The crystal and molecular structures and other properties of cycloheptatrienediiron hexacarbonyl have been investigated. The molecule in the crystal has approximate mirror symmetry with the iron atoms lying on opposite sides of the mirror plane; the nmr spectrum strongly suggests, though it cannot prove, that the same structure persists in solution. A systematic name which refers to this structure explicity is (1,2,3-trihapto-4,5,6-trihaptocycloheptatri-l,3,5-ene)diiron(Fe-Fe) hexacarbonyl. A simple formalism which, however, should not be taken as a precise and literal description of the electronic structure, considers the π-electron system of the C7H8 ring to be divided into two adjacent allyl groups, each of which forms a π complex with one of the iron atoms. The C-C bonds in the allyl groups have an average length of 1.401 ± 0.008 Å and the Fe-C(allyl) distances have average values of 2.15 ± 0.03 Å to the outer atoms and 2.042 ± 0.003 Å to the center atoms. The Fe-Fe distance is 2.87 Å. This structure contrasts strikingly with the structures of C8H8Ru2(CO)6 and C8H10Fe2(CO)6, in which the M-M axes are turned nearly 90° toward the direction of a possible mirror plane analogous to the one found in C7H8Fe2-(CO)6, but are nevertheless skew and quite unsymmetricaHy bonded. The significance of this structural difference on the interpretation of the fluxional behavior of the C8H8 and C8H10 compounds is considered. C7H8Fe2(CO)6 crystallizesin the space group Pbca with unit cell dimensions a = 24.269 ± 0.006, b = 11.431 ± 0.003, and c = 9.732 ± 0.003 Å, Z = 8; D(calcd) = 1.83 g cm-3; D(obsd) = 1.85 ± 0.01 g cm-3. The structure was solved and refined using 3111 reflections collected on a counter diffractometer with Mo Kα radiation. Corrections were made for absorption, secondary extinction, and anomalous effects of the Zr filter on background estimates of low-angle reflections. All atoms other than hydrogen were refined anisotropically; hydrogen atoms all refined well isotropically. Final conventional and weighted residuals weee 6.1 and 4.2%, respectively.
ASJC Scopus subject areas
- Colloid and Surface Chemistry