Iron complexes of the N(CH2CH2 S)33-(NS3) ligand with isocyanide co-ligands

Article abstract of DOI:10.1139/v00-198

The complexes NEt₄[Fe(NS₃)(CNR)] (1), [Fe{Fe(NS₃)(CNR)}₂-S,S′] (2), [Co{Fe(NS₃)(CNMe)}₂-S,S′] (3), and [Ni{Fe(NS₃)(CNMe)}₂-S,S′] (4) (R = Me,t-Bu, or C₆H

Full text of DOI:10.1139/v00-198

490
Iron complexes of the N(CH2CH2S)33−(NS3) ligand
with isocyanide co-ligands.
Lyndsey Cooper, Sian C. Davies, Jonathan R. Dilworth, David L. Hughes,
Marcin Konkol, Raymond L. Richards, J. Roger Sanders, and Piotr Sobota
Abstract: The complexes NEt4[Fe(NS3)(CNR)] (1), [Fe{Fe(NS3)(CNR)}2-S,S ′] (2), [Co{Fe(NS3)(CNMe)}2-S,S′] (3),
and [Ni{Fe(NS3)(CNMe)}2-S,S′] (4) (R = Me, t-Bu, or C6H11(Cy)) have been prepared and the X-ray crystal structures
of NEt4[Fe(NS3)(CNMe)] (1a) and [Fe{Fe(NS3)(CNCy)}2-S,S ′] (2c) have been determined. Mössbauer and IR spectro-
scopic data and room temperature magnetic moments for these complexes are reported.
Key words: iron, cobalt, nickel, thiolate, isocyanide.
Résumé : On a préparé les complexes de NEt4[Fe(NS3)(CNR)] (1), [Fe{Fe(NS3)(CNR)}2-S,S ′] (2),
[Co{Fe(NS3)(CNMe)}2-S,S ′] (3) et [Ni{Fe(NS3)(CNMe)}2-S,S ′] (4) (R = Me, t-Bu ou C6H11 (Cy)) et on a déterminé
les structures de NEt4[Fe(NS3)(CNMe)] (1a) et de [Fe{Fe(NS3)(CNCy)}2-S,S ′] (2c) par diffraction des rayons X. Pour
chacun de ces complexes, on a déterminé les spectres de Mössbauer et IR ainsi que les moments magnétiques à la
température ambiante.
Mots clés : fer, cobalt, nickel, thiolate, isocyanure.
[Traduit par la Rédaction] Cooper et al. 494
Introduction
strates to N2 such as CO, cyanides, isocyanides, and azide.
We have already reported or communicated some of our re-
sults for Mo (3), V (4), and Fe (5). The Fe(NS3) site is able
to bind CO with biologically relevant values of ν(C=O) (5).
We, therefore, searched for interactions of this site with
other small molecules which are able to function as alterna-
tive substrates for dinitrogen, and have developed chemistry
of isocyanides as detailed below.
We have been exploring the chemistry of the tripodal NS3
ligand N(CH2CH2S)33−(NS3) in order to investigate the abil-
ity of metal sites carrying this ligand to mimic the behaviour
of metal–sulfur sites in enzymes such as hydrogenases and
nitrogenase. In the former study, some of us have shown that
sulfur-bridged, binuclear complexes containing the {Fe(µ-
NS3)Ni} unit model structural aspects of iron–nickel
hydrogenase (1). Recently a rich chemistry of the tripodal
nitrogen-donor ligand [N(CH2CH2NSiMe3)3]3–(NN3), and its
analogues has been developed, including the preparation of
the tris(µ-dinitrogen) complex [Fe{N2Mo(NN3)}3] as well as
the monomer [Mo(NN3)(N2)] (2). This prompted us to inves-
tigate the ability of metal sites carrying the (NS3) ligand to
bind species on the route from N2 to NH3 such as N2H,
N2H2, and N2H4 and their derivatives, and alternative sub-
Results and discussion
The blue, mononuclear, terminal RNC complexes
NEt4[Fe(NS3)(CNR)] (R = Me (1a); t-Bu (1b); or C6H11
(Cy) (1c)) were obtained either by treatment of [Fe(acac)3]
and NS3H3 with RNC in presence of Et4N(OAc), or by re-
duction of NEt4[FeCl(NS3)] (5) with sodium amalgam in
presence of RNC (rxn. [1]). Compounds 1a and 1b form
blue crystals, but 1c could not be crystallized, nor obtained
analytically pure, although its spectroscopic data show it
clearly to be the analogue of 1a and 1b. In the solid, com-
pounds 1 are moderately stable to air, decomposing over 2 to
3 days, but they are more sensitive in solution.
Received August 30, 2000. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on May 23, 2001.
Dedicated to Professor Brian R. James on the occasion of his
65th birthday.
L.Cooper and J.R. Dilworth. Inorganic Chemical
Laboratory, University of Oxford, South Parks Road, Oxford
OX1 3QR, U.K.
[1]
NEt4[FeCl(NS3)] + Na + RNC
→ NEt4[Fe(NS3)(CNR)] + NaCl
S.C. Davies, D.L. Hughes, R.L. Richards1, and J.R.
Sanders. Department of Biological Chemistry, John Innes
Centre, Colney Lane, Norwich NR4 7UH, U.K.
M. Konkol and P. Sobota. Faculty of Chemistry, University
of Wroclaw, 14 F Joliot Curie, 50–383 Wroclaw, Poland.
(R = Me (1a), t-Bu (1b), or Cy (1c))
The complexes have the RNC ligand bound to five-
coordinated Fe in the linear mode as revealed by the X-ray
crystal structure of 1a. The structure (Fig. 1) is similar to
that of the carbonyl analogue (5), and consists essentially of
a trigonal bipyramid with the terminal MeNC ligand linearly
bound in the position trans to the apical N atom of the NS3
ligand, with the three S atoms lying in the equatorial plane.
1Corresponding author (present address: School of Chemistry,
Physics and Environmental Science, University of Sussex,
Brighton, Sussex BN1 9RQ, U.K.; telephone: 01 273 877 711;
fax: 01 273 677 196; e-mail: r.richards@sussex.ac.uk).
Can. J. Chem. 79: 490–494 (2001)
© 2001 NRC Canada
DOI: 10.1139/cjc-79-5/6-490

Cooper et al.
491
Fig. 2. View of the trinuclear complex [Fe{Fe(NS3)(CNCy)}2]
Fig. 1. The anion of NEt4[Fe(NS3)(CNMe)] (1a) showing the
disorder in the NS3 ligand and the atom numbering scheme.
(2c) with the pseudo-twofold symmetry axis vertical in the plane
of the paper. Only the major components of the disordered NS3
ligands are shown.
Table 1. Selected molecular dimensions in complex 1a.
(a) About the iron atom
Fe—S(1)
Fe—S(2)
Fe—S(3)
2.2953(5)
2.2908(5)
2.2926(6)
Fe—N(4)
Fe—C(5)
2.049(2)
1.805(2)
V(NS3) site is clearly less than that of the iron and rhenium
systems, in keeping with the inability of the vanadium site to
bind CO (4).
Compounds 1 are paramagnetic, with µeff values in the
range 2.61–2.58 µB corresponding to an S = 1 state, as ob-
served for the CO analogue (µeff = 2.79 µB) (5). Like the CO
analogue, their Mössbauer spectra show a doublet, but the
parameters (in the ranges: IS 0.36–0.32, QS 1.27–1.30 mm s–1),
are somewhat larger than those of the CO analogue (IS 0.22,
QS 0.99 mm s–1) (5).
S(2)-Fe-S(1)
S(3)-Fe-S(1)
N(4)-Fe-S(1)
C(5)-Fe-S(1)
S(2)-Fe-S(3)
119.09(2)
N(4)-Fe-S(2)
C(5)-Fe-S(2)
N(4)-Fe-S(3)
C(5)-Fe-S(3)
C(5)-Fe-N(4)
87.24(5)
90.48(6)
87.37(5)
94.69(6)
177.51(7)
118.73(2)
87.87(5)
92.35(6)
121.61(2)
(b) In the isocyanide ligand
C(5)—N(51)
N(51)—C(52)
1.169(3)
1.411(3)
N(51)-C(5)-Fe
C(5)-N(51)-C(52)
178.2(2)
169.3(2)
In addition to the mononuclear complexes, the paramag-
netic homo- and hetero-metallic linear cluster complexes
[Fe{Fe(NS3)(CNR)}2-S,S′ ] (2), [Co{Fe(NS3)(CNR)}2-S,S′]
(3), and [Ni{Fe(NS3)(CNR)}2-S,S′] (4) have been obtained
by two routes. The first route, which involves treatment of
[Fe(acac)3] with RNC and NS3H3, gives the very dark green
“all iron” complexes (2 a–c). The second and more general
route exploits the donor properties of the ligating S-atoms of
complexes 1 and allows the controlled synthesis of the
green-black hetero-atom linear clusters 3 and 4, as shown in
rxn. [2].
Note: Bond lengths are in angstroms (D), angles in degrees (°), Esds
are in parentheses.
Principal structural parameters are presented in Table 1 and
show that the Fe—N distance (2.049(2) Å) and average
Fe—S distances (2.2929(14) Å) are close to those of the CO
analogue, 2.035(7) and 2.274(5) Å respectively (5). The iron
atoms are displaced similarly toward the apical C atom,
0.1003(2) and 0.0893(11) Å in 1a and the CO analogue, re-
spectively, from the 3S equatorial plane. The Fe—C dis-
tance 1.805(2) Å and Fe-C-N angle 178.2(2)° are in the
expected ranges for linear RNC at an Fe(II) site.
[2]
2NEt4[Fe(NS3)(CNR)] + MCl2
→ [M{Fe(NS3)(CNR)}2-S,S ′] + 2NEt4Cl
As expected, compounds 1 have NC stretching frequen-
cies in the terminal range (2061–1940 cm–1). These values
are lower than those of the corresponding free ligands, in
keeping with the lowering of the CO stretching frequency on
binding CO to this site, which is clearly electron releasing.
The lowering of the NC frequency caused by binding to the
d6 Fe(NS3)– site is similar to that produced by binding the
analogous d4 Re(NS3) site e.g., both 1b and [Re(NS3)(CN-t-
Bu)] (6) have ν(NϵC) at 1975 cm–1, some 162 cm–1 lower
than the value for the free ligand. The d3 complex analogues
[V(NS3)(CNR)] (R = t-Bu or Cy) do not show such a lower-
ing of the CN stretching frequency (ν(NϵC) = 2173 cm–1 in
both cases) (4). The electron-releasing properties of the
(M = Fe, R = Me (2a), t-Bu (2b), Cy (2c);
M = Co, R = Me (3); M = Ni, R = Me (4))
The linear structure of complexes 2a–c is proven by the
X-ray crystal structure of 2c, shown in Fig. 2. The structure
consists of two trigonal bipyramidal Fe(NS3)(CNCy) units,
each of which bridges through two of its S atoms to a central
Fe, which has distorted tetrahedral symmetry and lies on an
approximate twofold symmetry axis. Principal structural pa-
rameters are presented in Table 2. Within the
Fe(NS3)(CNCy) units, the Fe—S distances involving the
four bridging S atoms average 2.265(4) Å, but those to the
non-bridging S atoms are shorter, mean 2.221(4) Å. The
© 2001 NRC Canada

492
Can. J. Chem. Vol. 79, 2001
Table 2. Selected molecular dimensions in complex 2c.
(a) About the iron atoms
The Mössbauer spectrum of complex 2c is in accord with
its structure, showing resonances corresponding to two dif-
ferent iron(II) sites, one having twice the intensity of the
other (Experimental). Since the Mössbauer spectra of 2a, 2b,
3, and 4 all have similar IS and QS values to those of 2c, all
of these complexes are considered to have an analogous lin-
ear cluster structure. The CO analogue has the same linear
structure also (5) and the members of this class of complex
have structural similarities to the linear clusters
[NEt4]3[Fe3S4(SPh)4] (7) and [NEt4]3[VFe2S4Cl4] (8).
The NC stretching frequencies of 2, 3, and 4 are increased
relative to the corresponding monomeric precursors (Experi-
mental). A similar increase was observed for the CO ana-
logue on passing from the monomer to the linear cluster
complexes (5). Clearly the ability of the Fe(NS3) site to re-
lease electron density to CO or RNC is reduced in the linear
clusters as a consequence of the loss of anionic charge and
by two of its sulfur ligands utilising lone pairs to bind a cen-
tral metal atom.
Fe(1)···Fe(2)
Fe(1)—S(1)
Fe(1)—S(2)
S(1)-Fe(1)-S(2)
S(1)-Fe(1)-S(5)
S(1)-Fe(1)-S(6)
Fe(2)—S(1)
Fe(2)—S(2)
Fe(2)—S(3)
2.716(2)
2.293(2)
2.318(2)
105.00(8)
114.10(8)
109.40(8)
2.275(2)
2.264(2)
2.217(3)
2.059(6)
1.822(9)
107.40(8)
121.59(10)
88.3(2)
98.5(3)
130.61(10)
87.8(2)
89.2(3)
87.8(2)
89.5(3)
173.1(3)
72.95(7)
Fe(1)···Fe(3)
Fe(1)—S(5)
Fe(1)—S(6)
S(5)-Fe(1)-S(2)
S(6)-Fe(1)-S(2)
S(5)-Fe(1)-S(6)
Fe(3)—S(5)
Fe(3)—S(6)
Fe(3)—S(7)
2.705(2)
2.301(2)
2.315(2)
110.76(8)
112.99(8)
104.80(8)
2.258(2)
2.262(2)
2.224(2)
2.044(6)
1.835(9)
108.02(8)
127.71(9)
88.5(2)
94.6(2)
123.98(9)
88.5(2)
93.5(3)
87.7(2)
87.9(3)
175.6(3)
72.78(7)
Fe(2)—N(4)
Fe(2)—C(5)
Fe(3)—N(8)
Fe(3)—C(9)
S(2)-Fe(2)-S(1)
S(3)-Fe(2)-S(1)
N(4)-Fe(2)-S(1)
C(5)-Fe(2)-S(1)
S(3)-Fe(2)-S(2)
N(4)-Fe(2)-S(2)
C(5)-Fe(2)-S(2)
N(4)-Fe(2)-S(3)
C(5)-Fe(2)-S(3)
C(5)-Fe(2)-N(4)
Fe(2)-S(1)-Fe(1)
S(5)-Fe(3)-S(6)
S(7)-Fe(3)-S(5)
N(8)-Fe(3)-S(5)
C(9)-Fe(3)-S(5)
S(7)-Fe(3)-S(6)
N(8)-Fe(3)-S(6)
C(9)-Fe(3)-S(6)
N(8)-Fe(3)-S(7)
C(9)-Fe(3)-S(7)
C(9)-Fe(3)-N(8)
Fe(3)-S(5)-Fe(1)
Conclusions
The Fe(NS3) site is able to support a number of co-ligands
including isocyanides, and its tendency to bridge through
sulfur can be used to synthesise linear cluster complexes.
The stretching frequencies of CO at mononuclear and linear
cluster Fe(NS3) sites have values which are similar to those
observed in stop-flow IR studies of Klebsiella pneumoniae
nitrogenase (5). Corresponding data for RNC interactions
with the enzyme are not yet available to ascertain how ex-
tensively the behaviour of the Fe(NS3) sites resembles that
of the enzyme.
C(14)-S(1)-Fe(1) 106.1(3)
Fe(2)-S(2)-Fe(1) 72.70(7)
C(24)-S(2)-Fe(1) 106.9(3)
C(58)-S(5)-Fe(1) 107.5(3)
Fe(3)-S(6)-Fe(1) 72.43(7)
C(68)-S(6)-Fe(1) 105.8(3)
(b) In the isocyanide ligands
1.148(9)
1.448(11) N(9)—C(91)
175.3(7)
C(5)-N(5)-C(51) 160.3(8)
C(9)—N(9)
1.153(9)
1.431(10)
176.2(7)
C(9)-N(9)-C(91) 160.2(8)
C(5)—N(5)
N(5)—C(51)
N(5)-C(5)-Fe(2)
N(9)-C(9)-Fe(3)
Experimental
Note: Bond lengths are in angstroms (D), angles in degrees (°), Esds
are in parentheses.
General
All operations were carried out under a dry dinitrogen at-
mosphere, using standard Schlenk techniques. Solvents were
distilled under dinitrogen from the appropriate drying agents
prior to use. Starting materials were obtained from Aldrich
Chemical Co. and used without further purification unless
stated otherwise. Methyl isocyanide was made by the reac-
tion of N-methylformamide with p-toluenesulfonyl chloride
in quinoline at 75°C and purified by trap-to-trap distillation
at 15 mm Hg (1 mm Hg = 133.222 Pa). NS3H3 was made by
a modification of the literature method (4, 9–11) via
tris(chloroethyl)amine hydrochloride (CAUTION-VESICANT)
This work was carried out in an enclosed Schlenk apparatus
whilst wearing heavy duty gloves and a face mask.
[FeCl2(MeCN)2], [FeCl2(DMSO)3] (DMSO = dimethyl-
sulfoxide), and their cobalt and nickel analogues were made
by heating the anhydrous metal chlorides in MeCN or
DMSO until they dissolved and crystallizing by adding di-
ethyl ether. IR spectra were recorded on PerkinElmer 883 or
Shimadzu FT-IR 810M instruments in Nujol™ mulls.
Mössbauer parameters were determined at 77 K by Dr D.J.
Evans and Mrs E. Barclay of this laboratory, using an ES-
technology MS105 spectrometer having a 925 MBq 57Co
source in a rhodium matrix at ambient temperature, refer-
enced against a 25 µm iron foil at 295 K. Magnetic moment
determinations at 293 K were in the solid state, using a
Fe—S distances about the central Fe have a mean value of
2.307(6) Å. The iron atoms Fe(2) and Fe(3) are displaced
from the planes of their three equatorially-arranged sulfur at-
oms by 0.0805(11) and 0.0696(10) Å, respectively, similar
to the values above for complex 1a and its CO analogue.
The apical N-Fe-C-N-C units are basically linear, with di-
mensions resembling those in 1a. The isocyanide C-N-C an-
gles in both ligands of 2c however, essentially identical at
160.25(1)°, deviate more from linearity than in 1a where the
angle is 169.3(2)°. Even greater deviations have been noted
in the ReIII complexes [Re(NS3)(CN-t-Bu)] and
[Re(NS3)(CNCH2COOMe)] where the C-N-C angles are
154.0(10) and 150.8(9)°, respectively (6). The limit of the
pseudo-symmetry is reached at the cyclohexyl ring junction;
both Cy rings have the chair conformation but the
C(51)—N(5) bond is equatorial with respect to the ring in
one isocyanide ligand, whereas, in the second, C(91)—N(9)
is axially orientated.
All the Fe atoms can be regarded as formally in oxidation
state two, but solid 2c has µeff = 1.72 µB per molecule at
20°C showing considerable electronic coupling, and 2a, 2b,
3, and 4 also show similar behaviour (see Experimental).
The detailed magnetic and electrochemical properties of
these and related complexes will form a separate study.
© 2001 NRC Canada

Cooper et al.
493
Johnson Matthey Gouy balance. Microanalyses were by Mr
A. Saunders of the University of East Anglia (CHN) or by
Southern Science, Falmer Laboratories, East Sussex (met-
als).
(mm s–1): IS 0.58, QS 2.04 (rel. intensity 1); IS 0.32, QS 1.39
(rel. intensity 2). µeff = 1.72 µB. IR (cm–1): 2098, 2065
(NϵC). Anal. calcd. for C22H42Fe3N4S6: C 36.6, H 5.8, N
7.8; found: C 36.7, H 5.6, N 7.7.
Preparation of [Fe{Fe(NS3)(CNCy)}2-S,S′] (2c)
Syntheses
This was made similarly using CyNC in ether, in 82%
yield with respect to Fe. Mössbauer (mm s–1): IS 0.67, QS
Preparation of Et4N[Fe(NS3)(CNMe)]·MeCN (1a)
[Fe(acac)3] (0.71 g, 2.0 mmol), Et4NOAc·4H2O (0.65 g,
2.5 mmol), and MeNC (0.4 g, 10 mmol) were stirred in
MeCN (10 mL) for a few minutes, then NS3H3 (0.6 g,
3 mmol) in MeCN (5 mL) was added, whereupon the solu-
tion turned blue. After 1 h it was filtered and MeCN (5 mL)
and ether (20 mL) were added as a layer. After 3 days large
blue crystals deposited, which were filtered off, washed with
MeCN:ether and then ether, and dried in a vacuum; yield
2.01 (rel. intensity 1); IS 0.30, QS 1.47 (rel. intensity 2). µeff
=
1.72 µB. IR (cm–1): 2084, 2060 (NϵC). Anal. calcd. for
C26H46Fe3N4S6: C 40.3, H 5.9, N 7.2; found: C 40.4, H 5.9,
N 7.4.
Preparation of [Co{Fe(NS3)(CNMe)}2-S,S′] (3)
[CoCl2(DMSO)3] (0.10 g, 0.3 mmol) in methanol (10 mL)
was added to Et4N[Fe(NS3)(CNMe)] (0.24, 0.6 mmol) in
methanol (20 mL). A black precipitate formed. The next day
this was filtered off, washed with methanol and ether, and
dried in a vacuum (yield: 0.06 g, 34%). Mössbauer (mm s–1):
IS 0.29, QS 1.52. IR (cm–1): 2105 (NϵC). Anal. calcd. for
C16H30CoFe2N4S6: C 30.0, H 4.7, N 8.7, Co 9.2, Fe 17.5;
found: C 29.7, H 4.9, N 8.2, Co 9.9, Fe 17.3.
0.35 g (38%). Mössbauer (mm s–1): IS 0.36, QS 1.27. µeff
=
2.61 µB (S = 1). IR (cm–1): 2291, 2246 (CϵN), 2061 (NϵC).
Anal. calcd. for C18H38FeN4S3: C 46.8, H 8.2, N 12.1;
found: C 46.3, H 8.2, N 11.7.
Preparation of Et4N[Fe(NS3)(CN-t-Bu)] (1b)
Et4N[FeCl(NS3] (0.83 g, 2 mmol) was treated with so-
dium amalgam (70 g, 0.5% Na) in MeCN (20 mL). After
20 min the solution became yellow and was filtered through
Celite™. t-BuNC (0.8 g, 10 mmol) was added immediately
to the filtrate, which became blue. Ether (60 mL) was then
added as a layer to give, after 2 h, dark blue microcrystals
(0.14 g, 15%), which were filtered off, washed with ether,
and dried in a vacuum. Mössbauer (mm s–1): IS 0.32, QS
1.30. µeff = 2.58 µB (S = 1). IR (cm–1): 1975 (NϵC). Anal.
calcd. for C19H41FeN3S3: C 49.2, H 8.9, N 9.1; found: C
48.1, H 8.9, N 8.7.
Preparation of [Ni{Fe(NS3)(CNMe)}2-S,S′] (4)
This was made similarly from [NiCl2(DMSO)3] in 76%
yield. Mössbauer (mm s–1): IS 0.27, QS 1.61. µeff = 2.26 µB.
IR (cm–1): 2103 (NϵC). Anal. calcd. for C16H30Fe2N4NiS6:
C 30.0, H 4.7, N 8.7, Fe 17.5, Nil 9.2; found: C 30.0, H 4.9,
N 8.2, Fe 15.6, Nil 9.1.
Crystal structure analyses
NEt4[Fe(NS3)(CNMe)]·MeCN (1a)
Crystal data: C8H20N·C8H15FeN2S3·C2H3N, MW = 462.5.
Orthorhombic, space group P212121 (No. 19), a = 16.664(2),
b = 14.2340(12), c = 9.929(2) Å, V = 2355.1(6) Å3, Z = 4,
Dc = 1.31 g cm–3, F(000) = 992, T = 140 K, µ (Mo Kα) =
9.2 cm–1, λ (Mo Kα) = 0.71069 Å.
Preparation of Et4N[Fe(NS3)(CNCy)] (1c)
This was made similarly from reduced Et4N[FeCl(NS3)]
by treatment with CyNC, in 35% yield. A good analysis was
not obtained (see text). Mössbauer (mm s–1): IS 0.33, QS
1.29. IR (cm–1): 2023, 1940 (NϵC). Anal. calcd. for
C21H43FeN3S3: C 51.5, H 8.8, N 8.6; found: C 49.1, H 8.2,
N 9.1.
Crystals are black, irregular octahedra; in thin section they
are blue, decomposing in air to orange over two to three
days. Most are twinned, and from preliminary photographic
examination, some crystals show small variations in cell pa-
rameters and diffraction intensities. One, ca. 0.83 × 0.48 ×
0.48 mm, sealed in a capillary tube, was mounted on an
Enraf–Nonius CAD4 diffractometer (with monochromated
radiation) for determination, at room temperature, of accu-
rate cell parameters (from the settings of 25 reflections, θ =
10 to 11°, each centred in four orientations). The sample,
shown to be twinned, was then cooled to 140 K, the cell pa-
rameters were re-determined, and diffraction intensities of
the major twin were recorded. Of the 3825 unique reflec-
tions to θmax = 30°, 3537 were “observed” with I > 2σI; the
00l reflections, common to both twins, were removed from
the data set, leaving 3819 and 3532 reflections, respectively.
During processing, corrections were applied for Lorentz
polarization effects, absorption (by semi empirical ψ-scan
methods), and to eliminate negative net intensities (by
Bayesian statistical methods). No deterioration correction
was necessary. The structure was determined by the direct
methods routines in the SHELXS program (12) and refined
by full-matrix least-squares methods, on F2’s, in SHELXL
(13). There is disorder in the N-bonded methylene groups in
Preparation of [Fe{Fe(NS3)(CNMe)}2-S,S′] (2a)
[Fe(acac)3] (0.71 g, 2 mmol) and MeNC (0.4 g, 10 mmol)
were dissolved in MeCN (40 mL), and NS3H3 (0.6 g,
3 mmol) in MeCN (5 mL) was added. The solution turned
dark red, but within 30 min it turned dark green and depos-
ited black needles after 3 h which were filtered off, washed
with ether, and dried in a vacuum (yield: 0.13 g, 0.2 mmol,
30% with respect to iron). Mössbauer (mm s–1): IS 0.59, QS
2.06 (rel. intensity 1); IS 0.33, QS 1.38 (rel. intensity 2). µeff
=
2.92 µB. IR (cm–1): 2099 (NϵC). Anal. calcd. for
C16H30Fe3N4S6: C 30.1, H 4.6, N 8.8; found: C 30.1, H 4.6,
N 8.9.
Preparation of [Fe{Fe(NS3)(CN-t-Bu)}2-S,S′] (2b)
[Fe(acac)3] (2.13 g, 6 mmol) and t-BuNC (3 g, 36 mmol)
were dissolved in ether (40 mL) and NS3H3 (1.2 g, 6 mmol)
was added. The mixture was stirred overnight and a brown
precipitate was formed which turned dark green on standing
overnight. It was filtered off, washed with ether, and dried in
a vacuum; yield 1.0 g (70% with respect to Fe). Mössbauer
© 2001 NRC Canada

494
Can. J. Chem. Vol. 79, 2001
the NS3 ligand, with occupancy ratio of 0.736:0.264(2). All
the non-hydrogen atoms were refined with anisotropic ther-
mal parameters. Hydrogen atoms were included in idealised
positions; later, the parameters of those in the cation, the
major component of NS3 ligand and the solvent molecule
were refined freely, while the remainder were set to ride on
those of the parent carbon atoms. At the conclusion of the
refinement, wR2 = 0.051 and R1 = 0.026 (13) for all 3819 re-
map, the highest peaks (to ca. 0.8 e Å–3) were all in the re-
gion of the iron-sulfur core of the molecule.
Acknowledgments
We thank the BBSRC and the EU (SOCRATES
programme) for support and Dr A. Trzeciak for helpful dis-
cussions.
2
2
flections weighted w = [σ2(Fo ) + 0.180P]–1 with P = (Fo
+
2
2Fc )/3; for the observed data only, R1 = 0.022. In the final
difference map, the highest peaks (to ca. 0.2 e Å–3) were
close to a methylene group in the cation. Scattering factors
for neutral atoms were taken from ref. 14. Computer pro-
grams used in this analysis have been noted above or in Ta-
ble 4 of ref. 15, and were run on a DEC-Alpha Station
200 4/100 in the Department of Biological Chemistry, John
Innes Centre.
References
1. S.C. Davies, D.J. Evans, D.L. Hughes, S.Longhurst, and J.R.
Sanders. Chem. Commun. 1935 (1999).
2. (a) M.B. O’Donoghue, N.C. Zanetti, W.M. Davis, and R.R.
Schrock. J. Am. Chem. Soc. 119, 2753 (1997); (b) M. B.
O’Donoghue, W. M. Davis, R. R. Schrock, and W. M. Reiff.
Inorg. Chem. 38, 243 (1999).
3. S.C. Davies, D.L. Hughes, R.L. Richards, and J.R. Sanders. J.
Chem. Soc. Dalton Trans. 719 (2000).
[Fe{Fe(NS3)(CNCy)}2-S,S′]·nH2O (2c)
4. (a) S.C. Davies, D.L. Hughes, Z. Janas, L. Jerzykiewicz, R.L.
Richards, J.R. Sanders, and P. Sobota. Chem. Commun. 1261
(1997); (b) S.C. Davies, D.L. Hughes, Z. Janas, L.
Jerzykiewicz, R.L. Richards, J.R. Sanders, J.E. Silverston, and
P. Sobota. Inorg. Chem. 39, 3485 (2000).
5. S.C. Davies, D.L. Hughes, R.L. Richards, and J.R. Sanders.
Chem. Commun. 2699 (1998).
6. M. Glaser, H. Spies, T. Lügger, and F.E. Hahn. J. Organomet.
Chem. 503, C 32 (1995) and refs. therein.
7. K.S. Hagen, A.D. Watson, and R.H. Holm. J. Am. Chem. Soc.
105, 3905 (1983).
8. Y. Do, E.D. Simhon, and R.H. Holm. Inorg. Chem. 24, 4635
(1985).
Crystal data: C26H46Fe3N4S6·n(H2O), with n ca. 0.2,
MW = 778.2. Monoclinic, space group P21/n (equiv. to No. 14),
a = 17.112(2), b = 11.3486(8), c = 17.313(2) Å, β = 97.693(8)°,
V = 3331.7(5) Å3, Z = 4, Dc = 1.551 g cm–3, F(000) = 1624,
T = 293 K, µ (Mo Kα) = 16.9 cm–1, λ (Mo Kα) = 0.71069 Å.
Crystals are black polyhedra. One, ca. 0.36 × 0.21 ×
0.17 mm, was mounted on a glass fibre and coated with ep-
oxy resin. Following a similar procedure to that described
above, 4058 unique reflections to θmax = 22° were measured
at room temperature; 2523 were observed with I > 2σI. One
reflection, whose intensity measurement was suspect, was
not included in the refinement process.
During refinement, both NS3 ligands were both found to
have two alternative conformations; these were refined inde-
pendently, each with its complement of hydrogen atoms in-
cluded in idealised positions and with temperature factors
riding on those of the parent carbon atoms. Hydrogen atoms
were included similarly in the cyclohexyl groups. The non-
hydrogen atoms, except for those in the minor components
in the disordered ligands, were refined with anisotropic ther-
mal parameters. A persistent difference peak was included
as a partially occupied water molecule. At the conclusion of
the refinement, wR2 = 0.132 and R12 = 0.086 (12) for the
4057 reflections weighted w = [σ2(Fo ) + (0.0593P)2]–1; for
the observed data only, R1 = 0.051. In the final difference
9 K. Ward. J. Am. Chem. Soc. 57, 914 (1935).
10. J. Harley-Mason. J. Chem. Soc. 320 (1947).
11. P. Barbaro, C. Bianchini, G. Scapacci, D. Masi, and P. Zanello.
Inorg. Chem. 33, 3180 (1994).
12. G.M. Sheldrick. Acta Crystallogr. Sect. A: Fundam.
Crystallogr. A46, 467 (1990).
13. G.M. Sheldrick. SHELXL. Program for crystal structure re-
finement. University of Göttingen, Germany. 1993.
14. International tables for X-ray crystallography. Vol. C. Kluwer
Academic Publishers, Dordrecht, Netherlands. 1992. pp. 500,
219, and 193.
15. S.N. Anderson, R.L. Richards, and D.L. Hughes. J. Chem.
Soc. Dalton Trans. 245 (1986).
© 2001 NRC Canada