Crystal and molecular structure of di-µ-dimethylstannylene-bis(carbonyl-π-cyclopentadienylcobalt): a metal ring compound

Abstract

Crystals of the title compound are triclinic, space group P, with Z= 2 in a unit cell of dimensions a= 11·23(2), b= 11·10(2), c= 7·82(1)Å, α= 95·7(2). β= 97·0(2), γ= 89·1(2)°. The structure was refined to R 0·085 for 1520 independent reflections measured on a diffractometer. There are two crystallographically distinct molecules in the unit cell, each located astride a centre of inversion; they show no significant differences in their molecular geometry but are differently oriented in the unit cell. Sn and Co atoms alternate around a planar four membered ring, the Sn atoms having only slightly distorted tetrahedral co-ordination, and Co having octahedral co-ordination if the cyclopentadienyl ring is assumed to occupy three sites. The idealised molecular symmetry is C_2h(2/m), with the two-fold axis through the Sn atoms and the mirror through the Co atoms, the CO groups, and bisecting the cyclopentadienyl rings which lie mutually trans across the plane of the metal-atom ring. In the C₅ ring, the carbon atom in the mirror plane is also diametrically opposite to the CO group attached to the same Co atom. Co–Sn [2·542(2)Å] is significantly shorter than expected, but Co–C(CO), Co–C(π-C₅H₅), and C–O are ‘normal’; Sn–Co–Sn is 78°. The carbonyl groups occupy trans‘axial’ positions and are inclined slightly inwards; mean Sn–C 2·20(1)Å, C–Sn–C only a little less than the tetrahedral value.