Derivatives of divalent germanium, tin, and lead. Part XII. Crystal and molecular structure of di-µ-bis(cyclopentadienyl)stannyl-bis(tetracarbonyliron)

Abstract

The product of the reaction between dicyclopentadienyltin and enneacarbonyldi-iron has been shown to be the dimeric species [{(C₅H₅)₂SnFe(CO)₄}₂] by an X-ray diffraction study. The structure was determined from diffractometer data by Patterson and Fourier techniques and refined to a final R of 0.049 using 2 767 independent non-zero reflections. Crystals are monoclinic, space group C2/c, a= 19.803(4), b= 8.938(1), c= 16.722(1)Å, β= 103.91 (1)°, Z= 4. The overall symmetry of the molecule is C_i, and the molecule is characterised by a central lozenge-shaped four-membered Fe₂Sn₂ ring r(Sn–Fe) 2.651(1), 2.670(1)Å; Fe–Sn–Fe 102.04(3)°, Sn–Fe–Sn 77.96(2)°. The geometry at the iron and tin atoms is distorted from regular octahedral and tetrahedral, respectively. The two cyclopentadienyl rings, which are not equivalent, are attached to each tin atom in a monohapto-fashion, illustrating the change in tin–ring bonding on reaction of (η⁵-C₅H₅)₂Sn with Fe₂(CO)₉. Unusually, the cyclopentadienyl rings are planar, rather than puckered as has been deduced previously for [{(η-C₅H₅)Fe(CO)₂}₂Sn(C₅H₅)₂] but still retain considerable diene character as inferred from the endocyclic C–C bond distances.