Rotational and hyperfine spectra for a sandwich titanium complex, C ₅H₅TiC₇H₇

Microwave spectroscopy measurements and density functional theory calculations are reported for the cyclopentadienyl cycloheptatrienyl titanium complex, C₅H₅TiC₇H₇. Rotational transition frequencies for this symmetric-top complex were measured in the 4-13 GHz range using a Flygare-Balle-type pulsed beam spectrometer. The spectroscopic constants obtained for the normal C₅H₅ ⁴⁸TiC₇H₇ isotopomer are B = 771.78907(38), D_J = 0.0000295(41), and D_JK = 0.001584(73) MHz. The quadrupole hyperfine splittings for C₅H₅ ⁴⁷TiC₇H₇ were clearly observed and the measured constants are B = 771.79024(32) MHz, D_J = 0.0000395(33), D _JK = 0.001646(24), and eQq_aa = 8.193(40) MHz. Analysis of the experimental and theoretical rotational constants indicates that the η⁷-C₇H₇Ti and η⁵-C ₅H₅Ti bond lengths in the gas phase are about 0.02 Å longer than those reported for the solid-state X-ray structure. The calculated Ti-C bond lengths are shorter for the C₇H₇ ligand (r(Ti-C) = 2.21 Å) than for the C₅H₅ ligand (r(Ti-C) = 2.34 Å), and the C₇H₇ H atoms are displaced 0.15 Å out of the C₇ plane, toward the Ti atom.