Super reduced Fe4S4 cluster of Balch's dithiolene series

Article abstract of DOI:10.1039/c2dt12184k

A super reduced Fe₄S₄ cluster with a sulfur based radical, [NBu₄]₄[Fe₃^IIIFe ^II(μ₃-S)₄(mnt)₃ ^6-(mnt)^1-]^4-, (1) (mnt, maleonitrile dithiolate) which evolves H₂S gas on treatment with acid under ambient conditions has been synthesized and structurally characterized. The Fe-S distances in 1 are in the range 2.246-2.383 A, in stark contrast to that of the known n = -2 member of the series based on the [Fe₄(μ ₃-S)₄(S₂C₂R₂) ₄]ⁿ unit (R = CF₃, Ph) with Fe-S bond lengths of 2.149-2.186 A. The EPR of 1 displays very weak signals at g, 4.03 and 2.38 along with a strong S-based radical EPR signal at g, 2.003 associated with five structured components tentatively assigned to hyperfine interaction arising out of the naturally abundant ⁵⁷Fe with = 88 G. The EPR profile resembles the reduced Fe-S cluster of CO inhibited Clostridium pasteurianum W5 hydrogenase or the Fe₄S₄ centers of wild-type enzyme, IspH treated with HMBPP or IPP. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt12184k

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PAPER
Super reduced Fe S cluster of Balch’s dithiolene series†
4
4
Ameerunisha Begum,* Golam Moula, Moumita Bose and Sabyasachi Sarkar*
Received 15th November 2011, Accepted 19th December 2011
DOI: 10.1039/c2dt12184k
III II
A super reduced Fe S cluster with a sulfur based radical, [NBu ] [Fe Fe (μ -S) (mnt) 6−(mnt)1−˙]4−˙,
4
4
4 4
3
3
4
3
(
1) (mnt, maleonitrile dithiolate) which evolves H S gas on treatment with acid under ambient conditions
2
has been synthesized and structurally characterized. The Fe–S distances in 1 are in the range
.246–2.383 Å, in stark contrast to that of the known n = −2 member of the series based on the
2
n
4 3 4 2 2 2 4 3
[Fe (μ -S) (S C R ) ] unit (R = CF , Ph) with Fe–S bond lengths of 2.149–2.186 Å. The EPR of 1
displays very weak signals at g, 4.03 and 2.38 along with a strong S-based radical EPR signal at g, 2.003
associated with five structured components tentatively assigned to hyperfine interaction arising out of the
57
naturally abundant Fe with <A> = 88 G. The EPR profile resembles the reduced Fe–S cluster of CO
inhibited Clostridium pasteurianum W5 hydrogenase or the Fe S centers of wild-type enzyme, IspH
4
4
treated with HMBPP or IPP.
6
–10
coordinated 1,2-dithiolene ligands.
The Fe–S frameworks in
Introduction
n
[
Fe (μ -S )(S C (CF ) ) ] (n = 0, −2) are considerably stable
4
3
4
2
2
3 2 4
The Fe–S clusters in hydrogenases shuttle electrons in catalyzing
and they undergo electron transfer reactions without a break-
down of the polynuclear skeleton. Dahl et al. reported that the
replacement of the four terminal S C (CF ) ligands in the
+
H ↔2H interconversion. [FeFe] hydrogenase from Clostridium
2
pasteurianum, contains a [Fe S ] cubane sub-cluster covalently
4
4
2
2
3 2
2
−
bridged by a cysteinate thiol to a [2Fe] sub-cluster, the center of
[
Fe (μ -S) (S C (CF ) ) ]
dianion with less π-acidic
S C (CN) ones should increase the Fe⋯Fe, S⋯S contacts and
the Fe–S bond distances. Because of the air sensitivity, n = −3
and n = −4 members of the electron transfer series were not iso-
1,2-dithiolene coordinated metal complexes are known
to undergo ligand centered oxidation/reduction involving dianio-
nic to neutral to dipositive complexes and S-based radicals.
Radical based metal-dithiolate systems are expected to show
unprecedented spectroscopic properties which are sometimes
strikingly similar to that of the biological active sites. Herein
we report the synthesis of the hitherto unknown most reduced
member of the electron transfer related series, [NBu ] [Fe -
3
Fe (μ -S) (mnt) (mnt) ˙] ˙, (1) (mnt, maleonitrile dithio-
late), its structure and unique EPR spectrum and its reactivity
with weak acids.
4
3
4
2
2
3 2 4
1
action. The [Fe S ] cubane sub-cluster transfers the electrons
4
4
2
2
2
2
obtained from pyruvate oxidation to the [2Fe] sub-cluster. The
EPR spectrum with multiple hyperfine components of the hydro-
genase of Clostridium pasteurianum W5 generated on exposure
to CO could not be assigned to any particular ligand binding.
Similar EPR spectra have been recently reported for the Fe4S
11,12
lated.
3
13–19
4
centers formed by the reduced, wild-type Aquifex aeolicus
enzyme, IsPH [E-4-hydroxy-3-methyl-but-2-enyl diphosphate
20
(HMBPP) reductase] and IPP (Isopentenyl diphosphate) or the
wild-type enzyme plus HMBPP. The results indicated the invol-
vement of an organometallic iron complex with HMBPP, a π/σ
III
4
4
2
II
6−
1− 4−
‘
metallacycle’ or η -alkenyl complex with iron–carbon (Fe–C)
3
4
3
bonds, although there was no evidence for the formation of allyl
4
radicals.
Active site analogues of Fe–S proteins, viz., [Fe (μ -S)
4
4
3
n−
5
(
SR)4] were reported by Holm et al. wherein these clusters
contained peripheral ligands with monodentate thiolates and the
Fe-sites were mostly of tetrahedral/pseudo tetrahedral nature.
Fe4S4 cluster compounds bearing terminal bidentate thiolates
with penta-coordinated Fe-sites have been comparatively less
investigated and there is a single example in the five membered
electron transfer related series (n = 0, −1, −2, −3 and −4) based
Results and discussion
The complex 1 was synthesized by the reaction of FeCl with
disodium maleonitrile dithiolate and Li2S in acetonitrile
3
(
CH CN) under Schlenk conditions and recrystallized from a
3
mixture of CH CN and diethyl ether. Its crystals are composed
3
n
of anions and tetrabutylammonium cations in a 1 : 4 ratio in the
asymmetric unit. The perspective view of the anionic part of the
complex 1 along with a tetrabutyl ammonium cation is displayed
in Fig. 1 and selected crystal data are presented in Table 1. The
crystal structure confirms the formation of tetrameric [Fe (μ -
on [Fe (μ -S) S C R ) ] (R = CF , Ph) unit with terminally
4
3
4
2
2
2 4
3
Department of Chemistry, Indian Institute of Technology, Kanpur,
Kanpur, 208016, India. E-mail: abya@iitk.ac.in; Fax: 915122597436;
Tel: 91512 2597265
4
3
S) ] cubane with terminal mnt coordination to the Fe centers.
4
†
CCDC reference number 788088. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt12184k
Six of the Fe–S distances are in range 2.246–2.276 Å whereas
3536 | Dalton Trans., 2012, 41, 3536–3540
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Fig. 2 The structure of the anionic part of 1 in a space filling model,
(a) front view and (b) rear view. Note the distortion in the Fe(4) environ-
ment in part (b).
Fig. 1 A perspective view of the anionic part of complex 1 along with
a tetrabutyl ammonium cation in 50% probability thermal ellipsoids.
Selected bond lengths, (Å): Fe(1)–S(1), 2.297(3); Fe(1)–S(2), 2.256(3);
Fe(1)–S(4), 2.256(3); Fe(1)–S(5), 2.265(3); Fe(1)–S(6), 2.264(3); Fe(2)–
S(1), 2.233(3); Fe(2)–S(2), 2.260(3); Fe(2)–S(3), 2.310(3); Fe(2)–S(7),
Table 2 C–S bond distances in
4 2 4 3 4
1 and in [AsPh ] [Fe (μ -S)
2
(S C
2
(CF
)
3 2
4
) ] (ref. 11)
a
Bond
1 (Å)
(Ref. 11) (Å)
S(9)–C(9)
S(5)–C(1)
S(6)–C(2)
S(7)–C(5)
S(8)–C(6)
S(10)–C(10)
S(11)–C(13)
S(12)–C(14)
1.717(10)
1.735(10)
1.751(10)
1.743(09)
1.742(10)
1.715(10)
1.747(10)
1.726(10)
1.66(3)
1.69(3)
1.70(3)
1.74(3)
1.75(3)
1.69(3)
1.75(4)
1.76(3)
2
.263(3); Fe(2)–S(8), 2.265(3); Fe(3)–S(2); 2.305(3), Fe(3)–S(3); 2.252
(3); Fe(3)–S(4); 2.326(3), Fe(3)–S(9); 2.376(3); Fe(3)–S(10), 2.383(3);
Fe(4)–S(1), 2.252(3); Fe(4)–S(3), 2.279(3); Fe(4)–S(4), 2.256(3); Fe(4)–
S(11), 2.276(3); Fe(4)–S(12), 2.246(3); S(12)⋯H(17B), 2.93.
Table 1 Crystal data for (1)
a
The atom numbers differ from those of 1. (see Ref. 11).
Compound
(1)
Empirical formula
Formula weight
T/K
80 4 12 12
C H144Fe N S
1882.19
120
2
−
complex [Fe (μ -S )(S C (CF ) ) ]
and in the range
4
3
4
2
2
3 2 4
Wavelength Mo-Kα (Å)
Crystal system/Space group
0.71073
3
.297–3.568 Å.
Monoclinic/P21/c
30.853(7)
11.326(2)
31.285(7)
116.611(3)
9774(4)/4
1.279
0.883
4016
2.2 to 28.34
23656
The notable feature in the structure of 1 is the considerably
shorter C–S bond distances (C(9)–S(9), 1.716 Å and C(10)–S
10), 1.715 Å) of the mnt ligand coordinated to Fe(3) and the
a/(Å)
b/(Å)
c/(Å)
β/(°)
(
3
elongated Fe(3)–S bond distances. This is an indication of the
oxidation of the ligand to its radical form and the possibility of
the existence of the iron(II) oxidation state at this particular site
Volume/Å /Z
−3
Density (Mg m
)
−
1
Absorption coefficient (mm
F(000)
θ range for data collection (°)
Unique reflections
)
(Fe(3)). It shows that there can be intramolecular electron trans-
fer within the {Fe S } core. 1,2-dithiolene metal complexes are
4
4
Observed reflections
8848
97%
Empirical
23656/5/979
1.038
0.1046
0.2272
known to undergo ligand centered oxidation/reduction involving
Completeness to θ = 26.00°
Absorption correction
Data/restraints/parameters
dianionic to neutral to di-positive complexes and it is reflected in
13–20
shortened C–S bond distances.
Within the {Fe (μ-S) }
4 4
2
framework, although all of the four iron atoms are chemically
identical, (all are coordinated to one terminal mnt ligand each)
three of the Fe atoms (Fe(1)–Fe(3)) are in square pyramidal
environments whereas the fourth Fe atom (Fe(4)) is severely dis-
torted towards a trigonal bipyramidal structure, as shown in the
space filling model (Fig. 2). Furthermore, intermolecular short
Goodness of fit on F
Final R
1
values [I > 2σ(I)]
2
Final wR(F ) values [I > 2σ(I)]
the remaining two Fe–S bond distances are 2.376 and 2.383 Å.
The Fe–S bond distances are considerably longer than those of
the n = −2 member of the electron transfer series, [Fe (μ -
contact between the mnt ligand attached to Fe(4) and the CH
group of the NBu cations [(S(12)⋯H(17B), 2.93 Å] is also
observed, which has been highlighted in Fig. 1.
2
4
3
4
n
11
S) S C (CF ) ) ] , viz., Fe–S, 2.149–2.186 Å. This might as
4
2
2
3 2 4
well due to the coordination of CF3 substituted dithiolene
ligands. The Fe–Fe separations within the iron tetrahedron found
in complex 1 (2.843–3.123 Å) are similar to those of the n =
The iron atom (Fe(3)), which is attached to the oxidized form
of the terminal mnt ligands, is displaced as long as 0.629 Å,
whereas the iron atoms Fe(1) and Fe(2) are displaced by 0.408
and 0.482 Å, respectively, from the basal plane formed by the S-
donor atoms, and the geometry around Fe(4) is severely distorted
−
2 member of the series and longer than those of the classical
5
,11
cubanes of Holm et al.
The S⋯S separations within the
sulfur tetrahedron of 1 are longer than those of the Balch’s
towards
a
trigonal bipyramidal structure. In the
n =
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Fig. 3 The electronic spectrum of 1 in CH
visible spectrum showing the presence of the IVCT band in 1 around λ,
00 nm.
3
CN, (0.14 mM); inset is the
8
Fig. 5 (a) The X-band EPR of 1 at room temperature (298 K) in the
range 0–6500 G with highlighted g-values on the top; (b) the X-band
EPR of 1 in the range 3225–3825 G showing hyperfine structure and
highlighted g-values on the top; (c) the EPR spectrum from Ref. 3.
reversible redox couple around E1/2, −0.258 V and four irrevers-
ible reductions in the region, E , −0.770 to −1.380 V. The
p
absorption band around λ ∼ 800 nm and the reversible redox
couple at E1/2, −0.258 V (Fig. 4, inset) suggest the possibility of
the presence of a ligand based radical which is corroborated by
the X-ray structural parameters of the oxidized ligand viz., the
C–S bond distances (C(9)–S(9), 1.716 Å and C(10)–S(10),
1.715 Å) of the mnt ligand coordinated to the Fe(3) center.
However, the EPR measurement of complex 1 confirmed that
it is paramagnetic and the solid state room temperature magnetic
3
Fig. 4 A cyclic voltammogram of 1 (0.1 mM) in CH CN (supporting
electrolyte, tetrabutylammonium perchlorate, 0.2 M); inset is the re-
versible redox couple at E1/2, −0.258 V at different scan rates, 50 to
−
1
5
00 mV s .
moment (μeff) of 2.8 μ is indicative of the presence of two odd
B
1
1
−
2 member of the series viz., [Fe (μ -S )(S C (CF ) ) ]2−, the
electrons in the system. This can result from the presence of
4
3
4
2
2
3 2 4
2
−
Fe atoms are displaced by 0.60 Å (average) above the basal
sulfur plane and most of the C–S bond distances of dithiolene
ligands are considerably shorter, viz., C–S, 1.759, 1.753, 1,752,
.739, 1.701, 1.693, 1.689, and 1.662 Å, as given in Table 2.
Complex 1 displays absorption bands around λ
three S bridged ferric ions of intermediate spins (s = 3/2) and
one ferrous ion of low spin along with one mnt ligand based
S-radical (s = 1/2) attached to the ferrous ion, Fe(3) resulting in
two net odd electrons. This might as well have happened as a
result of an intramolecular charge transfer from the mnt ligand to
the originally ferric center Fe(3) giving an mnt ligand based
radical and ferrous(Fe(3)) center.
1
(ε),
max
−1
−1
−1
−1
8
(
00 nm (1000 M cm ), 502 nm (2600 M cm ), 361 nm
8600 M cm ) and 270 nm (20 000 M cm ) in CH CN
−1
−1
−1
−1
3
(
Fig. 3). All the three low energy bands in 1 are additional com-
Whereas the Mossbauer spectra of the neutral and dianionic
6,11
−1
pared with 4-Fe and 8-Fe proteins’ electronic signature known to
be associated with the iron-sulfur chromophore. The band
around 800 nm in complex 1 can be assigned to an inter-
valence-charge transfer band (IVCT) which is observed in sulfur
forms
displayed doublets of δ = 0.32 and 0.39 mm s and
5
−1
ΔE = 1.68 and 1.64 mm s , the spectrum of 1, the most reduced
form of the series (n = −4), displayed a doublet of δ = 0.24 mm
−
1
−1
s
and ΔE = 1.42 mm s . The Mossbauer spectral data reflect
1
3–20
based radical containing complexes.
The cyclic voltam-
the identical iron environment of all four irons in 1 as well as in
metric profile of complex 1 in CH CN (Fig. 4) displayed a
the already known members of Balch series, which is contrary to
3
3538 | Dalton Trans., 2012, 41, 3536–3540
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the crystal structural and other spectroscopic data. Furthermore,
−0.200 V was conducted in CH CN and the GC analytical result
3
6,11
the Mossbauer spectral parameters of the reported members
and complex 1 indicate that the four Fe centers present inside the
Fe S ] unit can not be differentiated by Mossbauer spec-
of the gas evolved did not match with that of the standard H gas
2
value. Hence the gas evolved was analyzed chemically by insert-
ing cotton soaked with lead(II) acetate onto the lid of the electro-
chemical cell. The black coloration of the soaked cotton
[
4
4
trometry. The room temperature (298 K) solid state EPR spec-
trum of 1 displayed a strong signal with g, 2.003 at 298 K
confirmed the evolution of H S gas. Similarly, complex 1
2
(Fig. 5a) along with very weak signals at g, 4.03 and 2.38 sup-
evolves H S on treatment with dilute acetic acid under ambient
2
porting the presence of intermediate spin ferric ions. Interest-
ingly the strong EPR signal centering at g, 2.003 is flanked by
well resolved fine structure at g, 2.136, 2.083, 2.032, 1.974,
conditions i.e., without applying any elctrochemical potential.
This is reasonable because complex 1 contains acid labile inor-
ganic S groups similar to ferredoxin type clusters which on
2
−
1
.932 and 1.882 with the hyperfine coupling constant <A> = 88
protonation release H S gas.
2
G as shown in Fig. 5b. At low temperature (120 K), the intensity
of the EPR signals increased considerably but the EPR spectrum
remained almost identical.
Conclusions
The CO inhibited and reduced form of Clostridium pasteuria-
num W5 hydrogenase exposed to CO gas displayed an EPR
spectrum with similar fine structure, as shown in Fig. 5c, which
can not be assigned to any specific ligands, because when 90%
enriched CO was used only broadening of lines in the EPR spec-
trum was observed, whereas the fine structure was identical to
In summary, the fully reduced cluster 1 of the Balch series
which evolves H S gas on treatment with acid under ambient
2
conditions has been synthesized and structurally characterized.
This shows an interesting EPR spectrum that resembles that of
CO inhibited Clostridium pasteurianum W5 hydrogenase. A
comparative study of electronic spectroscopy and cyclic voltam-
metric properties of 1 reveals the presence of a sulfur based
radical inside the [Fe (μ -S )] cluster which is corroborated by
1
2
3
the naturally abundant CO containing system. A similar EPR
spectrum has been reported for the [Fe S ] center found in the
4
4
4
3
4
product formed by wild-type IsPH plus IPP or HMBPP, which
the short C–S bond lengths [(S(9)–C(9), 1.717(10) Å and S(10)–
C(10), 1.715(10) Å].
has been reported to be due to the formation of a unique organo-
4
metallic iron center rather than due to an organic radical. In the
3
former case, it is highly probable that CO binds at the four iron
centers leading to the formation of penta-coordinated iron
centers which might exhibit an EPR spectrum with such a
hyperfine structure and <A> values. Thus electronically 1 may
resemble this native reduced species under CO since all of its
four iron centers are penta-coordinated. We ascribe the EPR
signal exhibited by complex 1 to the S-based radical of the oxi-
dized mnt ligand attached to the low spin ferrous ion, (Fe(3)).
The hyperfine splitting observed is due to the interaction with
Experimental
Materials and methods
All solvents and chemicals were purchased from commercial
sources. Disodium maleonitrile dithiolate was synthesized by a
reported procedure. The electronic absorption spectroscopic
measurements were conducted on a Perkin–Elmer Lambda 35
spectrometer. Infrared spectra were measured on a Bruker Vertex
25
57
the nuclear moment of the naturally occurring low abundant Fe
nuclei (4Fe) in 1. The observation of such hyperfine interaction
even with low natural abundance is possible. A super hyperfine
interaction based on the low abundance of the naturally occur-
7
0 FT-IR spectrometer. X-band EPR spectral measurements were
done using a Bruker EMX Spectrometer. Solution magnetic
moment measurement was done by Evans’ method in DMF on a
JEOL DELTA2 NMR spectrometer (500 MHz). Vibrating
sample magnetic moment measurement was conducted on a
EV-7 VSM ADE-DMS-Magnetic instrument within the field
range of −17500 to +17500 Oe at room temperature
1
3
3−
ring
known.
C nuclei in the paramagnetic ion, Mo(CN) ]
is
8
2
1–23
(294–300 K). The data were corrected for diamagnetism of the
Reaction of complex 1 with acids
sample holder and diamagnetic corrections for complex 1 were
deduced from Pascal’s constants. Mossbauer spectra were
recorded using a conventional constant acceleration Mossbauer
spectrometer (Wissenscaftliche Electronik GmbH0) with Co in
Rh matrix as the Mossbauer source. Cyclic voltammetric studies
were carried out at 298 K on a BASi Epsilon-EC Bioanalytical
[
[
FeFe] hydrogenase from Clostridium pasteurianum, contains a
Fe (μ -S )] cubane sub-cluster covalently bridged by a cystei-
57
4
3
4
nate to a [2Fe] sub-cluster. In this system, the [2Fe] sub-cluster is
regarded as the center of action whereas the [Fe (μ -S )] cubane
sub-cluster is involved in the electron transfer which obtains
electrons from pyruvate oxidation. Electrochemical proton
4
3
4
systems in CH CN. Glassy carbon working, platinum wire
3
2
auxiliary and Ag/AgCl with 3.0 M KCl reference electrodes
were used. Tetrabutylammonium perchlorate (TBAP) of 0.2 M
reduction catalyzed by the model compounds is one of the
current methods of estimation of hydrogenase activity wherein
the catalytic efficiency is correlated to the shift of the reduction/
oxidation potentials positively towards zero volts (−0.41 V at pH
concentration was used as supporting electrolyte in CH CN. The
3
electrochemical proton reduction using complex 1 and TsOH
20,24
was conducted as reported previously.
2
0,24
7
.0).
Complex 1 was tested for its catalytic efficiency for
electrochemical proton reduction in CH CN. Upon addition of a
Generation of H S gas. Complex 1 (2 mmol) was taken in a
3
2
standard acid like p-toluene sulfonic acid, (TsOH) a reversible
redox couple at E1/2 ∼ −0.00 V was observed. Controlled poten-
two necked round bottomed flask fitted with a pressure equaliz-
ing funnel and the other neck of the flask was connected to a sul-
furic acid trap. The whole set up was purged with argon gas for
tial analysis of complex 1 containing excess of TsOH at E1/2
∼
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ox
3
0 min and then dil. CH COOH was added which resulted in a
−1.379 V vs. Ag/AgCl; Ep (irreversible), +0.686, +1.012 V vs.
3
moderate stream of gas bubbling. The gas was allowed to pass
through a colourless cotton soaked with a solution of lead(II)
acetate. The black coloration of the soaked cotton confirmed the
Ag/AgCl in CH CN–0.2M TBAwith a GC working electrode.
3
evolution of H S gas.
Acknowledgements
2
X-ray crystallographic measurement of 1. Single crystals of
A. B. thanks the Department of Science & Technology, (DST),
N. Delhi, India for the award of fast track scheme for young
scientists. G. M. and M. B. thank the Council of Scientific and
Industrial Research, N. Delhi for the award of doctoral
fellowships.
III II
6
complex 1 were isolated as [NBu ] [Fe Fe (μ -S) (mnt)
3
4
4
3
3
4
−
1− 4−
(
mnt) ˙] ˙ from the walls of the reaction flask at 10 °C.
Complex 1 is extremely air sensitive and good quality crystals
were not obtained. A crystal of better quality was used for the
intensity data collection at 100 K on a Bruker AXS Smart APEX
CCD diffractometer with graphite monochromated Mo-Kα radi-
ation (0.71073 Å). Data reduction and absorption corrections
were done using the SAINTPLUS program package. The struc-
ture was solved by direct and conventional Fourier methods and
Notes and references
1
J. W. Peters, W. N. Lawzilotta, B. J. Lemon and L. C. Seefeldt, Science,
998, 282, 1853.
M. W. W. Adams and E. I. Stiefel, Science, 1998, 282, 1842.
1
2
refined on F by the full-matrix least-squares technique using the
2
2
6
SHELXTL program package All non-hydrogen atoms were
refined anisotropically, H atoms at idealized positions in riding
mode. Selected crystallographic data of complex 1 are given in
Table 1. Detailed crystallographic data for 1 have been deposited
in the Cambridge Crystallographic data centre as no. CCDC
3 D. L. Erbes, R. H. Burris and W. H. Orme-Johnson, Proc. Natl. Acad.
Sci. U. S. A., 1975, 72, 4795.
4
W. Wang, K. Wang, Y.-L. Liu, J.-H No, J. Li, M. J. Nilges and
E. Oldfield, Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 4522.
5 T. Herskovitz, B. A. Averill, R. H. Holm, J. A Ibers, W. D. Phillips and
J. F. Weiher, Proc. Natl. Acad. Sci. U. S. A., 1972, 69, 2437.
6
7
A. L. Balch, J. Am. Chem. Soc., 1969, 91, 6962.
A. L. Balch, F. Roehrscheid and R. H. Holm, J. Am. Chem. Soc., 1965,
7
88088.† Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: (+44)1223-336-033) or e-mail: deposit@ccdc.cam.ac.uk.
87, 2301.
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T. Birchall, N. N. Greenwood and J. A. McCleverty, Nature, 1967, 215,
III II
Synthesis of [NBu ] [Fe Fe (μ -S) (mnt) 6−(mnt)1−˙]4−
˙
625.
4 4 3 3 4 3
1
0 R. Williams, E. Billig, J. H. Waters and H. B. Gray, J. Am. Chem. Soc.,
966, 88, 43.
1 T. H. Lemmen, J. A. Kocal, F. Yip-Kwai Lo, M. W. Chen and L. F. Dahl,
(
1). The reaction was done under inert (Schlenk) conditions.
1
Acetonitrile (40 ml) was purged with argon gas for 30 min and
disodium maleonitrile dithiolate (0.372 g, 2 mmol) was added
into it. The suspension was stirred for 20 min. followed by the
addition of FeCl (0.322 g, 2 mmol) and Li S (0.15 g, 3 mmol)
1
J. Am. Chem. Soc., 1981, 103, 1932.
1
1
2 T. Toan, B. K. Teo, J. A. Ferguson, T. J. Meyer and L. F. Dahl, J. Am.
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3 P. Ghosh, A. Begum, D. Herebian, E. Bothe, K. Hildenbrand,
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563.
3
2
under argon. The black colored reaction mixture was stirred for
h at room temperature and at the end tetrabutyl ammonium
8
14 K. Ray, T. Weyhermuller, F. Neese and K. Wieghardt, Inorg. Chem.,
bromide (0.665 g, 2 mmol) was added to the reaction mixture.
After a further 30 min, diethylether (100 ml) was added to the
reaction mixture. The reaction flask was closed and allowed to
stand at 10 °C for two days under argon to precipitate a dark
brownish-black colored precipitate. This was filtered, washed
with ether and stored under argon. (Yield, 0.7 g, 74%). Black
single crystals suitable for X-ray diffraction were isolated from
the walls of reaction flask. The crystals of 1 were extremely air
sensitive and perfect elemental analytical data could not be
obtained. Data for 1: Elemental analysis (%) calculated for
C H Fe N S , C, 51.05, H, 7.71, N, 8.93; Observed, C,
2
005, 44, 5345.
1
5 I. Shupack, E. Billig, R. J. H. Clark, R. Williams and H. B Gray, J. Am.
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7 K. Ray, T. Weyhermuller, A. Goossens, M. W. J. Craje and K. Wieghardt,
1
Inorg. Chem., 2003, 42, 4082.
18 R. K. Szilagyi, B. S. Lim, T. Glaser, R. H. Holm, B. Hedman,
K. D. Hodson and E. I. Solomon, J. Am. Chem. Soc., 2003, 125, 9158.
1
9 R. Sarangi, S. D. George, D. J. Rudd, R. K. Szilagyi, X. Ribas,
C. Rovira, M. Almeida, K. O. Hodgson, B. Hedman and E. I. Solomon,
J. Am. Chem. Soc., 2007, 129, 2316.
20 A. Begum, G. Moula and S. Sarkar, Chem.–Eur. J., 2010, 16, 12324.
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Chem. Phys. Lett., 1991, 184, 375.
8
0
144
4 12 12
−1
5
1.82, H, 7.16, N, 8.02. FT-IR (KBr disc, cm ): 3019(m), 2962
(
(
m), 2197(m, νCN), 1487s(m), 1401(w), 1243(w), 1147(w), 1020
2
2 G. Teschmit and R. Kirmse, Inorg. Chem. Commun., 1999, 2, 465.
23 R. Kirmse, S. Saluschke, E. Moeller, E. J. Reijerse, E. Gelerinter and
s) 602(br.) (w, weak, m, medium, s, strong). UV-visible in
−
1
−1
CH CN [λ/nm (ε/M cm )]: 800 (1000), 502 (2500), 361
N. V. Duffy, Angew. Chem., Int. Ed. Engl., 1994, 33, 1497.
3
2
2
4 A. Begum and S. Sarkar, Eur. J. Inorg. Chem., 2012, 40.
5 E. I. Stiefel, L. E. Bennett, Z. Dori, T. H. Crawford, C. Simo and
H. B. Gray, Inorg. Chem., 1970, 9, 281.
(8500), 270(19800). EPR, g, 4.03, 2.38, 2.146, 2.089, 2.035,
1
.983, 1.930, 1.881. μeff = 2.8 μ at 300 K. E = −0.258 V vs.
B
1/2
red
Ag/AgCl (ΔE = 80 mV); Ep (irreversible), −0.935, −1.136,
26 G. Sheldrick, Acta. Cryst., 2008, A64, 112.
3540 | Dalton Trans., 2012, 41, 3536–3540
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