A triclinic polymorph of bis­(μ2-ethane­thiol­ato)-1:2κ2 S:S;3:4κ2 S:S-(μ4-disulfido-1:2:3:4κ4 S:S:S′:S′)tetra­kis­[tricarbonyl­iron(II)](2 Fe—Fe)

Youtao Si; Hui Chen; Chang Neng Chen

doi:10.1107/S1600536811017405

. 2011 May 14;67(Pt 6):m752–m753. doi: 10.1107/S1600536811017405

A triclinic polymorph of bis(μ₂-ethanethiolato)-1:2κ² S:S;3:4κ² S:S-(μ₄-disulfido-1:2:3:4κ⁴ S:S:S′:S′)tetrakis[tricarbonyliron(II)](2 Fe—Fe)

Youtao Si ^a,^*, Hui Chen ^b, Chang Neng Chen ^b

PMCID: PMC3120318 PMID: 21754642

Abstract

Next to the monoclinic polymorph [Cheng et al. (2005 ▶). Acta Cryst. E61, m892–m894], the triclinic title compound, [Fe₄(C₂H₅S)₂(S₂)(CO)₁₂], is the second known form of this composition. The structure is composed of an [Fe₂(C₂H₅S)(S)(CO)₆] subcluster, which is linked to its counterpart by an inversion centre located at the mid-point of the central disulfide bond. The Fe₂S₂ core of each subcluster exhibits a butterfly-like shape, with two S atoms bridging two Fe atoms. In the subcluster, each Fe atom is coordinated in a distorted octahedral coordination by three terminal carbonyl C atoms, two S atoms and one Fe atom. The crystal packing is accomplished through van der Waals interactions.

Related literature

For more details about hydrogenases, including Fe—Fe hydrogenases, see: Darensbourg et al. (2000 ▶). Two procedures are mainly used for the synthesis of model compounds containing the Fe₂S₂ subcluster of Fe—Fe hydrogenases, see: Lawrence et al. (2001 ▶); Li & Rauchfuss (2002 ▶). The monoclinic polymorph (space group P2₁/c) of the title compound has been reported by Cheng et al. (2005 ▶).

Experimental

Crystal data

[Fe₄(C₂H₅S)₂(S₂)(CO)₁₂]
M _r = 745.88
Triclinic,
a = 8.365 (4) Å
b = 9.296 (5) Å
c = 10.209 (5) Å
α = 87.57 (2)°
β = 70.082 (17)°
γ = 66.103 (17)°
V = 678.2 (6) Å³
Z = 1
Mo Kα radiation
μ = 2.46 mm⁻¹
T = 293 K
0.15 × 0.12 × 0.03 mm

Data collection

Rigaku Mercury70 CCD diffractometer
Absorption correction: multi-scan (CrystalClear; Rigaku, 2002 ▶) T _min = 0.771, T _max = 1.000
5323 measured reflections
3060 independent reflections
1939 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.048
wR(F ²) = 0.100
S = 0.99
3060 reflections
163 parameters
H-atom parameters constrained
Δρ_max = 0.39 e Å⁻³
Δρ_min = −0.42 e Å⁻³

Data collection: CrystalClear (Rigaku, 2002 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: WinGX (Farrugia, 1999 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811017405/wm2485sup1.cif

e-67-0m752-sup1.cif^{(15.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811017405/wm2485Isup2.hkl

e-67-0m752-Isup2.hkl^{(150.1KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Fe1—C1	1.786 (5)
Fe1—C2	1.793 (5)
Fe1—C3	1.824 (5)
Fe1—S1	2.2393 (15)
Fe1—S2	2.2688 (16)
Fe1—Fe2	2.5183 (15)
Fe2—C5	1.789 (5)
Fe2—C6	1.794 (5)
Fe2—C4	1.806 (5)
Fe2—S1	2.2457 (15)
Fe2—S2	2.2711 (18)
S1—S1ⁱ	2.113 (2)

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Symmetry code: (i) Inline graphic .

Acknowledgments

We thank the National Natural Science Foundation of China (21071145) for financial support.

supplementary crystallographic information

Comment

Fe—Fe hydrogenases are enzymes capable of efficiently catalysing the reversible transformation between H⁺ and H₂ (Darensbourg et al., 2000). Chemists have been trying to achieve H₂ production technologies of practical use by studying the catalytic process by such kind of hydrogenases, aiming at solving the current energy problem. The well known active site of Fe—Fe hydrogenases, established by X-ray crystallographic and spectroscopic techniques, has an Fe₂S₂ cluster linked to a Fe₄S₄ cuboidal unit by a cysteine-S atom. While the Fe₄S₄ unit is assumed to be reponsible for transferring eletrons, the Fe₂S₂ cluster plays an important role in the catalysis process. Thus, many works concentrate on compounds containing the Fe₂S₂ cluster.

Two kinds of procedures are frequently used to synthesize model substances of the Fe₂S₂ cluster, e.g. Fe₂(SCH₂)₂NR(CO)₆. The first procedure is a condensation of (ClCH₂)₂NR and Li₂[Fe₂S₂(CO)₆], and the second is a condensation of Fe₂(SH)₂(CO)₆ with formaldehyde in the presence of primary amines (Lawrence et al., 2001; Li & Rauchfuss, 2002). In both cases, LiEt₃BH are used to cleave the S—S bond of the starting material Fe₂S₂(CO)₆. When trying to get some new complexes using the first procedure, we found some by-products which reflect the diversity of the reactivity of (FeS)_n clusters. Here we report a triclinic polymorph, (I), of [Fe₄(C₂H₅S)₂(S₂)(CO)₁₂]. Another monoclinic polymorph (space group P2₁/c) has been reported previously (Cheng et al., 2005).

As can be seen in Fig. 1, the crystallographically imposed center of inversion is located at the mid-point of the S1—S1A bond, and thus the asymmetric unit contains one half of the [Fe₄(C₂H₅S)₂(S₂)(CO)₁₂] formula unit. The two Fe atoms of the asymmetric unit (Fe1, Fe2) are linked through an Fe—Fe single bond and are bridged by two S atoms (S1, S2). Thus a butterfly-like arrangement is formed, with a dihedral angle between the two Fe₂S planes being 100.53 (6)°. The average Fe—S bond length is 2.256 (16) Å, and the average Fe—S—Fe angle is 67.9 (6)°. The octahedral coordination geometry around each Fe atom is completed by three carbonyl C atoms [average Fe—C distance 1.799 (14) Å, average C—Fe—C angle 97 (4)°].

The packing diagram is shown in Fig. 2. There is only one molecule in each unit cell, and neighbouring molecules pack along the a axis; the crystal is stabilized by van der Waals interactions.

In comparison with the monoclinic polymorph (Cheng et al., 2005), the configuration of the [Fe₄(C₂H₅S)₂(S₂)(CO)₁₂] molecules is different, just like the packing in the crystal.

Experimental

All experiments were carried out under an atmosphere of purified, oxygen-free and dry nitrogen using standard Schlenk techniques. THF and hexane were dried and freshly distilled prior to use according to standard methods. The commercially available products paraformaldehyde, [Fe(CO)₅], LiBEt₃H, F₃CCOOH and C₅H₉NH₂ were of reagent grade and were used as received. The starting material [Fe₂S₂(CO)₆] was prepared according to the literature.

[Fe₂S₂(CO)₆] (1 mmol, 0.344 g) was dissolved in dry THF (40 ml) under a nitrogen atmosphere and then cooled to 195 K with acetone and liquid nitrogen. After the solution was stirred for 30 minutes, LiBEt₃H (2 mmol) was added dropwise very slowly. At the midpoint of the addition, the color of the reaction mixture turned from red to dark green; for the rest of addition it remained green. After another 30 minutes, F₃CCOOH (2 mmol, 0.149 ml) was added. The new mixture was stirred for an additional hour. The cool solution was added to a mixture of paraformaldehyde (40 mmol, 1.2 g) and C₅H₉NH₂ (1 mmol, 1.98 ml) in THF which had been stirred for 10 h and cooled to 273 K. The last mixture was stirred for 24 h and the majority of the solvent was evaporated under vacuum. The remaining residual was filtered through silica gel. A red fraction was collected by elution with hexane. Recrystallization of the crude product from fresh distilled pentane in a fridge at 253 K for several days gave the title complex as a by-product in low and varing yields (<5%).