The gas-phase structure of chloroferrocene from microwave spectra

Abstract

Rotational spectra for ten isotopomers of chloroferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Rotational transitions due to both “a” and “b” dipole moments were measured in the 4–12 GHz range. Thirty rotational constants were determined from microwave data for the normal, Fe54, Fe57, Cl37, and six unique C13 isotopomers, by fitting the microwave data using a rigid rotor Hamiltonian with centrifugal distortion and quadrupole coupling terms. The moments of inertia of the isotopomers were used in Kraitchman and in least-squares fitting analyses to determine gas-phase structural parameters. The unsubstituted cyclopentadienyl (C5H5) ligand was determined to have essentially fivefold local symmetry, while the chlorinated cyclopentadienyl ligand shows small, but significant distortions from the fivefold symmetry. The C–Cl bond is bent 2.7(6)° from the plane of carbon atoms. This substituted C5H4Cl ligand is tilted 1.4(5)° with respect to the unsubstituted C5H5 ligand. The carbon atoms of the two cyclopentadienyl ligands are eclipsed, similar to normal ferrocene. The average Fe–C distance is 2.042(9) Å. The estimated displacement of C–H bonds out of the planes of the carbon atoms is 4(2)° away from the metal atom.