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Acta Cryst. (2011). E67, m752-m753    [ doi:10.1107/S1600536811017405 ]

A triclinic polymorph of bis([mu]2-ethanethiolato)-1:2[kappa]2S:S;3:4[kappa]2S:S-([mu]4-disulfido-1:2:3:4[kappa]4S:S:S':S')tetrakis[tricarbonyliron(II)](2 Fe-Fe)

Y. Si, H. Chen and C. N. Chen

Abstract top

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.

Comment top

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.

Related literature top

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 top

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%).

Refinement top

Hydrogen atoms were placed at idealized positions and allowed to ride on their parent atoms, with CH2 and CH3 bonds set equal to 0.97 and 0.96 Å, respectively and Uiso(H)=1.2Ueq(C) for hydrogen atoms of C7, and Uiso (H)=1.5Ueq (C) for hydrogen atoms of C8. The highest residual peak was located at 0.88 Å from S1.

Computing details top

Data collection: CrystalClear (Rigaku, 2002); cell refinement: CrystalClear (Rigaku, 2002); data reduction: CrystalClear (Rigaku, 2002); 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).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with atom labels and 20% probability displacement ellipsoids for all non-H atoms. [Symmetry operator A: -x, -y + 2, -z + 2.]
[Figure 2] Fig. 2. The packing diagram of (I), viewed down the b axis.
bis(µ2-ethanethiolato)-1:2κ2S:S;3:4κ2S:S- (µ4-disulfido-1:2:3:4κ4S:S:S':S')tetrakis [tricarbonyliron(II)](2 FeFe) top
Crystal data top
[Fe4(C2H5S)2(S2)(CO)12]Z = 1
Mr = 745.88F(000) = 370
Triclinic, P1Dx = 1.826 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 8.365 (4) ÅCell parameters from 1200 reflections
b = 9.296 (5) Åθ = 2.1–27.5°
c = 10.209 (5) ŵ = 2.46 mm1
α = 87.57 (2)°T = 293 K
β = 70.082 (17)°Prism, orange
γ = 66.103 (17)°0.15 × 0.12 × 0.03 mm
V = 678.2 (6) Å3
Data collection top
Rigaku Mercury70 CCD
diffractometer
3060 independent reflections
Radiation source: fine-focus sealed tube1939 reflections with I > 2σ(I)
graphiteRint = 0.036
CCD_Profile_fitting scansθmax = 27.5°, θmin = 2.4°
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2002)
h = 1010
Tmin = 0.771, Tmax = 1.000k = 1111
5323 measured reflectionsl = 1213
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.048Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.100H-atom parameters constrained
S = 0.99 w = 1/[σ2(Fo2) + (0.0419P)2]
where P = (Fo2 + 2Fc2)/3
3060 reflections(Δ/σ)max < 0.001
163 parametersΔρmax = 0.39 e Å3
0 restraintsΔρmin = 0.42 e Å3
Crystal data top
[Fe4(C2H5S)2(S2)(CO)12]γ = 66.103 (17)°
Mr = 745.88V = 678.2 (6) Å3
Triclinic, P1Z = 1
a = 8.365 (4) ÅMo Kα radiation
b = 9.296 (5) ŵ = 2.46 mm1
c = 10.209 (5) ÅT = 293 K
α = 87.57 (2)°0.15 × 0.12 × 0.03 mm
β = 70.082 (17)°
Data collection top
Rigaku Mercury70 CCD
diffractometer
3060 independent reflections
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2002)
1939 reflections with I > 2σ(I)
Tmin = 0.771, Tmax = 1.000Rint = 0.036
5323 measured reflectionsθmax = 27.5°
Refinement top
R[F2 > 2σ(F2)] = 0.048H-atom parameters constrained
wR(F2) = 0.100Δρmax = 0.39 e Å3
S = 0.99Δρmin = 0.42 e Å3
3060 reflectionsAbsolute structure: ?
163 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Fe10.31028 (8)1.00320 (7)0.78114 (6)0.03542 (19)
Fe20.33627 (9)0.73745 (7)0.86174 (7)0.03887 (19)
S10.06448 (15)0.94806 (12)0.89480 (11)0.0364 (3)
S20.37128 (16)0.79317 (13)0.63756 (12)0.0425 (3)
O20.2904 (5)1.1642 (4)1.0304 (4)0.0659 (10)
O10.7064 (5)0.9407 (5)0.6498 (4)0.0765 (12)
O30.1430 (6)1.2810 (4)0.6441 (4)0.0801 (13)
O50.3256 (6)0.7693 (4)1.1491 (4)0.0767 (12)
C10.5507 (7)0.9675 (5)0.6996 (5)0.0485 (12)
O60.7439 (5)0.5643 (5)0.7670 (5)0.0864 (14)
C30.2065 (7)1.1746 (6)0.6958 (5)0.0477 (12)
C60.5855 (8)0.6296 (6)0.8033 (5)0.0559 (14)
C20.2944 (6)1.1039 (5)0.9341 (5)0.0444 (11)
C50.3261 (7)0.7589 (5)1.0381 (6)0.0527 (13)
C40.2657 (8)0.5763 (6)0.8735 (6)0.0601 (14)
O40.2224 (8)0.4741 (5)0.8805 (6)0.1078 (17)
C70.1744 (7)0.8070 (6)0.5873 (5)0.0546 (13)
H7A0.06040.84650.66910.065*
H7B0.15890.88200.51860.065*
C80.2037 (11)0.6549 (7)0.5290 (9)0.124 (3)
H8A0.09840.66660.50440.187*
H8B0.21730.58090.59720.187*
H8C0.31490.61660.44680.187*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe10.0322 (4)0.0369 (4)0.0375 (4)0.0163 (3)0.0103 (3)0.0028 (3)
Fe20.0377 (4)0.0317 (3)0.0461 (4)0.0122 (3)0.0159 (3)0.0021 (3)
S10.0297 (6)0.0386 (6)0.0380 (6)0.0142 (5)0.0079 (5)0.0008 (5)
S20.0354 (6)0.0472 (7)0.0405 (6)0.0142 (5)0.0110 (5)0.0050 (5)
O20.078 (3)0.079 (2)0.058 (2)0.048 (2)0.024 (2)0.0046 (19)
O10.044 (2)0.109 (3)0.076 (3)0.041 (2)0.008 (2)0.001 (2)
O30.086 (3)0.063 (2)0.086 (3)0.018 (2)0.042 (3)0.027 (2)
O50.092 (3)0.077 (3)0.057 (2)0.020 (2)0.040 (2)0.009 (2)
C10.045 (3)0.055 (3)0.046 (3)0.025 (3)0.011 (2)0.005 (2)
O60.045 (2)0.079 (3)0.110 (3)0.004 (2)0.029 (2)0.025 (2)
C30.052 (3)0.048 (3)0.045 (3)0.022 (2)0.019 (2)0.008 (2)
C60.049 (3)0.049 (3)0.066 (4)0.010 (3)0.026 (3)0.005 (3)
C20.037 (3)0.049 (3)0.053 (3)0.024 (2)0.015 (2)0.007 (2)
C50.053 (3)0.043 (3)0.056 (3)0.010 (2)0.023 (3)0.008 (2)
C40.075 (4)0.047 (3)0.071 (4)0.030 (3)0.036 (3)0.015 (3)
O40.150 (5)0.074 (3)0.149 (4)0.078 (3)0.076 (4)0.033 (3)
C70.050 (3)0.062 (3)0.058 (3)0.021 (3)0.027 (3)0.001 (3)
C80.131 (7)0.086 (5)0.194 (9)0.029 (5)0.116 (7)0.027 (5)
Geometric parameters (Å, °) top
Fe1—C11.786 (5)O2—C21.137 (5)
Fe1—C21.793 (5)O1—C11.145 (5)
Fe1—C31.824 (5)O3—C31.123 (5)
Fe1—S12.2393 (15)O5—C51.140 (6)
Fe1—S22.2688 (16)O6—C61.138 (6)
Fe1—Fe22.5183 (15)C4—O41.138 (6)
Fe2—C51.789 (5)C7—C81.451 (7)
Fe2—C61.794 (5)C7—H7A0.9700
Fe2—C41.806 (5)C7—H7B0.9700
Fe2—S12.2457 (15)C8—H8A0.9600
Fe2—S22.2711 (18)C8—H8B0.9600
S1—S1i2.113 (2)C8—H8C0.9600
S2—C71.842 (5)
C1—Fe1—C290.8 (2)C4—Fe2—Fe1149.28 (16)
C1—Fe1—C399.4 (2)S1—Fe2—Fe155.72 (4)
C2—Fe1—C399.1 (2)S2—Fe2—Fe156.27 (4)
C1—Fe1—S1157.40 (15)S1i—S1—Fe1111.12 (8)
C2—Fe1—S194.02 (15)S1i—S1—Fe2111.36 (8)
C3—Fe1—S1101.64 (16)Fe1—S1—Fe268.32 (5)
C1—Fe1—S287.52 (16)C7—S2—Fe1114.87 (16)
C2—Fe1—S2156.70 (15)C7—S2—Fe2113.05 (18)
C3—Fe1—S2104.06 (16)Fe1—S2—Fe267.38 (5)
S1—Fe1—S279.39 (5)O1—C1—Fe1177.8 (5)
C1—Fe1—Fe2101.44 (15)O3—C3—Fe1179.3 (5)
C2—Fe1—Fe2101.42 (15)O6—C6—Fe2178.4 (5)
C3—Fe1—Fe2150.37 (16)O2—C2—Fe1177.7 (4)
S1—Fe1—Fe255.96 (4)O5—C5—Fe2177.8 (5)
S2—Fe1—Fe256.35 (5)O4—C4—Fe2179.6 (6)
C5—Fe2—C690.6 (2)C8—C7—S2111.8 (4)
C5—Fe2—C499.0 (2)C8—C7—H7A109.3
C6—Fe2—C4100.4 (2)S2—C7—H7A109.3
C5—Fe2—S194.44 (15)C8—C7—H7B109.3
C6—Fe2—S1156.35 (18)S2—C7—H7B109.3
C4—Fe2—S1101.55 (18)H7A—C7—H7B107.9
C5—Fe2—S2158.11 (17)C7—C8—H8A109.5
C6—Fe2—S287.54 (17)C7—C8—H8B109.5
C4—Fe2—S2102.75 (18)H8A—C8—H8B109.5
S1—Fe2—S279.21 (5)C7—C8—H8C109.5
C5—Fe2—Fe1102.83 (16)H8A—C8—H8C109.5
C6—Fe2—Fe1100.63 (17)H8B—C8—H8C109.5
Symmetry codes: (i) −x, −y+2, −z+2.
Table 1
Selected geometric parameters (Å)
top
Fe1—C11.786 (5)Fe2—C51.789 (5)
Fe1—C21.793 (5)Fe2—C61.794 (5)
Fe1—C31.824 (5)Fe2—C41.806 (5)
Fe1—S12.2393 (15)Fe2—S12.2457 (15)
Fe1—S22.2688 (16)Fe2—S22.2711 (18)
Fe1—Fe22.5183 (15)S1—S1i2.113 (2)
Symmetry codes: (i) −x, −y+2, −z+2.
references
References top

Cheng, L.-X., Ma, C.-B., Hu, M.-Q. & Chen, C.-N. (2005). Acta Cryst. E61, m892–m894.

Darensbourg, M. Y., Lyon, E. J. & Smee, J. J. (2000). Coord. Chem. Rev. 206, 533–561.

Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.

Lawrence, J. D., Li, H. X., Rauchfuss, T. B., Benard, M. & Rohmer, M. M. (2001). Angew. Chem. Int. Eng. Ed. 40, 1768–1771.

Li, H. & Rauchfuss, T. B. (2002). J. Am. Chem. Soc. 124, 726–727.

Rigaku (2002). CrystalClear. Rigaku Corporation, Tokyo, Japan.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.