Metal–metal bonding in co-ordination complexes. Part II. The crystal structure of µµ′(cis-stilbene-α,β-dithiolato)-bis(tricarbonyliron)

Abstract

A three-dimensional X-ray diffraction study has been made of µµ′(cis-stilbene-α,β-dithiolato)bis(tricarbonyliron), [(C₆H₅)CSFe(CO)₃]₂. The space group is P, a= 14·92, b= 17·37, c= 9·30 Å, α= 91·8°, β= 107·9°, γ= 107·8°, Z= 4.

The two iron and two sulphur atoms of each molecule are arranged in a nucleus of C_2v symmetry. The mean values for the various interatomic distances are: Fe–Fe, 2·507 Å; Fe–S, 2·259 Å; and S⋯S, 2·866 Å. The sulphur atoms are bridged through the CC segment of the cis-stilbene residue, the mean S–C distance being 1·78 Å. Three carbonyl groups complete the co-ordination of the iron atoms, the mean Fe–C length being 1·778 Å, and the mean C–O length 1·15 Å.

Exclusive of the phenyl groups, the two molecules are very similar and closely approximate C_2v symmetry. The two differ, however, with respect to the phenyl groups; in one the C–C_phenyl axes are twisted out of the S–CC–S plane by about 6° in opposite directions, giving a molecule with overall C₂ symmetry, in the other the twists are in the same direction and lead to an asymmetric molecule. This asymmetric molecule contains a number of very close approaches between the carbon atoms of the phenyl rings and this energetically unfavourable configuration is adopted to achieve an optimal packing of molecules within the crystal.

A comparison between the molecular dimensions found for this complex and for the related molecules [(C₂H₅)SFe(CO)₃]₂ and [SFe(CO)₃]₂ shows that small, but significant, differences occur in the iron–sulphur nucleus so as to accomodate the bridging group.