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

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Abstract
Crystals of [(Me2Sn)Fe(CO)4]2 are orthorhombic, space group Pbam, with Z= 4 in a unit cell of dimensions a= 12·08, b= 12·32, c= 13·61 Å. The structure was refined to R 0·12 for 544 independent reflexions: one of the two crystallographically distinct molecules shows short-range disorder. The tin and iron atoms alternate around a planar four-membered ring, with distorted octahedral co-ordination for the iron atoms and only slightly distorted tetrahedral co-ordination for the tin atoms. The idealised molecular symmetry is D2h(mmm). The two molecules are both astride centres of symmetry at the intersection of two-fold axes with mirror planes: in the first the tin atoms lie on the two-fold axis, in the second the iron atoms are so disposed. The Fe–Sn bond length of 2·647(8)Å corresponds closely to the covalent radius sum for FeII and SnIV, and the Fe–C and C–O mean distances are ‘normal’[1·68(8) and 1·27(8)Å]. The Sn–Fe–Sn angle, however, is 77°; the metal atoms and the ‘equatorial’ carbonyl groups are coplanar, while the ‘axial’ carbonyl groups bend slightly inwards. The mean Sn–C distance is 2·22(7)Å with a C–Sn–C angle not significantly different from tetrahedral.

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