Synthesis and crystal structure of decacarbonyl(μ3-3,7-dithianonane-1,9-dithiolato)bis(μ2-propane-1,3-dithiolato)nickel(II)tetrairon(II) dichloromethane disolvate

Synthesis and structural studies of a NiIIS4–2{2Fe2S}model for the H-cluster of [FeFe]-hydrogenase.


Chemical context
[FeFe]-hydrogenases are special enzymes in numerous microorganisms, which catalyse hydrogen evolution or splitting. Crystallographic and IR spectroscopic studies on [FeFe]hydrogenases have revealed that the active site of [FeFe]hydrogenases is comprised of a 2Fe2S butterfly structure containing diatomic ligands CO and CN À , a cysteinyl-S ligand connecting to a 4Fe4S subcluster, and a three-atom linker bridged between the two S atoms of the Fe 2 S 2 H-cluster (Tard et al., 2005;Tard & Pickett 2009).
Vigorous functional modelling studies have commenced with the [2Fe2S] subunit, but less attention has been paid in structural modelling studies to the overall H-cluster. The ISSN 2056-9890 4Fe4S sub-cluster was found to work as electrons relaying in numerous microorganisms. The 4Fe4S sub-cluster itself is a strong electron-donating group. The limited number of studies on the 4Fe4S sub-cluster encouraged us to synthesize the title compound, introducing bis(2-mercaptoethyl)-1,3-propanedithioethernickel(II) into the 2Fe2S cluster to mimic the 4Fe4S sub-cluster.
The introduction of bis(2-mercaptoethyl)-1,3-propanedithioethernickel(II) into the 2Fe2S cluster results in a significant red shift for the C O group in the IR spectrum; the highest and lowest absorption wave-numbers differ by 123 cm À1 , which suggests a significant difference in the electron density between the two Fe II ions. The IR signal therefore indicates that bis(2-mercaptoethyl)-1,3-propanedithioethernickel(II) can mimic the strong electron-donating ability of the 4Fe4S subcluster. The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity, and the disordered atoms of the CH 2 Cl 2 molecules are shown with suffix A. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; Ày þ 2; Àz þ 1; (ii) Àx þ 2; Ày þ 1; Àz; (iii)

Figure 2
A view along the c axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1), and H atoms not involved in these interactions have been omitted.
[110]; see Table 1 and Fig. 2. The dichloromethane solvent molecules are each partially disordered over two positions and only one is linked to the five-metal core complex by a C-HÁ Á ÁO hydrogen bond (Fig. 2

Experimental
All reactions and operations were carried out under a dry, prepurified nitrogen atmosphere with standard Schlenk techniques. All solvents were dried and distilled prior to use according to standard methods. The starting materials, Fe 2 (C 3 H 6 S 2 )(CO) 6 (A) and NiC 7 H 14 S 4 (B), were prepared according to literature methods (Maiolo et al., 1981). Me 3 NOÁ2H 2 O (1 mmol, 0.111 g) was added to a CH 3 CN solution of complex A (1 mmol, 0.168 g) under an N 2 atmosphere with stirring. A CH 2 Cl 2 /CH 3 OH (2:1) solution of complex B (0.5 mmol, 0.143 g) was added after 30 min. The colour of the solution changed gradually from red to dark red. After one h, the solvent was removed under reduced pressure. The residue was purified by column chromatography on silica gel using hexane as eluent to give the title compound as a red solid (yield 0.164 g, 51%). It is unstable in solution in air. Single crystals suitable for the X-ray diffraction study were obtained by slow evaporation of a solution in CH 2 Cl 2 /hexane (1:10, v/v) at 263 K. IR (CH 2 Cl 2 , cm À1 ): (CO) 2020 (

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were placed in calculated positions and refined as riding: C-H = 0.97 Å with U iso (H) = 1.2U eq (C). The dichloromethane solvent molecules are each partially disordered over two positions. That invol-ving atoms Cl1 and Cl2 have atoms Cl1/Cl1A and C24/C24A with fixed occupancies of 0.5 each, while that involving atoms Cl3 and Cl4 have atom Cl3/Cl3A with a refined occupancy ratio of 0.77 (6):0.23 (6).

Decacarbonyl(µ 3 -3,7-dithianonane-1,9-dithiolato)bis(µ 2 -propane-1,3-dithiolato)nickel(II)tetrairon(II) dichloromethane disolvate
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.