
) 5,6-dihydro-1,4-dithiin-2,3-dithiolate) and describe the
preparation of the selenium-containing analogues CpNi(ddds)
and CpNi(dsdt), together with similar complexes based on
benzenedithiol (i.e., CpNi(bdt) and CpNi(bds)). The X-ray
crystal structures and electrochemical and magnetic proper-
ties of the five novel CpNi dithiolene complexes have been
investigated in detail with special emphasis on (i) a NIR
absorption band observed in all complexes but at different
energies and (ii) the antiferromagnetic interactions present
in the crystalline phases, as reflected by the analysis of the
temperature dependence of the magnetic susceptibility.
Scheme 1
Scheme 2
Results and Discussion
Syntheses of CpNi Dithiolene and Diselenolene Com-
plexes. The described syntheses of these formally NiIII CpNi
dithiolene complexes involve a CpNi source and a dithiolene
transfer source, together with an appropriate redox match
between both partners. The formers can be the NiI cyclo-
pentadienylnickel carbonyl dimer [CpNi(CO)]2, the NiII
nickelocene [Cp2Ni], or the NiIII nickelocenium (Cp2Ni)(BF4).
Dithiolene sources can be 1,2-dithiete (or 1,2-dithioketone),15
[PhSb(dithiolene)],11,16 or the square-planar metal dithiolene
complexes, [M(dithiolene)2]n (M ) Ni, Pd, and Pt; n ) 0,
-1) and [Pt(dithiolene)2(dppe)] (dppe ) bis(diphenylphos-
phino)ethane).12,17 Some examples of those reactions are
shown in Schemes 1-3. In Scheme 1, the 2e oxidized forms
of the dithiolate react with low-valent CpNi sources (NiI in
[CpNi(CO)]2, NiII in [Cp2Ni]), while Scheme 2 involves the
reaction of a NiIII CpNi source with a protected dithiolate.
Satisfactory yields were only reported in those reactions
involving square-planar nickel dithiolene complexes in their
anioinic or neutral forms, as described in Scheme 3.
For the synthesis of the new complex [CpNi(dddt)] (dddt
) 5,6-dihydro-1,4-dithiin-2,3-dithiolate) described here, we
have therefore investigated different combinations of CpNi
and dithiolene transfer sources. The results of these reactions
are collected in Table 1 and will be discussed shortly, while
details of each entry can be found in the Experimental
Section. Entries 1-4 involve the thermal or photochemical
activation of a 1,3-dithiole-2-one to generate, as a reactive
(8) King, R. B. J. Am. Chem. Soc. 1963, 85, 1587.
(9) Wharton, E. J. Inorg. Nucl. Chem. Lett. 1971, 7, 307.
(10) Faulmann, C.; Delpech, F.; Malfant, I.; Cassoux, P. J. Chem. Soc.,
Dalton Trans. 1996, 2261.
(11) Fourmigue´, M.; Avarvari, N. Dalton Trans. 2005, 1365.
(12) Nomura, M.; Okuyama, R.; Fujita-Takayama, C.; Kajitani, M. Orga-
nometallics 2005, 24, 5110.
(13) Batail, P.; Boubekeur, K.; Fourmigue´, M.; Gabriel, J.-C. P. Chem.
Mater. 1998, 10, 3005.
(14) Kirk, M. L.; McNaughton, R. L.; Helton, M. E. Prog. Inorg. Chem.
2003, 52, 111.
(15) Bock, H.; Rittmeyer, P.; Stein, U. Chem. Ber. 1986, 119, 3766. (b)
Krespan, C. G. J. Am. Chem. Soc. 1961, 83, 3434.
(16) (a) Avarvari, N.; Fourmigue´, M. Inorg. Chem. 2001, 40, 2570. (b)
Avarvari, N.; Fourmigue´, M. Organometallics 2003, 22, 2042.
(17) Bowmaker, G. A.; Boyd, P. D. W.; Campbell, G. K. Inorg. Chem.
1983, 22, 1208.
Inorganic Chemistry, Vol. 45, No. 20, 2006 8195

Nomura et al.
reported;12,24,25,26 in this case, the corresponding oligomer [Ni-
(S2C2Ph2)]n has been also found, including the reaction of
Scheme 3b.
Scheme 3
Similarly, the reaction of [Ni(ddds)2], formulated as a
dimer in a solid state,27 with [Cp2Ni] produced [CpNi(ddds)]
in a 68% yield (entry 14). Finally, the reaction of the neutral,
quite insoluble [Ni(dsdt)2] complex28 with [Cp2Ni] in toluene
gave the expected [CpNi(dsdt)] complex in a low yield
(15%), probably together with an impurity which could not
be removed but which is clearly observed on the UV-vis-
NIR spectrum (see Figure 1). The CpNi dithiolene complexes
[CpNi(dddt)], [CpNi(ddds)], [CpNi(dsdt)], [CpNi(bdt)], and
[CpNi(bds)] are air-stable and soluble for normal organic
solvents (dichloromethane, toluene, acetone, and THF). Their
solubility decreases upon addition of n-hexane.
intermediate, the corresponding 1,2-dithioketone or 1,2-
dithiete (shown in Scheme 1),18 but the isolated yields do
not exceed 30% regardless of the nature of the CpNi source
(Cp2Ni or [CpNi(CO)]2). The shorter reaction time obtained
with [CpNi(CO)]2 (entry 3) can be attributed to the con-
comitant thermal activation of [CpNi(CO)]2 for decarbonyl-
ation.19 Entries 5-7 involve the reaction of the “naked”
dithiolate dddt2- with either the NiII [Cp2Ni] or [CpNi(cod)]-
BF4 or the NiIII [Cp2Ni]BF4 complexes, but the yields are
not satisfactory (<28%). Finally, the best yields (60-85%)
were obtained as described before11,12 with the square planar
monoanionic or neutral nickel dithiolene complexes, as
described in entries 8-13. Note, however, that the proper
CpNi source has to be found in each case since, for example,
the NiII [Cp2Ni] neutral complex does not react with
[Ni(dddt)2]- (entry 9), while an 86% yield of [CpNi(dddt)]
is obtained when using the NiII [CpNi(cod)]BF4 salt (entry
10), introducing the CpNi(cod)+ cationic species as a novel,
efficient source of CpNi in these syntheses.20 Similarly, the
neutral, formally NiIV, [Ni(dddt)2] complex21 was found to
be inert to the NiIII [Cp2Ni]BF4 (entry 12), while it reacts
efficiently with the reduced [Cp2Ni] or [CpNi(CO)]2 neutral
complexes (entries 11 and 13).
This last method was therefore used for the syntheses of
the new complexes described here, [CpNi(bdt)] (51% yield,
entry 16) and its diselenolene analogue [CpNi(bds)] (40%
yield, entry 17). In the reaction of [Cp2Ni] with [Ni(bdt)2],
the oligomer of the Ni monodithiolene [Ni(bdt)]n (n ) 6)
was isolated by column chromatography in a 31% yield.22
Generally, the neutral square-planar dithiolene complex has
stable “dithiolate” and reactive “dithioketone” ligands, which
are exhibited as [MII(dithiolate)(dithioketone)] (M ) Ni, Pd
and Pt).23 We assume that the coordinated dithioketone
moiety reacted with a CpNi source to form the CpNi
dithiolene complex, and then the remaining Ni(dithiolate)
moiety is oligomerized. Some dithiolene transfer reactions
using the square-planar complex [Ni(S2C2Ph2)2] have been
Electrochemical Data. The electrochemical behavior of
CpNi dithiolene and diselenolene complexes was investigated
by cyclic voltammetry (CV), and the redox potentials (vs
Fc/Fc+) are reported in Table 2, together with those of
previously reported CpNi complexes for comparison. Re-
versible oxidation and reduction waves were found in the
CVs of the five new complexes (see Supporting Information).
The redox potentials of the dithiolene complexes [CpNi-
(dddt)] and [CpNi(bdt)] were almost similar to those of the
corresponding diselenolene complexes [CpNi(ddds)] and
[CpNi(bds)], respectively. This similarity was also observed
between [CpNi(dmit)] and [CpNi(dsit)].11 Also similar
potentials are found between [CpNi(dddt)] and [CpNi(dsdt)],
indicating that the redox potentials do not depend strongly
on the nature of the chalcogen atoms. Note also that the
evolution of the reduction potential values for the different
complexes correlate well with that described for the square
planar bis(dithiolene) complexes with the electrochemical
series S2C2Me2 > S2C2Ph2 > dddt ≈ bdt > dmit > mnt,
starting with the most electron-rich dithiolate ligand. The
large stability window of these metallo mono-dithiolene
complexes, and its evolution with the nature of the coordi-
nated dithiolate let us infer a good thermodynamic stability
of such radical species.
Since the oxidation waves are reversible, the oxidized
species of CpNi dithiolene complexes are stable on the time
scale of CV measurement (V ) 100 mV s-1), excluding
[CpNi(mnt)].12 This oxidation behavior is different from that
of the 16-electron Co and Ru dithiolene complexes [CpCoIII-
(dddt)] and [(η6-C6R6)RuII(S2C2(COOMe)2)]. Indeed, upon
oxidation, the 15-electron cationic Co and Ru complexes
immediately form dimeric species29,30 because the complex
(18) (a) Kusters, W.; De Mayo, P. J. Am. Chem. Soc. 1974, 96, 3502. (b)
Schroth, W.; Bahn, H.; Zschernitz, R. Z. Chem. 1973, 13, 424. (c)
Schulz, R.; Schweig, A.; Hartke, K.; Koester, J. J. Am. Chem. Soc.
1983, 105, 4519.
(19) (a) Stanghellini, P. L.; Rossetti, R.; Gambino, O.; Cetini, G. Inorg.
Chem. 1971, 10, 2672. (b) Ellgen, P. C. Inorg. Chem. 1972, 11, 2279.
(c) Stanghellini, P. L.; Rossetti, R.; Gambino, O.; Cetini, G. Inorg.
Chim. Acta 1973, 7, 445. (d) Stanghellini, P. L.; Rossetti, R.; Gambino,
O.; Cetini, G. Inorg. Chim. Acta 1973, 10, 5.
(24) Schrauzer, G. N.; Mayweg, V.; Heinrich, W. J. Am. Chem. Soc. 1966,
88, 5174.
(25) Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263.
(b) Goddard, C. A.; Holm, R. H. Inorg. Chem. 1999, 38, 5389.
(26) Adams, H.; Morris, M. J.; Morris, S. A.; Motley, J. C. J. Organomet.
Chem. 2004, 689, 522.
(20) Salzer, A.; Court, T. L.; Werner, H. J. Organomet. Chem. 1973, 54,
325.
(21) Kim, H.; Kobayashi, A.; Sasaki, Y.; Kato, R.; Kobayashi, H. Bull.
Chem. Soc. Jpn. 1988, 61, 579.
(27) Fujiwara, H.; Ojima, E.; Kobayashi, H.; Courcet, T.; Malfant, I.;
Cassoux, P. Eur. J. Inorg. Chem. 1998, 1631.
(28) Abramov, M. A.; Petrov, M. L. Zh. Obsh. Khim. 1996, 66, 1678.
(29) Guyon, F.; Lucas, D.; Jourdain, I. V.; Fourmigue´, M.; Mugnier, Y.;
Cattey, H. Organometallics 2001, 20, 2421.
(30) Nomura, M.; Fujii, M.; Fukuda, K.; Sugiyama, T.; Yokoyama, Y.;
Kajitani, M. J. Organomet. Chem. 2005, 690, 1627.
(22) This oligomer was detected by TOF-Mass (no matrix): 1192 ([Ni-
(bdt)]6+).
(23) Schrauzer, G. N. Acc. Chem. Res. 1969, 2, 72.
8196 Inorganic Chemistry, Vol. 45, No. 20, 2006

[CpNi(dithiolene)] Neutral Radical Complexes
Table 1. Syntheses of CpNi Dithiolene Complexes
time
(h)
yield
(%)b
entry
dithiolene source
CpNi source
[Cp2Ni]
molar ratio
solvent
condition
product
1
2
3
4
5
6
7
8
OdC(dddt)
OdC(dddt)
OdC(dddt)
OdC(dddt)
Na2(dddt)
1:1
1:1
2:1
2:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
2:1
1:1
1:1
1:1
1:1
toluene
toluene
toluene
toluene
methanol
methanol
methanol
methanol
toluene
methanol
toluene
toluene
toluene
toluene
toluene
toluene
toluene
reflux
hν
reflux
24
24
6
24
0.5
0.5
0.5
2
2
2
2
2
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
[CpNi(dddt)]
a
[CpNi(dddt)]
[CpNi(dddt)]
a
[CpNi(dddt)]
[CpNi(ddds)]
[CpNi(dsdt)]
[CpNi(bdt)]
[CpNi(bds)]
29
30
29
15
6.5
28
17
59
0
86
62
0
65
68
15
51
40
[Cp2Ni]
[CpNi(CO)]2
[CpNi(CO)]2
[Cp2Ni]
[Cp2Ni](BF4)
[CpNi(cod)](BF4)
[Cp2Ni](BF4)
[Cp2Ni]
[CpNi(cod)](BF4)
[Cp2Ni]
[Cp2Ni](BF4)
[CpNi(CO)]2
[Cp2Ni]
hν
room temp
room temp
room temp
reflux
80 °C
reflux
80 °C
80 °C
80 °C
80 °C
80°C
Na2(dddt)
Na2(dddt)
(NBu4)[Ni(dddt)2]
(NBu4)[Ni(dddt)2]
(NBu4)[Ni(dddt)2]
[Ni(dddt)2]
[Ni(dddt)2]
[Ni(dddt)2]
[Ni(ddds)2]2
[Ni(dsdt)2]
9
10
11
12
13
14
15
16
17
2
2
2
2
[Cp2Ni]
[Cp2Ni]
[Cp2Ni]
[Ni(bdt)2]
[Ni(bds)2]
80 °C
80 °C
2
a No reaction. b Isolated yield.
Table 2. Redox Potentials of CpNi Dithiolene and Diselenolene
Complexes (E vs Fc+/Fc)a
coupling with the heavier selenium atoms. Preliminary DFT
calculations [UB3LYP/6-31G(d,p)]32 were performed to
estimate the g variation caused by the replacement of a
dithiolene moiety by a diselonene moiety: passing from
[CpNi(bdt)] to [CpNi(bds)] causes an increase in the
calculated gav value equal to 0.028, which is slightly smaller
than the experimental value of 0.041. It is worth mentioning
that the g values of CpNi dithiolene and diselenolene
complexes are smaller than those reported for the one-
electron-reduced species of the CpCo dithiolene complexes
[CpCoII(tfd)]- (g ) 2.454)30 and [CpCoII(mnt)]- (g )
∼2.5).33 This difference in the g values probably reflects a
difference in the spin localization: in [CpCo(dithiolene)]-
complexes, the spin is strongly localized on the central metal,
while in the CpNi dithiolene complexes, it appreciably
delocalizes on the dithiolene ligand (see below).11 However,
we could not detect the hyperfine structure resulting from
77Se in the diselenolene complexes [CpNi(ddds)] and [CpNi-
(bds)] because its natural abundance is too low (7.65%).
Work is in progress to prepare those selenolene complexes
marked with the 77Se isotope.
E1/2(red) ∆E ∆Ep E1/2(ox) ∆E ∆Ep
(V)
(mV) (mV)
(V)
(mV) (mV) ref
[CpNi(S2C2Me2)] -1.38
b
b
72
b
b
-0.04
+0.04
b
b
74
b
b
12
12
[CpNi(S2C2Ph2)]
[CpNi(ddds)]
-1.16
-1.07
108 +0.03
106 -0.02
86 -0.01
108 +0.30
92 +0.30
100 +0.28
100 +0.32
104 this
work
106 this
work
82 this
work
104 this
work
88 this
work
100 this
work
100 this
work
12
[CpNi(dddt)]
[CpNi(dsdt)]
[CpNi(bds)]
[CpNi(bdt)]
[CpNi(dmit)]
[CpNi(dsit)]
[CpNi(mnt)]
-1.06
-1.06
-1.04
-1.00
-0.72
-0.74
-0.64
72
66
74
68
b
74
68
74
72
b
b
b
b
b
+0.79c
b
b
a E1/2 ) (Ep + Ep/2)/2, ∆E ) |Ep - Ep/2|, ∆Ep ) |Epa - Epc|. b Not
available. c Irreversible.
alleviates an electron deficiency of the central metal. We
assume that the CpNi dithiolene complexes do not dimerize
upon oxidation to the cation because these oxidized com-
plexes are formally 16-electron species.
Electronic Transitions. Electronic absorption spectra were
measured in a CH2Cl2 solution between 300 and 1500 nm
Electron Paramagnetic Resonance. The EPR spectra of
CpNi dithiolene complexes in solution in dichloromethane
were measured at room temperature. They are composed of
a single line whose g factor was measured with respect to
DPPH: for [CpNi(dddt)], g ) 2.042; for [CpNi(dsdt)], g )
2.045; for [CpNi(ddds)], g ) 2.088; for [CpNi(bdt)], g )
2.054; and for [CpNi(bds)], g ) 2.095. In this work, EPR
measurements were also performed for [CpNi(dmit)] (g )
2.044) and [CpNi(dsit)] (g ) 2.089) for comparison purposes.
The g values of the CpNi dithiolene complexes are similar
to those of [CpNi(S2C2R2)] (g ) ∼2.041-2.048; R ) CF3,31
Ph, COOMe, Me, and CN),12 while the diselonene complexes
exhibit higher values because of the stronger spin-orbit
(32) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, H.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J.
B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
C.1; Gaussian, Inc: Pittsburgh, PA, 2003.
(31) Dessy, R. E.; Stary, F. E.; King, R. B.; Waldrop, M. J. Am. Chem.
Soc. 1966, 88, 471.
(33) McCleverty, J. A.; James, T. A.; Wharton, E. J. Inorg. Chem. 1969,
8, 1340.
Inorganic Chemistry, Vol. 45, No. 20, 2006 8197

Nomura et al.
Table 3. NIR Absorption Wavelengths, Associated Energies (E), and ꢀ
Values
Table 4. Electrochemical, Optical Properties, and Associated Energy
Levelsa
elec
opt
λmax
(nm)
E
(eV)
ꢀ
Eox
onset
Ered
onset
Eg
Eg
HOMO
(eV)
(M-1 cm-1
)
ref
(eV)
(eV)
[CpNi(dddt)]
[CpNi(dsdt)]
[CpNi(ddds)]
[CpNi(bdt)]
[CpNi(bds)]
[CpNi(dmit)]
[CpNi(dsit)]
[CpNi(mnt)]
-0.10
-0.08
-0.06
+0.20
+0.22
+0.21
+0.25
+0.65
-0.96
-0.98
-0.97
-0.92
-0.95
-0.66
-0.68
-0.55
0.86
0.90
0.91
1.12
1.17
0.87
0.93
1.20
0.93
-4.70
-4.72
-4.74
-5.00
-5.02
-5.01
-5.05
-5.45
[CpNi(dddt)]
[CpNi(ddds)]
[CpNi(dsdt)]
1012
1000
954
1.225
1.239
1.299
4700
3600
5500
this work
this work
this work
0.88
1.18
1.12
1.01
1.03
1.30
(1189)a
967
(1.043)a (2200)a
[CpNi(dmit)]
[CpNi(dsit)]
[CpNi(S2C2Ph2)]
[CpNi(S2C2Me2)]
[CpNi(bdt)]
[CpNi(bds)]
[CpNi(mnt)]
[CpNi(S2C2(CO2Me)2)]
1.282
1.308
1.465
1.485
1.717
1.727
1.776
1.784
6000
3200
2900
2600
2600
2800
2000
1500
this work
this work
12
948
846
835
722
718
698
695
12
elec
a Eg ) -(Eredonset - Eoxonset), HOMO (eV) ) -[Eonset - Eox(fer-
rocene)] - 4.8 with Eoxonset in V vs Fc+/Fc, Eox(ferrocene) ) 0 V vs
Fc+/Fc.
this work
this work
12
12
ligand one-electron promotion that possesses a small degree
of LMCT character.37,38
a Values in parentheses refer to the impurity absorption (see text).
The strong NIR absorptions observed here are particularly
surprising for metallo-mono(dithiolene) complexes since
complexes such as (L-N3)MoO(dithiolene) [(L-N3) ) hy-
drotris(3,5-dimethyl-1-pyrazolyl)borate] exhibit only very
weak absorption in the NIR region with ꢀ < 500 M-1 cm-1.39
The other family of mono(dithiolene) complexes investigated
so far are the luminescent M(diimine)(dithiolene) ones, such
as Zn(bipy)(bdt), characterized by a LLCT band in the visible
region.40 To get some, at least, qualitative insight on the
electronic structures of these complexes, the nature of the
NIR absorption band and its evolution with the dithiolene
ligand and the optical and electrochemical data were analyzed
in more detail to evaluate the HOMO/LUMO gap and
associated energies in the different complexes. From the
onset values of the oxidation potential and reduction
potential, an electrochemical gap (Egelec) can be determined
and compared with the optical gap (Egopt) determined from
the onset of the low-energy NIR absorption band. We note
(Table 4) that the electrochemically determined gaps are
approximately the same as the optically determined ones with
larger values systematically observed for the bdt/bds series,
as well as for the mnt complex. The HOMO values were
experimentally estimated by the onset of the oxidation
potential, taking the known reference level for ferrocene, 4.8
eV below the vacuum level,41 according to the following
equation: HOMO ) -[Eonset - Eox(ferrocene)] - 4.8. As
shown in Table 4, they strongly vary with the nature of the
dithiolate ligand, indicating that the optical transition ob-
served in the NIR region most probably involves energy
levels with a strong dithiolene contribution. The smaller gaps
being observed with the most electron-rich dithiolates
for the five new complexes, as well as for [CpNi(dmit)] and
[CpNi(dsit)]. As shown in Figure 1, in addition to the UV-
Figure 1. UV-vis-NIR absorbance in CH2Cl2.
vis absorption peaks, all complexes exhibit a strong NIR
(near-infrared) absorption (Table 3), observed around 1000
nm in the dddt/ddds/dsdt series, 955 nm in the dmit/dsit
series, and 720 nm in the bdt/bds series, while a much lower
absorption wavelength had been reported for [CpNi(mnt)]
at 700 nm.12 Such strong NIR absorptions have been known
for a long time34 in neutral or anionic square-planar bis-
(dithiolene) complexes and were investigated for their
applications as Q-switching laser dyes.35 Molar extinction
coefficients as high as 80 000 M-1 cm-1 were even reported
in neutral [M(R,R′timdt)2] (R,R′timdt ) N,N′-disubstituted
imidazolidine-2,4,5-trithione).36 Accordingly, the square-
planar bis(dithiolene) complexes have been the subject of
intense theoretical investigations in relation to their electronic
structures and can be described as an essentially ligand f
(37) Kirk, M. L.; McNaughton, R. L.; Helton, M. E. Prog. Inorg. Chem.
2003, 52, 111.
(38) Lim, B. S.; Fomitchev, D. V.; Holm, R. H. Inorg. Chem. 2001, 40,
4257.
(39) (a) Carducci, M. D.; Brown, C.; Solomon, E. I.; Enemark, J. H. J.
Am. Chem. Soc. 1994, 116, 11856. (b) Helton, M. E.; Gruhn, N. E.;
McNaughton, R.; Kirk, M. L. Inorg. Chem. 2000, 39, 2273. (c) Helton,
M. E.; Kirk, M. L. Inorg. Chem. 1999, 38, 4384. (d) Inscore, F. E.;
McNaughton, R.; Westcott, B. L.; Helton, M. E.; Jones, R. M.;
Dhawan, I. K.; Enemark, J. H.; Kirk, M. L. Inorg. Chem. 1999, 38,
1401.
(40) Cummings, S. D.; Eisenberg, R. Prog. Inorg. Chem. 2003, 52, 315.
(41) Wu, T. Y.; Sheu, R. B.; Chen, Y. Macromolecules 2004, 37, 725. (b)
Wu, T.-Y.; Sheu, R.-B.; Chen, Y. Macromolecules 2004, 37, 725.
(34) Mueller-Westerhoff, U. T.; Vance, B. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.,
Pergamon: Oxford, U.K., 1987.
(35) Mueller-Westerhoff, U. T.; Vance, B.; Yoon, D. I. Tetrahedron 1991,
47, 909.
(36) Aragoni, M. C.; Arca, M.; Demartin, F.; Devillanova, F. A.; Garau,
A.; Isaia, F.; Lelj, F.; Lippolis, V.; Verani, G. J. Am. Chem. Soc. 1999,
121, 7098.
8198 Inorganic Chemistry, Vol. 45, No. 20, 2006

[CpNi(dithiolene)] Neutral Radical Complexes
n
n
n
plexes such as Ni(dmit)2 , Ni(dddt)2 , or Ni(bdt)2 , n ) -2,
-1, 0, where the S/Se substitution to the corresponding Ni-
n
n
n
(dsit)2 , Ni(ddds)2 , or Ni(bds)2 does not generally provide
isostructural salts. Most probably here, the Cp ring partially
hides the chalcogen atoms engaged in the nickel coordination.
On the other hand, even slight modifications of the outer
substituents of the dithiolene or diselenolene core do modify
strongly the crystal packing, as observed here for [CpNi-
(dsdt)] which is not isostructural with [CpNi(dddt)] or [CpNi-
(ddds)].
Figure 2. ORTEP drawing of [CpNi(dsdt)]. Thermal ellipsoids are drawn
Intramolecular bond lengths are collected in Table S1 in
the Supporting Information, together with those of monoan-
ionic square planar bis-(dithiolene) or bis-(selenolene) com-
plexes for comparison purposes. The Ni-S bond lengths in
[CpNi(dddt)], [CpNi(dsdt)], and [CpNi(bdt)] (∼2.12 Å) are
shorter than the Ni-Se bond lengths in [CpNi(ddds)] and
[CpNi(bds)] (∼2.25 Å). Similar tendencies have been
observed in [CpNi(dmit)] versus [CpNi(dsit)],10,11 [Ni(dddt)2]-
versus [Ni(ddds)2]-,26,41 and [Ni(bdt)2]- versus [Ni(bds)2]-
(Table 2).42,55 The difference between the Ni-S and Ni-Se
bond lengths (∼0.13 Å) is almost equal to that between the
atomic covalent radius of sulfur and selenium. The bond
lengths of the CdC double bond in the dithiolene ligands
are intermediary between a C-C single and CdC double
bond length, illustrating that the oxidation of the formally
Ni(II) CpNi(dithiolene) complex to the neutral radical [CpNi-
(dithiolene)] essentially affects the dithiolene ligand. Fur-
thermore, the C1-C2 lengths in [CpNi(bdt)] and [CpNi(bds)]
(∼1.4 Å) is slightly longer than those of the other CpNi
dithiolene complexes (1.33-1.38 Å). This result is explained
by not only π conjugation in a dithiolene ring but also the π
conjugation of benzene ring, and this fact is also found in
[Ni(bdt)2] and [Ni(bds)2] (C1-C2 ) 1.39 Å).42,55 The largest
at the 50% probability level.
Figure 3. ORTEP drawing of the two crystallographically independent
molecules in the diselenolene complex [CpNi(bds)]. Thermal ellipsoids are
drawn at the 50% probability level.
allowed us to infer that even smaller ones with their
associated low energy NIR absorption band could be found
with very electron-rich dithiolates such as those used by
Mueller-Westerhoff in square-planar nickel dithiolene com-
plexes.33,34 For instance, on the basis of the evolution of the
E1/2(red) for the [CpNi(dithiolene)]-1f0 process reported in
Table 2, the bdt/bds complexes would be expected to exhibit
smaller gaps than the dmit/dsit complexes. This is not the
case, demonstrating that this NIR optical transition is not
related only to the HOMO level of the anionic [CpNi(dithio-
lene)]- complex.
Molecular Geometries. The structures of the five com-
plexes have been determined by X-ray crystal diffraction on
single crystals. [CpNi(dddt)] and its selenated analogue
[CpNi(ddds)] are isostructural: they crystallize in the mono-
clinic system, space group P21, with four crystallographically
independent molecules in the unit cell, corresponding to a 2
× 2 pseudoinversion center. The analogous [CpNi(dsdt)]
complex is not isostructural; it crystallizes in the monoclinic
system, space group P21/n, with one molecule in a general
position in the unit cell (Figure 2). Similarly, [CpNi(bdt)]
and its selenolene analogue [CpNi(bds)] are also isostructural;
they crystallize in the monoclinic system, space group P21/c
with two crystallographically independent molecules in the
unit cell (Figure 3).
(42) (a) McCleverty, J. A. Prog. Inorg. Chem. 1969, 10, 49. (b) Sugimori,
A.; Akiyama, T.; Kajitani, M.; Sugiyama, T. Bull. Chem. Soc. Jpn.
1999, 72, 879. (c) Kajitani, M.; Hagino, G.; Tamada, M.; Fujita, T.;
Sakurada, M.; Akiyama, T.; Sugimori, A. J. Am. Chem. Soc. 1996,
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(43) Miller, E. J.; Brill, T. B.; Rheingold, A. L.; Fultz, W. C. J. Am. Chem.
Soc. 1983, 105, 7580.
(44) Habe, S.; Yamada, T.; Nankawa, T.; Mizutani, J.; Murata, M.;
Nishihara, H. Inorg. Chem. 2003, 42, 1952.
(45) Xi, R.; Abe, M.; Suzuki, T.; Nishioka, T.; Isobe, K. J. Organomet.
Chem. 1997, 549, 117.
(46) Mashima, K.; Kaneyoshi, H.; Kaneko, S.; Mikami, A.; Tani, K.;
Nakamura, A. Organometallics 1997, 16, 1016.
(47) Ho¨rnig, A.; Englert, U.; Ko¨lle, U. J. Organomet. Chem. 1994, 464,
C25.
(48) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(49) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571.
(b) Schaefer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100,
5829.
(50) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211.
(51) (a) Ruiz, E.; Alemany, P.; Alvarez, S.; Cano, J. J. Am. Chem.. Soc.
1997, 119, 1297. (b) Ruiz, E.; Alvarez, S.; Rodriguez-Fortea, A.;
Alemany, P.; Pouillon, Y.; Massobrio, C. In Magnetism, Molecules
to Materials; Miller, J. S., Drillon, M., Eds.; Wiley VCH: Weinheim,
Germany, 2001; Vol. 2, p 227.
(52) Baker-Hawkes, M. J.; Billig, E.; Gray, H. B. J. Am. Chem. Soc. 1966,
88, 4870.
(53) Sandman, D. J.; Allen, G. W.; Acampora, L. A.; Stark, J. C.; Jansen,
S.; Jones, M. T.; Ashwell, G. J.; Foxman, B. M. Inorg. Chem. 1987,
26, 1664.
(54) Schultz, A. J.; Wang, H. H.; Soderholm, L. C.; Sifter, T. L.; Williams,
J. M.; Bechgaard, K.; Whangbo, M.-H. Inorg. Chem. 1987, 26, 3757.
(55) Kini, A. M.; Beno, M. A.; Williams, J. M. J. Chem. Soc., Chem.
Commun. 1987, 335.
Note that [CpNi(dmit)] and [CpNi(dsit)] were also found
to be isostructural, demonstrating that in these [CpNi-
(dithiolene)] series, the S/Se substitution in the metallacycle
does not substantially modify the packing of the molecules.
This contrasts with the square planar bis(dithiolene) com-
Inorganic Chemistry, Vol. 45, No. 20, 2006 8199

Nomura et al.
Figure 4. Projection along the c axis of the structure of [CpNi(dddt)].
deviations from the nickel-dithiolene and -diselenolene
planes are very small (See Table S2 in Supporting Informa-
tion), namely, these five-membered metallacycles are fully
planar. This fact can be seen for the pseudoaromaticity of
nickel-dithiolene and -diselenolene rings.42 In addition, the
Ni-bdt (nickel-dithiolene with benzene) and the Ni-bds
moieties are almost planar (largest deviations ) 0.0376 Å
in [CpNi(bdt)] and 0.0587 Å in [CpNi(bds)]). The dihedral
angles between Cp and nickel-dithiolene (or -diselenolene)
are almost a right angle. This result indicates that they are
typical two-legged piano-stool geometries.
Figure 5. Alternating chains of (top) [CpNi(dddt)] and (bottom) [CpNi-
(ddds)] radical complexes running along c.
Although [CpNi(bdt)] and [CpNi(bds)] are monomers,
some dimer structures have been reported in [CpCo(bdt)]2,43
[CpCo(bds)]2,44 [Cp*Rh(bdt)]2 (Cp* ) η5-pentamethyl cy-
clopentadienyl),45 [(η6-C6R6)Ru(bdt)]2,46 and [Cp*Ru(bdt)]2.47
In these Co, Rh, and Ru complexes, the corresponding
monomers have electron-poor metal centers (formal 15- or
16-electrons). As already determined above from the elec-
trochemical behavior, we assume that the CpNi dithiolene
and diselenolene complexes are not dimerized because these
complexes have more electron-rich metal centers (formal 17-
electrons) than those of the Co, Rh, and Ru dithiolene
complexes.
Figure 6. Detail of the uniform chain of [CpNi(dsdt)] radical complexes
running along a.
Solid State Structures and Magnetic Behavior. In the
solid state, the isostructural [CpNi(dddt)] and [CpNi(ddds)]
radical complexes organize into columns running along the
c axis (Figure 4), with intermolecular interactions between
columns which only involve the outer sulfur atoms of the
dithiine rings. The shortest S‚‚‚S intermolecular contacts are
observed at 3.81 and 3.86 Å, and it is anticipated that the
magnetic interactions through these S‚‚‚S contacts are most
probably weak since the SOMO in such complexes, as
already reported in [CpNi(dmit)],11 is essentially localized
on the NiS2C2 or NiSe2C2 metallacycles.
On the other hand, within the columns running along c
(Figure 5), short intermolecular S‚‚‚S, Se‚‚‚S, and Se‚‚‚Se
contacts involving chalcogen atoms of the metallacycles are
now identified, giving rise in both complexes to spin chains
running along c, with S‚‚‚S contacts of 3.75 and 4.05 Å in
[CpNi(dddt)] and Se‚‚‚Se contacts of 3.84 and 3.96 Å in
[CpNi(ddds)]. The situation is notably different in [CpNi-
(dsdt)] where similar but uniform spin chains are found to
run along the a axis (Figure 6).
Figure 7. Temperature dependence of the magnetic susceptibility of [CpNi-
(dddt)] (O), [CpNi(ddds)] (b), and [CpNi(dsdt)] (×). Solid lines are fits to
alternated chain models (see text).
K, demonstrating the presence of strong antiferromagnetic
interactions between the radical moieties, with stronger
interactions in the dsdt complex. A susceptibility maximum
is observed in all complexes, at 27 K in [CpNi(dddt)], 25 K
in [CpNi(ddds)], and at a higher temperature (45 K), as
anticipated from the θdsdt value, in [CpNi(dsdt)]. No field
dependence of the susceptibility below these temperature
maxima was observed, ruling out the possibility of an ordered
antiferromagnetic ground state in the three compounds.
On the basis of the structure descriptions given above for
the two isostructural [CpNi(dddt)] and [CpNi(ddds)] com-
plexes, an alternated chain model with J and RJ, 0 < R <
1, was used to fit the data, yielding close values: Jdddt/k )
-65 K (45 cm-1), Jddds/k ) -66 K (46 cm-1), Rdddt ) Rddds
) 0.7. On the other hand, a Heisenberg uniform chain model
The temperature dependence of the magnetic susceptibility
(Figure 7) of [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)]
reflects these different structural organizations. It exhibits
indeed a Curie-Weiss type behavior in the high-temperature
regime with θdddt ) -46 K, θddds ) -36 K, and θdsdt ) -58
8200 Inorganic Chemistry, Vol. 45, No. 20, 2006

[CpNi(dithiolene)] Neutral Radical Complexes
Figure 8. Projection view along the b axis of the unit cell of [CpNi(bdt)].
can be considered to fit the magnetic data of [CpNi(dsdt)].
However, such a model could not fit satisfactorily the
experimental data, and a slight alternation had to be
introduced in the chain model (R ) 0.9) to take into account
the activated part of the susceptibility below T(ømax), yielding
a J/k value of -77 K (53 cm-1). This failure to fit the
magnetic susceptibility down to low temperatures with the
Bonner-Fisher model probably reflects a tendency of the
uniform chains identified in the room-temperature X-ray
crystal structure of [CpNi(dsdt)] to undergo a weak dimer-
ization upon cooling which opens a gap in the energy
dispersion of the chain. Indeed, upon dimerization, an
alternated spin chain is formed, whose magnetic behavior is
characterized by a singlet ground state and an activated
susceptibility in the low-temperature region.
Figure 9. Temperature dependence of the magnetic susceptibility of [CpNi-
(bdt)] (O) and [CpNi(bds)] (b). Solid lines are fits to the Bleaney-Bower
singlet-triplet model with a Curie tail at the lowest temperatures (see text).
Figure 10. Detail of the dyadic association between A and B molecules
in [CpNi(bdt)] showing the Cp‚‚‚Cp face-to-face interaction.
At this stage, we can tentatively conclude that the strong
antiferromagnetic interaction observed in those complexes
can be attributed to this original Cp‚‚‚Cp overlap. Taking
this solid-state organization into account, we performed a
fit of the susceptibility data with a singlet-triplet model,
together with a contribution, observable at low temperatures,
of a Curie-type susceptibility (Curie tail) attributable to
paramagnetic defaults. The best fits afforded J/k values of
-402(4) (279 cm-1) and -451(6) K (313 cm-1), together
with Curie contribution of 0.8 and 2.6% S ) 1/2 species for
the [CpNi(bdt)] and [CpNi(bds)] complexes, respectively.
To strengthen this hypothesis, quantum calculations were
performed on the [CpNi(bdt)] complex to obtain the shape
of its SOMO, as well as the distribution of the spin density.
The calculations were performed with the Gaussian03 code31
with the hybrid B3LYP functional.48 We have employed a
triple-ú all-electron Gaussian basis set for the nickel atoms
and a double-ú basis set for the other elements proposed by
Schaefer et al.49 As shown in Figure 11, the SOMO is largely
distributed on the dithiolate ligand and the nickel atom, as
already observed for the SOMO of [CpNi(dmit)].11
As mentioned above, [CpNi(bdt)] and [CpNi(bds)] are
isostructural and crystallize with two crystallographically
independent molecules, A and B in the following. In the solid
state, the radical molecules organize perpendicular to each
other (Figure 8), and short intermolecular chalcogen‚‚‚
chalcogen contacts can hardly be identified as the shortest
intermolecular S‚‚‚S distances are 4.42 Å between the A
molecules and 4.75 Å between the B molecules in [CpNi-
(bdt)], and the shortest Se‚‚‚Se intermolecular distances are
found at 4.25 Å between the A molecules and 4.65 Å
between the B molecules in [CpNi(bds)].
It is therefore anticipated that the radical species are
essentially independent from each other and that the tem-
perature dependence of their magnetic susceptibility should
follow a Curie or Curie-Weiss law. As shown in Figure 9,
this is absolutely not the case: a broad susceptibility
maximum around room temperature is observed together with
a Curie contribution at the lowest temperatures. This behavior
testifies for the presence of strong antiferromagnetic inter-
actions, which cannot be attributed here to chalcogen‚‚‚
chalcogen or chalcogen‚‚‚nickel interactions. A closer in-
spection of the crystal structures of [CpNi(bdt)] and [CpNi-
(bds)] reveals an original feature which has not been seen
before in these series: an almost face-to-face arrangement
of the Cp rings of molecules A and B (Figure 10) with C‚
‚‚C intermolecular distances as short as 3.32 and 3.37 Å in
[CpNi(bdt)] and [CpNi(bds)], while the angles between the
Cp mean planes are 4.46 and 4.17° in [CpNi(bdt)] and [CpNi-
(bds)], respectively.
It is therefore expected that the antiferromagnetic inter-
actions would be dominated by interactions between the
dithiolate ligands when present. However, as shown in Table
5, Mu¨lliken and NBO50 analysis of the spin distribution show
that 40-42% of the spin density is delocalized on the nickel
atom, 31-32% on the two chalcogen atoms, and a far from
negligible 21% on the cyclopentadienyl ring. These results
confirm that, in the absence of any intermolecular S‚‚‚S or
Ni‚‚‚S interactions, the Cp‚‚‚Cp overlap observed in the
X-ray crystal structure of [CpNi(bdt)] can indeed justify the
strong antiferromagnetic interaction experimentally deduced
from the temperature dependence of the magnetic suscep-
tibility.
Inorganic Chemistry, Vol. 45, No. 20, 2006 8201

Nomura et al.
Figure 12. (top) Calculated SOMO of [CpNi(dddt)] (DFT UB3LYP/
triple-ú all-electron basis set for the iron atoms and a double-ú basis set for
the other elements). (bottom) Spin density distribution in [CpNi(dddt)]. The
isodensity surface represented corresponds to a value of 0.01 e-/bohr.3
Figure 11. (top) Calculated SOMO of [CpNi(bdt)] (DFT UB3LYP/triple-ú
all-electron basis set for the iron atoms and a double-ú basis set for the
other elements). (bottom) Spin density distribution in [CpNi(bdt)]. The
isodensity surface represented corresponds to a value of 0.01 e-/bohr.3
Conclusion
Table 5. Calculated Spin Density (Mulliken and NBO analysis) in
The investigation of novel synthetic procedures for the
preparation of these [CpNi(dt)] series has shown that the
partially oxidized dithiolene complexes [Ni(dt)2]1- react not
only with the air-sensitive NiIII [Cp2Ni]BF4 species, as
observed earlier,11,12 but also, in good yields, with the air
stable NiII [CpNi(cod)]BF4 complex, providing a very
efficient route particularly adapted to electron-poor dithiolate
ligands available as [Ni(dt)2]1- anions. On the other hand,
the oxidized [Ni(dt)2]0 complexes were shown to react not
only with the NiII [Cp2Ni] complex12 but also with the NiI
[CpNi(CO)]2 dimer with comparable and good yields. A
strong NIR absorption band is observed in all complexes,
but it is at a particularly low energy (1000 nm) in the dddt
and dmit complexes (and selenated analogues) when com-
pared with S2C2Me2, S2C2Ph2, bdt, or mnt complexes, where
it is observed between 750 and 800 nm. Finally, an original
intermolecular Cp‚‚‚Cp σ overlap has been identified in the
solid state structure of [CpNi(bdt)] and [CpNi(bds)] as the
only possible pathway for a strong antiferromagnetic inter-
action, which most probably finds its origin in a sizable spin
density distribution of the cyclopentadienyl ring, a very
original feature in organometallic radical complexes. Theo-
retical investigations are currently underway to (i) determine
the origin of the NIR absorption of these complexes,
particularly in [CpNi(dmit)] and [CpNi(dddt)], and (ii) to
quantitatively evaluate the magnetic coupling constants.51
[CpNi(bdt)] and [CpNi(dddt)] Complexes
Ni
S1 + S2
Cp
others
[CpNi(dddt)] Mulliken
[CpNi(dddt)] NBO
[CpNi(bdt)] Mulliken
[CpNi(bdt)] NBO
0.28
0.28
0.42
0.42
0.40
0.42
0.32
0.31
0.12
0.12
0.21
0.21
0.20
0.19
0.05
0.06
Similar calculations performed on the [CpNi(dddt)] com-
plex shows also a large delocalization of the SOMO, and as
shown in Figure 12, the spin density is largely delocalized
on the whole metallacycle with only 12% left on the Cp ring.
These observations justify a posteriori the assumption made
above that the strongest intermolecular interactions in [CpNi-
(dddt)] were essentially attributable to S‚‚‚S contacts. They
also give us some insight about the probable differences
between the two classes of complexes which were identified
above. Indeed, while both [CpNi(bdt)] and [CpNi(dddt)]
appeared to fit nicely in the well-established electrochemical
series known for square-planar bis(dithiolene) complexes
with S2C2Me2 > S2C2Ph2 > dddt ≈ bdt > dmit > mnt, the
much lower energy absorption band (1000 nm) observed only
in [CpNi(dddt)] and [CpNi(dmit)] identify those two com-
plexes as peculiar in the series and demonstrate unambigu-
ously that the energy of the NIR absorption band is not
uniquely correlated to differences in the HOMO energy level.
The above calculations tend to show that the presence of
thioalkyl or selenoalkyl substituents on the dithiolene core
induces a strong delocalization of the spin density on the
whole metallacycle, while in the other complexes, a sizable
spin density is observed on the cyclopentadienyl ring.
Experimental Section
General Remarks. All reactions were carried out under an argon
atmosphere by means of standard Schlenk techniques. All solvents
for chemical reactions were dried and distilled by Na benzophenone
(for toluene) or CaH2 (for methanol) before use. The square-planar
8202 Inorganic Chemistry, Vol. 45, No. 20, 2006

[CpNi(dithiolene)] Neutral Radical Complexes
Table 6. Crystallographic Data of CpNi Dithiolene and Diselenolene Complexes
CpNi(dddt)
C9H9NiS4
CpNi(ddds)
CpNi(dsdt)
CpNi(bdt)
C11H9NiS2
CpNi(bds)
C11H9NiSe2
formula
fw
C9H9NiS2Se2
397.91
C9H9NiS2Se2
397.91
304.11
264.01
357.81
cryst color
cryst size (mm)
cryst system
space group
a (Å)
black
black
black
black
brown
0.40 × 0.30 × 0.08
monoclinic
P21
9.1045(8)
20.766(2)
12.3642(11)
105.119(10)
2256.8(4)
293(2)
0.39 × 0.24 × 0.06
monoclinic
P21
9.2009(8)
20.963(2)
12.6630(11)
105.827(10)
2349.8(4)
293(2)
0.54 × 0.21 × 0.01
monoclinic
P21/n
6.2605(5)
21.146(2)
9.2234(7)
106.276(9)
1172.11(18)
293(2)
0.30 × 0.30 × 0.04
monoclinic
P21/c
15.1132(10)
9.3294(7)
16.3831(10)
110.596(7)
2162.3(3)
293(2)
0.54 × 0.24 × 0.04
monoclinic
P21/c
15.5585(15)
9.4950(7)
16.5769(16)
112.131(11)
2268.5(4)
293(2)
b (Å)
c (Å)
â (deg)
V (Å3)
T (K)
Z
D
8
8
4
8
8
calcd (g cm-3
)
1.790
2.413
17 675
8598 (0.0475)
6362
0.0394, 0.0954
0.0566, 0.1027
0.803
2.250
8.158
18 689
8585 (0.0621)
5867
0.0365, 0.0796
0.0681, 0.0935
0.945
2.255
8.178
9139
2148 (0.0907)
1457
0.0619, 0.1528
0.0862, 0.1761
0.945
1.622
2.133
20 329
4161 (0.0727)
2096
0.0340, 0.0788
0.0909, 0.1003
0.703
2.095
8.084
16 861
4341 (0.1018)
1987
0.0648, 0.1434
0.1354, 0.1739
0.840
µ (mm-1
total reflns
unique reflns (Rint
)
)
unique reflns (I > 2σ(I))
R1, R2 (I > 2σ(I))a
R1, R2 (all data)a
GOF
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc )2/∑wFo ]1/2
.
2
2
4
nickel dithiolene complexes, [Ni(dddt)2],21 [Ni(ddds)2]2,26 [Ni-
(dsdt)2],27 [Ni(bdt)2],52 [Ni(bds)2],53 and (NBu4)[Ni(dddt)2],54 were
synthesized by literature methods. OdC(dddt),55 [Cp2Ni](BF4),56
and [CpNi(cod)](BF4)20 were prepared by literature methods. [Cp2-
Ni] and [CpNi(CO)]2 were obtained from STREM Chemicals and
Aldrich Chemicals, respectively. Silica gel (Silica gel 60) was
obtained from MERCK, Ltd. The TOF-mass spectrum was recorded
on a Bruker Daltonics MALDI-TOF BIFLEX III mass spectrometer.
UV-vis and NIR spectra were recorded on Hitachi Model UV-
2500PC and PERKIN ELMER Model Lambda 19 UV/VIS/NIR
spectrometers, respectively. Elemental analyses were performed by
the “Service d’Analyse du CNRS” at Gif/Yvette, France. UV
irradiation for a photoreaction was performed with a high-pressure
Hg lamp (Applied Photophysics, Ltd).
Reactions of [Cp2Ni] or [CpNi(CO)]2 with the Neutral
Square-Planar Nickel Dithiolene and Diselenolene Complexes.
A toluene solution (50 mL) of [Cp2Ni] (38 mg, 0.2 mmol) and the
square-planar dithiolene complexes [Ni(dithiolene)2] (dithiolene )
dddt, ddds, bdt, and bds; 0.2 mmol) was reacted at 80 °C for 2 h.
After the solvent was removed under reduced pressure, the residue
was separated by a column chromatography (silica gel, dichlo-
romethane/n-hexane ) 1:1 (v/v)). The product was further purified
by recrystallization (n-hexane/dichloromethane). The corresponding
CpNi dithiolene complexes, [CpNi(dddt)] (black crystal, 62% yield),
[CpNi(ddds)] (black crystal, 68% yield), [CpNi(bdt)] (black crystal,
51% yield), and [CpNi(bds)] (brown crystal, 40% yield), were
obtained. The reaction of [CpNi(CO)]2 (30 mg, 0.1 mol) with [Ni-
(dddt)2] (84 mg, 0.2 mmol) was performed in the manner noted
above.
hexane/dichloromethane). [CpNi(dddt)] was obtained in a 59%
yield. [CpNi(cod)](BF4) (64 mg, 0.2 mmol) reacted with (NBu4)-
[Ni(dddt)2] (132 mg, 0.2 mmol) to give [CpNi(dddt)] in an 86%
yield.
Thermal Reactions of [Cp2Ni] or [CpNi(CO)]2 with OdC-
(dddt). A solution of [Cp2Ni] (94 mg, 0.5 mmol) and OdC(dddt)
(104 mg, 0.5 mmol) was reacted in refluxing toluene for 24 h. After
the reaction, silica gel was added to the reaction mixture, and then,
the remaining [Cp2Ni] was rapidly oxidized and adsorbed onto the
silica gel. The mixture was separated by column chromatography
(silica gel, dichloromethane/n-hexane ) 1:1 (v/v)). The black solid
of [CpNi(dddt)] was obtained in a 29% yield. The thermal reaction
of [CpNi(CO)]2 (76 mg, 0.25 mmol) with OdC(dddt) (104 mg,
0.5 mmol) was also performed, and [CpNi(dddt)] was isolated in a
29% yield.
Photoreactions of [Cp2Ni] or [CpNi(CO)]2 with OdC(dddt).
A toluene solution (300 mL) of [Cp2Ni] (57 mg, 0.3 mmol, c )
1.0 × 10-3 mol dm-3) and [OdC(dddt)] (63 mg, 0.3 mmol, c )
1.0 × 10-3 mol dm-3) was reacted for 24 h by using UV irradiation
from a high-pressure Hg lamp (400 W). After the reaction, a black
precipitate was filtered off, and the filtrate was evaporated under
reduced pressure. The residue was separated by a column chro-
matography (silica gel, dichloromethane/n-hexane ) 1:1 (v/v)). The
black solid of [CpNi(dddt)] was obtained in a 30% yield. The
photoreaction of [CpNi(CO)]2 (46 mg, 0.15 mmol, c ) 5.0 × 10-4
mol dm-3) with OdC(dddt) (63 mg, 0.3 mmol, c ) 1.0 × 10-3
mol dm-3) for 24 h also gave [CpNi(dddt)] in a 15% yield.
Reaction of [Cp2Ni], [Cp2Ni](BF4) or [CpNi(cod)](BF4) with
Na2(dddt). OdC(dddt) (63 mg, 0.3 mmol) was treated with 2 equiv
of sodium methoxide in a methanol solution (20 mL). The colorless
solution turned yellow after 1 h at room temperature. In this
moment, the naked 1,2-dithiolate of disodium salt (Na2(dddt)) is
generated. When [Cp2Ni](BF4) (83 mg, 0.3 mmol) was added into
this solution, the yellow solution immediately changed to brown.
The reaction mixture was further stirred at room temperature for
0.5 h. When air was blown into the solution, the brown solution
changed to greenish-brown. After the solvent was removed under
reduced pressure without heating, the residue was separated by a
column chromatography (silica gel, dichloromethane/n-hexane )
Reaction of [Cp2Ni](BF4) or [CpNi(cod)](BF4) with (NBu4)-
[Ni(dddt)2]. [Cp2Ni](BF4) (55 mg, 0.2 mmol) and (NBu4)[Ni(dddt)2]
(132 mg, 0.2 mmol) in methanol (50 mL) was reacted under reflux.
An initial green solution was rapidly changed to a black cloudy
solution. After the mixture reacted under reflux for 2 h, the solution
color changed to greenish brown. The solvent was removed under
reduced pressure, and the reaction mixture was separated by a
column chromatography (silica gel, dichloromethane/n-hexane )
1:1 (v/v)). The product was further purified by recrystallization (n-
(56) Miller, J. S.; Calabrese, J. C.; Rommelmann, H.; Chittipeddi, S. R.;
Zhang, J. H.; Reiff, W. M.; Epstein, A. J. J. Am. Chem. Soc. 1987,
109, 769.
Inorganic Chemistry, Vol. 45, No. 20, 2006 8203

Nomura et al.
1:1 (v/v)). [CpNi(dddt)] was obtained in a 28% yield. [Cp2Ni] or
[CpNi(cod)](BF4) reacted with Na2(dddt) in the same condition
noted above.
[CpNi(dddt)]. TOF-Mass (MALDI, 19 kV): m/z 303 (M+), 275
(M+ - (CH2)2). UV-vis-NIR (CH2Cl2, λmax (ꢀ)): 1012 (4700),
417 (4600), 329 (24 000), 270 nm (14 000). Anal. Calcd for C9H9-
NiS4: C, 35.54; H, 2.98; S, 42.17. Found: C, 35.64; H, 3.17; N,
42.12.
[CpNi(ddds)]. TOF-Mass (MALDI, 19 kV): m/z 399 (M+(80Se)),
371 (M+(80Se) - (CH2)2). UV-vis-NIR (CH2Cl2, λmax (ꢀ)): 1000
(3600), 395 (1800), 339 (23 000), 270 nm (15 000). Anal. Calcd
for C9H9NiS2Se2: C, 27.17; H, 2.28; S, 16.12. Found: C, 27.15;
H, 2.35; S, 16.32.
[CpNi(dsdt)]. TOF-Mass (MALDI, 19 kV): m/z 399 (M+(80Se)),
371 (M+(80Se) - (CH2)2). UV-vis-NIR (CH2Cl2, λmax (ꢀ)): 1189
(2200), 954 (5500), 327 nm (26 000). Anal. Calcd for C9H9NiS2-
Se2: C, 27.17; H, 2.28; S, 16.12. Found: C, 27.33; H, 2.46; S,
16.22.
[CpNi(bdt)]. TOF-Mass (MALDI, 19 kV): m/z 263 (M+). UV-
vis (CH2Cl2, λmax (ꢀ)): 722 (2600), 330 nm (15 000). Anal. Calcd
for C11H9NiS2: C, 50.04; H, 3.44; S, 24.29. Found: C, 50.17; H,
3.56; S, 24.42.
[CpNi(bds)]. TOF-Mass (MALDI, 19 kV): m/z 359 (M+). UV-
vis (CH2Cl2, λmax (ꢀ)): 718 (2800), 393 (4700), 341 nm (24 000).
Anal. Calcd for C11H9NiSe2: C, 36.92; H, 2.54. Found: C, 37.06;
H, 2.65.
working electrode. The Model CV-50W instrument from BAS Co.
was used for cyclic voltammetry (CV) measurements. CVs were
measured in 1.0 mmol dm-3 dichloromethane solutions of com-
plexes containing 0.1 mol dm-3 tetrabutylammonium hexafluoro-
phosphate (NBu4PF6) at 25 °C.
EPR Measurements. The preparations of sample solutions for
EPR measurements were carried out in a drybox; 1.0 mmol dm-3
dichloromethane solutions of complexes were prepared, except for
the solution of [CpNi(dsdt)], which was prepared in toluene solution.
The EPR spectra were recorded on a Bruker ESP 300 spectrometer
(X-band), except for that of [CpNi(dsdt)], which was investigated
on a Bruker EMX EPR spectrometer (X-band).
Magnetic Susceptibility Measurements. Magnetic susceptibility
measurements were performed on a Quantum Design MPMS-2
SQUID magnetometer operating on the range of 2-300 K at 5000
G with polycrystalline samples of [CpNi(dddt)] (17.88 mg), [CpNi-
(ddds)] (9.53 mg), [CpNi(dsdt)] (8.14 mg), [CpNi(bdt)] (19.73 mg),
and [CpNi(bds)] (58.4 mg). Gelatin capsules were used with a
magnetization contribution of -2.37 × 10-6 + (2.2 × 10-6/(T +
2)) emu G g-1 which was used for correction of the experimental
magnetization. Molar susceptibilities were then corrected for Pascal
diamagnetism. Fits to the alternated chain model are based on the
following expression (eq 1) of the spin Hamiltonian for an alternated
chain, -A2i-1 - (J) - A2i - (RJ) - A2i+1, while the susceptibility
of the [CpNi(bdt)] and [CpNi(bds)] complexes was fitted with eq
2 where x is the fraction of S ) 1/2 magnetic defaults
X-ray Diffraction Studies. The single crystals of CpNi dithi-
olene complexes were obtained by recrystallization from the
dichloromethane solutions and vapor diffusion of n-hexane into
those solutions. Crystals were mounted on the top of a thin glass
fiber. Data were collected on a Stoe Imaging Plate diffraction system
(IPDS) with graphite-monochromated Mo KR radiation (λ )
0.71073 Å) at room temperature. Structures were solved by direct
methods (SHELXS-97) and refined (SHELXL-97) by full-matrix
least-squares methods. Absorption corrections were applied. Hy-
drogen atoms were introduced at calculated positions (riding model),
included in structure factor calculations, and these were not refined.
Crystallographic data of complexes are summarized in Table 6.
CV Measurements. All electrochemical measurements were
performed under an argon atmosphere. Solvents for electrochemical
measurements were dried with 4 Å molecular sieves before use. A
platinum wire served as a counter electrode, and the Ag/AgCl
reference electrode was corrected for junction potentials by being
referenced internally to the ferrocene/ferrocenium (Fc/Fc+) couple.
A stationary platinum disk (1.6 mm in diameter) was used as a
H ) -J [SA SA + RSA SA ]
2i+1
(1)
(2)
∑
2i
2i-1
2i
Ng2â2
kT[3 + exp(-J/kT)]
Ng2â2
2kT
ø ) (1 - x)
+ x
Acknowledgment. We thank Prof. Masatsugu Kajitani
(Sophia University) for help with the CV measurements and
Dr Ph. Blanchard (CNRS-University of Angers) for help with
the NIR measurements. T.C. thanks the Ministerio de
Educacio´n y Ciencia (Spain) for a PhD grant.
Supporting Information Available: CIF files giving crystal-
lographic data for [CpNi(dddt)], [CpNi(ddds)], [CpNi(dsdt)], [CpNi-
(bdt)], and [CpNi(bds)], tables of bond distances and angles, and a
figure for the cyclic voltammetry. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC0608546
8204 Inorganic Chemistry, Vol. 45, No. 20, 2006