Metal–metal bonding in co-ordination complexes. Part III. The crystal structure of cyclopentadienyldicarbonyliron triphenyltin

Abstract

Crystalline cyclopentadienyldicarbonyliron triphenyltin has space group P2₁/c, a= 17·27, b= 32·86, c= 7·69 Å, β= 95° 10′, with two molecules in the asymmetric unit. A three-dimensional X-ray analysis (R= 5·6%) has shown that each molecule contains a covalent bond between the tin and iron atoms; Fe–Sn = 2·533 and 2·540 Å. The two carbonyl groups are attached to the iron atom almost at right angles to one another and to the Fe–Sn bond; Fe–C (av.)= 1·71 Å, C–O (av.)= 1·17 Å. The three-fold axis passing through the iron atom and relating these three ligand directions is almost perpendicular to the plane of the cyclopentadienyl ring but does not quite coincide with the five-fold axis of the ring. Within the limits of error, the C–C bonds of these rings are equivalent, the mean length being 1·396 Å. The Fe–centroid distances are 1·72 and 1·73 Å, and the mean Fe–C distance is 2·095 Å. The orientation of the cyclopentadienyl ring with respect to the Fe–C and Fe–Sn directions is the same in each case. By contrast, the orientation of ligands about the Fe–Sn axis is different in the two molecules, one being related to the other by a rotation about the axis of about 11°. This, coupled with differences in the relative orientations of the phenyl rings, means that the two molecules have different conformations. Each tin atom is approximately tetrahedrally co-ordinated. The mean Sn–C distance is 2·134 Å; the C–Sn–C angles are closed from the tetrahedral value to an average of 105·2°, the Fe–Sn–C angles being increased to an average of 113·4°. The covalent radius of iron in this compound is deduced to be about 1·13 Å, less than the metallic radius for this element.