CRYSTAL AND MOLECULAR-STRUCTURES OF DECAMETHYLMANGANOCENE AND DECAMETHYLFERROCENE - STATIC JAHN-TELLER DISTORTION IN A METALLOCENE

The crystal and molecular structures of bis(pentamethylcyclopentadienyl)manganese(II) and -iron(II) have been determined by single-crystal X-ray diffraction. The crystal packing of the two compounds is closely related and highly ordered, allowing a detailed comparison of structural parameters. Both metallocenes contain planar, staggered Me5Cp rings, The ferrocene corresponds to a molecular symmetry of D5dwith average Fe-C and C-C distances of 2.050 (2) and 1.419 (2) Å, respectively. The low-spin manganocene has an orbitally degenerate 2E2gground state in D5dsymmetry. This degeneracy is relieved in the solid state by (1) a distortion of the Cp rings in which C-C ring distances range from 1.409 (2) to 1.434 (2) Å and (2) a small slippage of the top and bottom halves of the metallocene “sandwich” to give Mn-C bond lengths which range from 2.105 (2) to 2.118 (2) Å. In both structures the methyl groups bend away from the metal atom 0.06 A from the Cp rings. Orange crystals of (C5(CH3)5)2Mn conform to the space group C2/c with a = 15.143 (4) Å, b = 12.248 (3) Å, c = 9.910 (3) Å, and 0 = 93.56 (3)°. For 2581 independent reflections with (F0 2) > 3σ(F0 2), R = 3.6%, Rw= 5.0%. Orange crystals of (C5(CH3)5)2Fe conform to the space group Cmca with a = 15.210 (3), b = 11.887 (2), and c = 9.968 (2) Å. For 1217 independent reflections with F0 23σ(F0 2), R = 3.9% and Rw= 5.5%. Both structures have four molecules per unit cell with Ci(Mn) and C2h(Fe) crystallographic site symmetry, respectively. © 1979, American Chemical Society. All rights reserved.