Crystal and molecular structure of di-µ-carbonyl-cis-µ-(1–5-η: 1′–5′-η-dicyclopentadienyldimethylsilane)bis(carbonyliron)(Fe–Fe)

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Abstract
Crystals of the title compound are monoclinic, space group P21/n, with Z= 4 in a unit cell of dimensions: a= 11·66, b= 13·27, c= 10·82 Å, β= 105° 50′. The structure was determined from diffractometer data by the symbolic addition method and refined to R 0·072 for 1309 independent reflections. The silicon atom is tetra-hedrally σ bonded to two methyl groups and to two cyclopentadienyl rings; the latter are in turn each π-bonded to one iron atom. The two iron atoms are bonded to one another (2·51 Å) and are also linked by two symmetrical carbonyl bridges; the four-membered ring so defined is non-planar, being folded along the Fe–Fe axis away from the C5 rings at an angle of ca. 160°. Each iron atom also carries one terminal carbonyl group, which makes the overall co-ordination approximately octahedral. The Si atom does not lie in the Fe2(CO)2(terminal) plane, nor are the cyclopentadienyl rings symmetrically related to it (though their centroids lie in it), and the overall symmetry of the molecule is only Cs(m). Reasons for this configuration are discussed. The Fe–C and C–O distances are as expected; the four Si–C distances relatively equal, mean 1·88 Å.

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