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The crystal structures of biferrocenyl Macdonald, Alaistair Cumming

Abstract

Biferrocenyi, C₅H₅,Fe,C₅H₄. C₅H₄ .Fe.C₅H₅., crystallises in the monoclinic system with a = 10.35, b = 7.87, c = 12,63Å and β = 131.72˚. The space group is P2₁/c and there are two molecules per unit cell, thus a molecular centre of symmetry is required which occurs at the mid-point of the carbon-carbon bond joining the ferrocene derivatives hence the molecular configuration is trans. The intensities of 1,111 reflections were measured by means of a scintillation counter using Mo K∝ radiation. The structure determination was based on heavy atom Patterson and Fourier methods and refined by least squares and differential syntheses. The final discrepancy, R, for the 896 observed reflections is 0.16. Each iron atom is sandwiched between two five-membered rings which are planar, almost parallel and 3.32Å apart. Their relative conformations are approximately midway between the staggered and the eclipsed. The two bonded rings are coplanar, the bond between the two being 1.48Å long. The mean bond lengths are Fe - C = 2.04 Åand C – C in the rings 1.40Å However there are deviations from five-fold symmetry in the rings which may be significant, furthermore these deviations are the same in both crystallographically independent rings, are similar to those found in ferrocene and may be related to the iron-carbon bonding pattern. All intermolecular contacts correspond to normal van der Waals interactions.

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