Microwave spectroscopy measurements of the gas-phase structure of cyclopentadienyltungsten tricarbonyl hydride

High-resolution microwave spectra for ¹³C isotopomers of cyclopentadienyltungsten tricarbonyl hydride were measured using a pulsed-beam Fourier transform microwave spectrometer system. The new rotational constants for the ¹³C isotopomers are combined with the previously obtained rotational constants for normal and deuterium isotopomers to obtain the gas-phase structure of cyclopentadienyltungsten tricarbonyl hydride. The new frequencies for the five unique ¹³C isotopomers were measured in the 5-7 GHz range for C ₅H ₅W(CO) ₃H. Kraitchman analysis and least-squares structure-fitting procedures were used to determine the structural parameters. The results from the structural fit yielded the W-H bond length, r ₀(W-H) = 1.79(2) Å, which agrees very well with the previously reported value, r _s(W-H) = 1.79(4) Å, obtained with a much smaller data set. The present study also yielded the distance from tungsten to the C ₅H ₅ ring, r(W-Cp) = 2.03(1) Å, which corresponds to an average W-C (of Cp) bond length of 2.37(2) Å. The experimental ring radius for Cp of r(Cp) = 1.20(2) Å corresponds to an average cyclopentadienyl C-C bond length of 1.423(4) Å. Deviations of near 0.02 Å from C ₅ symmetry for the W-C bond lengths for the Cp ligand and smaller deviations for the C-C bond lengths were obtained from the DFT calculations, and incorporating these deviations into the least-squares fit improved the standard deviation by a factor of 5. The average bond length from tungsten to the carbonyl carbons is r(W-CO) = 1.97(2) Å. Results obtained from the structural fit are in very close agreement with the experimental, Kraitchman analysis values. Results from new DFT calculations are given, with heavy-atom coordinates in very good agreement with experimental values, and a slightly shorter calculated W-H bond length, r _e(W-H) = 1.73 Å.